draft-ietf-openpgp-crypto-refresh-03.txt   draft-ietf-openpgp-crypto-refresh-04.txt 
Network Working Group W. Koch, Ed. Network Working Group W. Koch, Ed.
Internet-Draft GnuPG e.V. Internet-Draft GnuPG e.V.
Obsoletes: 4880, 5581, 6637 (if approved) P. Wouters, Ed. Obsoletes: 4880, 5581, 6637 (if approved) P. Wouters, Ed.
Intended status: Standards Track No Hats Intended status: Standards Track Aiven
Expires: 3 November 2021 2 May 2021 Expires: 21 April 2022 18 October 2021
OpenPGP Message Format OpenPGP Message Format
draft-ietf-openpgp-crypto-refresh-03 draft-ietf-openpgp-crypto-refresh-04
Abstract Abstract
{ Work in progress to update the OpenPGP specification from RFC4880 } { Work in progress to update the OpenPGP specification from RFC4880 }
This document specifies the message formats used in OpenPGP. OpenPGP This document specifies the message formats used in OpenPGP. OpenPGP
provides encryption with public-key or symmetric cryptographic provides encryption with public-key or symmetric cryptographic
algorithms, digital signatures, compression and key management. algorithms, digital signatures, compression and key management.
This document is maintained in order to publish all necessary This document is maintained in order to publish all necessary
skipping to change at page 1, line 44 skipping to change at page 1, line 44
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This Internet-Draft will expire on 3 November 2021. This Internet-Draft will expire on 21 April 2022.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.1. Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2. General functions . . . . . . . . . . . . . . . . . . . . . . 7 2. General functions . . . . . . . . . . . . . . . . . . . . . . 7
2.1. Confidentiality via Encryption . . . . . . . . . . . . . 7 2.1. Confidentiality via Encryption . . . . . . . . . . . . . 8
2.2. Authentication via Digital Signature . . . . . . . . . . 8 2.2. Authentication via Digital Signature . . . . . . . . . . 9
2.3. Compression . . . . . . . . . . . . . . . . . . . . . . . 8 2.3. Compression . . . . . . . . . . . . . . . . . . . . . . . 9
2.4. Conversion to Radix-64 . . . . . . . . . . . . . . . . . 9 2.4. Conversion to Radix-64 . . . . . . . . . . . . . . . . . 10
2.5. Signature-Only Applications . . . . . . . . . . . . . . . 9 2.5. Signature-Only Applications . . . . . . . . . . . . . . . 10
3. Data Element Formats . . . . . . . . . . . . . . . . . . . . 9 3. Data Element Formats . . . . . . . . . . . . . . . . . . . . 10
3.1. Scalar Numbers . . . . . . . . . . . . . . . . . . . . . 9 3.1. Scalar Numbers . . . . . . . . . . . . . . . . . . . . . 10
3.2. Multiprecision Integers . . . . . . . . . . . . . . . . . 9 3.2. Multiprecision Integers . . . . . . . . . . . . . . . . . 10
3.3. Key IDs . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.2.1. Using MPIs to encode other data . . . . . . . . . . . 11
3.4. Text . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.3. Key IDs . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.5. Time Fields . . . . . . . . . . . . . . . . . . . . . . . 10 3.4. Text . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.6. Keyrings . . . . . . . . . . . . . . . . . . . . . . . . 11 3.5. Time Fields . . . . . . . . . . . . . . . . . . . . . . . 11
3.7. String-to-Key (S2K) Specifiers . . . . . . . . . . . . . 11 3.6. Keyrings . . . . . . . . . . . . . . . . . . . . . . . . 12
3.7.1. String-to-Key (S2K) Specifier Types . . . . . . . . . 11 3.7. String-to-Key (S2K) Specifiers . . . . . . . . . . . . . 12
3.7.1.1. Simple S2K . . . . . . . . . . . . . . . . . . . 11 3.7.1. String-to-Key (S2K) Specifier Types . . . . . . . . . 12
3.7.1.2. Salted S2K . . . . . . . . . . . . . . . . . . . 12 3.7.1.1. Simple S2K . . . . . . . . . . . . . . . . . . . 12
3.7.1.3. Iterated and Salted S2K . . . . . . . . . . . . . 12 3.7.1.2. Salted S2K . . . . . . . . . . . . . . . . . . . 13
3.7.2. String-to-Key Usage . . . . . . . . . . . . . . . . . 13 3.7.1.3. Iterated and Salted S2K . . . . . . . . . . . . . 13
3.7.2.1. Secret-Key Encryption . . . . . . . . . . . . . . 13 3.7.1.4. Argon2 . . . . . . . . . . . . . . . . . . . . . 14
3.7.2.2. Symmetric-Key Message Encryption . . . . . . . . 14 3.7.2. String-to-Key Usage . . . . . . . . . . . . . . . . . 15
4. Packet Syntax . . . . . . . . . . . . . . . . . . . . . . . . 14 3.7.2.1. Secret-Key Encryption . . . . . . . . . . . . . . 15
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 14 3.7.2.2. Symmetric-Key Message Encryption . . . . . . . . 16
4.2. Packet Headers . . . . . . . . . . . . . . . . . . . . . 14 4. Packet Syntax . . . . . . . . . . . . . . . . . . . . . . . . 16
4.2.1. Old Format Packet Lengths . . . . . . . . . . . . . . 15 4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 16
4.2.2. New Format Packet Lengths . . . . . . . . . . . . . . 16 4.2. Packet Headers . . . . . . . . . . . . . . . . . . . . . 16
4.2.2.1. One-Octet Lengths . . . . . . . . . . . . . . . . 16 4.2.1. Old Format Packet Lengths . . . . . . . . . . . . . . 17
4.2.2.2. Two-Octet Lengths . . . . . . . . . . . . . . . . 16 4.2.2. New Format Packet Lengths . . . . . . . . . . . . . . 18
4.2.2.3. Five-Octet Lengths . . . . . . . . . . . . . . . 16 4.2.2.1. One-Octet Lengths . . . . . . . . . . . . . . . . 18
4.2.2.4. Partial Body Lengths . . . . . . . . . . . . . . 17 4.2.2.2. Two-Octet Lengths . . . . . . . . . . . . . . . . 18
4.2.3. Packet Length Examples . . . . . . . . . . . . . . . 17 4.2.2.3. Five-Octet Lengths . . . . . . . . . . . . . . . 18
4.3. Packet Tags . . . . . . . . . . . . . . . . . . . . . . . 18 4.2.2.4. Partial Body Lengths . . . . . . . . . . . . . . 19
5. Packet Types . . . . . . . . . . . . . . . . . . . . . . . . 19 4.2.3. Packet Length Examples . . . . . . . . . . . . . . . 19
5.1. Public-Key Encrypted Session Key Packets (Tag 1) . . . . 20 4.3. Packet Tags . . . . . . . . . . . . . . . . . . . . . . . 20
5.2. Signature Packet (Tag 2) . . . . . . . . . . . . . . . . 21 5. Packet Types . . . . . . . . . . . . . . . . . . . . . . . . 21
5.2.1. Signature Types . . . . . . . . . . . . . . . . . . . 21 5.1. Public-Key Encrypted Session Key Packets (Tag 1) . . . . 22
5.2.2. Version 3 Signature Packet Format . . . . . . . . . . 24 5.1.1. Algorithm Specific Fields for RSA encryption . . . . 22
5.2.3. Version 4 and 5 Signature Packet Formats . . . . . . 27 5.1.2. Algorithm Specific Fields for Elgamal encryption . . 22
5.2.3.1. Signature Subpacket Specification . . . . . . . . 29 5.1.3. Algorithm-Specific Fields for ECDH encryption . . . . 22
5.2.3.2. Signature Subpacket Types . . . . . . . . . . . . 32 5.1.4. Notes on PKESK . . . . . . . . . . . . . . . . . . . 23
5.2.3.3. Notes on Self-Signatures . . . . . . . . . . . . 32 5.2. Signature Packet (Tag 2) . . . . . . . . . . . . . . . . 23
5.2.3.4. Signature Creation Time . . . . . . . . . . . . . 33 5.2.1. Signature Types . . . . . . . . . . . . . . . . . . . 24
5.2.3.5. Issuer . . . . . . . . . . . . . . . . . . . . . 34 5.2.2. Version 3 Signature Packet Format . . . . . . . . . . 26
5.2.3.6. Key Expiration Time . . . . . . . . . . . . . . . 34 5.2.3. Version 4 and 5 Signature Packet Formats . . . . . . 29
5.2.3.7. Preferred Symmetric Algorithms . . . . . . . . . 34 5.2.3.1. Algorithm-Specific Fields for RSA signatures . . 30
5.2.3.8. Preferred Hash Algorithms . . . . . . . . . . . . 34 5.2.3.2. Algorithm-Specific Fields for DSA or ECDSA
5.2.3.9. Preferred Compression Algorithms . . . . . . . . 34 signatures . . . . . . . . . . . . . . . . . . . . 30
5.2.3.10. Signature Expiration Time . . . . . . . . . . . . 35 5.2.3.3. Algorithm-Specific Fields for EdDSA signatures . 30
5.2.3.11. Exportable Certification . . . . . . . . . . . . 35 5.2.3.4. Notes on Signatures . . . . . . . . . . . . . . . 31
5.2.3.12. Revocable . . . . . . . . . . . . . . . . . . . . 35 5.2.3.5. Signature Subpacket Specification . . . . . . . . 32
5.2.3.13. Trust Signature . . . . . . . . . . . . . . . . . 36 5.2.3.6. Signature Subpacket Types . . . . . . . . . . . . 34
5.2.3.14. Regular Expression . . . . . . . . . . . . . . . 36 5.2.3.7. Notes on Self-Signatures . . . . . . . . . . . . 35
5.2.3.15. Revocation Key . . . . . . . . . . . . . . . . . 36 5.2.3.8. Signature Creation Time . . . . . . . . . . . . . 36
5.2.3.16. Notation Data . . . . . . . . . . . . . . . . . . 37 5.2.3.9. Issuer . . . . . . . . . . . . . . . . . . . . . 36
5.2.3.17. Key Server Preferences . . . . . . . . . . . . . 38 5.2.3.10. Key Expiration Time . . . . . . . . . . . . . . . 36
5.2.3.18. Preferred Key Server . . . . . . . . . . . . . . 38 5.2.3.11. Preferred Symmetric Algorithms . . . . . . . . . 36
5.2.3.19. Primary User ID . . . . . . . . . . . . . . . . . 38 5.2.3.12. Preferred Hash Algorithms . . . . . . . . . . . . 37
5.2.3.20. Policy URI . . . . . . . . . . . . . . . . . . . 39 5.2.3.13. Preferred Compression Algorithms . . . . . . . . 37
5.2.3.21. Key Flags . . . . . . . . . . . . . . . . . . . . 39 5.2.3.14. Signature Expiration Time . . . . . . . . . . . . 37
5.2.3.22. Signer's User ID . . . . . . . . . . . . . . . . 41 5.2.3.15. Exportable Certification . . . . . . . . . . . . 37
5.2.3.23. Reason for Revocation . . . . . . . . . . . . . . 41 5.2.3.16. Revocable . . . . . . . . . . . . . . . . . . . . 38
5.2.3.24. Features . . . . . . . . . . . . . . . . . . . . 43 5.2.3.17. Trust Signature . . . . . . . . . . . . . . . . . 38
5.2.3.25. Signature Target . . . . . . . . . . . . . . . . 43 5.2.3.18. Regular Expression . . . . . . . . . . . . . . . 38
5.2.3.26. Embedded Signature . . . . . . . . . . . . . . . 44 5.2.3.19. Revocation Key . . . . . . . . . . . . . . . . . 39
5.2.3.27. Issuer Fingerprint . . . . . . . . . . . . . . . 44 5.2.3.20. Notation Data . . . . . . . . . . . . . . . . . . 39
5.2.4. Computing Signatures . . . . . . . . . . . . . . . . 44 5.2.3.21. Key Server Preferences . . . . . . . . . . . . . 40
5.2.4.1. Subpacket Hints . . . . . . . . . . . . . . . . . 47 5.2.3.22. Preferred Key Server . . . . . . . . . . . . . . 41
5.3. Symmetric-Key Encrypted Session Key Packets (Tag 3) . . . 47 5.2.3.23. Primary User ID . . . . . . . . . . . . . . . . . 41
5.4. One-Pass Signature Packets (Tag 4) . . . . . . . . . . . 48 5.2.3.24. Policy URI . . . . . . . . . . . . . . . . . . . 41
5.5. Key Material Packet . . . . . . . . . . . . . . . . . . . 49 5.2.3.25. Key Flags . . . . . . . . . . . . . . . . . . . . 42
5.5.1. Key Packet Variants . . . . . . . . . . . . . . . . . 49 5.2.3.26. Signer's User ID . . . . . . . . . . . . . . . . 43
5.5.1.1. Public-Key Packet (Tag 6) . . . . . . . . . . . . 49 5.2.3.27. Reason for Revocation . . . . . . . . . . . . . . 43
5.5.1.2. Public-Subkey Packet (Tag 14) . . . . . . . . . . 49 5.2.3.28. Features . . . . . . . . . . . . . . . . . . . . 45
5.5.1.3. Secret-Key Packet (Tag 5) . . . . . . . . . . . . 49 5.2.3.29. Signature Target . . . . . . . . . . . . . . . . 45
5.5.1.4. Secret-Subkey Packet (Tag 7) . . . . . . . . . . 50 5.2.3.30. Embedded Signature . . . . . . . . . . . . . . . 46
5.5.2. Public-Key Packet Formats . . . . . . . . . . . . . . 50 5.2.3.31. Issuer Fingerprint . . . . . . . . . . . . . . . 46
5.5.3. Secret-Key Packet Formats . . . . . . . . . . . . . . 51 5.2.3.32. Intended Recipient Fingerprint . . . . . . . . . 46
5.6. Algorithm-specific Parts of Keys . . . . . . . . . . . . 53 5.2.4. Computing Signatures . . . . . . . . . . . . . . . . 46
5.6.1. Algorithm-Specific Part for RSA Keys . . . . . . . . 53 5.2.4.1. Subpacket Hints . . . . . . . . . . . . . . . . . 49
5.6.2. Algorithm-Specific Part for DSA Keys . . . . . . . . 54 5.3. Symmetric-Key Encrypted Session Key Packets (Tag 3) . . . 49
5.6.3. Algorithm-Specific Part for Elgamal Keys . . . . . . 54 5.3.1. No v5 SKESK with SEIPD . . . . . . . . . . . . . . . 51
5.6.4. Algorithm-Specific Part for ECDSA Keys . . . . . . . 54 5.4. One-Pass Signature Packets (Tag 4) . . . . . . . . . . . 51
5.6.5. Algorithm-Specific Part for EdDSA Keys . . . . . . . 55 5.5. Key Material Packet . . . . . . . . . . . . . . . . . . . 52
5.6.6. Algorithm-Specific Part for ECDH Keys . . . . . . . . 55 5.5.1. Key Packet Variants . . . . . . . . . . . . . . . . . 52
5.7. Compressed Data Packet (Tag 8) . . . . . . . . . . . . . 56 5.5.1.1. Public-Key Packet (Tag 6) . . . . . . . . . . . . 52
5.8. Symmetrically Encrypted Data Packet (Tag 9) . . . . . . . 57 5.5.1.2. Public-Subkey Packet (Tag 14) . . . . . . . . . . 52
5.9. Marker Packet (Obsolete Literal Packet) (Tag 10) . . . . 58 5.5.1.3. Secret-Key Packet (Tag 5) . . . . . . . . . . . . 52
5.10. Literal Data Packet (Tag 11) . . . . . . . . . . . . . . 58 5.5.1.4. Secret-Subkey Packet (Tag 7) . . . . . . . . . . 52
5.11. Trust Packet (Tag 12) . . . . . . . . . . . . . . . . . . 59 5.5.2. Public-Key Packet Formats . . . . . . . . . . . . . . 53
5.12. User ID Packet (Tag 13) . . . . . . . . . . . . . . . . . 59 5.5.3. Secret-Key Packet Formats . . . . . . . . . . . . . . 54
5.13. User Attribute Packet (Tag 17) . . . . . . . . . . . . . 59 5.6. Algorithm-specific Parts of Keys . . . . . . . . . . . . 57
5.13.1. The Image Attribute Subpacket . . . . . . . . . . . 60 5.6.1. Algorithm-Specific Part for RSA Keys . . . . . . . . 57
5.6.2. Algorithm-Specific Part for DSA Keys . . . . . . . . 57
5.6.3. Algorithm-Specific Part for Elgamal Keys . . . . . . 57
5.6.4. Algorithm-Specific Part for ECDSA Keys . . . . . . . 58
5.6.5. Algorithm-Specific Part for EdDSA Keys . . . . . . . 58
5.6.6. Algorithm-Specific Part for ECDH Keys . . . . . . . . 59
5.7. Compressed Data Packet (Tag 8) . . . . . . . . . . . . . 59
5.8. Symmetrically Encrypted Data Packet (Tag 9) . . . . . . . 60
5.9. Marker Packet (Obsolete Literal Packet) (Tag 10) . . . . 61
5.10. Literal Data Packet (Tag 11) . . . . . . . . . . . . . . 61
5.11. Trust Packet (Tag 12) . . . . . . . . . . . . . . . . . . 62
5.12. User ID Packet (Tag 13) . . . . . . . . . . . . . . . . . 63
5.13. User Attribute Packet (Tag 17) . . . . . . . . . . . . . 63
5.13.1. The Image Attribute Subpacket . . . . . . . . . . . 64
5.14. Sym. Encrypted Integrity Protected Data Packet (Tag 5.14. Sym. Encrypted Integrity Protected Data Packet (Tag
18) . . . . . . . . . . . . . . . . . . . . . . . . . . 61 18) . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5.15. Modification Detection Code Packet (Tag 19) . . . . . . . 64 5.15. Modification Detection Code Packet (Tag 19) . . . . . . . 67
6. Radix-64 Conversions . . . . . . . . . . . . . . . . . . . . 65 5.16. AEAD Encrypted Data Packet (Tag 20) . . . . . . . . . . . 68
6.1. An Implementation of the CRC-24 in "C" . . . . . . . . . 65 5.16.1. EAX Mode . . . . . . . . . . . . . . . . . . . . . . 69
6.2. Forming ASCII Armor . . . . . . . . . . . . . . . . . . . 66 5.16.2. OCB Mode . . . . . . . . . . . . . . . . . . . . . . 70
6.3. Encoding Binary in Radix-64 . . . . . . . . . . . . . . . 69 6. Radix-64 Conversions . . . . . . . . . . . . . . . . . . . . 70
6.4. Decoding Radix-64 . . . . . . . . . . . . . . . . . . . . 71 6.1. An Implementation of the CRC-24 in "C" . . . . . . . . . 71
6.5. Examples of Radix-64 . . . . . . . . . . . . . . . . . . 71 6.2. Forming ASCII Armor . . . . . . . . . . . . . . . . . . . 71
6.6. Example of an ASCII Armored Message . . . . . . . . . . . 72 6.3. Encoding Binary in Radix-64 . . . . . . . . . . . . . . . 74
7. Cleartext Signature Framework . . . . . . . . . . . . . . . . 72 6.4. Decoding Radix-64 . . . . . . . . . . . . . . . . . . . . 76
7.1. Dash-Escaped Text . . . . . . . . . . . . . . . . . . . . 73 6.5. Examples of Radix-64 . . . . . . . . . . . . . . . . . . 76
8. Regular Expressions . . . . . . . . . . . . . . . . . . . . . 74 6.6. Example of an ASCII Armored Message . . . . . . . . . . . 77
9. Constants . . . . . . . . . . . . . . . . . . . . . . . . . . 74 7. Cleartext Signature Framework . . . . . . . . . . . . . . . . 77
9.1. Public-Key Algorithms . . . . . . . . . . . . . . . . . . 75 7.1. Dash-Escaped Text . . . . . . . . . . . . . . . . . . . . 78
9.2. ECC Curve OID . . . . . . . . . . . . . . . . . . . . . . 76 8. Regular Expressions . . . . . . . . . . . . . . . . . . . . . 79
9.3. Symmetric-Key Algorithms . . . . . . . . . . . . . . . . 76 9. Constants . . . . . . . . . . . . . . . . . . . . . . . . . . 79
9.4. Compression Algorithms . . . . . . . . . . . . . . . . . 77 9.1. Public-Key Algorithms . . . . . . . . . . . . . . . . . . 80
9.5. Hash Algorithms . . . . . . . . . . . . . . . . . . . . . 78 9.2. ECC Curves for OpenPGP . . . . . . . . . . . . . . . . . 82
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 79 9.2.1. Curve-Specific Wire Formats . . . . . . . . . . . . . 83
10.1. New String-to-Key Specifier Types . . . . . . . . . . . 79 9.3. Symmetric-Key Algorithms . . . . . . . . . . . . . . . . 84
10.2. New Packets . . . . . . . . . . . . . . . . . . . . . . 79 9.4. Compression Algorithms . . . . . . . . . . . . . . . . . 85
10.2.1. User Attribute Types . . . . . . . . . . . . . . . . 79 9.5. Hash Algorithms . . . . . . . . . . . . . . . . . . . . . 86
10.2.1.1. Image Format Subpacket Types . . . . . . . . . . 79 9.6. AEAD Algorithms . . . . . . . . . . . . . . . . . . . . . 87
10.2.2. New Signature Subpackets . . . . . . . . . . . . . . 80 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 87
10.2.2.1. Signature Notation Data Subpackets . . . . . . . 80 10.1. New String-to-Key Specifier Types . . . . . . . . . . . 87
10.2. New Packets . . . . . . . . . . . . . . . . . . . . . . 88
10.2.1. User Attribute Types . . . . . . . . . . . . . . . . 88
10.2.1.1. Image Format Subpacket Types . . . . . . . . . . 88
10.2.2. New Signature Subpackets . . . . . . . . . . . . . . 88
10.2.2.1. Signature Notation Data Subpackets . . . . . . . 89
10.2.2.2. Signature Notation Data Subpacket Notation 10.2.2.2. Signature Notation Data Subpacket Notation
Flags . . . . . . . . . . . . . . . . . . . . . . . 80 Flags . . . . . . . . . . . . . . . . . . . . . . . 89
10.2.2.3. Key Server Preference Extensions . . . . . . . . 81 10.2.2.3. Key Server Preference Extensions . . . . . . . . 89
10.2.2.4. Key Flags Extensions . . . . . . . . . . . . . . 81 10.2.2.4. Key Flags Extensions . . . . . . . . . . . . . . 89
10.2.2.5. Reason for Revocation Extensions . . . . . . . . 81 10.2.2.5. Reason for Revocation Extensions . . . . . . . . 90
10.2.2.6. Implementation Features . . . . . . . . . . . . 81 10.2.2.6. Implementation Features . . . . . . . . . . . . 90
10.2.3. New Packet Versions . . . . . . . . . . . . . . . . 82 10.2.3. New Packet Versions . . . . . . . . . . . . . . . . 90
10.3. New Algorithms . . . . . . . . . . . . . . . . . . . . . 82 10.3. New Algorithms . . . . . . . . . . . . . . . . . . . . . 90
10.3.1. Public-Key Algorithms . . . . . . . . . . . . . . . 82 10.3.1. Public-Key Algorithms . . . . . . . . . . . . . . . 91
10.3.2. Symmetric-Key Algorithms . . . . . . . . . . . . . . 83 10.3.2. Symmetric-Key Algorithms . . . . . . . . . . . . . . 91
10.3.3. Hash Algorithms . . . . . . . . . . . . . . . . . . 83 10.3.3. Hash Algorithms . . . . . . . . . . . . . . . . . . 91
10.3.4. Compression Algorithms . . . . . . . . . . . . . . . 84 10.3.4. Compression Algorithms . . . . . . . . . . . . . . . 92
11. Packet Composition . . . . . . . . . . . . . . . . . . . . . 84 10.3.5. Elliptic Curve Algorithms . . . . . . . . . . . . . 92
11.1. Transferable Public Keys . . . . . . . . . . . . . . . . 84 10.4. Elliptic Curve Point and Scalar Wire Formats . . . . . . 93
11.2. Transferable Secret Keys . . . . . . . . . . . . . . . . 85 10.5. Changes to existing registries . . . . . . . . . . . . . 93
11.3. OpenPGP Messages . . . . . . . . . . . . . . . . . . . . 86 11. Packet Composition . . . . . . . . . . . . . . . . . . . . . 93
11.4. Detached Signatures . . . . . . . . . . . . . . . . . . 86 11.1. Transferable Public Keys . . . . . . . . . . . . . . . . 93
12. Enhanced Key Formats . . . . . . . . . . . . . . . . . . . . 86 11.2. Transferable Secret Keys . . . . . . . . . . . . . . . . 95
12.1. Key Structures . . . . . . . . . . . . . . . . . . . . . 87 11.3. OpenPGP Messages . . . . . . . . . . . . . . . . . . . . 95
12.2. Key IDs and Fingerprints . . . . . . . . . . . . . . . . 88 11.4. Detached Signatures . . . . . . . . . . . . . . . . . . 96
13. Elliptic Curve Cryptography . . . . . . . . . . . . . . . . . 89 12. Enhanced Key Formats . . . . . . . . . . . . . . . . . . . . 96
13.1. Supported ECC Curves . . . . . . . . . . . . . . . . . . 89 12.1. Key Structures . . . . . . . . . . . . . . . . . . . . . 96
13.2. ECDSA and ECDH Conversion Primitives . . . . . . . . . . 90 12.2. Key IDs and Fingerprints . . . . . . . . . . . . . . . . 97
13.3. EdDSA Point Format . . . . . . . . . . . . . . . . . . . 91 13. Elliptic Curve Cryptography . . . . . . . . . . . . . . . . . 99
13.4. Key Derivation Function . . . . . . . . . . . . . . . . 91 13.1. Supported ECC Curves . . . . . . . . . . . . . . . . . . 99
13.5. EC DH Algorithm (ECDH) . . . . . . . . . . . . . . . . . 91 13.2. EC Point Wire Formats . . . . . . . . . . . . . . . . . 100
14. Notes on Algorithms . . . . . . . . . . . . . . . . . . . . . 94 13.2.1. SEC1 EC Point Wire Format . . . . . . . . . . . . . 100
14.1. PKCS#1 Encoding in OpenPGP . . . . . . . . . . . . . . . 94 13.2.2. Prefixed Native EC Point Wire Format . . . . . . . . 100
14.1.1. EME-PKCS1-v1_5-ENCODE . . . . . . . . . . . . . . . 94 13.2.3. Notes on EC Point Wire Formats . . . . . . . . . . . 101
14.1.2. EME-PKCS1-v1_5-DECODE . . . . . . . . . . . . . . . 95 13.3. EC Scalar Wire Formats . . . . . . . . . . . . . . . . . 101
14.1.3. EMSA-PKCS1-v1_5 . . . . . . . . . . . . . . . . . . 96 13.3.1. EC Octet String Wire Format . . . . . . . . . . . . 102
14.2. Symmetric Algorithm Preferences . . . . . . . . . . . . 97 13.3.2. Elliptic Curve Prefixed Octet String Wire Format . . 103
14.3. Other Algorithm Preferences . . . . . . . . . . . . . . 97 13.4. Key Derivation Function . . . . . . . . . . . . . . . . 103
14.3.1. Compression Preferences . . . . . . . . . . . . . . 98 13.5. EC DH Algorithm (ECDH) . . . . . . . . . . . . . . . . . 104
14.3.2. Hash Algorithm Preferences . . . . . . . . . . . . . 98 14. Notes on Algorithms . . . . . . . . . . . . . . . . . . . . . 107
14.4. Plaintext . . . . . . . . . . . . . . . . . . . . . . . 98 14.1. PKCS#1 Encoding in OpenPGP . . . . . . . . . . . . . . . 107
14.5. RSA . . . . . . . . . . . . . . . . . . . . . . . . . . 99 14.1.1. EME-PKCS1-v1_5-ENCODE . . . . . . . . . . . . . . . 107
14.6. DSA . . . . . . . . . . . . . . . . . . . . . . . . . . 99 14.1.2. EME-PKCS1-v1_5-DECODE . . . . . . . . . . . . . . . 108
14.7. Elgamal . . . . . . . . . . . . . . . . . . . . . . . . 99 14.1.3. EMSA-PKCS1-v1_5 . . . . . . . . . . . . . . . . . . 108
14.8. EdDSA . . . . . . . . . . . . . . . . . . . . . . . . . 100 14.2. Symmetric Algorithm Preferences . . . . . . . . . . . . 109
14.9. Reserved Algorithm Numbers . . . . . . . . . . . . . . . 100 14.3. Other Algorithm Preferences . . . . . . . . . . . . . . 110
14.10. OpenPGP CFB Mode . . . . . . . . . . . . . . . . . . . . 100 14.3.1. Compression Preferences . . . . . . . . . . . . . . 110
14.11. Private or Experimental Parameters . . . . . . . . . . . 102 14.3.2. Hash Algorithm Preferences . . . . . . . . . . . . . 111
14.12. Extension of the MDC System . . . . . . . . . . . . . . 102
14.13. Meta-Considerations for Expansion . . . . . . . . . . . 103 14.4. Plaintext . . . . . . . . . . . . . . . . . . . . . . . 111
15. Security Considerations . . . . . . . . . . . . . . . . . . . 103 14.5. RSA . . . . . . . . . . . . . . . . . . . . . . . . . . 111
16. Implementation Nits . . . . . . . . . . . . . . . . . . . . . 109 14.6. DSA . . . . . . . . . . . . . . . . . . . . . . . . . . 112
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 111 14.7. Elgamal . . . . . . . . . . . . . . . . . . . . . . . . 112
17.1. Normative References . . . . . . . . . . . . . . . . . . 111 14.8. EdDSA . . . . . . . . . . . . . . . . . . . . . . . . . 112
17.2. Informative References . . . . . . . . . . . . . . . . . 114 14.9. Reserved Algorithm Numbers . . . . . . . . . . . . . . . 113
Appendix A. Test vectors . . . . . . . . . . . . . . . . . . . . 115 14.10. OpenPGP CFB Mode . . . . . . . . . . . . . . . . . . . . 113
A.1. Sample EdDSA key . . . . . . . . . . . . . . . . . . . . 115 14.11. Private or Experimental Parameters . . . . . . . . . . . 115
A.2. Sample EdDSA signature . . . . . . . . . . . . . . . . . 116 14.12. Extension of the MDC System . . . . . . . . . . . . . . 115
Appendix B. Document Workflow . . . . . . . . . . . . . . . . . 116 14.13. Meta-Considerations for Expansion . . . . . . . . . . . 116
Appendix C. ECC Point compression flag bytes . . . . . . . . . . 117 15. Security Considerations . . . . . . . . . . . . . . . . . . . 116
Appendix D. Acknowledgements . . . . . . . . . . . . . . . . . . 117 16. Implementation Nits . . . . . . . . . . . . . . . . . . . . . 122
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 117 17. References . . . . . . . . . . . . . . . . . . . . . . . . . 124
17.1. Normative References . . . . . . . . . . . . . . . . . . 124
17.2. Informative References . . . . . . . . . . . . . . . . . 127
Appendix A. Test vectors . . . . . . . . . . . . . . . . . . . . 128
A.1. Sample EdDSA key . . . . . . . . . . . . . . . . . . . . 128
A.2. Sample EdDSA signature . . . . . . . . . . . . . . . . . 129
A.3. Sample AEAD-EAX encryption and decryption . . . . . . . . 129
A.3.1. Sample Parameters . . . . . . . . . . . . . . . . . . 129
A.3.2. Sample symmetric-key encrypted session key packet
(v5) . . . . . . . . . . . . . . . . . . . . . . . . 130
A.3.3. Starting AEAD-EAX decryption of CEK . . . . . . . . . 130
A.3.4. Initial Content Encryption Key . . . . . . . . . . . 131
A.3.5. Sample AEAD encrypted data packet . . . . . . . . . . 131
A.3.6. Decryption of data . . . . . . . . . . . . . . . . . 131
A.3.7. Complete AEAD-EAX encrypted packet sequence . . . . . 132
A.4. Sample AEAD-OCB encryption and decryption . . . . . . . . 132
A.4.1. Sample Parameters . . . . . . . . . . . . . . . . . . 132
A.4.2. Sample symmetric-key encrypted session key packet
(v5) . . . . . . . . . . . . . . . . . . . . . . . . 133
A.4.3. Starting AEAD-OCB decryption of CEK . . . . . . . . . 133
A.4.4. Initial Content Encryption Key . . . . . . . . . . . 134
A.4.5. Sample AEAD encrypted data packet . . . . . . . . . . 134
A.4.6. Decryption of data . . . . . . . . . . . . . . . . . 134
A.4.7. Complete AEAD-OCB encrypted packet sequence . . . . . 135
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 135
Appendix C. Document Workflow . . . . . . . . . . . . . . . . . 136
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 136
1. Introduction 1. Introduction
{ This is work in progress to update OpenPGP. Editorial notes are { This is work in progress to update OpenPGP. Editorial notes are
enclosed in curly braces. } enclosed in curly braces. }
This document provides information on the message-exchange packet This document provides information on the message-exchange packet
formats used by OpenPGP to provide encryption, decryption, signing, formats used by OpenPGP to provide encryption, decryption, signing,
and key management functions. It is a revision of RFC 4880, "OpenPGP and key management functions. It is a revision of RFC 4880, "OpenPGP
Message Format", which is a revision of RFC 2440, which itself Message Format", which is a revision of RFC 2440, which itself
replaces RFC 1991, "PGP Message Exchange Formats" [RFC1991] [RFC2440] replaces RFC 1991, "PGP Message Exchange Formats" [RFC1991] [RFC2440]
[RFC4880]. [RFC4880].
This document obsoletes: RFC 4880 (OpenPGP), RFC 5581 (Camellia This document obsoletes: RFC 4880 (OpenPGP), RFC 5581 (Camellia in
cipher) and RFC 6637 (ECC for OpenPGP). OpenPGP) and RFC 6637 (Elliptic Curves in OpenPGP).
1.1. Terms 1.1. Terms
* OpenPGP - This is a term for security software that uses PGP 5 as * OpenPGP - This is a term for security software that uses PGP 5 as
a basis, formalized in this document. a basis, formalized in this document.
* PGP - Pretty Good Privacy. PGP is a family of software systems * PGP - Pretty Good Privacy. PGP is a family of software systems
developed by Philip R. Zimmermann from which OpenPGP is based. developed by Philip R. Zimmermann from which OpenPGP is based.
* PGP 2 - This version of PGP has many variants; where necessary a * PGP 2 - This version of PGP has many variants; where necessary a
more detailed version number is used here. PGP 2 uses only RSA, more detailed version number is used here. PGP 2 uses only RSA,
MD5, and IDEA for its cryptographic transforms. An informational MD5, and IDEA for its cryptographic transforms. An informational
RFC, RFC 1991, was written describing this version of PGP. RFC, RFC 1991, was written describing this version of PGP.
* PGP 5 - This version of PGP is formerly known as "PGP 3" in the * PGP 5 - This version of PGP is formerly known as "PGP 3" in the
community. It has new formats and corrects a number of problems community. It has new formats and corrects a number of problems
in the PGP 2 design. It is referred to here as PGP 5 because that in the PGP 2 design. It is referred to here as PGP 5 because that
software was the first release of the "PGP 3" code base. software was the first release of the "PGP 3" code base.
skipping to change at page 10, line 32 skipping to change at page 11, line 25
The length field of an MPI describes the length starting from its The length field of an MPI describes the length starting from its
most significant non-zero bit. Thus, the MPI [00 02 01] is not most significant non-zero bit. Thus, the MPI [00 02 01] is not
formed correctly. It should be [00 01 01]. formed correctly. It should be [00 01 01].
Unused bits of an MPI MUST be zero. Unused bits of an MPI MUST be zero.
Also note that when an MPI is encrypted, the length refers to the Also note that when an MPI is encrypted, the length refers to the
plaintext MPI. It may be ill-formed in its ciphertext. plaintext MPI. It may be ill-formed in its ciphertext.
3.2.1. Using MPIs to encode other data
Note that MPIs are used in some places used to encode non-integer
data, such as an elliptic curve point (see Section 13.2, or an octet
string of known, fixed length (see Section 13.3). The wire
representation is the same: two octets of length in bits counted from
the first non-zero bit, followed by the smallest series of octets
that can represent the value while stripping off any leading zero
octets.
3.3. Key IDs 3.3. Key IDs
A Key ID is an eight-octet scalar that identifies a key. A Key ID is an eight-octet scalar that identifies a key.
Implementations SHOULD NOT assume that Key IDs are unique. Implementations SHOULD NOT assume that Key IDs are unique.
Section 12 describes how Key IDs are formed. Section 12 describes how Key IDs are formed.
3.4. Text 3.4. Text
Unless otherwise specified, the character set for text is the UTF-8 Unless otherwise specified, the character set for text is the UTF-8
[RFC3629] encoding of Unicode [ISO10646]. [RFC3629] encoding of Unicode [ISO10646].
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into symmetric-key encryption/decryption keys. They are used in two into symmetric-key encryption/decryption keys. They are used in two
places, currently: to encrypt the secret part of private keys in the places, currently: to encrypt the secret part of private keys in the
private keyring, and to convert passphrases to encryption keys for private keyring, and to convert passphrases to encryption keys for
symmetrically encrypted messages. symmetrically encrypted messages.
3.7.1. String-to-Key (S2K) Specifier Types 3.7.1. String-to-Key (S2K) Specifier Types
There are three types of S2K specifiers currently supported, and some There are three types of S2K specifiers currently supported, and some
reserved values: reserved values:
+============+==========================+ +========+==================+==================+=================+
| ID | S2K Type | | ID | S2K Type | Generate? | Reference |
+============+==========================+ +========+==================+==================+=================+
| 0 | Simple S2K | | 0 | Simple S2K | N | Section 3.7.1.1 |
+------------+--------------------------+ +--------+------------------+------------------+-----------------+
| 1 | Salted S2K | | 1 | Salted S2K | Only when string | Section 3.7.1.2 |
+------------+--------------------------+ | | | is high entropy | |
| 2 | Reserved value | +--------+------------------+------------------+-----------------+
+------------+--------------------------+ | 2 | Reserved value | N | |
| 3 | Iterated and Salted S2K | +--------+------------------+------------------+-----------------+
+------------+--------------------------+ | 3 | Iterated and | Y | Section 3.7.1.3 |
| 100 to 110 | Private/Experimental S2K | | | Salted S2K | | |
+------------+--------------------------+ +--------+------------------+------------------+-----------------+
| 4 | Argon2 | Y | Section 3.7.1.4 |
+--------+------------------+------------------+-----------------+
| 100 to | Private/ | As appropriate | |
| 110 | Experimental S2K | | |
+--------+------------------+------------------+-----------------+
Table 1: S2K type registry Table 1: S2K type registry
These are described in the subsections below. These are described in the subsections below.
3.7.1.1. Simple S2K 3.7.1.1. Simple S2K
This directly hashes the string to produce the key data. See below This directly hashes the string to produce the key data. See below
for how this hashing is done. for how this hashing is done.
Octet 0: 0x00 Octet 0: 0x00
Octet 1: hash algorithm Octet 1: hash algorithm
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Initially, one or more hash contexts are set up as with the other S2K Initially, one or more hash contexts are set up as with the other S2K
algorithms, depending on how many octets of key data are needed. algorithms, depending on how many octets of key data are needed.
Then the salt, followed by the passphrase data, is repeatedly hashed Then the salt, followed by the passphrase data, is repeatedly hashed
until the number of octets specified by the octet count has been until the number of octets specified by the octet count has been
hashed. The one exception is that if the octet count is less than hashed. The one exception is that if the octet count is less than
the size of the salt plus passphrase, the full salt plus passphrase the size of the salt plus passphrase, the full salt plus passphrase
will be hashed even though that is greater than the octet count. will be hashed even though that is greater than the octet count.
After the hashing is done, the data is unloaded from the hash After the hashing is done, the data is unloaded from the hash
context(s) as with the other S2K algorithms. context(s) as with the other S2K algorithms.
3.7.1.4. Argon2
This S2K method hashes the passphrase using Argon2, specified in
[RFC9106]. This provides memory-hardness, further protecting the
passphrase against brute-force attacks.
Octet 0: 0x04
Octets 1-16: 16-octet salt value
Octet 17: one-octet number of passes t
Octet 18: one-octet degree of parallelism p
Octet 19: one-octet exponent indicating the memory size m
The salt SHOULD be unique for each password.
The number of passes t and the degree of parallelism p MUST be non-
zero.
The memory size m is 2**encoded_m, where "encoded_m" is the encoded
memory size in Octet 19. The encoded memory size MUST be a value
from 3+ceil(log_2(p)) to 31, such that the decoded memory size m is a
value from 8*p to 2**31.
Argon2 is invoked with the passphrase as P, the salt as S, the values
of t, p and m as described above, the required key size as the tag
length T, 0x13 as the version v, and Argon2id as the type.
For the recommended values of t, p and m, see Section 4 of [RFC9106].
If the recommended value of m for a given application is not a power
of 2, it is RECOMMENDED to round up to the next power of 2 if the
resulting performance would be acceptable, and round down otherwise
(keeping in mind that m must be at least 8*p).
As an example, with the first recommended option (t=1, p=4, m=2**21),
the full S2K specifier would be:
04 XX XX XX XX XX XX XX XX XX XX XX XX XX XX XX
XX 01 04 15
(where XX represents a random octet of salt).
3.7.2. String-to-Key Usage 3.7.2. String-to-Key Usage
Simple S2K and Salted S2K specifiers are not particularly secure when Simple S2K and Salted S2K specifiers can be brute-forced when used
used with a low-entropy secret, such as those typically provided by with a low-entropy string, such as those typically provided by users.
users. Implementations SHOULD NOT use these methods on encryption of In addition, the usage of Simple S2K can lead to key and IV reuse
either keys and messages. (see Section 5.3). Therefore, when generating S2K specifiers,
implementations MUST NOT use Simple S2K, and SHOULD NOT use Salted
S2K unless the implementation knows that the string is high-entropy
(e.g., it generated the string itself using a known-good source of
randomness). It is RECOMMENDED that implementations use Argon2.
3.7.2.1. Secret-Key Encryption 3.7.2.1. Secret-Key Encryption
An S2K specifier can be stored in the secret keyring to specify how An S2K specifier can be stored in the secret keyring to specify how
to convert the passphrase to a key that unlocks the secret data. to convert the passphrase to a key that unlocks the secret data.
Older versions of PGP just stored a cipher algorithm octet preceding Older versions of PGP just stored a symmetric cipher algorithm octet
the secret data or a zero to indicate that the secret data was preceding the secret data or a zero to indicate that the secret data
unencrypted. The MD5 hash function was always used to convert the was unencrypted. The MD5 hash function was always used to convert
passphrase to a key for the specified cipher algorithm. the passphrase to a key for the specified cipher algorithm.
For compatibility, when an S2K specifier is used, the special value For compatibility, when an S2K specifier is used, the special value
254 or 255 is stored in the position where the hash algorithm octet 253, 254, or 255 is stored in the position where the cipher algorithm
would have been in the old data structure. This is then followed octet would have been in the old data structure. This is then
immediately by a one-octet algorithm identifier, and then by the S2K followed immediately by a one-octet algorithm identifier, and then by
specifier as encoded above. the S2K specifier as encoded above.
Therefore, preceding the secret data there will be one of these Therefore, preceding the secret data there will be one of these
possibilities: possibilities:
0: secret data is unencrypted (no passphrase) 0: secret data is unencrypted (no passphrase)
255 or 254: followed by algorithm octet and S2K specifier 255, 254, or 253: followed by algorithm octet and S2K specifier
Cipher alg: use Simple S2K algorithm using MD5 hash Cipher alg: use Simple S2K algorithm using MD5 hash
This last possibility, the cipher algorithm number with an implicit This last possibility, the cipher algorithm number with an implicit
use of MD5 and IDEA, is provided for backward compatibility; it MAY use of MD5 and IDEA, is provided for backward compatibility; it MAY
be understood, but SHOULD NOT be generated, and is deprecated. be understood, but SHOULD NOT be generated, and is deprecated.
These are followed by an Initial Vector of the same length as the These are followed by an Initial Vector of the same length as the
block size of the cipher for the decryption of the secret values, if block size of the cipher for the decryption of the secret values, if
they are encrypted, and then the secret-key values themselves. they are encrypted, and then the secret-key values themselves.
3.7.2.2. Symmetric-Key Message Encryption 3.7.2.2. Symmetric-Key Message Encryption
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| 13 | User ID Packet | | 13 | User ID Packet |
+----------+----------------------------------------------------+ +----------+----------------------------------------------------+
| 14 | Public-Subkey Packet | | 14 | Public-Subkey Packet |
+----------+----------------------------------------------------+ +----------+----------------------------------------------------+
| 17 | User Attribute Packet | | 17 | User Attribute Packet |
+----------+----------------------------------------------------+ +----------+----------------------------------------------------+
| 18 | Sym. Encrypted and Integrity Protected Data Packet | | 18 | Sym. Encrypted and Integrity Protected Data Packet |
+----------+----------------------------------------------------+ +----------+----------------------------------------------------+
| 19 | Modification Detection Code Packet | | 19 | Modification Detection Code Packet |
+----------+----------------------------------------------------+ +----------+----------------------------------------------------+
| 20 | Reserved (AEAD Encrypted Data) | | 20 | AEAD Encrypted Data Packet |
+----------+----------------------------------------------------+ +----------+----------------------------------------------------+
| 60 to 63 | Private or Experimental Values | | 60 to 63 | Private or Experimental Values |
+----------+----------------------------------------------------+ +----------+----------------------------------------------------+
Table 2: Packet type registry Table 2: Packet type registry
5. Packet Types 5. Packet Types
5.1. Public-Key Encrypted Session Key Packets (Tag 1) 5.1. Public-Key Encrypted Session Key Packets (Tag 1)
A Public-Key Encrypted Session Key packet holds the session key used Zero or more Public-Key Encrypted Session Key packets and/or
to encrypt a message. Zero or more Public-Key Encrypted Session Key Symmetric-Key Encrypted Session Key packets may precede an encryption
packets and/or Symmetric-Key Encrypted Session Key packets may container (i.e. a Symmetrically Encrypted Integrity Protected Data
precede a Symmetrically Encrypted Data Packet, which holds an packet, an AEAD Encrypted Data packet, or -- for historic data -- a
encrypted message. The message is encrypted with the session key, Symmetrically Encrypted Data packet), which holds an encrypted
and the session key is itself encrypted and stored in the Encrypted message. The message is encrypted with the session key, and the
Session Key packet(s). The Symmetrically Encrypted Data Packet is session key is itself encrypted and stored in the Encrypted Session
preceded by one Public-Key Encrypted Session Key packet for each Key packet(s). The encryption container is preceded by one Public-
OpenPGP key to which the message is encrypted. The recipient of the Key Encrypted Session Key packet for each OpenPGP key to which the
message finds a session key that is encrypted to their public key, message is encrypted. The recipient of the message finds a session
decrypts the session key, and then uses the session key to decrypt key that is encrypted to their public key, decrypts the session key,
the message. and then uses the session key to decrypt the message.
The body of this packet consists of: The body of this packet consists of:
* A one-octet number giving the version number of the packet type. * A one-octet number giving the version number of the packet type.
The currently defined value for packet version is 3. The currently defined value for packet version is 3.
* An eight-octet number that gives the Key ID of the public key to * An eight-octet number that gives the Key ID of the public key to
which the session key is encrypted. If the session key is which the session key is encrypted. If the session key is
encrypted to a subkey, then the Key ID of this subkey is used here encrypted to a subkey, then the Key ID of this subkey is used here
instead of the Key ID of the primary key. instead of the Key ID of the primary key.
* A one-octet number giving the public-key algorithm used. * A one-octet number giving the public-key algorithm used.
* A string of octets that is the encrypted session key. This string * A string of octets that is the encrypted session key. This string
takes up the remainder of the packet, and its contents are takes up the remainder of the packet, and its contents are
dependent on the public-key algorithm used. dependent on the public-key algorithm used.
Algorithm Specific Fields for RSA encryption: 5.1.1. Algorithm Specific Fields for RSA encryption
- Multiprecision integer (MPI) of RSA encrypted value m**e mod n. * Multiprecision integer (MPI) of RSA-encrypted value m**e mod n.
Algorithm Specific Fields for Elgamal encryption: 5.1.2. Algorithm Specific Fields for Elgamal encryption
- MPI of Elgamal (Diffie-Hellman) value g**k mod p. * MPI of Elgamal (Diffie-Hellman) value g**k mod p.
- MPI of Elgamal (Diffie-Hellman) value m * y**k mod p. * MPI of Elgamal (Diffie-Hellman) value m * y**k mod p.
Algorithm-Specific Fields for ECDH encryption: 5.1.3. Algorithm-Specific Fields for ECDH encryption
- MPI of an EC point representing an ephemeral public key. * MPI of an EC point representing an ephemeral public key, in the
point format associated with the curve as specified in
Section 9.2.
- a one-octet size, followed by a symmetric key encoded using the * A one-octet size, followed by a symmetric key encoded using the
method described in Section 13.5. method described in Section 13.5.
5.1.4. Notes on PKESK
The value "m" in the above formulas is derived from the session key The value "m" in the above formulas is derived from the session key
as follows. First, the session key is prefixed with a one-octet as follows. First, the session key is prefixed with a one-octet
algorithm identifier that specifies the symmetric encryption algorithm identifier that specifies the symmetric encryption
algorithm used to encrypt the following Symmetrically Encrypted Data algorithm used to encrypt the following encryption container. Then a
Packet. Then a two-octet checksum is appended, which is equal to the two-octet checksum is appended, which is equal to the sum of the
sum of the preceding session key octets, not including the algorithm preceding session key octets, not including the algorithm identifier,
identifier, modulo 65536. This value is then encoded as described in modulo 65536. This value is then encoded as described in PKCS#1
PKCS#1 block encoding EME-PKCS1-v1_5 in Section 7.2.1 of [RFC3447] to block encoding EME-PKCS1-v1_5 in Section 7.2.1 of [RFC3447] to form
form the "m" value used in the formulas above. See Section 14.1 in the "m" value used in the formulas above. See Section 14.1 in this
this document for notes on OpenPGP's use of PKCS#1. document for notes on OpenPGP's use of PKCS#1.
Note that when an implementation forms several PKESKs with one Note that when an implementation forms several PKESKs with one
session key, forming a message that can be decrypted by several keys, session key, forming a message that can be decrypted by several keys,
the implementation MUST make a new PKCS#1 encoding for each key. the implementation MUST make a new PKCS#1 encoding for each key.
An implementation MAY accept or use a Key ID of zero as a "wild card" An implementation MAY accept or use a Key ID of zero as a "wild card"
or "speculative" Key ID. In this case, the receiving implementation or "speculative" Key ID. In this case, the receiving implementation
would try all available private keys, checking for a valid decrypted would try all available private keys, checking for a valid decrypted
session key. This format helps reduce traffic analysis of messages. session key. This format helps reduce traffic analysis of messages.
skipping to change at page 28, line 33 skipping to change at page 30, line 33
unhashed subpackets; a pointer incremented by this number will unhashed subpackets; a pointer incremented by this number will
skip over the unhashed subpackets. skip over the unhashed subpackets.
* Unhashed subpacket data set (zero or more subpackets). * Unhashed subpacket data set (zero or more subpackets).
* Two-octet field holding the left 16 bits of the signed hash value. * Two-octet field holding the left 16 bits of the signed hash value.
* One or more multiprecision integers comprising the signature. * One or more multiprecision integers comprising the signature.
This portion is algorithm specific: This portion is algorithm specific:
Algorithm-Specific Fields for RSA signatures: 5.2.3.1. Algorithm-Specific Fields for RSA signatures
- Multiprecision integer (MPI) of RSA signature value m**d mod n.
Algorithm-Specific Fields for DSA or ECDSA signatures: * Multiprecision integer (MPI) of RSA signature value m**d mod n.
- MPI of DSA or ECDSA value r. 5.2.3.2. Algorithm-Specific Fields for DSA or ECDSA signatures
- MPI of DSA or ECDSA value s. * MPI of DSA or ECDSA value r.
Algorithm-Specific Fields for EdDSA signatures: * MPI of DSA or ECDSA value s.
- MPI of an EC point r. 5.2.3.3. Algorithm-Specific Fields for EdDSA signatures
- EdDSA value s, in MPI, in the little endian representation. * Two MPI-encoded values, whose contents and formatting depend on
the choice of curve used (see Section 9.2.1).
The format of R and S for use with EdDSA is described in [RFC8032].
A version 3 signature MUST NOT be created and MUST NOT be used with A version 3 signature MUST NOT be created and MUST NOT be used with
EdDSA. EdDSA.
5.2.3.3.1. Algorithm-Specific Fields for Ed25519 signatures
The two MPIs for Ed25519 use octet strings R and S as described in
[RFC8032].
* MPI of an EC point R, represented as a (non-prefixed) native
(little-endian) octet string up to 32 octets.
* MPI of EdDSA value S, also in (non-prefixed) native little-endian
format with a length up to 32 octets.
5.2.3.3.2. Algorithm-Specific Fields for Ed448 signatures
For Ed448 signatures, the native signature format is used as
described in [RFC8032]. The two MPIs are composed as follows:
* The first MPI has a body of 58 octets: a prefix 0x40 octet,
followed by 57 octets of the native signature.
* The second MPI is set to 0 (this is a placeholder, and is unused).
Note that an MPI with a value of 0 is encoded on the wire as a
pair of zero octets: "00 00".
5.2.3.4. Notes on Signatures
The concatenation of the data being signed and the signature data The concatenation of the data being signed and the signature data
from the version number through the hashed subpacket data (inclusive) from the version number through the hashed subpacket data (inclusive)
is hashed. The resulting hash value is what is signed. The high 16 is hashed. The resulting hash value is what is signed. The high 16
bits (first two octets) of the hash are included in the Signature bits (first two octets) of the hash are included in the Signature
packet to provide a way to reject some invalid signatures without packet to provide a way to reject some invalid signatures without
performing a signature verification. performing a signature verification.
There are two fields consisting of Signature subpackets. The first There are two fields consisting of Signature subpackets. The first
field is hashed with the rest of the signature data, while the second field is hashed with the rest of the signature data, while the second
is unhashed. The second set of subpackets is not cryptographically is unhashed. The second set of subpackets is not cryptographically
protected by the signature and should include only advisory protected by the signature and should include only advisory
information. information.
The difference between a V4 and V5 signature is that the latter The difference between a V4 and V5 signature is that the latter
includes additional meta data. includes additional meta data.
The algorithms for converting the hash function result to a signature The algorithms for converting the hash function result to a signature
are described in a section below. are described in a section below.
5.2.3.1. Signature Subpacket Specification 5.2.3.5. Signature Subpacket Specification
A subpacket data set consists of zero or more Signature subpackets. A subpacket data set consists of zero or more Signature subpackets.
In Signature packets, the subpacket data set is preceded by a two- In Signature packets, the subpacket data set is preceded by a two-
octet scalar count of the length in octets of all the subpackets. A octet scalar count of the length in octets of all the subpackets. A
pointer incremented by this number will skip over the subpacket data pointer incremented by this number will skip over the subpacket data
set. set.
Each subpacket consists of a subpacket header and a body. The header Each subpacket consists of a subpacket header and a body. The header
consists of: consists of:
skipping to change at page 30, line 19 skipping to change at page 32, line 40
if the 1st octet >= 192 and < 255, then if the 1st octet >= 192 and < 255, then
lengthOfLength = 2 lengthOfLength = 2
subpacketLen = ((1st_octet - 192) << 8) + (2nd_octet) + 192 subpacketLen = ((1st_octet - 192) << 8) + (2nd_octet) + 192
if the 1st octet = 255, then if the 1st octet = 255, then
lengthOfLength = 5 lengthOfLength = 5
subpacket length = [four-octet scalar starting at 2nd_octet] subpacket length = [four-octet scalar starting at 2nd_octet]
The value of the subpacket type octet may be: The value of the subpacket type octet may be:
+============+===========================================+ +============+========================================+
| Type | Description | | Type | Description |
+============+===========================================+ +============+========================================+
| 0 | Reserved | | 0 | Reserved |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 1 | Reserved | | 1 | Reserved |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 2 | Signature Creation Time | | 2 | Signature Creation Time |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 3 | Signature Expiration Time | | 3 | Signature Expiration Time |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 4 | Exportable Certification | | 4 | Exportable Certification |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 5 | Trust Signature | | 5 | Trust Signature |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 6 | Regular Expression | | 6 | Regular Expression |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 7 | Revocable | | 7 | Revocable |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 8 | Reserved | | 8 | Reserved |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 9 | Key Expiration Time | | 9 | Key Expiration Time |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 10 | Placeholder for backward compatibility | | 10 | Placeholder for backward compatibility |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 11 | Preferred Symmetric Algorithms | | 11 | Preferred Symmetric Algorithms |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 12 | Revocation Key | | 12 | Revocation Key |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 13 to 15 | Reserved | | 13 to 15 | Reserved |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 16 | Issuer | | 16 | Issuer |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 17 to 19 | Reserved | | 17 to 19 | Reserved |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 20 | Notation Data | | 20 | Notation Data |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 21 | Preferred Hash Algorithms | | 21 | Preferred Hash Algorithms |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 22 | Preferred Compression Algorithms | | 22 | Preferred Compression Algorithms |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 23 | Key Server Preferences | | 23 | Key Server Preferences |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 24 | Preferred Key Server | | 24 | Preferred Key Server |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 25 | Primary User ID | | 25 | Primary User ID |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 26 | Policy URI | | 26 | Policy URI |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 27 | Key Flags | | 27 | Key Flags |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 28 | Signer's User ID | | 28 | Signer's User ID |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 29 | Reason for Revocation | | 29 | Reason for Revocation |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 30 | Features | | 30 | Features |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 31 | Signature Target | | 31 | Signature Target |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 32 | Embedded Signature | | 32 | Embedded Signature |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 33 | Issuer Fingerprint | | 33 | Issuer Fingerprint |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 34 | Reserved (Preferred AEAD Algorithms) | | 34 | Reserved (Preferred AEAD Algorithms) |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 35 | Reserved (Intended Recipient Fingerprint) | | 35 | Intended Recipient Fingerprint |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 37 | Reserved (Attested Certifications) | | 37 | Reserved (Attested Certifications) |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 38 | Reserved (Key Block) | | 38 | Reserved (Key Block) |
+------------+-------------------------------------------+ +------------+----------------------------------------+
| 100 to 110 | Private or experimental | | 100 to 110 | Private or experimental |
+------------+-------------------------------------------+ +------------+----------------------------------------+
Table 6: Subpacket type registry Table 6: Subpacket type registry
An implementation SHOULD ignore any subpacket of a type that it does An implementation SHOULD ignore any subpacket of a type that it does
not recognize. not recognize.
Bit 7 of the subpacket type is the "critical" bit. If set, it Bit 7 of the subpacket type is the "critical" bit. If set, it
denotes that the subpacket is one that is critical for the evaluator denotes that the subpacket is one that is critical for the evaluator
of the signature to recognize. If a subpacket is encountered that is of the signature to recognize. If a subpacket is encountered that is
marked critical but is unknown to the evaluating software, the marked critical but is unknown to the evaluating software, the
evaluator SHOULD consider the signature to be in error. evaluator SHOULD consider the signature to be in error.
skipping to change at page 32, line 23 skipping to change at page 34, line 40
evaluator that it would prefer a new, unknown feature to generate an evaluator that it would prefer a new, unknown feature to generate an
error than be ignored. error than be ignored.
Implementations SHOULD implement the three preferred algorithm Implementations SHOULD implement the three preferred algorithm
subpackets (11, 21, and 22), as well as the "Reason for Revocation" subpackets (11, 21, and 22), as well as the "Reason for Revocation"
subpacket. Note, however, that if an implementation chooses not to subpacket. Note, however, that if an implementation chooses not to
implement some of the preferences, it is required to behave in a implement some of the preferences, it is required to behave in a
polite manner to respect the wishes of those users who do implement polite manner to respect the wishes of those users who do implement
these preferences. these preferences.
5.2.3.2. Signature Subpacket Types 5.2.3.6. Signature Subpacket Types
A number of subpackets are currently defined. Some subpackets apply A number of subpackets are currently defined. Some subpackets apply
to the signature itself and some are attributes of the key. to the signature itself and some are attributes of the key.
Subpackets that are found on a self-signature are placed on a Subpackets that are found on a self-signature are placed on a
certification made by the key itself. Note that a key may have more certification made by the key itself. Note that a key may have more
than one User ID, and thus may have more than one self-signature, and than one User ID, and thus may have more than one self-signature, and
differing subpackets. differing subpackets.
A subpacket may be found either in the hashed or unhashed subpacket A subpacket may be found either in the hashed or unhashed subpacket
sections of a signature. If a subpacket is not hashed, then the sections of a signature. If a subpacket is not hashed, then the
information in it cannot be considered definitive because it is not information in it cannot be considered definitive because it is not
part of the signature proper. part of the signature proper.
5.2.3.3. Notes on Self-Signatures 5.2.3.7. Notes on Self-Signatures
A self-signature is a binding signature made by the key to which the A self-signature is a binding signature made by the key to which the
signature refers. There are three types of self-signatures, the signature refers. There are three types of self-signatures, the
certification signatures (types 0x10-0x13), the direct-key signature certification signatures (types 0x10-0x13), the direct-key signature
(type 0x1F), and the subkey binding signature (type 0x18). For (type 0x1F), and the subkey binding signature (type 0x18). For
certification self-signatures, each User ID may have a self- certification self-signatures, each User ID may have a self-
signature, and thus different subpackets in those self-signatures. signature, and thus different subpackets in those self-signatures.
For subkey binding signatures, each subkey in fact has a self- For subkey binding signatures, each subkey in fact has a self-
signature. Subpackets that appear in a certification self-signature signature. Subpackets that appear in a certification self-signature
apply to the user name, and subpackets that appear in the subkey apply to the user name, and subpackets that appear in the subkey
skipping to change at page 33, line 26 skipping to change at page 35, line 45
meaning that varies with the signature type. Revoking the self- meaning that varies with the signature type. Revoking the self-
signature on a User ID effectively retires that user name. The self- signature on a User ID effectively retires that user name. The self-
signature is a statement, "My name X is tied to my signing key K" and signature is a statement, "My name X is tied to my signing key K" and
is corroborated by other users' certifications. If another user is corroborated by other users' certifications. If another user
revokes their certification, they are effectively saying that they no revokes their certification, they are effectively saying that they no
longer believe that name and that key are tied together. Similarly, longer believe that name and that key are tied together. Similarly,
if the users themselves revoke their self-signature, then the users if the users themselves revoke their self-signature, then the users
no longer go by that name, no longer have that email address, etc. no longer go by that name, no longer have that email address, etc.
Revoking a binding signature effectively retires that subkey. Revoking a binding signature effectively retires that subkey.
Revoking a direct-key signature cancels that signature. Please see Revoking a direct-key signature cancels that signature. Please see
Section 5.2.3.23 for more relevant detail. Section 5.2.3.27 for more relevant detail.
Since a self-signature contains important information about the key's Since a self-signature contains important information about the key's
use, an implementation SHOULD allow the user to rewrite the self- use, an implementation SHOULD allow the user to rewrite the self-
signature, and important information in it, such as preferences and signature, and important information in it, such as preferences and
key expiration. key expiration.
It is good practice to verify that a self-signature imported into an It is good practice to verify that a self-signature imported into an
implementation doesn't advertise features that the implementation implementation doesn't advertise features that the implementation
doesn't support, rewriting the signature as appropriate. doesn't support, rewriting the signature as appropriate.
An implementation that encounters multiple self-signatures on the An implementation that encounters multiple self-signatures on the
same object may resolve the ambiguity in any way it sees fit, but it same object may resolve the ambiguity in any way it sees fit, but it
is RECOMMENDED that priority be given to the most recent self- is RECOMMENDED that priority be given to the most recent self-
signature. signature.
5.2.3.4. Signature Creation Time 5.2.3.8. Signature Creation Time
(4-octet time field) (4-octet time field)
The time the signature was made. The time the signature was made.
MUST be present in the hashed area. MUST be present in the hashed area.
5.2.3.5. Issuer 5.2.3.9. Issuer
(8-octet Key ID) (8-octet Key ID)
The OpenPGP Key ID of the key issuing the signature. If the version The OpenPGP Key ID of the key issuing the signature. If the version
of that key is greater than 4, this subpacket MUST NOT be included in of that key is greater than 4, this subpacket MUST NOT be included in
the signature. the signature.
5.2.3.6. Key Expiration Time 5.2.3.10. Key Expiration Time
(4-octet time field) (4-octet time field)
The validity period of the key. This is the number of seconds after The validity period of the key. This is the number of seconds after
the key creation time that the key expires. If this is not present the key creation time that the key expires. If this is not present
or has a value of zero, the key never expires. This is found only on or has a value of zero, the key never expires. This is found only on
a self-signature. a self-signature.
5.2.3.7. Preferred Symmetric Algorithms 5.2.3.11. Preferred Symmetric Algorithms
(array of one-octet values) (array of one-octet values)
Symmetric algorithm numbers that indicate which algorithms the key Symmetric algorithm numbers that indicate which algorithms the key
holder prefers to use. The subpacket body is an ordered list of holder prefers to use. The subpacket body is an ordered list of
octets with the most preferred listed first. It is assumed that only octets with the most preferred listed first. It is assumed that only
algorithms listed are supported by the recipient's software. algorithms listed are supported by the recipient's software.
Algorithm numbers are in Section 9.3. This is only found on a self- Algorithm numbers are in Section 9.3. This is only found on a self-
signature. signature.
5.2.3.8. Preferred Hash Algorithms 5.2.3.12. Preferred Hash Algorithms
(array of one-octet values) (array of one-octet values)
Message digest algorithm numbers that indicate which algorithms the Message digest algorithm numbers that indicate which algorithms the
key holder prefers to receive. Like the preferred symmetric key holder prefers to receive. Like the preferred symmetric
algorithms, the list is ordered. Algorithm numbers are in algorithms, the list is ordered. Algorithm numbers are in
Section 9.5. This is only found on a self-signature. Section 9.5. This is only found on a self-signature.
5.2.3.9. Preferred Compression Algorithms 5.2.3.13. Preferred Compression Algorithms
(array of one-octet values) (array of one-octet values)
Compression algorithm numbers that indicate which algorithms the key Compression algorithm numbers that indicate which algorithms the key
holder prefers to use. Like the preferred symmetric algorithms, the holder prefers to use. Like the preferred symmetric algorithms, the
list is ordered. Algorithm numbers are in Section 9.4. If this list is ordered. Algorithm numbers are in Section 9.4. If this
subpacket is not included, ZIP is preferred. A zero denotes that subpacket is not included, ZIP is preferred. A zero denotes that
uncompressed data is preferred; the key holder's software might have uncompressed data is preferred; the key holder's software might have
no compression software in that implementation. This is only found no compression software in that implementation. This is only found
on a self-signature. on a self-signature.
5.2.3.10. Signature Expiration Time 5.2.3.14. Signature Expiration Time
(4-octet time field) (4-octet time field)
The validity period of the signature. This is the number of seconds The validity period of the signature. This is the number of seconds
after the signature creation time that the signature expires. If after the signature creation time that the signature expires. If
this is not present or has a value of zero, it never expires. this is not present or has a value of zero, it never expires.
5.2.3.11. Exportable Certification 5.2.3.15. Exportable Certification
(1 octet of exportability, 0 for not, 1 for exportable) (1 octet of exportability, 0 for not, 1 for exportable)
This subpacket denotes whether a certification signature is This subpacket denotes whether a certification signature is
"exportable", to be used by other users than the signature's issuer. "exportable", to be used by other users than the signature's issuer.
The packet body contains a Boolean flag indicating whether the The packet body contains a Boolean flag indicating whether the
signature is exportable. If this packet is not present, the signature is exportable. If this packet is not present, the
certification is exportable; it is equivalent to a flag containing a certification is exportable; it is equivalent to a flag containing a
1. 1.
skipping to change at page 35, line 42 skipping to change at page 38, line 16
any local certifications. In normal operation, there won't be any, any local certifications. In normal operation, there won't be any,
assuming the import is performed on an exported key. However, there assuming the import is performed on an exported key. However, there
are instances where this can reasonably happen. For example, if an are instances where this can reasonably happen. For example, if an
implementation allows keys to be imported from a key database in implementation allows keys to be imported from a key database in
addition to an exported key, then this situation can arise. addition to an exported key, then this situation can arise.
Some implementations do not represent the interest of a single user Some implementations do not represent the interest of a single user
(for example, a key server). Such implementations always trim local (for example, a key server). Such implementations always trim local
certifications from any key they handle. certifications from any key they handle.
5.2.3.12. Revocable 5.2.3.16. Revocable
(1 octet of revocability, 0 for not, 1 for revocable) (1 octet of revocability, 0 for not, 1 for revocable)
Signature's revocability status. The packet body contains a Boolean Signature's revocability status. The packet body contains a Boolean
flag indicating whether the signature is revocable. Signatures that flag indicating whether the signature is revocable. Signatures that
are not revocable have any later revocation signatures ignored. They are not revocable have any later revocation signatures ignored. They
represent a commitment by the signer that he cannot revoke his represent a commitment by the signer that he cannot revoke his
signature for the life of his key. If this packet is not present, signature for the life of his key. If this packet is not present,
the signature is revocable. the signature is revocable.
5.2.3.13. Trust Signature 5.2.3.17. Trust Signature
(1 octet "level" (depth), 1 octet of trust amount) (1 octet "level" (depth), 1 octet of trust amount)
Signer asserts that the key is not only valid but also trustworthy at Signer asserts that the key is not only valid but also trustworthy at
the specified level. Level 0 has the same meaning as an ordinary the specified level. Level 0 has the same meaning as an ordinary
validity signature. Level 1 means that the signed key is asserted to validity signature. Level 1 means that the signed key is asserted to
be a valid trusted introducer, with the 2nd octet of the body be a valid trusted introducer, with the 2nd octet of the body
specifying the degree of trust. Level 2 means that the signed key is specifying the degree of trust. Level 2 means that the signed key is
asserted to be trusted to issue level 1 trust signatures, i.e., that asserted to be trusted to issue level 1 trust signatures, i.e., that
it is a "meta introducer". Generally, a level n trust signature it is a "meta introducer". Generally, a level n trust signature
asserts that a key is trusted to issue level n-1 trust signatures. asserts that a key is trusted to issue level n-1 trust signatures.
The trust amount is in a range from 0-255, interpreted such that The trust amount is in a range from 0-255, interpreted such that
values less than 120 indicate partial trust and values of 120 or values less than 120 indicate partial trust and values of 120 or
greater indicate complete trust. Implementations SHOULD emit values greater indicate complete trust. Implementations SHOULD emit values
of 60 for partial trust and 120 for complete trust. of 60 for partial trust and 120 for complete trust.
5.2.3.14. Regular Expression 5.2.3.18. Regular Expression
(null-terminated regular expression) (null-terminated regular expression)
Used in conjunction with trust Signature packets (of level > 0) to Used in conjunction with trust Signature packets (of level > 0) to
limit the scope of trust that is extended. Only signatures by the limit the scope of trust that is extended. Only signatures by the
target key on User IDs that match the regular expression in the body target key on User IDs that match the regular expression in the body
of this packet have trust extended by the trust Signature subpacket. of this packet have trust extended by the trust Signature subpacket.
The regular expression uses the same syntax as the Henry Spencer's The regular expression uses the same syntax as the Henry Spencer's
"almost public domain" regular expression [REGEX] package. A "almost public domain" regular expression [REGEX] package. A
description of the syntax is found in Section 8. description of the syntax is found in Section 8.
5.2.3.15. Revocation Key 5.2.3.19. Revocation Key
(1 octet of class, 1 octet of public-key algorithm ID, 20 or 32 (1 octet of class, 1 octet of public-key algorithm ID, 20 or 32
octets of fingerprint) octets of fingerprint)
V4 keys use the full 20 octet fingerprint; V5 keys use the full 32 V4 keys use the full 20 octet fingerprint; V5 keys use the full 32
octet fingerprint octet fingerprint
Authorizes the specified key to issue revocation signatures for this Authorizes the specified key to issue revocation signatures for this
key. Class octet must have bit 0x80 set. If the bit 0x40 is set, key. Class octet must have bit 0x80 set. If the bit 0x40 is set,
then this means that the revocation information is sensitive. Other then this means that the revocation information is sensitive. Other
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If the "sensitive" flag is set, the keyholder feels this subpacket If the "sensitive" flag is set, the keyholder feels this subpacket
contains private trust information that describes a real-world contains private trust information that describes a real-world
sensitive relationship. If this flag is set, implementations SHOULD sensitive relationship. If this flag is set, implementations SHOULD
NOT export this signature to other users except in cases where the NOT export this signature to other users except in cases where the
data needs to be available: when the signature is being sent to the data needs to be available: when the signature is being sent to the
designated revoker, or when it is accompanied by a revocation designated revoker, or when it is accompanied by a revocation
signature from that revoker. Note that it may be appropriate to signature from that revoker. Note that it may be appropriate to
isolate this subpacket within a separate signature so that it is not isolate this subpacket within a separate signature so that it is not
combined with other subpackets that need to be exported. combined with other subpackets that need to be exported.
5.2.3.16. Notation Data 5.2.3.20. Notation Data
(4 octets of flags, 2 octets of name length (M), 2 octets of value (4 octets of flags, 2 octets of name length (M), 2 octets of value
length (N), M octets of name data, N octets of value data) length (N), M octets of name data, N octets of value data)
This subpacket describes a "notation" on the signature that the This subpacket describes a "notation" on the signature that the
issuer wishes to make. The notation has a name and a value, each of issuer wishes to make. The notation has a name and a value, each of
which are strings of octets. There may be more than one notation in which are strings of octets. There may be more than one notation in
a signature. Notations can be used for any extension the issuer of a signature. Notations can be used for any extension the issuer of
the signature cares to make. The "flags" field holds four octets of the signature cares to make. The "flags" field holds four octets of
flags. flags.
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Since the user namespace is in the form of an email address, Since the user namespace is in the form of an email address,
implementers MAY wish to arrange for that address to reach a person implementers MAY wish to arrange for that address to reach a person
who can be consulted about the use of the named tag. Note that due who can be consulted about the use of the named tag. Note that due
to UTF-8 encoding, not all valid user space name tags are valid email to UTF-8 encoding, not all valid user space name tags are valid email
addresses. addresses.
If there is a critical notation, the criticality applies to that If there is a critical notation, the criticality applies to that
specific notation and not to notations in general. specific notation and not to notations in general.
5.2.3.17. Key Server Preferences 5.2.3.21. Key Server Preferences
(N octets of flags) (N octets of flags)
This is a list of one-bit flags that indicate preferences that the This is a list of one-bit flags that indicate preferences that the
key holder has about how the key is handled on a key server. All key holder has about how the key is handled on a key server. All
undefined flags MUST be zero. undefined flags MUST be zero.
First octet: First octet:
+======+===========+============================================+ +======+===========+============================================+
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+======+===========+============================================+ +======+===========+============================================+
| 0x80 | No-modify | The key holder requests that this key only | | 0x80 | No-modify | The key holder requests that this key only |
| | | be modified or updated by the key holder | | | | be modified or updated by the key holder |
| | | or an administrator of the key server. | | | | or an administrator of the key server. |
+------+-----------+--------------------------------------------+ +------+-----------+--------------------------------------------+
Table 8: Key server preferences flag registry (first octet) Table 8: Key server preferences flag registry (first octet)
This is found only on a self-signature. This is found only on a self-signature.
5.2.3.18. Preferred Key Server 5.2.3.22. Preferred Key Server
(String) (String)
This is a URI of a key server that the key holder prefers be used for This is a URI of a key server that the key holder prefers be used for
updates. Note that keys with multiple User IDs can have a preferred updates. Note that keys with multiple User IDs can have a preferred
key server for each User ID. Note also that since this is a URI, the key server for each User ID. Note also that since this is a URI, the
key server can actually be a copy of the key retrieved by ftp, http, key server can actually be a copy of the key retrieved by ftp, http,
finger, etc. finger, etc.
5.2.3.19. Primary User ID 5.2.3.23. Primary User ID
(1 octet, Boolean) (1 octet, Boolean)
This is a flag in a User ID's self-signature that states whether this This is a flag in a User ID's self-signature that states whether this
User ID is the main User ID for this key. It is reasonable for an User ID is the main User ID for this key. It is reasonable for an
implementation to resolve ambiguities in preferences, etc. by implementation to resolve ambiguities in preferences, etc. by
referring to the primary User ID. If this flag is absent, its value referring to the primary User ID. If this flag is absent, its value
is zero. If more than one User ID in a key is marked as primary, the is zero. If more than one User ID in a key is marked as primary, the
implementation may resolve the ambiguity in any way it sees fit, but implementation may resolve the ambiguity in any way it sees fit, but
it is RECOMMENDED that priority be given to the User ID with the most it is RECOMMENDED that priority be given to the User ID with the most
recent self-signature. recent self-signature.
When appearing on a self-signature on a User ID packet, this When appearing on a self-signature on a User ID packet, this
subpacket applies only to User ID packets. When appearing on a self- subpacket applies only to User ID packets. When appearing on a self-
signature on a User Attribute packet, this subpacket applies only to signature on a User Attribute packet, this subpacket applies only to
User Attribute packets. That is to say, there are two different and User Attribute packets. That is to say, there are two different and
independent "primaries" -- one for User IDs, and one for User independent "primaries" -- one for User IDs, and one for User
Attributes. Attributes.
5.2.3.20. Policy URI 5.2.3.24. Policy URI
(String) (String)
This subpacket contains a URI of a document that describes the policy This subpacket contains a URI of a document that describes the policy
under which the signature was issued. under which the signature was issued.
5.2.3.21. Key Flags 5.2.3.25. Key Flags
(N octets of flags) (N octets of flags)
This subpacket contains a list of binary flags that hold information This subpacket contains a list of binary flags that hold information
about a key. It is a string of octets, and an implementation MUST about a key. It is a string of octets, and an implementation MUST
NOT assume a fixed size. This is so it can grow over time. If a NOT assume a fixed size. This is so it can grow over time. If a
list is shorter than an implementation expects, the unstated flags list is shorter than an implementation expects, the unstated flags
are considered to be zero. The defined flags are as follows: are considered to be zero. The defined flags are as follows:
First octet: First octet:
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decision is left wholly up to the implementation; the authors of this decision is left wholly up to the implementation; the authors of this
document do not claim any special wisdom on the issue and realize document do not claim any special wisdom on the issue and realize
that accepted opinion may change. that accepted opinion may change.
The "split key" (0x10) and "group key" (0x80) flags are placed on a The "split key" (0x10) and "group key" (0x80) flags are placed on a
self-signature only; they are meaningless on a certification self-signature only; they are meaningless on a certification
signature. They SHOULD be placed only on a direct-key signature signature. They SHOULD be placed only on a direct-key signature
(type 0x1F) or a subkey signature (type 0x18), one that refers to the (type 0x1F) or a subkey signature (type 0x18), one that refers to the
key the flag applies to. key the flag applies to.
5.2.3.22. Signer's User ID 5.2.3.26. Signer's User ID
(String) (String)
This subpacket allows a keyholder to state which User ID is This subpacket allows a keyholder to state which User ID is
responsible for the signing. Many keyholders use a single key for responsible for the signing. Many keyholders use a single key for
different purposes, such as business communications as well as different purposes, such as business communications as well as
personal communications. This subpacket allows such a keyholder to personal communications. This subpacket allows such a keyholder to
state which of their roles is making a signature. state which of their roles is making a signature.
This subpacket is not appropriate to use to refer to a User Attribute This subpacket is not appropriate to use to refer to a User Attribute
packet. packet.
5.2.3.23. Reason for Revocation 5.2.3.27. Reason for Revocation
(1 octet of revocation code, N octets of reason string) (1 octet of revocation code, N octets of reason string)
This subpacket is used only in key revocation and certification This subpacket is used only in key revocation and certification
revocation signatures. It describes the reason why the key or revocation signatures. It describes the reason why the key or
certificate was revoked. certificate was revoked.
The first octet contains a machine-readable code that denotes the The first octet contains a machine-readable code that denotes the
reason for the revocation: reason for the revocation:
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revoked signature is the self-signature for certifying a User ID, a revoked signature is the self-signature for certifying a User ID, a
revocation denotes that that user name is no longer in use. Such a revocation denotes that that user name is no longer in use. Such a
revocation SHOULD include a 0x20 code. revocation SHOULD include a 0x20 code.
Note that any signature may be revoked, including a certification on Note that any signature may be revoked, including a certification on
some other person's key. There are many good reasons for revoking a some other person's key. There are many good reasons for revoking a
certification signature, such as the case where the keyholder leaves certification signature, such as the case where the keyholder leaves
the employ of a business with an email address. A revoked the employ of a business with an email address. A revoked
certification is no longer a part of validity calculations. certification is no longer a part of validity calculations.
5.2.3.24. Features 5.2.3.28. Features
(N octets of flags) (N octets of flags)
The Features subpacket denotes which advanced OpenPGP features a The Features subpacket denotes which advanced OpenPGP features a
user's implementation supports. This is so that as features are user's implementation supports. This is so that as features are
added to OpenPGP that cannot be backwards-compatible, a user can added to OpenPGP that cannot be backwards-compatible, a user can
state that they can use that feature. The flags are single bits that state that they can use that feature. The flags are single bits that
indicate that a given feature is supported. indicate that a given feature is supported.
This subpacket is similar to a preferences subpacket, and only This subpacket is similar to a preferences subpacket, and only
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Defined features are as follows: Defined features are as follows:
First octet: First octet:
+=========+============================================+ +=========+============================================+
| feature | definition | | feature | definition |
+=========+============================================+ +=========+============================================+
| 0x01 | Modification Detection (packets 18 and 19) | | 0x01 | Modification Detection (packets 18 and 19) |
+---------+--------------------------------------------+ +---------+--------------------------------------------+
| 0x02 | Reserved (AEAD Data & v5 SKESK) | | 0x02 | AEAD Encrypted Data (packet 20) |
+---------+--------------------------------------------+ +---------+--------------------------------------------+
| 0x04 | Version 5 Public-Key Packet format and | | 0x04 | Reserved |
| | corresponding new fingerprint format |
+---------+--------------------------------------------+ +---------+--------------------------------------------+
Table 12: Features registry Table 12: Features registry
If an implementation implements any of the defined features, it If an implementation implements any of the defined features, it
SHOULD implement the Features subpacket, too. SHOULD implement the Features subpacket, too.
An implementation may freely infer features from other suitable An implementation may freely infer features from other suitable
implementation-dependent mechanisms. implementation-dependent mechanisms.
5.2.3.25. Signature Target 5.2.3.29. Signature Target
(1 octet public-key algorithm, 1 octet hash algorithm, N octets hash) (1 octet public-key algorithm, 1 octet hash algorithm, N octets hash)
This subpacket identifies a specific target signature to which a This subpacket identifies a specific target signature to which a
signature refers. For revocation signatures, this subpacket provides signature refers. For revocation signatures, this subpacket provides
explicit designation of which signature is being revoked. For a explicit designation of which signature is being revoked. For a
third-party or timestamp signature, this designates what signature is third-party or timestamp signature, this designates what signature is
signed. All arguments are an identifier of that target signature. signed. All arguments are an identifier of that target signature.
The N octets of hash data MUST be the size of the hash of the The N octets of hash data MUST be the size of the hash of the
signature. For example, a target signature with a SHA-1 hash MUST signature. For example, a target signature with a SHA-1 hash MUST
have 20 octets of hash data. have 20 octets of hash data.
5.2.3.26. Embedded Signature 5.2.3.30. Embedded Signature
(1 signature packet body) (1 signature packet body)
This subpacket contains a complete Signature packet body as specified This subpacket contains a complete Signature packet body as specified
in Section 5.2. It is useful when one signature needs to refer to, in Section 5.2. It is useful when one signature needs to refer to,
or be incorporated in, another signature. or be incorporated in, another signature.
5.2.3.27. Issuer Fingerprint 5.2.3.31. Issuer Fingerprint
(1 octet key version number, N octets of fingerprint) (1 octet key version number, N octets of fingerprint)
The OpenPGP Key fingerprint of the key issuing the signature. This The OpenPGP Key fingerprint of the key issuing the signature. This
subpacket SHOULD be included in all signatures. If the version of subpacket SHOULD be included in all signatures. If the version of
the issuing key is 4 and an Issuer subpacket is also included in the the issuing key is 4 and an Issuer subpacket is also included in the
signature, the key ID of the Issuer subpacket MUST match the low 64 signature, the key ID of the Issuer subpacket MUST match the low 64
bits of the fingerprint. bits of the fingerprint.
Note that the length N of the fingerprint for a version 4 key is 20 Note that the length N of the fingerprint for a version 4 key is 20
octets; for a version 5 key N is 32. octets; for a version 5 key N is 32.
5.2.3.32. Intended Recipient Fingerprint
(1 octet key version number, N octets of fingerprint)
The OpenPGP Key fingerprint of the intended recipient primary key.
If one or more subpackets of this type are included in a signature,
it SHOULD be considered valid only in an encrypted context, where the
key it was encrypted to is one of the indicated primary keys, or one
of their subkeys. This can be used to prevent forwarding a signature
outside of its intended, encrypted context.
Note that the length N of the fingerprint for a version 4 key is 20
octets; for a version 5 key N is 32.
5.2.4. Computing Signatures 5.2.4. Computing Signatures
All signatures are formed by producing a hash over the signature All signatures are formed by producing a hash over the signature
data, and then using the resulting hash in the signature algorithm. data, and then using the resulting hash in the signature algorithm.
For binary document signatures (type 0x00), the document data is For binary document signatures (type 0x00), the document data is
hashed directly. For text document signatures (type 0x01), the hashed directly. For text document signatures (type 0x01), the
document is canonicalized by converting line endings to <CR><LF>, and document is canonicalized by converting line endings to <CR><LF>, and
the resulting data is hashed. the resulting data is hashed.
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- the hashed subpacket body, - the hashed subpacket body,
- the two octets 0x04 and 0xFF, - the two octets 0x04 and 0xFF,
- a four-octet big-endian number that is the length of the hashed - a four-octet big-endian number that is the length of the hashed
data from the Signature packet stopping right before the 0x04, data from the Signature packet stopping right before the 0x04,
0xff octets. 0xff octets.
The four-octet big-endian number is considered to be an The four-octet big-endian number is considered to be an
unsigned integer modulo 2^32. unsigned integer modulo 2**32.
* A V5 signature hashes the packet body starting from its first * A V5 signature hashes the packet body starting from its first
field, the version number, through the end of the hashed subpacket field, the version number, through the end of the hashed subpacket
data and a final extra trailer. Thus, the hashed fields are: data and a final extra trailer. Thus, the hashed fields are:
- the signature version (0x05), - the signature version (0x05),
- the signature type, - the signature type,
- the public-key algorithm, - the public-key algorithm,
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o a four-octet number that indicates a date, o a four-octet number that indicates a date,
- the two octets 0x05 and 0xFF, - the two octets 0x05 and 0xFF,
- a eight-octet big-endian number that is the length of the - a eight-octet big-endian number that is the length of the
hashed data from the Signature packet stopping right before the hashed data from the Signature packet stopping right before the
0x05, 0xff octets. 0x05, 0xff octets.
The three data items hashed for document signatures need to The three data items hashed for document signatures need to
mirror the values of the Literal Data packet. For detached and mirror the values of the Literal Data packet. For detached and
cleartext signatures 6 zero bytes are hashed instead. cleartext signatures 6 zero octets are hashed instead.
After all this has been hashed in a single hash context, the After all this has been hashed in a single hash context, the
resulting hash field is used in the signature algorithm and placed at resulting hash field is used in the signature algorithm and placed at
the end of the Signature packet. the end of the Signature packet.
5.2.4.1. Subpacket Hints 5.2.4.1. Subpacket Hints
It is certainly possible for a signature to contain conflicting It is certainly possible for a signature to contain conflicting
information in subpackets. For example, a signature may contain information in subpackets. For example, a signature may contain
multiple copies of a preference or multiple expiration times. In multiple copies of a preference or multiple expiration times. In
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Some apparent conflicts may actually make sense -- for example, Some apparent conflicts may actually make sense -- for example,
suppose a keyholder has a V3 key and a V4 key that share the same RSA suppose a keyholder has a V3 key and a V4 key that share the same RSA
key material. Either of these keys can verify a signature created by key material. Either of these keys can verify a signature created by
the other, and it may be reasonable for a signature to contain an the other, and it may be reasonable for a signature to contain an
issuer subpacket for each key, as a way of explicitly tying those issuer subpacket for each key, as a way of explicitly tying those
keys to the signature. keys to the signature.
5.3. Symmetric-Key Encrypted Session Key Packets (Tag 3) 5.3. Symmetric-Key Encrypted Session Key Packets (Tag 3)
The Symmetric-Key Encrypted Session Key packet holds the symmetric- The Symmetric-Key Encrypted Session Key (SKESK) packet holds the
key encryption of a session key used to encrypt a message. Zero or symmetric-key encryption of a session key used to encrypt a message.
more Public-Key Encrypted Session Key packets and/or Symmetric-Key Zero or more Public-Key Encrypted Session Key packets and/or
Encrypted Session Key packets may precede a Symmetrically Encrypted Symmetric-Key Encrypted Session Key packets may precede a an
Data packet that holds an encrypted message. The message is encryption container (i.e. a Symmetrically Encrypted Integrity
encrypted with a session key, and the session key is itself encrypted Protected Data packet, an AEAD Encrypted Data packet, or -- for
and stored in the Encrypted Session Key packet or the Symmetric-Key historic data -- a Symmetrically Encrypted Data packet) that holds an
Encrypted Session Key packet. encrypted message. The message is encrypted with a session key, and
the session key is itself encrypted and stored in the Encrypted
Session Key packet or the Symmetric-Key Encrypted Session Key packet.
If the Symmetrically Encrypted Data packet is preceded by one or more If the encryption container is preceded by one or more Symmetric-Key
Symmetric-Key Encrypted Session Key packets, each specifies a Encrypted Session Key packets, each specifies a passphrase that may
passphrase that may be used to decrypt the message. This allows a be used to decrypt the message. This allows a message to be
message to be encrypted to a number of public keys, and also to one encrypted to a number of public keys, and also to one or more
or more passphrases. This packet type is new and is not generated by passphrases. This packet type is new and is not generated by PGP 2
PGP 2 or PGP version 5.0. or PGP version 5.0.
The body of this packet consists of: A version 4 Symmetric-Key Encrypted Session Key packet consists of:
* A one-octet version number. The only currently defined version is * A one-octet version number with value 4.
4.
* A one-octet number describing the symmetric algorithm used. * A one-octet number describing the symmetric algorithm used.
* A string-to-key (S2K) specifier, length as defined above. * A string-to-key (S2K) specifier, length as defined above.
* Optionally, the encrypted session key itself, which is decrypted * Optionally, the encrypted session key itself, which is decrypted
with the string-to-key object. with the string-to-key object.
If the encrypted session key is not present (which can be detected on If the encrypted session key is not present (which can be detected on
the basis of packet length and S2K specifier size), then the S2K the basis of packet length and S2K specifier size), then the S2K
algorithm applied to the passphrase produces the session key for algorithm applied to the passphrase produces the session key for
decrypting the message, using the symmetric cipher algorithm from the decrypting the message, using the symmetric cipher algorithm from the
Symmetric-Key Encrypted Session Key packet. Symmetric-Key Encrypted Session Key packet.
If the encrypted session key is present, the result of applying the If the encrypted session key is present, the result of applying the
S2K algorithm to the passphrase is used to decrypt just that S2K algorithm to the passphrase is used to decrypt just that
encrypted session key field, using CFB mode with an IV of all zeros. encrypted session key field, using CFB mode with an IV of all zeros.
The decryption result consists of a one-octet algorithm identifier The decryption result consists of a one-octet algorithm identifier
that specifies the symmetric-key encryption algorithm used to encrypt that specifies the symmetric-key encryption algorithm used to encrypt
the following Symmetrically Encrypted Data packet, followed by the the following encryption container, followed by the session key
session key octets themselves. octets themselves.
Note: because an all-zero IV is used for this decryption, the S2K Note: because an all-zero IV is used for this decryption, the S2K
specifier MUST use a salt value, either a Salted S2K or an Iterated- specifier MUST use a salt value, either a Salted S2K or an Iterated-
Salted S2K. The salt value will ensure that the decryption key is Salted S2K. The salt value will ensure that the decryption key is
not repeated even if the passphrase is reused. not repeated even if the passphrase is reused.
A version 5 Symmetric-Key Encrypted Session Key packet consists of:
* A one-octet version number with value 5.
* A one-octet cipher algorithm.
* A one-octet AEAD algorithm.
* A string-to-key (S2K) specifier, length as defined above.
* A starting initialization vector of size specified by the AEAD
algorithm.
* The encrypted session key itself, which is decrypted with the
string-to-key object using the given cipher and AEAD mode.
* An authentication tag for the AEAD mode.
The encrypted session key is encrypted using one of the AEAD
algorithms specified for the AEAD Encrypted Data Packet. Note that
no chunks are used and that there is only one authentication tag.
The Packet Tag in new format encoding (bits 7 and 6 set, bits 5-0
carry the packet tag), the packet version number, the cipher
algorithm octet, and the AEAD algorithm octet are given as additional
data. For example, the additional data used with EAX and AES-128
consists of the octets 0xC3, 0x05, 0x07, and 0x01.
5.3.1. No v5 SKESK with SEIPD
Note that unlike the AEAD Encrypted Data Packet (AED, see
Section 5.16), the Symmetrically Encrypted Integrity Protected Data
Packet (SEIPD, see Section 5.14) does not internally indicate what
cipher algorithm to use to decrypt it. Since the v5 SKESK packet's
encrypted payload only indicates the key used, not the choice of
cipher algorithm used for the subsequent encrypted data, a v5 SKESK
packet can only provide a session key for an AED packet, and MUST NOT
be used to provide a session key for a SEIPD Packet.
5.4. One-Pass Signature Packets (Tag 4) 5.4. One-Pass Signature Packets (Tag 4)
The One-Pass Signature packet precedes the signed data and contains The One-Pass Signature packet precedes the signed data and contains
enough information to allow the receiver to begin calculating any enough information to allow the receiver to begin calculating any
hashes needed to verify the signature. It allows the Signature hashes needed to verify the signature. It allows the Signature
packet to be placed at the end of the message, so that the signer can packet to be placed at the end of the message, so that the signer can
compute the entire signed message in one pass. compute the entire signed message in one pass.
A One-Pass Signature does not interoperate with PGP 2.6.x or earlier. A One-Pass Signature does not interoperate with PGP 2.6.x or earlier.
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* A four-octet number denoting the time that the key was created. * A four-octet number denoting the time that the key was created.
* A one-octet number denoting the public-key algorithm of this key. * A one-octet number denoting the public-key algorithm of this key.
* A series of multiprecision integers comprising the key material. * A series of multiprecision integers comprising the key material.
This is algorithm-specific and described in Section 5.6. This is algorithm-specific and described in Section 5.6.
The version 5 format is similar to the version 4 format except for The version 5 format is similar to the version 4 format except for
the addition of a count for the key material. This count helps the addition of a count for the key material. This count helps
parsing secret key packets (which are an extension of the public key parsing secret key packets (which are an extension of the public key
packet format) in the case of an unknown algoritm. In addition, packet format) in the case of an unknown algorithm. In addition,
fingerprints of version 5 keys are calculated differently from fingerprints of version 5 keys are calculated differently from
version 4 keys, as described in the section "Enhanced Key Formats". version 4 keys, as described in the section "Enhanced Key Formats".
A version 5 packet contains: A version 5 packet contains:
* A one-octet version number (5). * A one-octet version number (5).
* A four-octet number denoting the time that the key was created. * A four-octet number denoting the time that the key was created.
* A one-octet number denoting the public-key algorithm of this key. * A one-octet number denoting the public-key algorithm of this key.
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* One octet indicating string-to-key usage conventions. Zero * One octet indicating string-to-key usage conventions. Zero
indicates that the secret-key data is not encrypted. 255 or 254 indicates that the secret-key data is not encrypted. 255 or 254
indicates that a string-to-key specifier is being given. Any indicates that a string-to-key specifier is being given. Any
other value is a symmetric-key encryption algorithm identifier. A other value is a symmetric-key encryption algorithm identifier. A
version 5 packet MUST NOT use the value 255. version 5 packet MUST NOT use the value 255.
* Only for a version 5 packet, a one-octet scalar octet count of the * Only for a version 5 packet, a one-octet scalar octet count of the
next 4 optional fields. next 4 optional fields.
* [Optional] If string-to-key usage octet was 255 or 254, a one- * [Optional] If string-to-key usage octet was 255, 254, or 253, a
octet symmetric encryption algorithm. one-octet symmetric encryption algorithm.
* [Optional] If string-to-key usage octet was 255 or 254, a string- * [Optional] If string-to-key usage octet was 253, a one-octet AEAD
to-key specifier. The length of the string-to-key specifier is algorithm.
implied by its type, as described above.
* [Optional] If secret data is encrypted (string-to-key usage octet * [Optional] If string-to-key usage octet was 255, 254, or 253, a
not zero), an Initial Vector (IV) of the same length as the string-to-key specifier. The length of the string-to-key
cipher's block size. specifier is implied by its type, as described above.
* [Optional] If string-to-key usage octet was 253 (i.e. the secret
data is AEAD-encrypted), an initialization vector (IV) of size
specified by the AEAD algorithm (see Section 5.16), which is used
as the nonce for the AEAD algorithm.
* [Optional] If string-to-key usage octet was 255, 254, or a cipher
algorithm identifier (i.e. the secret data is CFB-encrypted), an
initialization vector (IV) of the same length as the cipher's
block size.
* Only for a version 5 packet, a four-octet scalar octet count for * Only for a version 5 packet, a four-octet scalar octet count for
the following secret key material. This includes the encrypted the following secret key material. This includes the encrypted
SHA-1 hash or AEAD tag if the string-to-key usage octet is 254 or SHA-1 hash or AEAD tag if the string-to-key usage octet is 254 or
253. 253.
* Plain or encrypted multiprecision integers comprising the secret * Plain or encrypted multiprecision integers comprising the secret
key data. This is algorithm-specific and described in section key data. This is algorithm-specific and described in section
Section 5.6. Section 5.6. If the string-to-key usage octet is 253, then an
AEAD authentication tag is part of that data. If the string-to-
key usage octet is 254, a 20-octet SHA-1 hash of the plaintext of
the algorithm-specific portion is appended to plaintext and
encrypted with it. If the string-to-key usage octet is 255 or
another nonzero value (i.e., a symmetric-key encryption algorithm
identifier), a two-octet checksum of the plaintext of the
algorithm-specific portion (sum of all octets, mod 65536) is
appended to plaintext and encrypted with it. (This is deprecated
and SHOULD NOT be used, see below.)
* If the string-to-key usage octet is zero or 255, then a two-octet * If the string-to-key usage octet is zero, then a two-octet
checksum of the plaintext of the algorithm-specific portion (sum checksum of the algorithm-specific portion (sum of all octets, mod
of all octets, mod 65536). If the string-to-key usage octet was 65536).
254, then a 20-octet SHA-1 hash of the plaintext of the algorithm-
specific portion. This checksum or hash is encrypted together
with the algorithm-specific fields (if string-to-key usage octet
is not zero). Note that for all other values, a two-octet
checksum is required.
Note that the version 5 packet format adds two count values to help Note that the version 5 packet format adds two count values to help
parsing packets with unknown S2K or public key algorithms. parsing packets with unknown S2K or public key algorithms.
Secret MPI values can be encrypted using a passphrase. If a string- Secret MPI values can be encrypted using a passphrase. If a string-
to-key specifier is given, that describes the algorithm for to-key specifier is given, that describes the algorithm for
converting the passphrase to a key, else a simple MD5 hash of the converting the passphrase to a key, else a simple MD5 hash of the
passphrase is used. Implementations MUST use a string-to-key passphrase is used. Implementations MUST use a string-to-key
specifier; the simple hash is for backward compatibility and is specifier; the simple hash is for backward compatibility and is
deprecated, though implementations MAY continue to use existing deprecated, though implementations MAY continue to use existing
private keys in the old format. The cipher for encrypting the MPIs private keys in the old format. The cipher for encrypting the MPIs
is specified in the Secret-Key packet. is specified in the Secret-Key packet.
Encryption/decryption of the secret data is done in CFB mode using Encryption/decryption of the secret data is done using the key
the key created from the passphrase and the Initial Vector from the created from the passphrase and the initialization vector from the
packet. A different mode is used with V3 keys (which are only RSA) packet. If the string-to-key usage octet is not 253, CFB mode is
used. A different mode is used with V3 keys (which are only RSA)
than with other key formats. With V3 keys, the MPI bit count prefix than with other key formats. With V3 keys, the MPI bit count prefix
(i.e., the first two octets) is not encrypted. Only the MPI non- (i.e., the first two octets) is not encrypted. Only the MPI non-
prefix data is encrypted. Furthermore, the CFB state is prefix data is encrypted. Furthermore, the CFB state is
resynchronized at the beginning of each new MPI value, so that the resynchronized at the beginning of each new MPI value, so that the
CFB block boundary is aligned with the start of the MPI data. CFB block boundary is aligned with the start of the MPI data.
With V4 and V5 keys, a simpler method is used. All secret MPI values With V4 and V5 keys, a simpler method is used. All secret MPI values
are encrypted in CFB mode, including the MPI bitcount prefix. are encrypted, including the MPI bitcount prefix.
If the string-to-key usage octet is 253, the encrypted MPI values are
encrypted as one combined plaintext using one of the AEAD algorithms
specified for the AEAD Encrypted Data Packet. Note that no chunks
are used and that there is only one authentication tag. As
additional data, the Packet Tag in new format encoding (bits 7 and 6
set, bits 5-0 carry the packet tag), followed by the public key
packet fields, starting with the packet version number, are passed to
the AEAD algorithm. For example, the additional data used with a
Secret-Key Packet of version 4 consists of the octets 0xC5, 0x04,
followed by four octets of creation time, one octet denoting the
public-key algorithm, and the algorithm-specific public-key
parameters. For a Secret-Subkey Packet, the first octet would be
0xC7. For a version 5 key packet, the second octet would be 0x05,
and the four-octet octet count of the public key material would be
included as well (see Section 5.5.2).
The two-octet checksum that follows the algorithm-specific portion is The two-octet checksum that follows the algorithm-specific portion is
the algebraic sum, mod 65536, of the plaintext of all the algorithm- the algebraic sum, mod 65536, of the plaintext of all the algorithm-
specific octets (including MPI prefix and data). With V3 keys, the specific octets (including MPI prefix and data). With V3 keys, the
checksum is stored in the clear. With V4 keys, the checksum is checksum is stored in the clear. With V4 keys, the checksum is
encrypted like the algorithm-specific data. This value is used to encrypted like the algorithm-specific data. This value is used to
check that the passphrase was correct. However, this checksum is check that the passphrase was correct. However, this checksum is
deprecated; an implementation SHOULD NOT use it, but should rather deprecated; an implementation SHOULD NOT use it, but should rather
use the SHA-1 hash denoted with a usage octet of 254. The reason for use the SHA-1 hash denoted with a usage octet of 254. The reason for
this is that there are some attacks that involve undetectably this is that there are some attacks that involve undetectably
modifying the secret key. modifying the secret key. If the string-to-key usage octet is 253 no
checksum or SHA-1 hash is used but the authentication tag of the AEAD
algorithm follows.
5.6. Algorithm-specific Parts of Keys 5.6. Algorithm-specific Parts of Keys
The public and secret key format specifies algorithm-specific parts The public and secret key format specifies algorithm-specific parts
of a key. The following sections describe them in detail. of a key. The following sections describe them in detail.
5.6.1. Algorithm-Specific Part for RSA Keys 5.6.1. Algorithm-Specific Part for RSA Keys
The public key is this series of multiprecision integers: The public key is this series of multiprecision integers:
skipping to change at page 54, line 45 skipping to change at page 58, line 15
secret). secret).
The secret key is this single multiprecision integer: The secret key is this single multiprecision integer:
* MPI of Elgamal secret exponent x. * MPI of Elgamal secret exponent x.
5.6.4. Algorithm-Specific Part for ECDSA Keys 5.6.4. Algorithm-Specific Part for ECDSA Keys
The public key is this series of values: The public key is this series of values:
* a variable-length field containing a curve OID, formatted as * A variable-length field containing a curve OID, which is formatted
follows: as follows:
- a one-octet size of the following field; values 0 and 0xFF are - A one-octet size of the following field; values 0 and 0xFF are
reserved for future extensions, reserved for future extensions,
- the octets representing a curve OID, defined in Section 9.2; - The octets representing a curve OID (defined in Section 9.2);
* a MPI of an EC point representing a public key. * MPI of an EC point representing a public key.
The secret key is this single multiprecision integer: The secret key is this single multiprecision integer:
* MPI of an integer representing the secret key, which is a scalar * MPI of an integer representing the secret key, which is a scalar
of the public EC point. of the public EC point.
5.6.5. Algorithm-Specific Part for EdDSA Keys 5.6.5. Algorithm-Specific Part for EdDSA Keys
The public key is this series of values: The public key is this series of values:
* a variable-length field containing a curve OID, formatted as * A variable-length field containing a curve OID, formatted as
follows: follows:
- a one-octet size of the following field; values 0 and 0xFF are - A one-octet size of the following field; values 0 and 0xFF are
reserved for future extensions, reserved for future extensions,
- the octets representing a curve OID, defined in Section 9.2; - The octets representing a curve OID, defined in Section 9.2;
* a MPI of an EC point representing a public key Q as described * An MPI of an EC point representing a public key Q in prefixed
under EdDSA Point Format below. native form (see Section 13.2.2).
The secret key is this single multiprecision integer: The secret key is this single multiprecision integer:
* MPI of an integer representing the secret key, which is a scalar * An MPI-encoded octet string representing the native form of the
of the public EC point. secret key, in the curve-specific format described in
Section 9.2.1.
See [RFC8032] for more details about the native octet strings.
5.6.6. Algorithm-Specific Part for ECDH Keys 5.6.6. Algorithm-Specific Part for ECDH Keys
The public key is this series of values: The public key is this series of values:
* a variable-length field containing a curve OID, formatted as * A variable-length field containing a curve OID, which is formatted
follows: as follows:
- a one-octet size of the following field; values 0 and 0xFF are - A one-octet size of the following field; values 0 and 0xFF are
reserved for future extensions, reserved for future extensions,
- the octets representing a curve OID, defined in Section 9.2; - Octets representing a curve OID, defined in Section 9.2;
* a MPI of an EC point representing a public key; * MPI of an EC point representing a public key, in the point format
associated with the curve as specified in Section 9.2.1
* a variable-length field containing KDF parameters, formatted as * A variable-length field containing KDF parameters, which is
follows: formatted as follows:
- a one-octet size of the following fields; values 0 and 0xff are - A one-octet size of the following fields; values 0 and 0xFF are
reserved for future extensions; reserved for future extensions,
- a one-octet value 1, reserved for future extensions; - A one-octet value 1, reserved for future extensions,
- a one-octet hash function ID used with a KDF;
- a one-octet algorithm ID for the symmetric algorithm used to - A one-octet hash function ID used with a KDF,
- A one-octet algorithm ID for the symmetric algorithm used to
wrap the symmetric key used for the message encryption; see wrap the symmetric key used for the message encryption; see
Section 13.5 for details. Section 13.5 for details.
Observe that an ECDH public key is composed of the same sequence of Observe that an ECDH public key is composed of the same sequence of
fields that define an ECDSA key, plus the KDF parameters field. fields that define an ECDSA key plus the KDF parameters field.
The secret key is this single multiprecision integer: The secret key is this single multiprecision integer:
* MPI of an integer representing the secret key, which is a scalar * An MPI representing the secret key, in the curve-specific format
of the public EC point. described in Section 9.2.1.
5.7. Compressed Data Packet (Tag 8) 5.7. Compressed Data Packet (Tag 8)
The Compressed Data packet contains compressed data. Typically, this The Compressed Data packet contains compressed data. Typically, this
packet is found as the contents of an encrypted packet, or following packet is found as the contents of an encrypted packet, or following
a Signature or One-Pass Signature packet, and contains a literal data a Signature or One-Pass Signature packet, and contains a literal data
packet. packet.
The body of this packet consists of: The body of this packet consists of:
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5.14. Sym. Encrypted Integrity Protected Data Packet (Tag 18) 5.14. Sym. Encrypted Integrity Protected Data Packet (Tag 18)
The Symmetrically Encrypted Integrity Protected Data packet is a The Symmetrically Encrypted Integrity Protected Data packet is a
variant of the Symmetrically Encrypted Data packet. It is a new variant of the Symmetrically Encrypted Data packet. It is a new
feature created for OpenPGP that addresses the problem of detecting a feature created for OpenPGP that addresses the problem of detecting a
modification to encrypted data. It is used in combination with a modification to encrypted data. It is used in combination with a
Modification Detection Code packet. Modification Detection Code packet.
There is a corresponding feature in the features Signature subpacket There is a corresponding feature in the features Signature subpacket
that denotes that an implementation can properly use this packet that denotes that an implementation can properly use this packet
type. An implementation MUST support decrypting these packets and type. An implementation MUST support decrypting and generating these
SHOULD prefer generating them to the older Symmetrically Encrypted packets. An implementation SHOULD specifically denote support for
Data packet when possible. Since this data packet protects against this packet, but it MAY infer it from other mechanisms.
modification attacks, this standard encourages its proliferation.
While blanket adoption of this data packet would create
interoperability problems, rapid adoption is nevertheless important.
An implementation SHOULD specifically denote support for this packet,
but it MAY infer it from other mechanisms.
For example, an implementation might infer from the use of a cipher For example, an implementation might infer from the use of a cipher
such as Advanced Encryption Standard (AES) or Twofish that a user such as Advanced Encryption Standard (AES) or Twofish that a user
supports this feature. It might place in the unhashed portion of supports this feature. It might place in the unhashed portion of
another user's key signature a Features subpacket. It might also another user's key signature a Features subpacket. It might also
present a user with an opportunity to regenerate their own self- present a user with an opportunity to regenerate their own self-
signature with a Features subpacket. signature with a Features subpacket.
This packet contains data encrypted with a symmetric-key algorithm This packet contains data encrypted with a symmetric-key algorithm
and protected against modification by the SHA-1 hash algorithm. When and protected against modification by the SHA-1 hash algorithm. When
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* A one-octet version number. The only currently defined value is * A one-octet version number. The only currently defined value is
1. 1.
* Encrypted data, the output of the selected symmetric-key cipher * Encrypted data, the output of the selected symmetric-key cipher
operating in Cipher Feedback mode with shift amount equal to the operating in Cipher Feedback mode with shift amount equal to the
block size of the cipher (CFB-n where n is the block size). block size of the cipher (CFB-n where n is the block size).
The symmetric cipher used MUST be specified in a Public-Key or The symmetric cipher used MUST be specified in a Public-Key or
Symmetric-Key Encrypted Session Key packet that precedes the Symmetric-Key Encrypted Session Key packet that precedes the
Symmetrically Encrypted Data packet. In either case, the cipher Symmetrically Encrypted Integrity Protected Data packet. In either
algorithm octet is prefixed to the session key before it is case, the cipher algorithm octet is prefixed to the session key
encrypted. before it is encrypted.
The data is encrypted in CFB mode, with a CFB shift size equal to the The data is encrypted in CFB mode, with a CFB shift size equal to the
cipher's block size. The Initial Vector (IV) is specified as all cipher's block size. The Initial Vector (IV) is specified as all
zeros. Instead of using an IV, OpenPGP prefixes an octet string to zeros. Instead of using an IV, OpenPGP prefixes an octet string to
the data before it is encrypted. The length of the octet string the data before it is encrypted. The length of the octet string
equals the block size of the cipher in octets, plus two. The first equals the block size of the cipher in octets, plus two. The first
octets in the group, of length equal to the block size of the cipher, octets in the group, of length equal to the block size of the cipher,
are random; the last two octets are each copies of their 2nd are random; the last two octets are each copies of their 2nd
preceding octet. For example, with a cipher whose block size is 128 preceding octet. For example, with a cipher whose block size is 128
bits or 16 octets, the prefix data will contain 16 random octets, bits or 16 octets, the prefix data will contain 16 random octets,
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prefix data, the tag octet, and length octet of the Modification prefix data, the tag octet, and length octet of the Modification
Detection Code packet. Detection Code packet.
Note that the Modification Detection Code packet MUST always use a Note that the Modification Detection Code packet MUST always use a
new format encoding of the packet tag, and a one-octet encoding of new format encoding of the packet tag, and a one-octet encoding of
the packet length. The reason for this is that the hashing rules for the packet length. The reason for this is that the hashing rules for
modification detection include a one-octet tag and one-octet length modification detection include a one-octet tag and one-octet length
in the data hash. While this is a bit restrictive, it reduces in the data hash. While this is a bit restrictive, it reduces
complexity. complexity.
5.16. AEAD Encrypted Data Packet (Tag 20)
This packet contains data encrypted with an authenticated encryption
and additional data (AEAD) construction. When it has been decrypted,
it will typically contain other packets (often a Literal Data packet
or Compressed Data packet).
The body of this packet starts with:
* A one-octet version number. The only currently defined value is
1.
When the version is 1, it is followed by the following fields:
* A one-octet cipher algorithm.
* A one-octet AEAD algorithm.
* A one-octet chunk size.
* A initialization vector of size specified by the AEAD algorithm.
* Encrypted data, the output of the selected symmetric-key cipher
operating in the given AEAD mode.
* A final, summary authentication tag for the AEAD mode.
An AEAD encrypted data packet consists of one or more chunks of data.
The plaintext of each chunk is of a size specified using the chunk
size octet using the method specified below.
The encrypted data consists of the encryption of each chunk of
plaintext, followed immediately by the relevant authentication tag.
If the last chunk of plaintext is smaller than the chunk size, the
ciphertext for that data may be shorter; it is nevertheless followed
by a full authentication tag.
For each chunk, the AEAD construction is given the Packet Tag in new
format encoding (bits 7 and 6 set, bits 5-0 carry the packet tag),
version number, cipher algorithm octet, AEAD algorithm octet, chunk
size octet, and an eight-octet, big-endian chunk index as additional
data. The index of the first chunk is zero. For example, the
additional data of the first chunk using EAX and AES-128 with a chunk
size of 2**16 octets consists of the octets 0xD4, 0x01, 0x07, 0x01,
0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, and 0x00.
After the final chunk, the AEAD algorithm is used to produce a final
authentication tag encrypting the empty string. This AEAD instance
is given the additional data specified above, plus an eight-octet,
big-endian value specifying the total number of plaintext octets
encrypted. This allows detection of a truncated ciphertext. Please
note that the big-endian number representing the chunk index in the
additional data is increased accordingly, although it's not really a
chunk.
The chunk size octet specifies the size of chunks using the following
formula (in C), where c is the chunk size octet:
chunk_size = ((uint64_t)1 << (c + 6))
An implementation MUST accept chunk size octets with values from 0 to
16. An implementation MUST NOT create data with a chunk size octet
value larger than 16 (4 MiB chunks).
A unique, random, unpredictable initialization vector MUST be used
for each message. Failure to do so for each message can lead to a
catastrophic failure depending on the choice of AEAD mode and
symmetric key reuse.
5.16.1. EAX Mode
The EAX AEAD Algorithm used in this document is defined in [EAX].
The EAX algorithm can only use block ciphers with 16-octet blocks.
The initialization vector is 16 octets long. EAX authentication tags
are 16 octets long.
The nonce for EAX mode is computed by treating the initialization
vector as a 16-octet, big-endian value and exclusive-oring the low
eight octets of it with the chunk index.
5.16.2. OCB Mode
The OCB AEAD Algorithm used in this document is defined in [RFC7253].
The OCB algorithm can only use block ciphers with 16-octet blocks.
The initialization vector is 15 octets long. OCB authentication tags
are 16 octets long.
The nonce for OCB mode is computed by the exclusive-oring of the
initialization vector as a 15-octet, big endian value, against the
chunk index.
6. Radix-64 Conversions 6. Radix-64 Conversions
As stated in the introduction, OpenPGP's underlying native As stated in the introduction, OpenPGP's underlying native
representation for objects is a stream of arbitrary octets, and some representation for objects is a stream of arbitrary octets, and some
systems desire these objects to be immune to damage caused by systems desire these objects to be immune to damage caused by
character set translation, data conversions, etc. character set translation, data conversions, etc.
In principle, any printable encoding scheme that met the requirements In principle, any printable encoding scheme that met the requirements
of the unsafe channel would suffice, since it would not change the of the unsafe channel would suffice, since it would not change the
underlying binary bit streams of the native OpenPGP data structures. underlying binary bit streams of the native OpenPGP data structures.
skipping to change at page 68, line 4 skipping to change at page 73, line 14
The format of an Armor Header is that of a key-value pair. A colon The format of an Armor Header is that of a key-value pair. A colon
(":" 0x38) and a single space (0x20) separate the key and value. (":" 0x38) and a single space (0x20) separate the key and value.
OpenPGP should consider improperly formatted Armor Headers to be OpenPGP should consider improperly formatted Armor Headers to be
corruption of the ASCII Armor. Unknown keys should be reported to corruption of the ASCII Armor. Unknown keys should be reported to
the user, but OpenPGP should continue to process the message. the user, but OpenPGP should continue to process the message.
Note that some transport methods are sensitive to line length. While Note that some transport methods are sensitive to line length. While
there is a limit of 76 characters for the Radix-64 data there is a limit of 76 characters for the Radix-64 data
(Section 6.3), there is no limit to the length of Armor Headers. (Section 6.3), there is no limit to the length of Armor Headers.
Care should be taken that the Armor Headers are short enough to Care should be taken that the Armor Headers are short enough to
survive transport. One way to do this is to repeat an Armor Header survive transport. One way to do this is to repeat an Armor Header
Key multiple times with different values for each so that no one line Key multiple times with different values for each so that no one line
is overly long. is overly long.
Currently defined Armor Header Keys are as follows: Currently defined Armor Header Keys are as follows:
* "Version", which states the OpenPGP implementation and version * "Version", which states the OpenPGP implementation and version
used to encode the message. used to encode the message. To minimize metadata, implementations
SHOULD NOT emit this key and its corresponding value except for
debugging purposes with explicit user consent.
* "Comment", a user-defined comment. OpenPGP defines all text to be * "Comment", a user-defined comment. OpenPGP defines all text to be
in UTF-8. A comment may be any UTF-8 string. However, the whole in UTF-8. A comment may be any UTF-8 string. However, the whole
point of armoring is to provide seven-bit-clean data. point of armoring is to provide seven-bit-clean data.
Consequently, if a comment has characters that are outside the US- Consequently, if a comment has characters that are outside the US-
ASCII range of UTF, they may very well not survive transport. ASCII range of UTF, they may very well not survive transport.
* "MessageID", a 32-character string of printable characters. The * "MessageID", a 32-character string of printable characters. The
string must be the same for all parts of a multi-part message that string must be the same for all parts of a multi-part message that
uses the "PART X" Armor Header. MessageID strings should be uses the "PART X" Armor Header. MessageID strings should be
skipping to change at page 72, line 30 skipping to change at page 77, line 30
8-bit: 00010100 11111011 10011100 | 00000011 8-bit: 00010100 11111011 10011100 | 00000011
pad with 0000 pad with 0000
6-bit: 000101 001111 101110 011100 | 000000 110000 6-bit: 000101 001111 101110 011100 | 000000 110000
Decimal: 5 15 46 28 0 48 Decimal: 5 15 46 28 0 48
pad with = = pad with = =
Output: F P u c A w = = Output: F P u c A w = =
6.6. Example of an ASCII Armored Message 6.6. Example of an ASCII Armored Message
-----BEGIN PGP MESSAGE----- -----BEGIN PGP MESSAGE-----
Version: OpenPrivacy 0.99
yDgBO22WxBHv7O8X7O/jygAEzol56iUKiXmV+XmpCtmpqQUKiQrFqclFqUDBovzS yDgBO22WxBHv7O8X7O/jygAEzol56iUKiXmV+XmpCtmpqQUKiQrFqclFqUDBovzS
vBSFjNSiVHsuAA== vBSFjNSiVHsuAA==
=njUN =njUN
-----END PGP MESSAGE----- -----END PGP MESSAGE-----
Note that this example has extra indenting; an actual armored message Note that this example has extra indenting; an actual armored message
would have no leading whitespace. would have no leading whitespace.
7. Cleartext Signature Framework 7. Cleartext Signature Framework
skipping to change at page 73, line 37 skipping to change at page 78, line 37
An implementation SHOULD add a line break after the cleartext, but An implementation SHOULD add a line break after the cleartext, but
MAY omit it if the cleartext ends with a line break. This is for MAY omit it if the cleartext ends with a line break. This is for
visual clarity. visual clarity.
7.1. Dash-Escaped Text 7.1. Dash-Escaped Text
The cleartext content of the message must also be dash-escaped. The cleartext content of the message must also be dash-escaped.
Dash-escaped cleartext is the ordinary cleartext where every line Dash-escaped cleartext is the ordinary cleartext where every line
starting with a dash "-" (0x2D) is prefixed by the sequence dash "-" starting with a "-" (HYPHEN-MINUS, U+002D) is prefixed by the
(0x2D) and space ` ` (0x20). This prevents the parser from sequence "-" (HYPHEN-MINUS, U+002D) and " " (SPACE, U+0020). This
recognizing armor headers of the cleartext itself. An implementation prevents the parser from recognizing armor headers of the cleartext
MAY dash-escape any line, SHOULD dash-escape lines commencing "From" itself. An implementation MAY dash-escape any line, SHOULD dash-
followed by a space, and MUST dash-escape any line commencing in a escape lines commencing "From" followed by a space, and MUST dash-
dash. The message digest is computed using the cleartext itself, not escape any line commencing in a dash. The message digest is computed
the dash-escaped form. using the cleartext itself, not the dash-escaped form.
As with binary signatures on text documents, a cleartext signature is As with binary signatures on text documents, a cleartext signature is
calculated on the text using canonical <CR><LF> line endings. The calculated on the text using canonical <CR><LF> line endings. The
line ending (i.e., the <CR><LF>) before the "-----BEGIN PGP line ending (i.e., the <CR><LF>) before the "-----BEGIN PGP
SIGNATURE-----" line that terminates the signed text is not SIGNATURE-----" line that terminates the signed text is not
considered part of the signed text. considered part of the signed text.
When reversing dash-escaping, an implementation MUST strip the string When reversing dash-escaping, an implementation MUST strip the string
"-" if it occurs at the beginning of a line, and SHOULD warn on "-" "-" if it occurs at the beginning of a line, and SHOULD warn on "-"
and any character other than a space at the beginning of a line. and any character other than a space at the beginning of a line.
skipping to change at page 75, line 9 skipping to change at page 80, line 9
Note that these tables are not exhaustive lists; an implementation Note that these tables are not exhaustive lists; an implementation
MAY implement an algorithm not on these lists, so long as the MAY implement an algorithm not on these lists, so long as the
algorithm numbers are chosen from the private or experimental algorithm numbers are chosen from the private or experimental
algorithm range. algorithm range.
See Section 14 for more discussion of the algorithms. See Section 14 for more discussion of the algorithms.
9.1. Public-Key Algorithms 9.1. Public-Key Algorithms
+========+===================================================+ +===+==============+==========+=============+===========+===========+
| ID | Algorithm | | ID|Algorithm |Public Key|Secret Key | Signature |PKESK |
+========+===================================================+ | | |Format |Format | Format |Format |
| 1 | RSA (Encrypt or Sign) [HAC] | +===+==============+==========+=============+===========+===========+
+--------+---------------------------------------------------+ | 1|RSA (Encrypt |MPI(n), |MPI(d), | MPI(m**d |MPI(m**e |
| 2 | RSA Encrypt-Only [HAC] | | |or Sign) [HAC]|MPI(e) |MPI(p), | mod n) |mod n) |
+--------+---------------------------------------------------+ | | |[Section |MPI(q), | [Section |[Section |
| 3 | RSA Sign-Only [HAC] | | | |5.6.1] |MPI(u) | 5.2.3.1] |5.1.1] |
+--------+---------------------------------------------------+ +---+--------------+----------+-------------+-----------+-----------+
| 16 | Elgamal (Encrypt-Only) [ELGAMAL] [HAC] | | 2|RSA Encrypt- |MPI(n), |MPI(d), | N/A |MPI(m**e |
+--------+---------------------------------------------------+ | |Only [HAC] |MPI(e) |MPI(p), | |mod n) |
| 17 | DSA (Digital Signature Algorithm) [FIPS186] [HAC] | | | |[Section |MPI(q), | |[Section |
+--------+---------------------------------------------------+ | | |5.6.1] |MPI(u) | |5.1.1] |
| 18 | ECDH public key algorithm | +---+--------------+----------+-------------+-----------+-----------+
+--------+---------------------------------------------------+ | 3|RSA Sign-Only |MPI(n), |MPI(d), | MPI(m**d |N/A |
| 19 | ECDSA public key algorithm [FIPS186] | | |[HAC] |MPI(e) |MPI(p), | mod n) | |
+--------+---------------------------------------------------+ | | |[Section |MPI(q), | [Section | |
| 20 | Reserved (formerly Elgamal Encrypt or Sign) | | | |5.6.1] |MPI(u) | 5.2.3.1] | |
+--------+---------------------------------------------------+ +---+--------------+----------+-------------+-----------+-----------+
| 21 | Reserved for Diffie-Hellman (X9.42, as defined | | 16|Elgamal |MPI(p), |MPI(x) | N/A |MPI(g**k |
| | for IETF-S/MIME) | | |(Encrypt-Only)|MPI(g), | | |mod p), MPI|
+--------+---------------------------------------------------+ | |[ELGAMAL] |MPI(y) | | |(m * y**k |
| 22 | EdDSA [RFC8032] | | |[HAC] |[Section | | |mod p) |
+--------+---------------------------------------------------+ | | |5.6.3] | | |[Section |
| 23 | Reserved (AEDH) | | | | | | |5.1.2] |
+--------+---------------------------------------------------+ +---+--------------+----------+-------------+-----------+-----------+
| 24 | Reserved (AEDSA) | | 17|DSA (Digital |MPI(p), |MPI(x) | MPI(r), |N/A |
+--------+---------------------------------------------------+ | |Signature |MPI(q), | | MPI(s) | |
| 100 to | Private/Experimental algorithm | | |Algorithm) |MPI(g), | | [Section | |
| 110 | | | |[FIPS186] |MPI(y) | | 5.2.3.2] | |
+--------+---------------------------------------------------+ | |[HAC] |[Section | | | |
| | |5.6.2] | | | |
+---+--------------+----------+-------------+-----------+-----------+
| 18|ECDH public |OID, |MPI(secret) | N/A |MPI(point |
| |key algorithm |MPI(point | | |in curve- |
| | |in curve- | | |specific |
| | |specific | | |point |
| | |point | | |format), |
| | |format), | | |size octet,|
| | |KDFParams | | |encoded key|
| | |[see | | |[Section |
| | |Section | | |9.2.1, |
| | |9.2.1, | | |Section |
| | |Section | | |5.1.3, |
| | |5.6.6] | | |Section |
| | | | | |13.5] |
+---+--------------+----------+-------------+-----------+-----------+
| 19|ECDSA public |OID, |MPI(secret) | MPI(r), |N/A |
| |key algorithm |MPI(point | | MPI(s) | |
| |[FIPS186] |in SEC1 | | [Section | |
| | |format) | | 5.2.3.2] | |
| | |[Section | | | |
| | |5.6.4] | | | |
+---+--------------+----------+-------------+-----------+-----------+
| 20|Reserved | | | | |
| |(formerly | | | | |
| |Elgamal | | | | |
| |Encrypt or | | | | |
| |Sign) | | | | |
+---+--------------+----------+-------------+-----------+-----------+
| 21|Reserved for | | | | |
| |Diffie-Hellman| | | | |
| |(X9.42, as | | | | |
| |defined for | | | | |
| |IETF-S/MIME) | | | | |
+---+--------------+----------+-------------+-----------+-----------+
| 22|EdDSA |OID, |MPI(value in | MPI, MPI |N/A |
| |[RFC8032] |MPI(point |curve- | [see | |
| | |in |specific | Section | |
| | |prefixed |format) [see | 9.2.1, | |
| | |native |Section | Section | |
| | |format) |9.2.1] | 5.2.3.3] | |
| | |[Section | | | |
| | |5.6.5] | | | |
+---+--------------+----------+-------------+-----------+-----------+
| 23|Reserved | | | | |
| |(AEDH) | | | | |
+---+--------------+----------+-------------+-----------+-----------+
| 24|Reserved | | | | |
| |(AEDSA) | | | | |
+---+--------------+----------+-------------+-----------+-----------+
|100|Private/ | | | | |
| to|Experimental | | | | |
|110|algorithm | | | | |
+---+--------------+----------+-------------+-----------+-----------+
Table 15: Public-key algorithm registry Table 15: Public-key algorithm registry
Implementations MUST implement DSA for signatures, and Elgamal for Implementations MUST implement DSA for signatures, and Elgamal for
encryption. Implementations SHOULD implement RSA keys (1). RSA encryption. Implementations SHOULD implement RSA keys (1). RSA
Encrypt-Only (2) and RSA Sign-Only (3) are deprecated and SHOULD NOT Encrypt-Only (2) and RSA Sign-Only (3) are deprecated and SHOULD NOT
be generated, but may be interpreted. See Section 14.5. See be generated, but may be interpreted. See Section 14.5. See
Section 14.9 for notes on Elgamal Encrypt or Sign (20), and X9.42 Section 14.9 for notes on Elgamal Encrypt or Sign (20), and X9.42
(21). Implementations MAY implement any other algorithm. (21). Implementations MAY implement any other algorithm.
A compatible specification of ECDSA is given in [RFC6090] as "KT-I A compatible specification of ECDSA is given in [RFC6090] as "KT-I
Signatures" and in [SEC1]; ECDH is defined in Section 13.5 this Signatures" and in [SEC1]; ECDH is defined in Section 13.5 of this
document. document.
9.2. ECC Curve OID 9.2. ECC Curves for OpenPGP
The parameter curve OID is an array of octets that define a named The parameter curve OID is an array of octets that define a named
curve. The table below specifies the exact sequence of bytes for curve.
each named curve referenced in this document:
+========================+=====+=================+============+ The table below specifies the exact sequence of octets for each named
| ASN.1 Object | OID | Curve OID bytes | Curve name | curve referenced in this document. It also specifies which public
| Identifier | len | in hexadecimal | | key algorithms the curve can be used with, as well as the size of
| | | representation | | expected elements in octets:
+========================+=====+=================+============+
| 1.2.840.10045.3.1.7 | 8 | 2A 86 48 CE 3D | NIST P-256 |
| | | 03 01 07 | |
+------------------------+-----+-----------------+------------+
| 1.3.132.0.34 | 5 | 2B 81 04 00 22 | NIST P-384 |
+------------------------+-----+-----------------+------------+
| 1.3.132.0.35 | 5 | 2B 81 04 00 23 | NIST P-521 |
+------------------------+-----+-----------------+------------+
| 1.3.6.1.4.1.11591.15.1 | 9 | 2B 06 01 04 01 | Ed25519 |
| | | DA 47 0F 01 | |
+------------------------+-----+-----------------+------------+
| 1.3.6.1.4.1.3029.1.5.1 | 10 | 2B 06 01 04 01 | Curve25519 |
| | | 97 55 01 05 01 | |
+------------------------+-----+-----------------+------------+
Table 16: ECC Curve OID registry +======================+===+==============+==========+======+=======+
|ASN.1 Object |OID|Curve OID |Curve name|Usage |Field |
|Identifier |len|octets in | | |Size |
| | |hexadecimal | | |(fsize)|
| | |representation| | | |
+======================+===+==============+==========+======+=======+
|1.2.840.10045.3.1.7 |8 |2A 86 48 CE 3D|NIST P-256|ECDSA,|32 |
| | |03 01 07 | |ECDH | |
+----------------------+---+--------------+----------+------+-------+
|1.3.132.0.34 |5 |2B 81 04 00 22|NIST P-384|ECDSA,|48 |
| | | | |ECDH | |
+----------------------+---+--------------+----------+------+-------+
|1.3.132.0.35 |5 |2B 81 04 00 23|NIST P-521|ECDSA,|66 |
| | | | |ECDH | |
+----------------------+---+--------------+----------+------+-------+
|1.3.6.1.4.1.11591.15.1|9 |2B 06 01 04 01|Ed25519 |EdDSA |32 |
| | |DA 47 0F 01 | | | |
+----------------------+---+--------------+----------+------+-------+
|1.3.101.113 |3 |2B 65 71 |Ed448 |EdDSA |57 |
+----------------------+---+--------------+----------+------+-------+
|1.3.6.1.4.1.3029.1.5.1|10 |2B 06 01 04 01|Curve25519|ECDH |32 |
| | |97 55 01 05 01| | | |
+----------------------+---+--------------+----------+------+-------+
|1.3.101.111 |3 |2B 65 6F |X448 |ECDH |56 |
+----------------------+---+--------------+----------+------+-------+
Table 16: ECC Curve OID and usage registry
The "Field Size (fsize)" column represents the field size of the
group in number of octets, rounded up, such that x or y coordinates
for a point on the curve, native point representations, or scalars
with high enough entropy for the curve can be represented in that
many octets.
The sequence of octets in the third column is the result of applying The sequence of octets in the third column is the result of applying
the Distinguished Encoding Rules (DER) to the ASN.1 Object Identifier the Distinguished Encoding Rules (DER) to the ASN.1 Object Identifier
with subsequent truncation. The truncation removes the two fields of with subsequent truncation. The truncation removes the two fields of
encoded Object Identifier. The first omitted field is one octet encoded Object Identifier. The first omitted field is one octet
representing the Object Identifier tag, and the second omitted field representing the Object Identifier tag, and the second omitted field
is the length of the Object Identifier body. For example, the is the length of the Object Identifier body. For example, the
complete ASN.1 DER encoding for the NIST P-256 curve OID is "06 08 2A complete ASN.1 DER encoding for the NIST P-256 curve OID is "06 08 2A
86 48 CE 3D 03 01 07", from which the first entry in the table above 86 48 CE 3D 03 01 07", from which the first entry in the table above
is constructed by omitting the first two octets. Only the truncated is constructed by omitting the first two octets. Only the truncated
sequence of octets is the valid representation of a curve OID. sequence of octets is the valid representation of a curve OID.
9.2.1. Curve-Specific Wire Formats
Some Elliptic Curve Public Key Algorithms use different conventions
for specific fields depending on the curve in use. Each field is
always formatted as an MPI, but with a curve-specific framing. This
table summarizes those distinctions.
+============+========+========+=========+===========+==============+
| Curve |ECDH |ECDH |EdDSA |EdDSA |EdDSA |
| |Point |Secret |Secret |Signature |Signature |
| |Format |Key MPI |Key MPI |first MPI |second MPI |
+============+========+========+=========+===========+==============+
| NIST P-256 |SEC1 |integer |N/A |N/A |N/A |
+------------+--------+--------+---------+-----------+--------------+
| NIST P-384 |SEC1 |integer |N/A |N/A |N/A |
+------------+--------+--------+---------+-----------+--------------+
| NIST P-521 |SEC1 |integer |N/A |N/A |N/A |
+------------+--------+--------+---------+-----------+--------------+
| Ed25519 |N/A |N/A |32 octets|32 octets |32 octets of S|
| | | |of secret|of R | |
+------------+--------+--------+---------+-----------+--------------+
| Ed448 |N/A |N/A |prefixed |prefixed |0 [this is an |
| | | |57 octets|114 octets |unused |
| | | |of secret|of |placeholder] |
| | | | |signature | |
+------------+--------+--------+---------+-----------+--------------+
| Curve25519 |prefixed|integer |N/A |N/A |N/A |
| |native | | | | |
+------------+--------+--------+---------+-----------+--------------+
| X448 |prefixed|prefixed|N/A |N/A |N/A |
| |native |56 | | | |
| | |octets | | | |
| | |of | | | |
| | |secret | | | |
+------------+--------+--------+---------+-----------+--------------+
Table 17: Curve-specific wire formats
For the native octet-string forms of EdDSA values, see [RFC8032].
For the native octet-string forms of ECDH secret scalars and points,
see [RFC7748].
9.3. Symmetric-Key Algorithms 9.3. Symmetric-Key Algorithms
+========+=======================================+ +==========+====================================================+
| ID | Algorithm | | ID | Algorithm |
+========+=======================================+ +==========+====================================================+
| 0 | Plaintext or unencrypted data | | 0 | Plaintext or unencrypted data |
+--------+---------------------------------------+ +----------+----------------------------------------------------+
| 1 | IDEA [IDEA] | | 1 | IDEA [IDEA] |
+--------+---------------------------------------+ +----------+----------------------------------------------------+
| 2 | TripleDES (DES-EDE, [SCHNEIER], [HAC] | | 2 | TripleDES (DES-EDE, [SCHNEIER], [HAC] - 168 bit |
| | - 168 bit key derived from 192) | | | key derived from 192) |
+--------+---------------------------------------+ +----------+----------------------------------------------------+
| 3 | CAST5 (128 bit key, as per [RFC2144]) | | 3 | CAST5 (128 bit key, as per [RFC2144]) |
+--------+---------------------------------------+ +----------+----------------------------------------------------+
| 4 | Blowfish (128 bit key, 16 rounds) | | 4 | Blowfish (128 bit key, 16 rounds) [BLOWFISH] |
| | [BLOWFISH] | +----------+----------------------------------------------------+
+--------+---------------------------------------+ | 5 | Reserved |
| 5 | Reserved | +----------+----------------------------------------------------+
+--------+---------------------------------------+ | 6 | Reserved |
| 6 | Reserved | +----------+----------------------------------------------------+
+--------+---------------------------------------+ | 7 | AES with 128-bit key [AES] |
| 7 | AES with 128-bit key [AES] | +----------+----------------------------------------------------+
+--------+---------------------------------------+ | 8 | AES with 192-bit key |
| 8 | AES with 192-bit key | +----------+----------------------------------------------------+
+--------+---------------------------------------+ | 9 | AES with 256-bit key |
| 9 | AES with 256-bit key | +----------+----------------------------------------------------+
+--------+---------------------------------------+ | 10 | Twofish with 256-bit key [TWOFISH] |
| 10 | Twofish with 256-bit key [TWOFISH] | +----------+----------------------------------------------------+
+--------+---------------------------------------+ | 11 | Camellia with 128-bit key [RFC3713] |
| 11 | Camellia with 128-bit key [RFC3713] | +----------+----------------------------------------------------+
+--------+---------------------------------------+ | 12 | Camellia with 192-bit key |
| 12 | Camellia with 192-bit key | +----------+----------------------------------------------------+
+--------+---------------------------------------+ | 13 | Camellia with 256-bit key |
| 13 | Camellia with 256-bit key | +----------+----------------------------------------------------+
+--------+---------------------------------------+ | 100 to | Private/Experimental algorithm |
| 100 to | Private/Experimental algorithm | | 110 | |
| 110 | | +----------+----------------------------------------------------+
+--------+---------------------------------------+ | 253, 254 | Reserved to avoid collision with Secret Key |
| and 255 | Encryption (see Section 3.7.2.1 and Section 5.5.3) |
+----------+----------------------------------------------------+
Table 17: Symmetric-key algorithm registry Table 18: Symmetric-key algorithm registry
Implementations MUST implement TripleDES. Implementations SHOULD Implementations MUST implement TripleDES. Implementations SHOULD
implement AES-128 and CAST5. Implementations that interoperate with implement AES-128 and CAST5. Implementations that interoperate with
PGP 2.6 or earlier need to support IDEA, as that is the only PGP 2.6 or earlier need to support IDEA, as that is the only
symmetric cipher those versions use. Implementations MAY implement symmetric cipher those versions use. Implementations MAY implement
any other algorithm. any other algorithm.
9.4. Compression Algorithms 9.4. Compression Algorithms
+============+================================+ +============+================================+
skipping to change at page 78, line 9 skipping to change at page 86, line 8
+------------+--------------------------------+ +------------+--------------------------------+
| 1 | ZIP [RFC1951] | | 1 | ZIP [RFC1951] |
+------------+--------------------------------+ +------------+--------------------------------+
| 2 | ZLIB [RFC1950] | | 2 | ZLIB [RFC1950] |
+------------+--------------------------------+ +------------+--------------------------------+
| 3 | BZip2 [BZ2] | | 3 | BZip2 [BZ2] |
+------------+--------------------------------+ +------------+--------------------------------+
| 100 to 110 | Private/Experimental algorithm | | 100 to 110 | Private/Experimental algorithm |
+------------+--------------------------------+ +------------+--------------------------------+
Table 18: Compression algorithm registry Table 19: Compression algorithm registry
Implementations MUST implement uncompressed data. Implementations Implementations MUST implement uncompressed data. Implementations
SHOULD implement ZIP. Implementations MAY implement any other SHOULD implement ZIP. Implementations MAY implement any other
algorithm. algorithm.
9.5. Hash Algorithms 9.5. Hash Algorithms
+============+================================+=============+ +============+================================+=============+
| ID | Algorithm | Text Name | | ID | Algorithm | Text Name |
+============+================================+=============+ +============+================================+=============+
skipping to change at page 78, line 51 skipping to change at page 86, line 50
+------------+--------------------------------+-------------+ +------------+--------------------------------+-------------+
| 12 | SHA3-256 [FIPS202] | "SHA3-256" | | 12 | SHA3-256 [FIPS202] | "SHA3-256" |
+------------+--------------------------------+-------------+ +------------+--------------------------------+-------------+
| 13 | Reserved | | | 13 | Reserved | |
+------------+--------------------------------+-------------+ +------------+--------------------------------+-------------+
| 14 | SHA3-512 [FIPS202] | "SHA3-512" | | 14 | SHA3-512 [FIPS202] | "SHA3-512" |
+------------+--------------------------------+-------------+ +------------+--------------------------------+-------------+
| 100 to 110 | Private/Experimental algorithm | | | 100 to 110 | Private/Experimental algorithm | |
+------------+--------------------------------+-------------+ +------------+--------------------------------+-------------+
Table 19: Hash algorithm registry Table 20: Hash algorithm registry
Implementations MUST implement SHA-1. Implementations MAY implement Implementations MUST implement SHA-1. Implementations MAY implement
other algorithms. MD5 is deprecated. other algorithms. MD5 is deprecated.
9.6. AEAD Algorithms
+========+======================+===========+====================+
| ID | Algorithm | IV length | authentication tag |
| | | (octets) | length (octets) |
+========+======================+===========+====================+
| 1 | EAX [EAX] | 16 | 16 |
+--------+----------------------+-----------+--------------------+
| 2 | OCB [RFC7253] | 15 | 16 |
+--------+----------------------+-----------+--------------------+
| 100 to | Private/Experimental | | |
| 110 | algorithm | | |
+--------+----------------------+-----------+--------------------+
Table 21: AEAD algorithm registry
10. IANA Considerations 10. IANA Considerations
Because this document obsoletes [RFC4880], IANA is requested to
update all registration information that references [RFC4880] to
instead reference this RFC.
OpenPGP is highly parameterized, and consequently there are a number OpenPGP is highly parameterized, and consequently there are a number
of considerations for allocating parameters for extensions. This of considerations for allocating parameters for extensions. This
section describes how IANA should look at extensions to the protocol section describes how IANA should look at extensions to the protocol
as described in this document. as described in this document.
10.1. New String-to-Key Specifier Types 10.1. New String-to-Key Specifier Types
OpenPGP S2K specifiers contain a mechanism for new algorithms to turn OpenPGP S2K specifiers contain a mechanism for new algorithms to turn
a string into a key. This specification creates a registry of S2K a string into a key. This specification creates a registry of S2K
specifier types. The registry includes the S2K type, the name of the specifier types. The registry includes the S2K type, the name of the
S2K, and a reference to the defining specification. The initial S2K, and a reference to the defining specification. The initial
values for this registry can be found in Section 3.7.1. Adding a new values for this registry can be found in Section 3.7.1. Adding a new
S2K specifier MUST be done through the SPECIFICATION REQUIRED method, S2K specifier MUST be done through the SPECIFICATION REQUIRED method,
as described in [RFC8126]. as described in [RFC8126].
IANA should add a column "Generate?" to the S2K type registry, with
initial values taken from Section 3.7.1.
10.2. New Packets 10.2. New Packets
Major new features of OpenPGP are defined through new packet types. Major new features of OpenPGP are defined through new packet types.
This specification creates a registry of packet types. The registry This specification creates a registry of packet types. The registry
includes the packet type, the name of the packet, and a reference to includes the packet type, the name of the packet, and a reference to
the defining specification. The initial values for this registry can the defining specification. The initial values for this registry can
be found in Section 4.3. Adding a new packet type MUST be done be found in Section 4.3. Adding a new packet type MUST be done
through the RFC REQUIRED method, as described in [RFC8126]. through the RFC REQUIRED method, as described in [RFC8126].
10.2.1. User Attribute Types 10.2.1. User Attribute Types
skipping to change at page 80, line 4 skipping to change at page 88, line 33
[RFC8126]. [RFC8126].
10.2.1.1. Image Format Subpacket Types 10.2.1.1. Image Format Subpacket Types
Within User Attribute packets, there is an extensible mechanism for Within User Attribute packets, there is an extensible mechanism for
other types of image-based User Attributes. This specification other types of image-based User Attributes. This specification
creates a registry of Image Attribute subpacket types. The registry creates a registry of Image Attribute subpacket types. The registry
includes the Image Attribute subpacket type, the name of the Image includes the Image Attribute subpacket type, the name of the Image
Attribute subpacket, and a reference to the defining specification. Attribute subpacket, and a reference to the defining specification.
The initial values for this registry can be found in Section 5.13.1. The initial values for this registry can be found in Section 5.13.1.
Adding a new Image Attribute subpacket type MUST be done through the Adding a new Image Attribute subpacket type MUST be done through the
SPECIFICATION REQUIRED method, as described in [RFC8126]. SPECIFICATION REQUIRED method, as described in [RFC8126].
10.2.2. New Signature Subpackets 10.2.2. New Signature Subpackets
OpenPGP signatures contain a mechanism for signed (or unsigned) data OpenPGP signatures contain a mechanism for signed (or unsigned) data
to be added to them for a variety of purposes in the Signature to be added to them for a variety of purposes in the Signature
subpackets as discussed in Section 5.2.3.1. This specification subpackets as discussed in Section 5.2.3.5. This specification
creates a registry of Signature subpacket types. The registry creates a registry of Signature subpacket types. The registry
includes the Signature subpacket type, the name of the subpacket, and includes the Signature subpacket type, the name of the subpacket, and
a reference to the defining specification. The initial values for a reference to the defining specification. The initial values for
this registry can be found in Section 5.2.3.1. Adding a new this registry can be found in Section 5.2.3.5. Adding a new
Signature subpacket MUST be done through the SPECIFICATION REQUIRED Signature subpacket MUST be done through the SPECIFICATION REQUIRED
method, as described in [RFC8126]. method, as described in [RFC8126].
10.2.2.1. Signature Notation Data Subpackets 10.2.2.1. Signature Notation Data Subpackets
OpenPGP signatures further contain a mechanism for extensions in OpenPGP signatures further contain a mechanism for extensions in
signatures. These are the Notation Data subpackets, which contain a signatures. These are the Notation Data subpackets, which contain a
key/value pair. Notations contain a user space that is completely key/value pair. Notations contain a user space that is completely
unmanaged and an IETF space. unmanaged and an IETF space.
This specification creates a registry of Signature Notation Data This specification creates a registry of Signature Notation Data
types. The registry includes the Signature Notation Data type, the types. The registry includes the Signature Notation Data type, the
name of the Signature Notation Data, its allowed values, and a name of the Signature Notation Data, its allowed values, and a
reference to the defining specification. The initial values for this reference to the defining specification. The initial values for this
registry can be found in Section 5.2.3.16. Adding a new Signature registry can be found in Section 5.2.3.20. Adding a new Signature
Notation Data subpacket MUST be done through the SPECIFICATION Notation Data subpacket MUST be done through the SPECIFICATION
REQUIRED method, as described in [RFC8126]. REQUIRED method, as described in [RFC8126].
10.2.2.2. Signature Notation Data Subpacket Notation Flags 10.2.2.2. Signature Notation Data Subpacket Notation Flags
This specification creates a new registry of Signature Notation Data This specification creates a new registry of Signature Notation Data
Subpacket Notation Flags. The registry includes the columns "Flag", Subpacket Notation Flags. The registry includes the columns "Flag",
"Description", "Security Recommended", "Interoperability "Description", "Security Recommended", "Interoperability
Recommended", and "Reference". The initial values for this registry Recommended", and "Reference". The initial values for this registry
can be found in Section 5.2.3.16. Adding a new item MUST be done can be found in Section 5.2.3.20. Adding a new item MUST be done
through the SPECIFICATION REQUIRED method, as described in [RFC8126]. through the SPECIFICATION REQUIRED method, as described in [RFC8126].
10.2.2.3. Key Server Preference Extensions 10.2.2.3. Key Server Preference Extensions
OpenPGP signatures contain a mechanism for preferences to be OpenPGP signatures contain a mechanism for preferences to be
specified about key servers. This specification creates a registry specified about key servers. This specification creates a registry
of key server preferences. The registry includes the key server of key server preferences. The registry includes the key server
preference, the name of the preference, and a reference to the preference, the name of the preference, and a reference to the
defining specification. The initial values for this registry can be defining specification. The initial values for this registry can be
found in Section 5.2.3.17. Adding a new key server preference MUST found in Section 5.2.3.21. Adding a new key server preference MUST
be done through the SPECIFICATION REQUIRED method, as described in be done through the SPECIFICATION REQUIRED method, as described in
[RFC8126]. [RFC8126].
10.2.2.4. Key Flags Extensions 10.2.2.4. Key Flags Extensions
OpenPGP signatures contain a mechanism for flags to be specified OpenPGP signatures contain a mechanism for flags to be specified
about key usage. This specification creates a registry of key usage about key usage. This specification creates a registry of key usage
flags. The registry includes the key flags value, the name of the flags. The registry includes the key flags value, the name of the
flag, and a reference to the defining specification. The initial flag, and a reference to the defining specification. The initial
values for this registry can be found in Section 5.2.3.21. Adding a values for this registry can be found in Section 5.2.3.25. Adding a
new key usage flag MUST be done through the SPECIFICATION REQUIRED new key usage flag MUST be done through the SPECIFICATION REQUIRED
method, as described in [RFC8126]. method, as described in [RFC8126].
10.2.2.5. Reason for Revocation Extensions 10.2.2.5. Reason for Revocation Extensions
OpenPGP signatures contain a mechanism for flags to be specified OpenPGP signatures contain a mechanism for flags to be specified
about why a key was revoked. This specification creates a registry about why a key was revoked. This specification creates a registry
of "Reason for Revocation" flags. The registry includes the "Reason of "Reason for Revocation" flags. The registry includes the "Reason
for Revocation" flags value, the name of the flag, and a reference to for Revocation" flags value, the name of the flag, and a reference to
the defining specification. The initial values for this registry can the defining specification. The initial values for this registry can
be found in Section 5.2.3.23. Adding a new feature flag MUST be done be found in Section 5.2.3.27. Adding a new feature flag MUST be done
through the SPECIFICATION REQUIRED method, as described in [RFC8126]. through the SPECIFICATION REQUIRED method, as described in [RFC8126].
10.2.2.6. Implementation Features 10.2.2.6. Implementation Features
OpenPGP signatures contain a mechanism for flags to be specified OpenPGP signatures contain a mechanism for flags to be specified
stating which optional features an implementation supports. This stating which optional features an implementation supports. This
specification creates a registry of feature-implementation flags. specification creates a registry of feature-implementation flags.
The registry includes the feature-implementation flags value, the The registry includes the feature-implementation flags value, the
name of the flag, and a reference to the defining specification. The name of the flag, and a reference to the defining specification. The
initial values for this registry can be found in Section 5.2.3.24. initial values for this registry can be found in Section 5.2.3.28.
Adding a new feature-implementation flag MUST be done through the Adding a new feature-implementation flag MUST be done through the
SPECIFICATION REQUIRED method, as described in [RFC8126]. SPECIFICATION REQUIRED method, as described in [RFC8126].
Also see Section 14.13 for more information about when feature flags Also see Section 14.13 for more information about when feature flags
are needed. are needed.
10.2.3. New Packet Versions 10.2.3. New Packet Versions
The core OpenPGP packets all have version numbers, and can be revised The core OpenPGP packets all have version numbers, and can be revised
by introducing a new version of an existing packet. This by introducing a new version of an existing packet. This
skipping to change at page 82, line 47 skipping to change at page 91, line 24
This document requests IANA register the following new public-key This document requests IANA register the following new public-key
algorithm: algorithm:
+====+============================+========================+ +====+============================+========================+
| ID | Algorithm | Reference | | ID | Algorithm | Reference |
+====+============================+========================+ +====+============================+========================+
| 22 | EdDSA public key algorithm | This doc, Section 14.8 | | 22 | EdDSA public key algorithm | This doc, Section 14.8 |
+----+----------------------------+------------------------+ +----+----------------------------+------------------------+
Table 20: New public-Key algorithms registered Table 22: New public-Key algorithms registered
[ Note to RFC-Editor: Please remove the table above on publication. ] [ Note to RFC-Editor: Please remove the table above on publication. ]
10.3.2. Symmetric-Key Algorithms 10.3.2. Symmetric-Key Algorithms
OpenPGP specifies a number of symmetric-key algorithms. This OpenPGP specifies a number of symmetric-key algorithms. This
specification creates a registry of symmetric-key algorithm specification creates a registry of symmetric-key algorithm
identifiers. The registry includes the algorithm name, its key sizes identifiers. The registry includes the algorithm name, its key sizes
and block size, and a reference to the defining specification. The and block size, and a reference to the defining specification. The
initial values for this registry can be found in Section 9.3. Adding initial values for this registry can be found in Section 9.3. Adding
skipping to change at page 83, line 39 skipping to change at page 92, line 15
+====+===========+===========+ +====+===========+===========+
| ID | Algorithm | Reference | | ID | Algorithm | Reference |
+====+===========+===========+ +====+===========+===========+
| 12 | SHA3-256 | This doc | | 12 | SHA3-256 | This doc |
+----+-----------+-----------+ +----+-----------+-----------+
| 13 | Reserved | | | 13 | Reserved | |
+----+-----------+-----------+ +----+-----------+-----------+
| 14 | SHA3-512 | This doc | | 14 | SHA3-512 | This doc |
+----+-----------+-----------+ +----+-----------+-----------+
Table 21: New hash Table 23: New hash
algorithms registered algorithms registered
[Notes to RFC-Editor: Please remove the table above on publication. [Notes to RFC-Editor: Please remove the table above on publication.
It is desirable not to reuse old or reserved algorithms because some It is desirable not to reuse old or reserved algorithms because some
existing tools might print a wrong description. The ID 13 has been existing tools might print a wrong description. The ID 13 has been
reserved so that the SHA3 algorithm IDs align nicely with their SHA2 reserved so that the SHA3 algorithm IDs align nicely with their SHA2
counterparts.] counterparts.]
10.3.4. Compression Algorithms 10.3.4. Compression Algorithms
OpenPGP specifies a number of compression algorithms. This OpenPGP specifies a number of compression algorithms. This
specification creates a registry of compression algorithm specification creates a registry of compression algorithm
identifiers. The registry includes the algorithm name and a identifiers. The registry includes the algorithm name and a
reference to the defining specification. The initial values for this reference to the defining specification. The initial values for this
registry can be found in Section 9.4. Adding a new compression key registry can be found in Section 9.4. Adding a new compression key
algorithm MUST be done through the SPECIFICATION REQUIRED method, as algorithm MUST be done through the SPECIFICATION REQUIRED method, as
described in [RFC8126]. described in [RFC8126].
10.3.5. Elliptic Curve Algorithms
This document requests IANA add a registry of elliptic curves for use
in OpenPGP.
Each curve is identified on the wire by OID, and is acceptable for
use in certain OpenPGP public key algorithms. The table's initial
headings and values can be found in Section 9.2. Adding a new
elliptic curve algorithm to OpenPGP MUST be done through the
SPECIFICATION REQUIRED method, as described in [RFC8126]. If the new
curve can be used for ECDH or EdDSA, it must also be added to the
"Curve-specific wire formats" table described in Section 9.2.1.
10.4. Elliptic Curve Point and Scalar Wire Formats
This document requests IANA add a registry of wire formats that
represent elliptic curve points. The table's initial headings and
values can be found in Section 13.2. Adding a new EC point wire
format MUST be done through the SPECIFICATION REQUIRED method, as
described in [RFC8126].
This document also requests IANA add a registry of wire formats that
represent scalars for use with elliptic curve cryptography. The
table's initial headings and values can be found in Section 13.3.
Adding a new EC scalar wire format MUST be done through the
SPECIFICATION REQUIRED method, as described in [RFC8126].
This document also requests that IANA add a registry mapping curve-
specific MPI octet-string encoding conventions for ECDH and EdDSA.
The table's initial headings and values can be found in
Section 9.2.1. Adding a new elliptic curve algorithm to OpenPGP MUST
be done through the SPECIFICATION REQUIRED method, as described in
[RFC8126], and requires adding an entry to this table if the curve is
to be used with either EdDSA or ECDH.
10.5. Changes to existing registries
This document requests IANA add the following wire format columns to
the OpenPGP public-key algorithm registry:
* Public Key Format
* Secret Key Format
* Signature Format
* PKESK Format
And populate them with the values found in Section 9.1.
11. Packet Composition 11. Packet Composition
OpenPGP packets are assembled into sequences in order to create OpenPGP packets are assembled into sequences in order to create
messages and to transfer keys. Not all possible packet sequences are messages and to transfer keys. Not all possible packet sequences are
meaningful and correct. This section describes the rules for how meaningful and correct. This section describes the rules for how
packets should be placed into sequences. packets should be placed into sequences.
11.1. Transferable Public Keys 11.1. Transferable Public Keys
OpenPGP users may transfer public keys. The essential elements of a OpenPGP users may transfer public keys. The essential elements of a
skipping to change at page 86, line 27 skipping to change at page 96, line 9
Compressed Message :- Compressed Data Packet. Compressed Message :- Compressed Data Packet.
Literal Message :- Literal Data Packet. Literal Message :- Literal Data Packet.
ESK :- Public-Key Encrypted Session Key Packet | Symmetric-Key ESK :- Public-Key Encrypted Session Key Packet | Symmetric-Key
Encrypted Session Key Packet. Encrypted Session Key Packet.
ESK Sequence :- ESK | ESK Sequence, ESK. ESK Sequence :- ESK | ESK Sequence, ESK.
Encrypted Data :- Symmetrically Encrypted Data Packet | Encrypted Data :- Symmetrically Encrypted Data Packet |
Symmetrically Encrypted Integrity Protected Data Packet Symmetrically Encrypted Integrity Protected Data Packet | AEAD
Encrypted Data Packet
Encrypted Message :- Encrypted Data | ESK Sequence, Encrypted Data. Encrypted Message :- Encrypted Data | ESK Sequence, Encrypted Data.
One-Pass Signed Message :- One-Pass Signature Packet, OpenPGP One-Pass Signed Message :- One-Pass Signature Packet, OpenPGP
Message, Corresponding Signature Packet. Message, Corresponding Signature Packet.
Signed Message :- Signature Packet, OpenPGP Message | One-Pass Signed Message :- Signature Packet, OpenPGP Message | One-Pass
Signed Message. Signed Message.
In addition, decrypting a Symmetrically Encrypted Data packet or a In addition, decrypting a Symmetrically Encrypted and Integrity
Symmetrically Encrypted Integrity Protected Data packet as well as Protected Data packet, an AEAD Encrypted Data packet, or -- for
decompressing a Compressed Data packet must yield a valid OpenPGP historic data -- a Symmetrically Encrypted Data packet must yield a
Message. valid OpenPGP Message. Decompressing a Compressed Data packet must
also yield a valid OpenPGP Message.
Note that some subtle combinations that are formally acceptable by
this grammar are nonetheless unacceptable. For example, a v5 SKESK
packet cannot effectively precede a SEIPD packet, since that
combination does not include any information about the choice of
symmetric cipher used for SEIPD (see Section 5.3.1 for more details).
11.4. Detached Signatures 11.4. Detached Signatures
Some OpenPGP applications use so-called "detached signatures". For Some OpenPGP applications use so-called "detached signatures". For
example, a program bundle may contain a file, and with it a second example, a program bundle may contain a file, and with it a second
file that is a detached signature of the first file. These detached file that is a detached signature of the first file. These detached
signatures are simply a Signature packet stored separately from the signatures are simply a Signature packet stored separately from the
data for which they are a signature. data for which they are a signature.
12. Enhanced Key Formats 12. Enhanced Key Formats
skipping to change at page 87, line 29 skipping to change at page 97, line 20
The format of an OpenPGP V4 key that uses multiple public keys is The format of an OpenPGP V4 key that uses multiple public keys is
similar except that the other keys are added to the end as "subkeys" similar except that the other keys are added to the end as "subkeys"
of the primary key. of the primary key.
Primary-Key Primary-Key
[Revocation Self Signature] [Revocation Self Signature]
[Direct Key Signature...] [Direct Key Signature...]
User ID [Signature ...] User ID [Signature ...]
[User ID [Signature ...] ...] [User ID [Signature ...] ...]
[User Attribute [Signature ...] ...] [User Attribute [Signature ...] ...]
[[Subkey [Binding-Signature-Revocation] [[Subkey [Binding-Signature-Revocation ...]
Primary-Key-Binding-Signature] ...] Subkey-Binding-Signature ...] ...]
A subkey always has a single signature after it that is issued using
the primary key to tie the two keys together. This binding signature
may be in either V3 or V4 format, but SHOULD be V4. Subkeys that can
issue signatures MUST have a V4 binding signature due to the REQUIRED
embedded primary key binding signature.
In the above diagram, if the binding signature of a subkey has been A subkey always has at least one subkey binding signature after it
revoked, the revoked key may be removed, leaving only one key. that is issued using the primary key to tie the two keys together.
These binding signatures may be in either V3 or V4 format, but SHOULD
be V4. Subkeys that can issue signatures MUST have a V4 binding
signature due to the REQUIRED embedded primary key binding signature.
In a V4 key, the primary key MUST be a key capable of certification. In a V4 key, the primary key MUST be a key capable of certification.
The subkeys may be keys of any other type. There may be other The subkeys may be keys of any other type. There may be other
constructions of V4 keys, too. For example, there may be a single- constructions of V4 keys, too. For example, there may be a single-
key RSA key in V4 format, a DSA primary key with an RSA encryption key RSA key in V4 format, a DSA primary key with an RSA encryption
key, or RSA primary key with an Elgamal subkey, etc. key, or RSA primary key with an Elgamal subkey, etc.
It is also possible to have a signature-only subkey. This permits a It is also possible to have a signature-only subkey. This permits a
primary key that collects certifications (key signatures), but is primary key that collects certifications (key signatures), but is
used only for certifying subkeys that are used for encryption and used only for certifying subkeys that are used for encryption and
skipping to change at page 88, line 23 skipping to change at page 98, line 13
and MD5 are deprecated. and MD5 are deprecated.
A V4 fingerprint is the 160-bit SHA-1 hash of the octet 0x99, A V4 fingerprint is the 160-bit SHA-1 hash of the octet 0x99,
followed by the two-octet packet length, followed by the entire followed by the two-octet packet length, followed by the entire
Public-Key packet starting with the version field. The Key ID is the Public-Key packet starting with the version field. The Key ID is the
low-order 64 bits of the fingerprint. Here are the fields of the low-order 64 bits of the fingerprint. Here are the fields of the
hash material, with the example of a DSA key: hash material, with the example of a DSA key:
a.1) 0x99 (1 octet) a.1) 0x99 (1 octet)
a.2) two-octet scalar octet count of (b)-(e) a.2) two-octet, big-endian scalar octet count of (b)-(e)
b) version number = 4 (1 octet); b) version number = 4 (1 octet);
c) timestamp of key creation (4 octets); c) timestamp of key creation (4 octets);
d) algorithm (1 octet): 17 = DSA (example); d) algorithm (1 octet): 17 = DSA (example);
e) Algorithm-specific fields. e) Algorithm-specific fields.
Algorithm-Specific Fields for DSA keys (example): Algorithm-Specific Fields for DSA keys (example):
skipping to change at page 89, line 40 skipping to change at page 99, line 31
material, they will have different Key IDs as well as different material, they will have different Key IDs as well as different
fingerprints. fingerprints.
Finally, the Key ID and fingerprint of a subkey are calculated in the Finally, the Key ID and fingerprint of a subkey are calculated in the
same way as for a primary key, including the 0x99 (V3 and V4 key) or same way as for a primary key, including the 0x99 (V3 and V4 key) or
0x9A (V5 key) as the first octet (even though this is not a valid 0x9A (V5 key) as the first octet (even though this is not a valid
packet ID for a public subkey). packet ID for a public subkey).
13. Elliptic Curve Cryptography 13. Elliptic Curve Cryptography
This section descripes algorithms and parameters used with Elliptic This section describes algorithms and parameters used with Elliptic
Curve Cryptography (ECC) keys. A thorough introduction to ECC can be Curve Cryptography (ECC) keys. A thorough introduction to ECC can be
found in [KOBLITZ]. found in [KOBLITZ].
13.1. Supported ECC Curves 13.1. Supported ECC Curves
This document references three named prime field curves, defined in This document references three named prime field curves defined in
[FIPS186] as "Curve P-256", "Curve P-384", and "Curve P-521". [FIPS186] as "Curve P-256", "Curve P-384", and "Curve P-521". These
Further curve "Curve25519", defined in [RFC7748] is referenced for three [FIPS186] curves can be used with ECDSA and ECDH public key
use with Ed25519 (EdDSA signing) and X25519 (encryption). algorithms. Additionally, curve "Curve25519" and "Curve448" are
referenced for use with Ed25519 and Ed448 (EdDSA signing, see
[RFC8032]); and X25519 and X448 (ECDH encryption, see [RFC7748]).
The named curves are referenced as a sequence of bytes in this The named curves are referenced as a sequence of octets in this
document, called throughout, curve OID. Section 9.2 describes in document, called throughout, curve OID. Section 9.2 describes in
detail how this sequence of bytes is formed. detail how this sequence of octets is formed.
13.2. ECDSA and ECDH Conversion Primitives 13.2. EC Point Wire Formats
This document defines the uncompressed point format for ECDSA and A point on an elliptic curve will always be represented on the wire
ECDH and a custom compression format for certain curves. The point as an MPI. Each curve uses a specific point format for the data
is encoded in the Multiprecision Integer (MPI) format. within the MPI itself. Each format uses a designated prefix octet to
ensure that the high octet has at least one bit set to make the MPI a
constant size.
For an uncompressed point the content of the MPI is: +=================+================+================+
| Name | Wire Format | Reference |
+=================+================+================+
| SEC1 | 0x04 || x || y | Section 13.2.1 |
+-----------------+----------------+----------------+
| Prefixed native | 0x40 || native | Section 13.2.2 |
+-----------------+----------------+----------------+
Table 24: Elliptic Curve Point Wire Formats
13.2.1. SEC1 EC Point Wire Format
For a SEC1-encoded (uncompressed) point the content of the MPI is:
B = 04 || x || y B = 04 || x || y
where x and y are coordinates of the point P = (x, y), each encoded where x and y are coordinates of the point P = (x, y), and each is
in the big-endian format and zero-padded to the adjusted underlying encoded in the big-endian format and zero-padded to the adjusted
field size. The adjusted underlying field size is the underlying underlying field size. The adjusted underlying field size is the
field size that is rounded up to the nearest 8-bit boundary. This underlying field size rounded up to the nearest 8-bit boundary, as
encoding is compatible with the definition given in [SEC1]. noted in the "fsize" column in Section 9.2. This encoding is
compatible with the definition given in [SEC1].
13.2.2. Prefixed Native EC Point Wire Format
For a custom compressed point the content of the MPI is: For a custom compressed point the content of the MPI is:
B = 40 || x B = 40 || p
where x is the x coordinate of the point P encoded to the rules where p is the public key of the point encoded using the rules
defined for the specified curve. This format is used for ECDH keys defined for the specified curve. This format is used for ECDH keys
based on curves expressed in Montgomery form. based on curves expressed in Montgomery form, and for points when
using EdDSA.
Therefore, the exact size of the MPI payload is 515 bits for "Curve 13.2.3. Notes on EC Point Wire Formats
P-256", 771 for "Curve P-384", 1059 for "Curve P-521", and 263 for
Curve25519. Given the above definitions, the exact size of the MPI payload for an
encoded point is 515 bits for "Curve P-256", 771 for "Curve P-384",
1059 for "Curve P-521", 263 for both "Curve25519" and "Ed25519", 463
for "Ed448", and 455 for "X448". For example, the length of a EdDSA
public key for the curve Ed25519 is 263 bits: 7 bits to represent the
0x40 prefix octet and 32 octets for the native value of the public
key.
Even though the zero point, also called the point at infinity, may Even though the zero point, also called the point at infinity, may
occur as a result of arithmetic operations on points of an elliptic occur as a result of arithmetic operations on points of an elliptic
curve, it SHALL NOT appear in data structures defined in this curve, it SHALL NOT appear in data structures defined in this
document. document.
If other conversion methods are defined in the future, a compliant Each particular curve uses a designated wire format for the point
application MUST NOT use a new format when in doubt that any found in its public key or ECDH data structure. An implementation
recipient can support it. Consider, for example, that while both the MUST NOT use a different wire format for a point than the wire format
public key and the per-recipient ECDH data structure, respectively associated with the curve.
defined in Section 5.6.6 and Section 5.1, contain an encoded point
field, the format changes to the field in Section 5.1 only affect a
given recipient of a given message.
13.3. EdDSA Point Format 13.3. EC Scalar Wire Formats
The EdDSA algorithm defines a specific point compression format. To Some non-curve values in elliptic curve cryptography (e.g. secret
indicate the use of this compression format and to make sure that the keys and signature components) are not points on a curve, but are
key can be represented in the Multiprecision Integer (MPI) format the also encoded on the wire in OpenPGP as an MPI.
octet string specifying the point is prefixed with the octet 0x40.
This encoding is an extension of the encoding given in [SEC1] which
uses 0x04 to indicate an uncompressed point.
For example, the length of a public key for the curve Ed25519 is 263 Because of different patterns of deployment, some curves treat these
bit: 7 bit to represent the 0x40 prefix octet and 32 octets for the values as opaque bit strings with the high bit set, while others are
native value of the public key. treated as actual integers, encoded in the standard OpenPGP big-
endian form. The choice of encoding is specific to the public key
algorithm in use.
+==========+=====================================+===========+
| Type | Description | Reference |
+==========+=====================================+===========+
| integer | An integer, big-endian encoded as a | Section |
| | standard OpenPGP MPI | 3.2 |
+----------+-------------------------------------+-----------+
| octet | An octet string of fixed length, | Section |
| string | that may be shorter on the wire due | 13.3.1 |
| | to leading zeros being stripped by | |
| | the MPI encoding, and may need to | |
| | be zero-padded before usage | |
+----------+-------------------------------------+-----------+
| prefixed | An octet string of fixed length N, | Section |
| N octets | prefixed with octet 0x40 to ensure | 13.3.2 |
| | no leading zero octet | |
+----------+-------------------------------------+-----------+
Table 25: Elliptic Curve Scalar Encodings
13.3.1. EC Octet String Wire Format
Some opaque strings of octets are represented on the wire as an MPI
by simply stripping the leading zeros and counting the remaining
bits. These strings are of known, fixed length. They are
represented in this document as "MPI(N octets of X)" where "N" is the
expected length in octets of the octet string.
For example, a five-octet opaque string ("MPI(5 octets of X)") where
"X" has the value "00 02 ee 19 00" would be represented on the wire
as an MPI like so: "00 1a 02 ee 19 00".
To encode "X" to the wire format, we set the MPI's two-octet bit
counter to the value of the highest set bit (bit 26, or 0x001a), and
do not transfer the leading all-zero octet to the wire.
To reverse the process, an implementation that knows this value has
an expected length of 5 octets can take the following steps:
* ensure that the MPI's two-octet bitcount is less than or equal to
40 (5 octets of 8 bits)
* allocate 5 octets, setting all to zero initially
* copy the MPI data octets (without the two count octets) into the
lower octets of the allocated space
13.3.2. Elliptic Curve Prefixed Octet String Wire Format
Another way to ensure that a fixed-length bytestring is encoded
simply to the wire while remaining in MPI format is to prefix the
bytestring with a dedicated non-zero octet. This specification uses
0x40 as the prefix octet. This is represented in this standard as
"MPI(prefixed N octets of X)", where "N" is the known bytestring
length.
For example, a five-octet opaque string using "MPI(prefixed 5 octets
of X)" where "X" has the value "00 02 ee 19 00" would be written to
the wire form as: "00 2f 40 00 02 ee 19 00".
To encode the string, we prefix it with the octet 0x40 (whose 7th bit
is set), then set the MPI's two-octet bit counter to 47 (0x002f, 7
bits for the prefix octet and 40 bits for the string).
To decode the string from the wire, an implementation that knows that
the variable is formed in this way can:
* ensure that the first three octets of the MPI (the two bit-count
octets plus the prefix octet) are "00 2f 40", and
* use the remainder of the MPI directly off the wire.
Note that this is a similar approach to that used in the EC point
encodings found in Section 13.2.2.
13.4. Key Derivation Function 13.4. Key Derivation Function
A key derivation function (KDF) is necessary to implement the EC A key derivation function (KDF) is necessary to implement EC
encryption. The Concatenation Key Derivation Function (Approved encryption. The Concatenation Key Derivation Function (Approved
Alternative 1) [SP800-56A] with the KDF hash function that is Alternative 1) [SP800-56A] with the KDF hash function that is
SHA2-256 [FIPS180] or stronger is REQUIRED. SHA2-256 [FIPS180] or stronger is REQUIRED.
For convenience, the synopsis of the encoding method is given below For convenience, the synopsis of the encoding method is given below
with significant simplifications attributable to the restricted with significant simplifications attributable to the restricted
choice of hash functions in this document. However, [SP800-56A] is choice of hash functions in this document. However, [SP800-56A] is
the normative source of the definition. the normative source of the definition.
// Implements KDF( X, oBits, Param ); // Implements KDF( X, oBits, Param );
skipping to change at page 91, line 44 skipping to change at page 104, line 19
// Param - octets representing the parameters // Param - octets representing the parameters
// Assumes that oBits <= hBits // Assumes that oBits <= hBits
// Convert the point X to the octet string: // Convert the point X to the octet string:
// ZB' = 04 || x || y // ZB' = 04 || x || y
// and extract the x portion from ZB' // and extract the x portion from ZB'
ZB = x; ZB = x;
MB = Hash ( 00 || 00 || 00 || 01 || ZB || Param ); MB = Hash ( 00 || 00 || 00 || 01 || ZB || Param );
return oBits leftmost bits of MB. return oBits leftmost bits of MB.
Note that ZB in the KDF description above is the compact Note that ZB in the KDF description above is the compact
representation of X, defined in Section 4.2 of [RFC6090]. representation of X as defined in Section 4.2 of [RFC6090].
13.5. EC DH Algorithm (ECDH) 13.5. EC DH Algorithm (ECDH)
The method is a combination of an ECC Diffie-Hellman method to The method is a combination of an ECC Diffie-Hellman method to
establish a shared secret, a key derivation method to process the establish a shared secret, a key derivation method to process the
shared secret into a derived key, and a key wrapping method that uses shared secret into a derived key, and a key wrapping method that uses
the derived key to protect a session key used to encrypt a message. the derived key to protect a session key used to encrypt a message.
The One-Pass Diffie-Hellman method C(1, 1, ECC CDH) [SP800-56A] MUST The One-Pass Diffie-Hellman method C(1, 1, ECC CDH) [SP800-56A] MUST
be implemented with the following restrictions: the ECC CDH primitive be implemented with the following restrictions: the ECC CDH primitive
employed by this method is modified to always assume the cofactor as employed by this method is modified to always assume the cofactor is
1, the KDF specified in Section 13.4 is used, and the KDF parameters 1, the KDF specified in Section 13.4 is used, and the KDF parameters
specified below are used. specified below are used.
The KDF parameters are encoded as a concatenation of the following 5 The KDF parameters are encoded as a concatenation of the following 5
variable-length and fixed-length fields, compatible with the variable-length and fixed-length fields, which are compatible with
definition of the OtherInfo bitstring [SP800-56A]: the definition of the OtherInfo bitstring [SP800-56A]:
* a variable-length field containing a curve OID, formatted as * A variable-length field containing a curve OID, which is formatted
follows: as follows:
- a one-octet size of the following field - A one-octet size of the following field,
- the octets representing a curve OID, defined in Section 9.2 - The octets representing a curve OID defined in Section 9.2;
* a one-octet public key algorithm ID defined in Section 9.1 * A one-octet public key algorithm ID defined in Section 9.1;
* a variable-length field containing KDF parameters, identical to * A variable-length field containing KDF parameters, which are
the corresponding field in the ECDH public key, formatted as identical to the corresponding field in the ECDH public key, and
follows: are formatted as follows:
- a one-octet size of the following fields; values 0 and 0xff are - A one-octet size of the following fields; values 0 and 0xFF are
reserved for future extensions reserved for future extensions,
- a one-octet value 01, reserved for future extensions - A one-octet value 0x01, reserved for future extensions,
- a one-octet hash function ID used with the KDF - A one-octet hash function ID used with the KDF,
- a one-octet algorithm ID for the symmetric algorithm used to - A one-octet algorithm ID for the symmetric algorithm used to
wrap the symmetric key for message encryption; see Section 13.5 wrap the symmetric key for message encryption; see Section 13.5
for details for details;
* 20 octets representing the UTF-8 encoding of the string "Anonymous * 20 octets representing the UTF-8 encoding of the string "Anonymous
Sender ", which is the octet sequence 41 6E 6F 6E 79 6D 6F 75 Sender ", which is the octet sequence 41 6E 6F 6E 79 6D 6F 75
73 20 53 65 6E 64 65 72 20 20 20 20 73 20 53 65 6E 64 65 72 20 20 20 20;
* 20 octets representing a recipient encryption subkey or a master * 20 octets representing a recipient encryption subkey or a primary
key fingerprint, identifying the key material that is needed for key fingerprint identifying the key material that is needed for
the decryption. For version 5 keys the 20 leftmost octets of the decryption (for version 5 keys the 20 leftmost octets of the
fingerprint are used. fingerprint are used).
The size of the KDF parameters sequence, defined above, is either 54 The size of the KDF parameters sequence, defined above, is either 54
for the NIST curve P-256, 51 for the curves P-384 and P-521, or 56 for the NIST curve P-256, 51 for the curves P-384 and P-521, 56 for
for Curve25519. Curve25519, or 49 for X448.
The key wrapping method is described in [RFC3394]. KDF produces a The key wrapping method is described in [RFC3394]. The KDF produces
symmetric key that is used as a key-encryption key (KEK) as specified a symmetric key that is used as a key-encryption key (KEK) as
in [RFC3394]. Refer to Section 15 for the details regarding the specified in [RFC3394]. Refer to Section 15 for the details
choice of the KEK algorithm, which SHOULD be one of three AES regarding the choice of the KEK algorithm, which SHOULD be one of
algorithms. Key wrapping and unwrapping is performed with the three AES algorithms. Key wrapping and unwrapping is performed with
default initial value of [RFC3394]. the default initial value of [RFC3394].
The input to the key wrapping method is the value "m" derived from The input to the key wrapping method is the value "m" derived from
the session key, as described in Section 5.1, "Public-Key Encrypted the session key, as described in Section 5.1, "Public-Key Encrypted
Session Key Packets (Tag 1)", except that the PKCS #1.5 padding step Session Key Packets (Tag 1)", except that the PKCS #1.5 padding step
is omitted. The result is padded using the method described in is omitted. The result is padded using the method described in
[PKCS5] to the 8-byte granularity. For example, the following [PKCS5] to an 8-octet granularity. For example, the following
AES-256 session key, in which 32 octets are denoted from k0 to k31, AES-256 session key, in which 32 octets are denoted from k0 to k31,
is composed to form the following 40 octet sequence: is composed to form the following 40 octet sequence:
09 k0 k1 ... k31 s0 s1 05 05 05 05 05 09 k0 k1 ... k31 s0 s1 05 05 05 05 05
The octets s0 and s1 above denote the checksum. This encoding allows The octets s0 and s1 above denote the checksum. This encoding allows
the sender to obfuscate the size of the symmetric encryption key used the sender to obfuscate the size of the symmetric encryption key used
to encrypt the data. For example, assuming that an AES algorithm is to encrypt the data. For example, assuming that an AES algorithm is
used for the session key, the sender MAY use 21, 13, and 5 bytes of used for the session key, the sender MAY use 21, 13, and 5 octets of
padding for AES-128, AES-192, and AES-256, respectively, to provide padding for AES-128, AES-192, and AES-256, respectively, to provide
the same number of octets, 40 total, as an input to the key wrapping the same number of octets, 40 total, as an input to the key wrapping
method. method.
The output of the method consists of two fields. The first field is The output of the method consists of two fields. The first field is
the MPI containing the ephemeral key used to establish the shared the MPI containing the ephemeral key used to establish the shared
secret. The second field is composed of the following two fields: secret. The second field is composed of the following two subfields:
* a one-octet encoding the size in octets of the result of the key * One octet encoding the size in octets of the result of the key
wrapping method; the value 255 is reserved for future extensions; wrapping method; the value 255 is reserved for future extensions;
* up to 254 octets representing the result of the key wrapping * Up to 254 octets representing the result of the key wrapping
method, applied to the 8-byte padded session key, as described method, applied to the 8-octet padded session key, as described
above. above.
Note that for session key sizes 128, 192, and 256 bits, the size of Note that for session key sizes 128, 192, and 256 bits, the size of
the result of the key wrapping method is, respectively, 32, 40, and the result of the key wrapping method is, respectively, 32, 40, and
48 octets, unless the size obfuscation is used. 48 octets, unless size obfuscation is used.
For convenience, the synopsis of the encoding method is given below; For convenience, the synopsis of the encoding method is given below;
however, this section, [SP800-56A], and [RFC3394] are the normative however, this section, [SP800-56A], and [RFC3394] are the normative
sources of the definition. sources of the definition.
* Obtain the authenticated recipient public key R * Obtain the authenticated recipient public key R
* Generate an ephemeral key pair {v, V=vG} * Generate an ephemeral key pair {v, V=vG}
* Compute the shared point S = vR; * Compute the shared point S = vR;
* m = symm_alg_ID || session key || checksum || pkcs5_padding; * m = symm_alg_ID || session key || checksum || pkcs5_padding;
* curve_OID_len = (byte)len(curve_OID); * curve_OID_len = (octet)len(curve_OID);
* Param = curve_OID_len || curve_OID || public_key_alg_ID || 03 || * Param = curve_OID_len || curve_OID || public_key_alg_ID || 03 ||
01 || KDF_hash_ID || KEK_alg_ID for AESKeyWrap || "Anonymous 01 || KDF_hash_ID || KEK_alg_ID for AESKeyWrap || "Anonymous
Sender " || recipient_fingerprint; Sender " || recipient_fingerprint;
* Z_len = the key size for the KEK_alg_ID used with AESKeyWrap * Z_len = the key size for the KEK_alg_ID used with AESKeyWrap
* Compute Z = KDF( S, Z_len, Param ); * Compute Z = KDF( S, Z_len, Param );
* Compute C = AESKeyWrap( Z, m ) as per [RFC3394] * Compute C = AESKeyWrap( Z, m ) as per [RFC3394]
* VB = convert point V to the octet string * VB = convert point V to the octet string
* Output (MPI(VB) || len(C) || C). * Output (MPI(VB) || len(C) || C).
The decryption is the inverse of the method given. Note that the The decryption is the inverse of the method given. Note that the
recipient obtains the shared secret by calculating recipient obtains the shared secret by calculating
S = rV = rvG, where (r,R) is the recipient's key pair. S = rV = rvG, where (r,R) is the recipient's key pair.
Consistent with Section 5.14, Modification Detection Code (MDC) MUST Consistent with Section 5.16 and Section 5.14, AEAD encryption or a
be used anytime the symmetric key is protected by ECDH. Modification Detection Code (MDC) MUST be used anytime the symmetric
key is protected by ECDH.
14. Notes on Algorithms 14. Notes on Algorithms
14.1. PKCS#1 Encoding in OpenPGP 14.1. PKCS#1 Encoding in OpenPGP
This standard makes use of the PKCS#1 functions EME-PKCS1-v1_5 and This standard makes use of the PKCS#1 functions EME-PKCS1-v1_5 and
EMSA-PKCS1-v1_5. However, the calling conventions of these functions EMSA-PKCS1-v1_5. However, the calling conventions of these functions
has changed in the past. To avoid potential confusion and has changed in the past. To avoid potential confusion and
interoperability problems, we are including local copies in this interoperability problems, we are including local copies in this
document, adapted from those in PKCS#1 v2.1 [RFC3447]. [RFC3447] document, adapted from those in PKCS#1 v2.1 [RFC3447]. [RFC3447]
skipping to change at page 100, line 14 skipping to change at page 113, line 5
14.8. EdDSA 14.8. EdDSA
Although the EdDSA algorithm allows arbitrary data as input, its use Although the EdDSA algorithm allows arbitrary data as input, its use
with OpenPGP requires that a digest of the message is used as input with OpenPGP requires that a digest of the message is used as input
(pre-hashed). See section Section 5.2.4, "Computing Signatures" for (pre-hashed). See section Section 5.2.4, "Computing Signatures" for
details. Truncation of the resulting digest is never applied; the details. Truncation of the resulting digest is never applied; the
resulting digest value is used verbatim as input to the EdDSA resulting digest value is used verbatim as input to the EdDSA
algorithm. algorithm.
For clarity: while [RFC8032] describes different variants of EdDSA,
OpenPGP uses the "pure" variant (PureEdDSA). The hashing that
happens with OpenPGP is done as part of the standard OpenPGP
signature process, and that hash itself is fed as the input message
to the PureEdDSA algorithm.
As specified in [RFC8032], Ed448 also expects a "context string". In
OpenPGP, Ed448 is used with the empty string as a context string.
14.9. Reserved Algorithm Numbers 14.9. Reserved Algorithm Numbers
A number of algorithm IDs have been reserved for algorithms that A number of algorithm IDs have been reserved for algorithms that
would be useful to use in an OpenPGP implementation, yet there are would be useful to use in an OpenPGP implementation, yet there are
issues that prevent an implementer from actually implementing the issues that prevent an implementer from actually implementing the
algorithm. These are marked in Section 9.1 as "reserved for". algorithm. These are marked in Section 9.1 as "reserved for".
The reserved public-key algorithm X9.42 (21) does not have the The reserved public-key algorithm X9.42 (21) does not have the
necessary parameters, parameter order, or semantics defined. The necessary parameters, parameter order, or semantics defined. The
same is currently true for reserved public-key algorithms AEDH (23) same is currently true for reserved public-key algorithms AEDH (23)
skipping to change at page 104, line 40 skipping to change at page 117, line 40
+---------------------+-----------+--------------------+ +---------------------+-----------+--------------------+
| 2048 | 224 | 112 | | 2048 | 224 | 112 |
+---------------------+-----------+--------------------+ +---------------------+-----------+--------------------+
| 3072 | 256 | 128 | | 3072 | 256 | 128 |
+---------------------+-----------+--------------------+ +---------------------+-----------+--------------------+
| 7680 | 384 | 192 | | 7680 | 384 | 192 |
+---------------------+-----------+--------------------+ +---------------------+-----------+--------------------+
| 15360 | 512 | 256 | | 15360 | 512 | 256 |
+---------------------+-----------+--------------------+ +---------------------+-----------+--------------------+
Table 22: Key length equivalences Table 26: Key length equivalences
* There is a somewhat-related potential security problem in * There is a somewhat-related potential security problem in
signatures. If an attacker can find a message that hashes to the signatures. If an attacker can find a message that hashes to the
same hash with a different algorithm, a bogus signature structure same hash with a different algorithm, a bogus signature structure
can be constructed that evaluates correctly. can be constructed that evaluates correctly.
For example, suppose Alice DSA signs message M using hash For example, suppose Alice DSA signs message M using hash
algorithm H. Suppose that Mallet finds a message M' that has the algorithm H. Suppose that Mallet finds a message M' that has the
same hash value as M with H'. Mallet can then construct a same hash value as M with H'. Mallet can then construct a
signature block that verifies as Alice's signature of M' with H'. signature block that verifies as Alice's signature of M' with H'.
skipping to change at page 107, line 39 skipping to change at page 120, line 39
| Curve name | ECC | RSA | Hash size strength, | Symmetric | | Curve name | ECC | RSA | Hash size strength, | Symmetric |
| | | strength | informative | key size | | | | strength | informative | key size |
+============+=====+==============+=====================+===========+ +============+=====+==============+=====================+===========+
| NIST P-256 | 256 | 3072 | 256 | 128 | | NIST P-256 | 256 | 3072 | 256 | 128 |
+------------+-----+--------------+---------------------+-----------+ +------------+-----+--------------+---------------------+-----------+
| NIST P-384 | 384 | 7680 | 384 | 192 | | NIST P-384 | 384 | 7680 | 384 | 192 |
+------------+-----+--------------+---------------------+-----------+ +------------+-----+--------------+---------------------+-----------+
| NIST P-521 | 521 | 15360 | 512 | 256 | | NIST P-521 | 521 | 15360 | 512 | 256 |
+------------+-----+--------------+---------------------+-----------+ +------------+-----+--------------+---------------------+-----------+
Table 23: Elliptic Curve cryptographic guidance Table 27: Elliptic Curve cryptographic guidance
* Requirement levels indicated elsewhere in this document lead to * Requirement levels indicated elsewhere in this document lead to
the following combinations of algorithms in the OpenPGP profile: the following combinations of algorithms in the OpenPGP profile:
MUST implement NIST curve P-256 / SHA2-256 / AES-128, SHOULD MUST implement NIST curve P-256 / SHA2-256 / AES-128, SHOULD
implement NIST curve P-521 / SHA2-512 / AES-256, MAY implement implement NIST curve P-521 / SHA2-512 / AES-256, MAY implement
NIST curve P-384 / SHA2-384 / AES-256, among other allowed NIST curve P-384 / SHA2-384 / AES-256, among other allowed
combinations. combinations.
Consistent with the table above, the following table defines the Consistent with the table above, the following table defines the
KDF hash algorithm and the AES KEK encryption algorithm that KDF hash algorithm and the AES KEK encryption algorithm that
skipping to change at page 108, line 16 skipping to change at page 121, line 16
| Curve name | Recommended KDF | Recommended KEK | | Curve name | Recommended KDF | Recommended KEK |
| | hash algorithm | encryption algorithm | | | hash algorithm | encryption algorithm |
+============+=================+======================+ +============+=================+======================+
| NIST P-256 | SHA2-256 | AES-128 | | NIST P-256 | SHA2-256 | AES-128 |
+------------+-----------------+----------------------+ +------------+-----------------+----------------------+
| NIST P-384 | SHA2-384 | AES-192 | | NIST P-384 | SHA2-384 | AES-192 |
+------------+-----------------+----------------------+ +------------+-----------------+----------------------+
| NIST P-521 | SHA2-512 | AES-256 | | NIST P-521 | SHA2-512 | AES-256 |
+------------+-----------------+----------------------+ +------------+-----------------+----------------------+
Table 24: Elliptic Curve KDF and KEK recommendations Table 28: Elliptic Curve KDF and KEK recommendations
* This document explicitly discourages the use of algorithms other * This document explicitly discourages the use of algorithms other
than AES as a KEK algorithm because backward compatibility of the than AES as a KEK algorithm because backward compatibility of the
ECDH format is not a concern. The KEK algorithm is only used ECDH format is not a concern. The KEK algorithm is only used
within the scope of a Public-Key Encrypted Session Key Packet, within the scope of a Public-Key Encrypted Session Key Packet,
which represents an ECDH key recipient of a message. Compare this which represents an ECDH key recipient of a message. Compare this
with the algorithm used for the session key of the message, which with the algorithm used for the session key of the message, which
MAY be different from a KEK algorithm. MAY be different from a KEK algorithm.
Compliant applications SHOULD implement, advertise through key Compliant applications SHOULD implement, advertise through key
preferences, and use the strongest algorithms specified in this preferences, and use the strongest algorithms specified in this
document. document.
Note that the symmetric algorithm preference list may make it Note that the symmetric algorithm preference list may make it
impossible to use the balanced strength of symmetric key impossible to use the balanced strength of symmetric key
algorithms for a corresponding public key. For example, the algorithms for a corresponding public key. For example, the
presence of the symmetric key algorithm IDs and their order in the presence of the symmetric key algorithm IDs and their order in the
key preference list affects the algorithm choices available to the key preference list affects the algorithm choices available to the
encoding side, which in turn may make the adherence to the table encoding side, which in turn may make the adherence to the table
above infeasible. Therefore, compliance with this specification above infeasible. Therefore, compliance with this specification
is a concern throughout the life of the key, starting immediately is a concern throughout the life of the key starting immediately
after the key generation when the key preferences are first added after the key generation when the key preferences are first added
to a key. It is generally advisable to position a symmetric to a key. It is generally advisable to position a symmetric
algorithm ID of strength matching the public key at the head of algorithm ID of strength matching the public key at the head of
the key preference list. the key preference list.
Encryption to multiple recipients often results in an unordered Encryption to multiple recipients often results in an unordered
intersection subset. For example, if the first recipient's set is intersection subset. For example, if the first recipient's set is
{A, B} and the second's is {B, A}, the intersection is an {A, B} and the second's is {B, A}, the intersection is an
unordered set of two algorithms, A and B. In this case, a unordered set of two algorithms, A and B. In this case, a
compliant application SHOULD choose the stronger encryption compliant application SHOULD choose the stronger encryption
algorithm. algorithm.
Resource constraints, such as limited computational power, is a Resource constraints, such as limited computational power, are a
likely reason why an application might prefer to use the weakest reason why an application might prefer to use the weakest
algorithm. On the other side of the spectrum are applications algorithm. On the other side of the spectrum are applications
that can implement every algorithm defined in this document. Most that can implement every algorithm defined in this document. Most
applications are expected to fall into either of two categories. applications are expected to fall into either of these two
A compliant application in the second, or strongest, category categories. A compliant application in the second, or strongest,
SHOULD prefer AES-256 to AES-192. category SHOULD prefer AES-256 to AES-192.
SHA-1 MUST NOT be used with the ECDSA or the KDF in the ECDH SHA-1 MUST NOT be used with the ECDSA or the KDF in the ECDH
method. method.
MDC MUST be used when a symmetric encryption key is protected by MDC MUST be used when a symmetric encryption key is protected by
ECDH. None of the ECC methods described in this document are ECDH. None of the ECC methods described in this document are
allowed with deprecated V3 keys. allowed with deprecated V3 keys.
Side channel attacks are a concern when a compliant application's Side channel attacks are a concern when a compliant application's
use of the OpenPGP format can be modeled by a decryption or use of the OpenPGP format can be modeled by a decryption or
signing oracle model, for example, when an application is a signing oracle, for example, when an application is a network
network service performing decryption to unauthenticated remote service performing decryption to unauthenticated remote users.
users. ECC scalar multiplication operations used in ECDSA and ECC scalar multiplication operations used in ECDSA and ECDH are
ECDH are vulnerable to side channel attacks. Countermeasures can vulnerable to side channel attacks. Countermeasures can often be
often be taken at the higher protocol level, such as limiting the taken at the higher protocol level, such as limiting the number of
number of allowed failures or time-blinding of the operations allowed failures or time-blinding of the operations associated
associated with each network interface. Mitigations at the scalar with each network interface. Mitigations at the scalar
multiplication level seek to eliminate any measurable distinction multiplication level seek to eliminate any measurable distinction
between the ECC point addition and doubling operations. between the ECC point addition and doubling operations.
16. Implementation Nits 16. Implementation Nits
This section is a collection of comments to help an implementer, This section is a collection of comments to help an implementer,
particularly with an eye to backward compatibility. Previous particularly with an eye to backward compatibility. Previous
implementations of PGP are not OpenPGP compliant. Often the implementations of PGP are not OpenPGP compliant. Often the
differences are small, but small differences are frequently more differences are small, but small differences are frequently more
vexing than large differences. Thus, this is a non-comprehensive vexing than large differences. Thus, this is a non-comprehensive
skipping to change at page 111, line 39 skipping to change at page 124, line 39
[BLOWFISH] Schneier, B., "Description of a New Variable-Length Key, [BLOWFISH] Schneier, B., "Description of a New Variable-Length Key,
64-Bit Block Cipher (Blowfish)", Fast Software Encryption, 64-Bit Block Cipher (Blowfish)", Fast Software Encryption,
Cambridge Security Workshop Proceedings Springer-Verlag, Cambridge Security Workshop Proceedings Springer-Verlag,
1994, pp191-204, December 1993, 1994, pp191-204, December 1993,
<http://www.counterpane.com/bfsverlag.html>. <http://www.counterpane.com/bfsverlag.html>.
[BZ2] Seward, J., "The Bzip2 and libbzip2 home page", 2010, [BZ2] Seward, J., "The Bzip2 and libbzip2 home page", 2010,
<http://www.bzip.org/>. <http://www.bzip.org/>.
[EAX] Bellare, M., Rogaway, P., and D. Wagner, "A Conventional
Authenticated-Encryption Mode", April 2003.
[ELGAMAL] Elgamal, T., "A Public-Key Cryptosystem and a Signature [ELGAMAL] Elgamal, T., "A Public-Key Cryptosystem and a Signature
Scheme Based on Discrete Logarithms", IEEE Transactions on Scheme Based on Discrete Logarithms", IEEE Transactions on
Information Theory v. IT-31, n. 4, 1985, pp. 469-472, Information Theory v. IT-31, n. 4, 1985, pp. 469-472,
1985. 1985.
[FIPS180] National Institute of Standards and Technology, U.S. [FIPS180] National Institute of Standards and Technology, U.S.
Department of Commerce, "Secure Hash Standard (SHS), FIPS Department of Commerce, "Secure Hash Standard (SHS), FIPS
180-4", August 2015, 180-4", August 2015,
<http://dx.doi.org/10.6028/NIST.FIPS.180-4>. <http://dx.doi.org/10.6028/NIST.FIPS.180-4>.
skipping to change at page 113, line 37 skipping to change at page 126, line 41
[RFC3713] Matsui, M., Nakajima, J., and S. Moriai, "A Description of [RFC3713] Matsui, M., Nakajima, J., and S. Moriai, "A Description of
the Camellia Encryption Algorithm", RFC 3713, the Camellia Encryption Algorithm", RFC 3713,
DOI 10.17487/RFC3713, April 2004, DOI 10.17487/RFC3713, April 2004,
<https://www.rfc-editor.org/info/rfc3713>. <https://www.rfc-editor.org/info/rfc3713>.
[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086, "Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC4086, June 2005, DOI 10.17487/RFC4086, June 2005,
<https://www.rfc-editor.org/info/rfc4086>. <https://www.rfc-editor.org/info/rfc4086>.
[RFC7253] Krovetz, T. and P. Rogaway, "The OCB Authenticated-
Encryption Algorithm", RFC 7253, DOI 10.17487/RFC7253, May
2014, <https://www.rfc-editor.org/info/rfc7253>.
[RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves [RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", RFC 7748, DOI 10.17487/RFC7748, January for Security", RFC 7748, DOI 10.17487/RFC7748, January
2016, <https://www.rfc-editor.org/info/rfc7748>. 2016, <https://www.rfc-editor.org/info/rfc7748>.
[RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital [RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
Signature Algorithm (EdDSA)", RFC 8032, Signature Algorithm (EdDSA)", RFC 8032,
DOI 10.17487/RFC8032, January 2017, DOI 10.17487/RFC8032, January 2017,
<https://www.rfc-editor.org/info/rfc8032>. <https://www.rfc-editor.org/info/rfc8032>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
[RFC9106] Biryukov, A., Dinu, D., Khovratovich, D., and S.
Josefsson, "Argon2 Memory-Hard Function for Password
Hashing and Proof-of-Work Applications", RFC 9106,
DOI 10.17487/RFC9106, September 2021,
<https://www.rfc-editor.org/info/rfc9106>.
[SCHNEIER] Schneier, B., "Applied Cryptography Second Edition: [SCHNEIER] Schneier, B., "Applied Cryptography Second Edition:
protocols, algorithms, and source code in C", 1996. protocols, algorithms, and source code in C", 1996.
[SP800-56A] [SP800-56A]
Barker, E., Johnson, D., and M. Smid, "Recommendation for Barker, E., Johnson, D., and M. Smid, "Recommendation for
Pair-Wise Key Establishment Schemes Using Discrete Pair-Wise Key Establishment Schemes Using Discrete
Logarithm Cryptography", NIST Special Publication 800-56A Logarithm Cryptography", NIST Special Publication 800-56A
Revision 1, March 2007. Revision 1, March 2007.
[TWOFISH] Schneier, B., Kelsey, J., Whiting, D., Wagner, D., Hall, [TWOFISH] Schneier, B., Kelsey, J., Whiting, D., Wagner, D., Hall,
skipping to change at page 116, line 33 skipping to change at page 129, line 41
The entire signature packet is thus: The entire signature packet is thus:
88 5e 04 00 16 08 00 06 05 02 55 f9 5f 95 00 0a 88 5e 04 00 16 08 00 06 05 02 55 f9 5f 95 00 0a
09 10 8c fd e1 21 97 96 5a 9a f6 22 01 00 56 f9 09 10 8c fd e1 21 97 96 5a 9a f6 22 01 00 56 f9
0c ca 98 e2 10 26 37 bd 98 3f db 16 c1 31 df d2 0c ca 98 e2 10 26 37 bd 98 3f db 16 c1 31 df d2
7e d8 2b f4 dd e5 60 6e 0d 75 6a ed 33 66 01 00 7e d8 2b f4 dd e5 60 6e 0d 75 6a ed 33 66 01 00
d0 9c 4f a1 15 27 f0 38 e0 f5 7f 22 01 d8 2f 2e d0 9c 4f a1 15 27 f0 38 e0 f5 7f 22 01 d8 2f 2e
a2 c9 03 32 65 fa 6c eb 48 9e 85 4b ae 61 b4 04 a2 c9 03 32 65 fa 6c eb 48 9e 85 4b ae 61 b4 04
Appendix B. Document Workflow A.3. Sample AEAD-EAX encryption and decryption
Encryption is performed with the string "Hello, world!", using
AES-128 with AEAD-EAX encryption.
A.3.1. Sample Parameters
S2K:
type 3
Iterations:
524288 (144), SHA2-256
Salt:
cd5a9f70fbe0bc65
A.3.2. Sample symmetric-key encrypted session key packet (v5)
Packet header:
c3 3e
Version, algorithms, S2K fields:
05 07 01 03 08 cd 5a 9f 70 fb e0 bc 65 90
AEAD IV:
bc 66 9e 34 e5 00 dc ae dc 5b 32 aa 2d ab 02 35
AEAD encrypted CEK:
9d ee 19 d0 7c 34 46 c4 31 2a 34 ae 19 67 a2 fb
Authentication tag:
7e 92 8e a5 b4 fa 80 12 bd 45 6d 17 38 c6 3c 36
A.3.3. Starting AEAD-EAX decryption of CEK
The derived key is:
b2 55 69 b9 54 32 45 66 45 27 c4 97 6e 7a 5d 6e
Authenticated Data:
c3 05 07 01
Nonce:
bc 66 9e 34 e5 00 dc ae dc 5b 32 aa 2d ab 02 35
Decrypted CEK:
86 f1 ef b8 69 52 32 9f 24 ac d3 bf d0 e5 34 6d
A.3.4. Initial Content Encryption Key
This key would typically be extracted from an SKESK or PKESK. In
this example, it is extracted from an SKESK packet, as described
above.
CEK:
86 f1 ef b8 69 52 32 9f 24 ac d3 bf d0 e5 34 6d
A.3.5. Sample AEAD encrypted data packet
Packet header:
d4 4a
Version, AES-128, EAX, Chunk bits (14):
01 07 01 0e
IV:
b7 32 37 9f 73 c4 92 8d e2 5f ac fe 65 17 ec 10
AEAD-EAX Encrypted data chunk #0:
5d c1 1a 81 dc 0c b8 a2 f6 f3 d9 00 16 38 4a 56
fc 82 1a e1 1a e8
Chunk #0 authentication tag:
db cb 49 86 26 55 de a8 8d 06 a8 14 86 80 1b 0f
Final (zero-size chunk #1) authentication tag:
f3 87 bd 2e ab 01 3d e1 25 95 86 90 6e ab 24 76
A.3.6. Decryption of data
Starting AEAD-EAX decryption of data, using the CEK.
Chunk #0:
Authenticated data:
d4 01 07 01 0e 00 00 00 00 00 00 00 00
Nonce:
b7 32 37 9f 73 c4 92 8d e2 5f ac fe 65 17 ec 10
Decrypted chunk #0.
Literal data packet with the string contents "Hello, world!\n".
cb 14 62 00 00 00 00 00 48 65 6c 6c 6f 2c 20 77
6f 72 6c 64 21 0a
Authenticating final tag:
Authenticated data:
d4 01 07 01 0e 00 00 00 00 00 00 00 01 00 00 00
00 00 00 00 16
Nonce:
b7 32 37 9f 73 c4 92 8d e2 5f ac fe 65 17 ec 11
A.3.7. Complete AEAD-EAX encrypted packet sequence
Symmetric-key encrypted session key packet (v5):
c3 3e 05 07 01 03 08 cd 5a 9f 70 fb e0 bc 65 90
bc 66 9e 34 e5 00 dc ae dc 5b 32 aa 2d ab 02 35
9d ee 19 d0 7c 34 46 c4 31 2a 34 ae 19 67 a2 fb
7e 92 8e a5 b4 fa 80 12 bd 45 6d 17 38 c6 3c 36
AEAD encrypted data packet:
d4 4a 01 07 01 0e b7 32 37 9f 73 c4 92 8d e2 5f
ac fe 65 17 ec 10 5d c1 1a 81 dc 0c b8 a2 f6 f3
d9 00 16 38 4a 56 fc 82 1a e1 1a e8 db cb 49 86
26 55 de a8 8d 06 a8 14 86 80 1b 0f f3 87 bd 2e
ab 01 3d e1 25 95 86 90 6e ab 24 76
A.4. Sample AEAD-OCB encryption and decryption
Encryption is performed with the string "Hello, world!" using AES-128
with AEAD-OCB encryption.
A.4.1. Sample Parameters
S2K:
type 3
Iterations:
524288 (144), SHA2-256
Salt:
9f0b7da3e5ea6477
A.4.2. Sample symmetric-key encrypted session key packet (v5)
Packet header:
c3 3d
Version, algorithms, S2K fields:
05 07 02 03 08 9f 0b 7d a3 e5 ea 64 77 90
AEAD IV:
99 e3 26 e5 40 0a 90 93 6c ef b4 e8 eb a0 8c
AEAD encrypted CEK:
67 73 71 6d 1f 27 14 54 0a 38 fc ac 52 99 49 da
Authentication tag:
c5 29 d3 de 31 e1 5b 4a eb 72 9e 33 00 33 db ed
A.4.3. Starting AEAD-OCB decryption of CEK
The derived key is:
eb 9d a7 8a 9d 5d f8 0e c7 02 05 96 39 9b 65 08
Authenticated Data:
c3 05 07 02
Nonce:
99 e3 26 e5 40 0a 90 93 6c ef b4 e8 eb a0 8c
Decrypted CEK:
d1 f0 1b a3 0e 13 0a a7 d2 58 2c 16 e0 50 ae 44
A.4.4. Initial Content Encryption Key
This key would typically be extracted from an SKESK or PKESK. In
this example, it is extracted from an SKESK packet, as described
above.
Decrypted CEK:
d1 f0 1b a3 0e 13 0a a7 d2 58 2c 16 e0 50 ae 44
A.4.5. Sample AEAD encrypted data packet
Packet header:
d4 49
Version, AES-128, OCB, Chunk bits (14):
01 07 02 0e
IV:
5e d2 bc 1e 47 0a be 8f 1d 64 4c 7a 6c 8a 56
AEAD-OCB Encrypted data chunk #0:
7b 0f 77 01 19 66 11 a1 54 ba 9c 25 74 cd 05 62
84 a8 ef 68 03 5c
Chunk #0 authentication tag:
62 3d 93 cc 70 8a 43 21 1b b6 ea f2 b2 7f 7c 18
Final (zero-size chunk #1) authentication tag:
d5 71 bc d8 3b 20 ad d3 a0 8b 73 af 15 b9 a0 98
A.4.6. Decryption of data
Starting AEAD-OCB decryption of data, using the CEK.
Chunk #0:
Authenticated data:
d4 01 07 02 0e 00 00 00 00 00 00 00 00
Nonce:
5e d2 bc 1e 47 0a be 8f 1d 64 4c 7a 6c 8a 56
Decrypted chunk #0.
Literal data packet with the string contents "Hello, world!\n".
cb 14 62 00 00 00 00 00 48 65 6c 6c 6f 2c 20 77
6f 72 6c 64 21 0a
Authenticating final tag:
Authenticated data:
d4 01 07 02 0e 00 00 00 00 00 00 00 01 00 00 00
00 00 00 00 16
Nonce:
5e d2 bc 1e 47 0a be 8f 1d 64 4c 7a 6c 8a 57
A.4.7. Complete AEAD-OCB encrypted packet sequence
Symmetric-key encrypted session key packet (v5):
c3 3d 05 07 02 03 08 9f 0b 7d a3 e5 ea 64 77 90
99 e3 26 e5 40 0a 90 93 6c ef b4 e8 eb a0 8c 67
73 71 6d 1f 27 14 54 0a 38 fc ac 52 99 49 da c5
29 d3 de 31 e1 5b 4a eb 72 9e 33 00 33 db ed
AEAD encrypted data packet:
d4 49 01 07 02 0e 5e d2 bc 1e 47 0a be 8f 1d 64
4c 7a 6c 8a 56 7b 0f 77 01 19 66 11 a1 54 ba 9c
25 74 cd 05 62 84 a8 ef 68 03 5c 62 3d 93 cc 70
8a 43 21 1b b6 ea f2 b2 7f 7c 18 d5 71 bc d8 3b
20 ad d3 a0 8b 73 af 15 b9 a0 98
Appendix B. Acknowledgements
This memo also draws on much previous work from a number of other
authors, including: Derek Atkins, Charles Breed, Dave Del Torto, Marc
Dyksterhouse, Gail Haspert, Gene Hoffman, Paul Hoffman, Ben Laurie,
Raph Levien, Colin Plumb, Will Price, David Shaw, William Stallings,
Mark Weaver, and Philip R. Zimmermann.
Appendix C. Document Workflow
This document is built from markdown using ruby-kramdown-rfc2629 This document is built from markdown using ruby-kramdown-rfc2629
(https://rubygems.org/gems/kramdown-rfc2629), and tracked using git (https://rubygems.org/gems/kramdown-rfc2629), and tracked using git
(https://git-scm.com/). The markdown source under development can be (https://git-scm.com/). The markdown source under development can be
found in the file "crypto-refresh.md" in the "main" branch of the git found in the file "crypto-refresh.md" in the "main" branch of the git
repository (https://gitlab.com/openpgp-wg/rfc4880bis). Discussion of repository (https://gitlab.com/openpgp-wg/rfc4880bis). Discussion of
this document should take place on the openpgp@ietf.org mailing list this document should take place on the openpgp@ietf.org mailing list
(https://www.ietf.org/mailman/listinfo/openpgp). (https://www.ietf.org/mailman/listinfo/openpgp).
A non-substantive editorial nit can be submitted directly as a merge A non-substantive editorial nit can be submitted directly as a merge
skipping to change at page 117, line 7 skipping to change at page 136, line 28
request, but should simultaneously be sent to the mailing list for request, but should simultaneously be sent to the mailing list for
discussion. discussion.
An open problem can be recorded and tracked as an issue An open problem can be recorded and tracked as an issue
(https://gitlab.com/openpgp-wg/rfc4880bis/-/issues) in the gitlab (https://gitlab.com/openpgp-wg/rfc4880bis/-/issues) in the gitlab
issue tracker, but discussion of the issue should take place on the issue tracker, but discussion of the issue should take place on the
mailing list. mailing list.
[Note to RFC-Editor: Please remove this section on publication.] [Note to RFC-Editor: Please remove this section on publication.]
Appendix C. ECC Point compression flag bytes
This specification introduces the new flag byte 0x40 to indicate the
point compression format. The value has been chosen so that the high
bit is not cleared and thus to avoid accidental sign extension. Two
other values might also be interesting for other ECC specifications:
Flag Description
---- -----------
0x04 Standard flag for uncompressed format
0x40 Native point format of the curve follows
0x41 Only X coordinate follows.
0x42 Only Y coordinate follows.
Appendix D. Acknowledgements
This memo also draws on much previous work from a number of other
authors, including: Derek Atkins, Charles Breed, Dave Del Torto, Marc
Dyksterhouse, Gail Haspert, Gene Hoffman, Paul Hoffman, Ben Laurie,
Raph Levien, Colin Plumb, Will Price, David Shaw, William Stallings,
Mark Weaver, and Philip R. Zimmermann.
Authors' Addresses Authors' Addresses
Werner Koch (editor) Werner Koch (editor)
GnuPG e.V. GnuPG e.V.
Rochusstr. 44 Rochusstr. 44
40479 Duesseldorf 40479 Duesseldorf
Germany Germany
Email: wk@gnupg.org Email: wk@gnupg.org
URI: https://gnupg.org/verein URI: https://gnupg.org/verein
Paul Wouters (editor) Paul Wouters (editor)
No Hats Aiven
Email: paul@nohats.ca Email: paul.wouters@aiven.io
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