draft-ietf-cose-msg-03.txt   draft-ietf-cose-msg-04.txt 
COSE Working Group J. Schaad COSE Working Group J. Schaad
Internet-Draft August Cellars Internet-Draft August Cellars
Intended status: Informational August 9, 2015 Intended status: Informational B. Campbell
Expires: February 10, 2016 Expires: February 29, 2016 Ping Identity
August 28, 2015
CBOR Encoded Message Syntax CBOR Encoded Message Syntax
draft-ietf-cose-msg-03 draft-ietf-cose-msg-04
Abstract Abstract
Concise Binary Object Representation (CBOR) is data format designed Concise Binary Object Representation (CBOR) is data format designed
for small code size and small message size. There is a need for the for small code size and small message size. There is a need for the
ability to have the basic security services defined for this data ability to have the basic security services defined for this data
format. This document specifies how to do signatures, message format. This document specifies how to do signatures, message
authentication codes and encryption using this data format. authentication codes and encryption using this data format.
Contributing to this document Contributing to this document
skipping to change at page 1, line 42 skipping to change at page 1, line 43
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 10, 2016. This Internet-Draft will expire on February 29, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Design changes from JOSE . . . . . . . . . . . . . . . . 5 1.1. Design changes from JOSE . . . . . . . . . . . . . . . . 5
1.2. Requirements Terminology . . . . . . . . . . . . . . . . 5 1.2. Requirements Terminology . . . . . . . . . . . . . . . . 5
1.3. CBOR Grammar . . . . . . . . . . . . . . . . . . . . . . 6 1.3. CBOR Grammar . . . . . . . . . . . . . . . . . . . . . . 5
1.4. CBOR Related Terminology . . . . . . . . . . . . . . . . 6 1.4. CBOR Related Terminology . . . . . . . . . . . . . . . . 6
1.5. Document Terminology . . . . . . . . . . . . . . . . . . 7 1.5. Document Terminology . . . . . . . . . . . . . . . . . . 6
1.6. Mandatory to Implement Algorithms . . . . . . . . . . . . 7 1.6. Mandatory to Implement Algorithms . . . . . . . . . . . . 7
2. The COSE_MSG structure . . . . . . . . . . . . . . . . . . . 7 2. The COSE_MSG structure . . . . . . . . . . . . . . . . . . . 7
3. Header Parameters . . . . . . . . . . . . . . . . . . . . . . 10 3. Header Parameters . . . . . . . . . . . . . . . . . . . . . . 9
3.1. COSE Headers . . . . . . . . . . . . . . . . . . . . . . 12 3.1. Common COSE Headers Parameters . . . . . . . . . . . . . 10
4. Signing Structure . . . . . . . . . . . . . . . . . . . . . . 15 4. Signing Structure . . . . . . . . . . . . . . . . . . . . . . 13
4.1. Externally Supplied Data . . . . . . . . . . . . . . . . 17 4.1. Externally Supplied Data . . . . . . . . . . . . . . . . 14
4.2. Signing and Verification Process . . . . . . . . . . . . 17 4.2. Signing and Verification Process . . . . . . . . . . . . 15
5. Encryption object . . . . . . . . . . . . . . . . . . . . . . 19 5. Encryption object . . . . . . . . . . . . . . . . . . . . . . 16
5.1. Key Management Methods . . . . . . . . . . . . . . . . . 20 5.1. Recipient Algorithm Classes . . . . . . . . . . . . . . . 17
5.2. Encryption Algorithm for AEAD algorithms . . . . . . . . 20 5.2. Encryption Algorithm for AEAD algorithms . . . . . . . . 18
5.3. Encryption algorithm for AE algorithms . . . . . . . . . 21 5.3. Encryption algorithm for AE algorithms . . . . . . . . . 19
6. MAC objects . . . . . . . . . . . . . . . . . . . . . . . . . 22 6. MAC objects . . . . . . . . . . . . . . . . . . . . . . . . . 19
7. Key Structure . . . . . . . . . . . . . . . . . . . . . . . . 23 7. Key Structure . . . . . . . . . . . . . . . . . . . . . . . . 21
7.1. COSE Key Common Parameters . . . . . . . . . . . . . . . 24 7.1. COSE Key Common Parameters . . . . . . . . . . . . . . . 22
8. Signature Algorithms . . . . . . . . . . . . . . . . . . . . 27 8. Signature Algorithms . . . . . . . . . . . . . . . . . . . . 24
8.1. ECDSA . . . . . . . . . . . . . . . . . . . . . . . . . . 28 8.1. ECDSA . . . . . . . . . . . . . . . . . . . . . . . . . . 25
8.1.1. Security Considerations . . . . . . . . . . . . . . . 29 8.1.1. Security Considerations . . . . . . . . . . . . . . . 26
8.2. RSASSA-PSS . . . . . . . . . . . . . . . . . . . . . . . 30 8.2. RSASSA-PSS . . . . . . . . . . . . . . . . . . . . . . . 27
8.2.1. Security Considerations . . . . . . . . . . . . . . . 30 8.2.1. Security Considerations . . . . . . . . . . . . . . . 27
9. Message Authentication (MAC) Algorithms . . . . . . . . . . . 31 9. Message Authentication (MAC) Algorithms . . . . . . . . . . . 28
9.1. Hash-based Message Authentication Codes (HMAC) . . . . . 31 9.1. Hash-based Message Authentication Codes (HMAC) . . . . . 28
9.1.1. Security Considerations . . . . . . . . . . . . . . . 32 9.1.1. Security Considerations . . . . . . . . . . . . . . . 29
9.2. AES Message Authentication Code (AES-CBC-MAC) . . . . . . 32 9.2. AES Message Authentication Code (AES-CBC-MAC) . . . . . . 29
9.2.1. Security Considerations . . . . . . . . . . . . . . . 33 9.2.1. Security Considerations . . . . . . . . . . . . . . . 30
10. Content Encryption Algorithms . . . . . . . . . . . . . . . . 33 10. Content Encryption Algorithms . . . . . . . . . . . . . . . . 30
10.1. AES GCM . . . . . . . . . . . . . . . . . . . . . . . . 33 10.1. AES GCM . . . . . . . . . . . . . . . . . . . . . . . . 31
10.1.1. Security Considerations . . . . . . . . . . . . . . 34 10.1.1. Security Considerations . . . . . . . . . . . . . . 31
10.2. AES CCM . . . . . . . . . . . . . . . . . . . . . . . . 34 10.2. AES CCM . . . . . . . . . . . . . . . . . . . . . . . . 32
10.2.1. Security Considerations . . . . . . . . . . . . . . 36 10.2.1. Security Considerations . . . . . . . . . . . . . . 34
10.3. ChaCha20 and Poly1305 . . . . . . . . . . . . . . . . . 37 10.3. ChaCha20 and Poly1305 . . . . . . . . . . . . . . . . . 35
10.3.1. Security Considerations . . . . . . . . . . . . . . 37 10.3.1. Security Considerations . . . . . . . . . . . . . . 35
11. Key Derivation Functions (KDF) . . . . . . . . . . . . . . . 38 11. Key Derivation Functions (KDF) . . . . . . . . . . . . . . . 36
11.1. HMAC-based Extract-and-Expand Key Derivation Function 11.1. HMAC-based Extract-and-Expand Key Derivation Function
(HKDF) . . . . . . . . . . . . . . . . . . . . . . . . . 38 (HKDF) . . . . . . . . . . . . . . . . . . . . . . . . . 36
11.2. Context Information Structure . . . . . . . . . . . . . 39 11.2. Context Information Structure . . . . . . . . . . . . . 38
12. Key Management Algorithms . . . . . . . . . . . . . . . . . . 42 12. Recipient Algorithm Classes . . . . . . . . . . . . . . . . . 42
12.1. Direct Encryption . . . . . . . . . . . . . . . . . . . 43 12.1. Direct Encryption . . . . . . . . . . . . . . . . . . . 42
12.1.1. Direct Key . . . . . . . . . . . . . . . . . . . . . 43 12.1.1. Direct Key . . . . . . . . . . . . . . . . . . . . . 42
12.1.2. Direct Key with KDF . . . . . . . . . . . . . . . . 44 12.1.2. Direct Key with KDF . . . . . . . . . . . . . . . . 43
12.2. Key Wrapping . . . . . . . . . . . . . . . . . . . . . . 45 12.2. Key Wrapping . . . . . . . . . . . . . . . . . . . . . . 44
12.2.1. AES Key Wrapping . . . . . . . . . . . . . . . . . . 46 12.2.1. AES Key Wrapping . . . . . . . . . . . . . . . . . . 45
12.3. Key Encryption . . . . . . . . . . . . . . . . . . . . . 47 12.3. Key Encryption . . . . . . . . . . . . . . . . . . . . . 45
12.3.1. RSAES-OAEP . . . . . . . . . . . . . . . . . . . . . 47 12.3.1. RSAES-OAEP . . . . . . . . . . . . . . . . . . . . . 46
12.4. Direct Key Agreement . . . . . . . . . . . . . . . . . . 48 12.4. Direct Key Agreement . . . . . . . . . . . . . . . . . . 46
12.4.1. ECDH . . . . . . . . . . . . . . . . . . . . . . . . 49 12.4.1. ECDH . . . . . . . . . . . . . . . . . . . . . . . . 48
12.5. Key Agreement with KDF . . . . . . . . . . . . . . . . . 52 12.5. Key Agreement with KDF . . . . . . . . . . . . . . . . . 51
12.5.1. ECDH . . . . . . . . . . . . . . . . . . . . . . . . 52 12.5.1. ECDH . . . . . . . . . . . . . . . . . . . . . . . . 51
12.6. Password . . . . . . . . . . . . . . . . . . . . . . . . 52 13. Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
12.6.1. PBES2 . . . . . . . . . . . . . . . . . . . . . . . 53 13.1. Elliptic Curve Keys . . . . . . . . . . . . . . . . . . 52
13. Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 13.1.1. Single Coordinate Curves . . . . . . . . . . . . . . 53
13.1. Elliptic Curve Keys . . . . . . . . . . . . . . . . . . 54 13.1.2. Double Coordinate Curves . . . . . . . . . . . . . . 54
13.1.1. Single Coordinate Curves . . . . . . . . . . . . . . 54 13.2. RSA Keys . . . . . . . . . . . . . . . . . . . . . . . . 55
13.1.2. Double Coordinate Curves . . . . . . . . . . . . . . 55 13.3. Symmetric Keys . . . . . . . . . . . . . . . . . . . . . 56
13.2. RSA Keys . . . . . . . . . . . . . . . . . . . . . . . . 56 14. CBOR Encoder Restrictions . . . . . . . . . . . . . . . . . . 57
13.3. Symmetric Keys . . . . . . . . . . . . . . . . . . . . . 57 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 57
14. CBOR Encoder Restrictions . . . . . . . . . . . . . . . . . . 58 15.1. CBOR Tag assignment . . . . . . . . . . . . . . . . . . 57
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 58 15.2. COSE Header Parameter Registry . . . . . . . . . . . . . 58
15.1. CBOR Tag assignment . . . . . . . . . . . . . . . . . . 58 15.3. COSE Header Algorithm Label Table . . . . . . . . . . . 58
15.2. COSE Object Labels Registry . . . . . . . . . . . . . . 59 15.4. COSE Algorithm Registry . . . . . . . . . . . . . . . . 59
15.3. COSE Header Parameter Registry . . . . . . . . . . . . . 59 15.5. COSE Key Common Parameter Registry . . . . . . . . . . . 60
15.4. COSE Header Algorithm Label Table . . . . . . . . . . . 60 15.6. COSE Key Type Parameter Registry . . . . . . . . . . . . 61
15.5. COSE Algorithm Registry . . . . . . . . . . . . . . . . 60 15.7. COSE Elliptic Curve Registry . . . . . . . . . . . . . . 61
15.6. COSE Key Common Parameter Registry . . . . . . . . . . . 61
15.7. COSE Key Type Parameter Registry . . . . . . . . . . . . 62
15.8. Media Type Registration . . . . . . . . . . . . . . . . 62 15.8. Media Type Registration . . . . . . . . . . . . . . . . 62
15.8.1. COSE Security Message . . . . . . . . . . . . . . . 62 15.8.1. COSE Security Message . . . . . . . . . . . . . . . 62
15.8.2. COSE Key media type . . . . . . . . . . . . . . . . 64 15.8.2. COSE Key media type . . . . . . . . . . . . . . . . 64
16. Security Considerations . . . . . . . . . . . . . . . . . . . 66 16. Security Considerations . . . . . . . . . . . . . . . . . . . 66
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 66 17. References . . . . . . . . . . . . . . . . . . . . . . . . . 66
17.1. Normative References . . . . . . . . . . . . . . . . . . 66 17.1. Normative References . . . . . . . . . . . . . . . . . . 66
17.2. Informative References . . . . . . . . . . . . . . . . . 67 17.2. Informative References . . . . . . . . . . . . . . . . . 66
Appendix A. AEAD and AE algorithms . . . . . . . . . . . . . . . 69 Appendix A. Three Levels of Recipient Information . . . . . . . 69
Appendix B. Three Levels of Recipient Information . . . . . . . 70 Appendix B. Examples . . . . . . . . . . . . . . . . . . . . . . 70
Appendix C. Examples . . . . . . . . . . . . . . . . . . . . . . 72 B.1. Examples of MAC messages . . . . . . . . . . . . . . . . 71
C.1. Examples of MAC messages . . . . . . . . . . . . . . . . 72 B.1.1. Shared Secret Direct MAC . . . . . . . . . . . . . . 71
C.1.1. Shared Secret Direct MAC . . . . . . . . . . . . . . 72 B.1.2. ECDH Direct MAC . . . . . . . . . . . . . . . . . . . 72
C.1.2. ECDH Direct MAC . . . . . . . . . . . . . . . . . . . 73 B.1.3. Wrapped MAC . . . . . . . . . . . . . . . . . . . . . 73
C.1.3. Wrapped MAC . . . . . . . . . . . . . . . . . . . . . 74 B.1.4. Multi-recipient MAC message . . . . . . . . . . . . . 74
C.1.4. Multi-recipient MAC message . . . . . . . . . . . . . 74 B.2. Examples of Encrypted Messages . . . . . . . . . . . . . 76
C.2. Examples of Encrypted Messages . . . . . . . . . . . . . 76 B.2.1. Direct ECDH . . . . . . . . . . . . . . . . . . . . . 76
C.2.1. Direct ECDH . . . . . . . . . . . . . . . . . . . . . 76 B.2.2. Direct plus Key Derivation . . . . . . . . . . . . . 76
C.2.2. Direct plus Key Derivation . . . . . . . . . . . . . 76 B.3. Examples of Signed Message . . . . . . . . . . . . . . . 77
C.3. Examples of Signed Message . . . . . . . . . . . . . . . 77 B.3.1. Single Signature . . . . . . . . . . . . . . . . . . 77
C.3.1. Single Signature . . . . . . . . . . . . . . . . . . 77 B.3.2. Multiple Signers . . . . . . . . . . . . . . . . . . 78
C.3.2. Multiple Signers . . . . . . . . . . . . . . . . . . 78 B.4. COSE Keys . . . . . . . . . . . . . . . . . . . . . . . . 79
C.4. COSE Keys . . . . . . . . . . . . . . . . . . . . . . . . 79 B.4.1. Public Keys . . . . . . . . . . . . . . . . . . . . . 79
C.4.1. Public Keys . . . . . . . . . . . . . . . . . . . . . 79 B.4.2. Private Keys . . . . . . . . . . . . . . . . . . . . 81
C.4.2. Private Keys . . . . . . . . . . . . . . . . . . . . 81 Appendix C. Document Updates . . . . . . . . . . . . . . . . . . 83
Appendix D. COSE Header Algorithm Label Table . . . . . . . . . 83 C.1. Version -03 to -04 . . . . . . . . . . . . . . . . . . . 84
Appendix E. Document Updates . . . . . . . . . . . . . . . . . . 84 C.2. Version -02 to -03 . . . . . . . . . . . . . . . . . . . 84
E.1. Version -02 to -03 . . . . . . . . . . . . . . . . . . . 84 C.3. Version -02 to -03 . . . . . . . . . . . . . . . . . . . 84
E.2. Version -02 to -03 . . . . . . . . . . . . . . . . . . . 84 C.4. Version -01 to -2 . . . . . . . . . . . . . . . . . . . . 84
E.3. Version -01 to -2 . . . . . . . . . . . . . . . . . . . . 84 C.5. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 85
E.4. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 86
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 87
1. Introduction 1. Introduction
There has been an increased focus on the small, constrained devices There has been an increased focus on the small, constrained devices
that make up the Internet of Things (IOT). One of the standards that that make up the Internet of Things (IOT). One of the standards that
has come of of this process is the Concise Binary Object has come of of this process is the Concise Binary Object
Representation (CBOR). CBOR extended the data model of the Representation (CBOR). CBOR extended the data model of the
JavaScript Object Notation (JSON) by allowing for binary data among JavaScript Object Notation (JSON) by allowing for binary data among
other changes. CBOR is being adopted by several of the IETF working other changes. CBOR is being adopted by several of the IETF working
groups dealing with the IOT world as their encoding of data groups dealing with the IOT world as their encoding of data
structures. CBOR was designed specifically to be both small in terms structures. CBOR was designed specifically to be both small in terms
of messages transport and implementation size as well having a schema of messages transport and implementation size as well having a schema
free decoder. A need exists to provide basic message security free decoder. A need exists to provide basic message security
services for IOT and using CBOR as the message encoding format makes services for IOT and using CBOR as the message encoding format makes
sense. sense.
The JOSE working group produced a set of documents The JOSE working group produced a set of documents
[RFC7515][RFC7516][RFC7517][RFC7518] that defined how to perform [RFC7515][RFC7516][RFC7517][RFC7518] that defined how to perform
encryption, signatures and message authentication (MAC) operations encryption, signatures and message authentication (MAC) operations
for JavaScript Object Notation (JSON) documents and then to encode for JSON documents and then to encode the results using the JSON
the results using the JSON format [RFC7159]. This document does the format [RFC7159]. This document does the same work for use with the
same work for use with the Concise Binary Object Representation CBOR [RFC7049] document format. While there is a strong attempt to
(CBOR) [RFC7049] document format. While there is a strong attempt to
keep the flavor of the original JOSE documents, two considerations keep the flavor of the original JOSE documents, two considerations
are taken into account: are taken into account:
o CBOR has capabilities that are not present in JSON and should be o CBOR has capabilities that are not present in JSON and should be
used. One example of this is the fact that CBOR has a method of used. One example of this is the fact that CBOR has a method of
encoding binary directly without first converting it into a base64 encoding binary directly without first converting it into a base64
encoded string. encoded string.
o The author did not always agree with some of the decisions made by o COSE is not a direct copy of the JOSE specification. In the
the JOSE working group. Many of these decisions have been re- process of creating COSE, decisions that were made for JOSE were
examined, and where it seems to the author to be superior or re-examined. In many cases different results were decided on as
simpler, replaced. the criteria were not always the same as for JOSE.
1.1. Design changes from JOSE 1.1. Design changes from JOSE
o Define a top level message structure so that encrypted, signed and o Define a top level message structure so that encrypted, signed and
MACed messages can easily identified and still have a consistent MACed messages can easily identified and still have a consistent
view. view.
o Signed messages separate the concept of protected and unprotected o Signed messages separate the concept of protected and unprotected
parameters that are for the content and the signature. parameters that are for the content and the signature.
o Key management has been made to be more uniform. All key o Recipient processing has been made more uniform. A recipient
management techniques are represented as a recipient rather than structure is required for all recipients rather than only for
only have some of them be so. some.
o MAC messages are separated from signed messages. o MAC messages are separated from signed messages.
o MAC messages have the ability to do key management on the MAC o MAC messages have the ability to do use all recipient algorithms
authentication key. on the MAC authentication key.
o Use binary encodings for binary data rather than base64url o Use binary encodings for binary data rather than base64url
encodings. encodings.
o Combine the authentication tag for encryption algorithms with the o Combine the authentication tag for encryption algorithms with the
ciphertext. ciphertext.
o Remove the flattened mode of encoding. Forcing the use of an o Remove the flattened mode of encoding. Forcing the use of an
array of recipients at all times forces the message size to be two array of recipients at all times forces the message size to be two
bytes larger, but one gets a corresponding decrease in the bytes larger, but one gets a corresponding decrease in the
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1.4. CBOR Related Terminology 1.4. CBOR Related Terminology
In JSON, maps are called objects and only have one kind of map key: a In JSON, maps are called objects and only have one kind of map key: a
string. In COSE, we use both strings and integers (both negative and string. In COSE, we use both strings and integers (both negative and
non-negative integers) as map keys, as well as data items to identify non-negative integers) as map keys, as well as data items to identify
specific choices. The integers (both positive and negative) are used specific choices. The integers (both positive and negative) are used
for compactness of encoding and easy comparison. (Generally, in this for compactness of encoding and easy comparison. (Generally, in this
document the value zero is going to be reserved and not used.) Since document the value zero is going to be reserved and not used.) Since
the work "key" is mainly used in its other meaning, as a the work "key" is mainly used in its other meaning, as a
cryptographic key, we use the term "label" for this usage of either cryptographic key, we use the term "label" for this usage of either
an integer or a string to identify map keys and choice data items. an integer or a string to identify map keys and choose data items.
The CDLL grammar that defines a type that represents a label is given The CDLL grammar that defines a type that represents a label is given
below: below:
label = int / tstr label = int / tstr
values = any values = any
1.5. Document Terminology 1.5. Document Terminology
In this document we use the following terminology: [CREF2] In this document we use the following terminology: [CREF2]
skipping to change at page 7, line 52 skipping to change at page 7, line 41
o Advertising in the certificate (capabilities extension) [RFC4262] o Advertising in the certificate (capabilities extension) [RFC4262]
o Minimum requirements for the S/MIME which have been updated over o Minimum requirements for the S/MIME which have been updated over
time [RFC2633][RFC5751] time [RFC2633][RFC5751]
2. The COSE_MSG structure 2. The COSE_MSG structure
The COSE_MSG structure is a top level CBOR object that corresponds to The COSE_MSG structure is a top level CBOR object that corresponds to
the DataContent type in the Cryptographic Message Syntax (CMS) the DataContent type in the Cryptographic Message Syntax (CMS)
[RFC5652]. This structure allows for a top level message to be sent [RFC5652]. [CREF4] This structure allows for a top level message to
that could be any of the different security services. The security be sent that could be any of the different security services. The
service is identified within the message. security service is identified within the message.
The COSE_Tagged_MSG CBOR type takes the COSE_MSG and prepends a CBOR The COSE_Tagged_MSG CBOR type takes the COSE_MSG and prepends a CBOR
tag of TBD1 to the encoding of COSE_MSG. By having both a tagged and tag of TBD1 to the encoding of COSE_MSG. By having both a tagged and
untagged version of the COSE_MSG structure, it becomes easy to either untagged version of the COSE_MSG structure, it becomes easy to either
use COSE_MSG as a top level object or embedded in another object. use COSE_MSG as a top level object or embedded in another object.
The tagged version allows for a method of placing the COSE_MSG The tagged version allows for a method of placing the COSE_MSG
structure into a choice, using a consistent tag value to determine structure into a choice, using a consistent tag value to determine
that this is a COSE object. that this is a COSE object.
The existence of the COSE_MSG and COSE_Tagged_MSG CBOR data types are The existence of the COSE_MSG and COSE_Tagged_MSG CBOR data types are
not intended to prevent protocols from using the individual security not intended to prevent protocols from using the individual security
primitives directly. Where only a single service is required, that primitives directly. Where only a single service is required, that
structure can be used directly. structure can be used directly.
Each of the top-level security objects use a CBOR map as the base Each of the top-level security objects use a CBOR array as the base
structure. Items in the map at the top level are identified by a structure.
label. The type of the value associated with the label is determined
by the definition of the label.
The set of labels present in a security object is not restricted to
those defined in this document. However, it is not recommended that
additional fields be added to a structure unless this is going to be
done in a closed environment. When new fields need to be added, it
is recommended that a new message type be created so that processing
of the field can be ensured. Using an older structure with a new
field means that any security properties of the new field will not be
enforced. Before a new field is added at the outer level, strong
consideration needs to be given to defining a new header field and
placing it into the protected headers. Applications should make a
determination if non-standardized fields are going to be permitted.
It is suggested that libraries allow for an option to fail parsing if
non-standardized fields exist, this is especially true if they do not
allow for access to the fields in other ways.
A label 'msg_type' is defined to distinguish between the different A field 'msg_type' is defined to distinguish between the different
structures when they appear as part of a COSE_MSG object. [CREF4] structures when they appear as part of a COSE_MSG object. [CREF5]
[CREF5] [CREF6]
0 - Reserved. 0 - Reserved.
1 - Signed Message. 1 - Signed Message.
2 - Encrypted Message 2 - Encrypted Message
3 - Authenticated Message (MACed message) 3 - Authenticated Message (MACed message)
Implementations MUST be prepared to find an integer under this label Implementations MUST be prepared to find an integer in this field
that does not correspond to the values 1 to 3. If this is found then that does not correspond to the values 1 to 3. If this is found then
the client MUST stop attempting to parse the structure and fail. The the client MUST stop attempting to process the structure and fail.
value of 0 is reserved and not to be used. If the value of 0 is The value of 0 is reserved and not to be used. If the value of 0 is
found, then clients MUST fail processing the structure. found, then clients MUST fail processing the structure.
Implementations need to recognize that the set of values might be Implementations need to recognize that the set of values might be
extended at a later date, but they should not provide a security extended at a later date, but they should not provide a security
service based on guesses of what is there. service based on guesses of what is there.
NOTE: Is there any reason to allow for a marker of a COSE_Key
structure and allow it to be a COSE_MSG? Doing so does allow for a
security risk, but may simplify the code. [CREF6]
The CDDL grammar that corresponds to the above is: The CDDL grammar that corresponds to the above is:
COSE_MSG = COSE_Sign / COSE_MSG = COSE_Sign /
COSE_encrypt / COSE_encrypt /
COSE_mac COSE_mac
COSE_Tagged_MSG = #6.999(COSE_MSG) ; Replace 999 with TBD1 COSE_Tagged_MSG = #6.999(COSE_MSG) ; Replace 999 with TBD1
; msg_type values ; msg_type values
msg_type_reserved=0 msg_type_reserved=0
msg_type_signed=1 msg_type_signed=1
msg_type_encrypted=2 msg_type_encrypted=2
msg_type_mac=3 msg_type_mac=3
The top level of each of the COSE message structures are encoded as The top level of each of the COSE message structures are encoded as
maps. We use an integer to distinguish between the different arrays.
security message types. By searching for the integer under the label
identified by msg_type (which is in turn an integer), one can
determine which security message is being used and thus what syntax
is for the rest of the elements in the map.
+-------------+--------+--------------------------------------------+
| name | number | comments |
+-------------+--------+--------------------------------------------+
| msg_type | 1 | Occurs only in top level messages |
| | | |
| protected | 2 | Occurs in all structures |
| | | |
| unprotected | 3 | Occurs in all structures |
| | | |
| payload | 4 | Contains the content of the structure |
| | | |
| signatures | 5 | For COSE_Sign - array of signatures |
| | | |
| signature | 6 | For COSE_signature only |
| | | |
| ciphertext | 4 | TODO: Should we reuse the same as payload |
| | | or not? |
| | | |
| recipients | 9 | For COSE_encrypt and COSE_mac |
| | | |
| tag | 10 | For COSE_mac only |
+-------------+--------+--------------------------------------------+
Table 1: COSE Map Labels
The CDDL grammar that provides the label values is:
; message_labels
msg_type=1
protected=2
unprotected=3
payload=4
signatures=5
signature=6
ciphertext=4
recipients=9
tag=10
3. Header Parameters 3. Header Parameters
The structure of COSE has been designed to have two buckets of The structure of COSE has been designed to have two buckets of
information that are not considered to be part of the payload itself, information that are not considered to be part of the payload itself,
but are used for holding information about algorithms, keys, or but are used for holding information about content, algorithms, keys,
evaluation hints for the processing of the layer. These two buckets or evaluation hints for the processing of the layer. These two
are available for use in all of the structures in this document buckets are available for use in all of the structures in this
except for keys. While these buckets can be present, they may not document except for keys. While these buckets can be present, they
all be usable in all instances. For example, while the protected may not all be usable in all instances. For example, while the
bucket is defined as part of recipient structures, most of the protected bucket is defined as part of recipient structures, most of
algorithms that are used for recipients do not provide the necessary the algorithms that are used for recipients do not provide the
functionality to provide the needed protection and thus the bucket necessary functionality to provide the needed protection and thus the
should not be used. bucket should not be used.
Both buckets are implemented as CBOR maps. The map key is a 'label' Both buckets are implemented as CBOR maps. The map key is a 'label'
(Section 1.4). The value portion is dependent on the definition for (Section 1.4). The value portion is dependent on the definition for
the label. Both maps use the same set of label/value pairs. The the label. Both maps use the same set of label/value pairs. The
integer range for labels has been divided into several sections with integer and string values for labels has been divided into several
a standard range, a private range, and a range that is dependent on sections with a standard range, a private range, and a range that is
the algorithm selected. The defined labels can be found in the 'COSE dependent on the algorithm selected. The defined labels can be found
Header Parameters' IANA registry (Section 15.3). in the 'COSE Header Parameters' IANA registry (Section 15.2).
Two buckets are provided for each layer: [CREF7] Two buckets are provided for each layer: [CREF7]
protected contains parameters about the current layer that are to be protected contains parameters about the current layer that are to be
cryptographically protected. This bucket MUST NOT be used if it cryptographically protected. This bucket MUST be empty if it is
is not going to be included in a cryptographic computation. This not going to be included in a cryptographic computation. This
bucket is encoded in the message as a binary object. This value bucket is encoded in the message as a binary object. This value
is obtained by CBOR encoding the protected map and wrapping it in is obtained by CBOR encoding the protected map and wrapping it in
a bstr object. This wrapping allows for the encoding of the a bstr object. Senders SHOULD encode an empty protected map as a
zero length binary object (it is shorter). Recipients MUST accept
both a zero length binary value and a zero length map encoded in
the binary value. The wrapping allows for the encoding of the
protected map to be transported with a greater chance that it will protected map to be transported with a greater chance that it will
not be altered in transit. (Badly behaved intermediates could not be altered in transit. (Badly behaved intermediates could
decode and re-encode, but this will result in a failure to verify decode and re-encode, but this will result in a failure to verify
unless the re-encoded byte string is identical to the decoded byte unless the re-encoded byte string is identical to the decoded byte
string.) This finesses the problem of all parties needing to be string.) This finesses the problem of all parties needing to be
able to do a common connical encoding. able to do a common canonical encoding.
unprotected contains parameters about the current layer that are not unprotected contains parameters about the current layer that are not
cryptographically protected. cryptographically protected.
Only parameters that deal with the current layer are to be placed at Only parameters that deal with the current layer are to be placed at
that layer. As an example of this, the parameter 'content type' that layer. As an example of this, the parameter 'content type'
describes the content of the message being carried in the message. describes the content of the message being carried in the message.
As such this parameter is placed only the the content layer and is As such this parameter is placed only the the content layer and is
not placed in the key managment or signature layers. In principle, not placed in the recipient or signature layers. In principle, one
one should be able to process any given layer without reference to should be able to process any given layer without reference to any
any other layer. (The only data that should need to cross layers is other layer. (The only data that should need to cross layers is the
the cryptographic key.) cryptographic key.)
The presence of both buckets is optional, however the requirement The presence of both buckets is required. The parameters that go
that the 'alg' parameter be present at each level effectively imposes into the buckets come from the IANA "COSE Header Parameters"
a requirement that one of the buckets will always be present. The (Section 15.2). Some common parameters are defined in the next
parameters that go into the buckets come from the IANA "COSE Header section, but a number of parameters are defined throughout this
Parameters" (Section 15.3). Some common parameters are defined in document.
the next section, but a number of parameters are defined throughout
this document.
The CDDL fragment that describes the two buckets is: The CDDL fragment that describes the two buckets is:
header_map = {+ label => any } header_map = {+ label => any }
Headers = ( Headers = (
? protected => bstr, ; Contains a header_map protected : bstr, ; Contains a header_map
? unprotected => header_map unprotected : header_map
) )
3.1. COSE Headers 3.1. Common COSE Headers Parameters
This document defines a set of common header parameters. A summary This section defines a set of common header parameters. A summary of
of the parameters defined in this section can be found in Table 2. those parameters can be found in Table 1. This table should be
This table should be consulted to determine the value of label used consulted to determine the value of label used as well as the type of
as well as the type of the value. the value.
The set of header parameters defined in this section are: The set of header parameters defined in this section are:
alg This parameter is used to indicate the algorithm used for the alg This parameter is used to indicate the algorithm used for the
security processing. This parameter MUST be present at each level security processing. This parameter MUST be present at each level
of a signed, encrypted or authenticated message. The value is of a signed, encrypted or authenticated message. The value is
taken from the 'COSE Algorithm Registry' (see Section 15.4). taken from the 'COSE Algorithm Registry' (see Section 15.3).
crit This parameter is used to ensure that applications will take crit This parameter is used to ensure that applications will take
appropriate action based on the values found. The parameter is appropriate action based on the values found. The parameter is
used to indicate which protected header labels an application that used to indicate which protected header labels an application that
is processing a message is required to understand. The value is is processing a message is required to understand. The value is
an array of COSE Header Labels. When present, this parameter MUST an array of COSE Header Labels. When present, this parameter MUST
be placed in the protected header bucket. be placed in the protected header bucket.
* Integer labels in the range of 0 to 10 SHOULD be omitted. * Integer labels in the range of 0 to 10 SHOULD be omitted.
skipping to change at page 12, line 48 skipping to change at page 11, line 10
are algorithm dependent. If an application can correctly are algorithm dependent. If an application can correctly
process an algorithm, it can be assumed that it will correctly process an algorithm, it can be assumed that it will correctly
process all of the parameters associated with that algorithm. process all of the parameters associated with that algorithm.
(The algorithm range is -1 to -65536, it is assumed that the (The algorithm range is -1 to -65536, it is assumed that the
higher end will deal with more optional algorithm specific higher end will deal with more optional algorithm specific
items.) items.)
The header parameter values indicated by 'crit' can be processed The header parameter values indicated by 'crit' can be processed
by either the security library code or by an application using a by either the security library code or by an application using a
security library, the only requirement is that the parameter is security library, the only requirement is that the parameter is
processed. processed. If the 'crit' value list includes a value for which
the parameter is not in the protected bucket, this is a fatal
error in processing the message.
content type This parameter is used to indicate the content type of content type This parameter is used to indicate the content type of
the data in the payload or ciphertext fields. [CREF8] Integers the data in the payload or ciphertext fields. Integers are from
are from the XXXXX[CREF9] IANA registry table. Strings are from the 'CoAP Content-Formats' IANA registry table. Strings are from
the IANA 'mime-content types' registry. Applications SHOULD the IANA 'Media Types' registry. Applications SHOULD provide this
provide this parameter if the content structure is potentially parameter if the content structure is potentially ambiguous.
ambiguous.
kid This parameter one of the ways that can be used to find the key kid This parameter one of the ways that can be used to find the key
to be used. The value of this parameter is matched against the to be used. The value of this parameter is matched against the
'kid' field in a COSE_Key structure. Applications MUST NOT assume 'kid' member in a COSE_Key structure. Applications MUST NOT
that 'kid' values are unique. There may be more than one key with assume that 'kid' values are unique. There may be more than one
the same 'kid' value, it may be required that all of the keys need key with the same 'kid' value, it may be required that all of the
to be checked to find the correct one. The internal structure of keys need to be checked to find the correct one. The internal
'kid' values is not defined and generally cannot be relied on by structure of 'kid' values is not defined and generally cannot be
applications. Key identifier values are hints about which key to relied on by applications. Key identifier values are hints about
use, they are not directly a security critical field, for this which key to use, they are not directly a security critical field,
reason they can normally be placed in the unprotected headers for this reason they can be placed in the unprotected headers
bucket. bucket.
nonce This parameter holds either a nonce or Initialization Vector nonce This parameter holds either a nonce or Initialization Vector
value. The value can be used either as a counter value for a value. The value can be used either as a counter value for a
protocol or as an IV for an algorithm. TODO: Talk about zero protocol or as an IV for an algorithm.
extending the value in some cases. [CREF10]
+----------+-------+----------+-------------+-----------------------+ +----------+-------+----------+-----------------+-------------------+
| name | label | value | value | description | | name | label | value | value registry | description |
| | | type | registry | | | | | type | | |
+----------+-------+----------+-------------+-----------------------+ +----------+-------+----------+-----------------+-------------------+
| alg | 1 | int / | COSE | Integers are taken | | alg | 1 | int / | COSE Algorithm | Integers are |
| | | tstr | Algorithm | from table --POINT TO | | | | tstr | Registry | taken from table |
| | | | Registry | REGISTRY-- | | | | | | --POINT TO |
| | | | | | | | | | | REGISTRY-- |
| crit | 2 | [+ | COSE Header | integer values are | | | | | | |
| | | label] | Label | from -- POINT TO | | crit | 2 | [+ | COSE Header | integer values |
| | | | Registry | REGISTRY -- | | | | label] | Label Registry | are from -- |
| | | | | | | | | | | POINT TO REGISTRY |
| content | 3 | tstr / | media-types | Value is either a | | | | | | -- |
| type | | int | registry | media-type or an | | | | | | |
| | | | | integer from the | | content | 3 | tstr / | CoAP Content- | Value is either a |
| | | | | media-type registry | | type | | int | Formats or | Media Type or an |
| | | | | | | | | | Media Types | integer from the |
| jku | * | tstr | | URL to COSE key | | | | | registry | CoAP Content |
| | | | | object | | | | | | Format registry |
| | | | | | | | | | | |
| jwk | * | COSE_Key | | contains a COSE key | | jku | * | tstr | | URL to COSE key |
| | | | | not a JWK key | | | | | | object |
| | | | | | | | | | | |
| kid | 4 | bstr | | key identifier | | jwk | * | COSE_Key | | contains a COSE |
| | | | | | | | | | | key not a JWK key |
| nonce | 5 | bstr | | Nonce or | | | | | | |
| | | | | Initialization Vector | | kid | 4 | bstr | | key identifier |
| | | | | (IV) | | | | | | |
| | | | | | | nonce | 5 | bstr | | Nonce or |
| x5c | * | bstr* | | X.509 Certificate | | | | | | Initialization |
| | | | | Chain | | | | | | Vector (IV) |
| | | | | | | | | | | |
| x5t | * | bstr | | SHA-1 thumbprint of | | x5c | * | bstr* | | X.509 Certificate |
| | | | | key | | | | | | Chain |
| | | | | | | | | | | |
| x5t#S256 | * | bstr | | SHA-256 thumbprint of | | x5t | * | bstr | | SHA-1 thumbprint |
| | | | | key | | | | | | of key |
| | | | | | | | | | | |
| x5u | * | tstr | | URL for X.509 | | x5t#S256 | * | bstr | | SHA-256 |
| | | | | certificate | | | | | | thumbprint of key |
| | | | | | | | | | | |
| zip | * | int / | | Integers are taken | | x5u | * | tstr | | URL for X.509 |
| | | tstr | | from the table | | | | | | certificate |
| | | | | --POINT TO REGISTRY-- | | | | | | |
+----------+-------+----------+-------------+-----------------------+ | zip | * | int / | | Integers are |
| | | tstr | | taken from the |
| | | | | table --POINT TO |
| | | | | REGISTRY-- |
+----------+-------+----------+-----------------+-------------------+
Table 2: Common Header Parameters Table 1: Common Header Parameters
OPEN ISSUES: OPEN ISSUES:
1. Which of the following items do we want to have standardized in 1. Which of the following items do we want to have standardized in
this document: jku, jwk, x5c, x5t, x5t#S256, x5u, zip this document: jku, jwk, x5c, x5t, x5t#S256, x5u, zip
2. I am currently torn on the question "Should epk and iv/nonce be 2. I am currently torn on the question "Should epk and iv/nonce be
algorithm specific or generic headers?" They are really specific algorithm specific or generic headers?" They are really specific
to an algorithm and can potentially be defined in different ways to an algorithm and can potentially be defined in different ways
for different algorithms. As an example, it would make sense to for different algorithms. As an example, it would make sense to
skipping to change at page 16, line 10 skipping to change at page 13, line 46
than one signature. For example, the COSE_Sign structure might than one signature. For example, the COSE_Sign structure might
include signatures generated with the RSA signature algorithm and include signatures generated with the RSA signature algorithm and
with the Elliptic Curve Digital Signature Algorithm (ECDSA) signature with the Elliptic Curve Digital Signature Algorithm (ECDSA) signature
algorithm. This allows recipients to verify the signature associated algorithm. This allows recipients to verify the signature associated
with one algorithm or the other. (The original source of this text with one algorithm or the other. (The original source of this text
is [RFC5652].) More detailed information on multiple signature is [RFC5652].) More detailed information on multiple signature
evaluation can be found in [RFC5752]. evaluation can be found in [RFC5752].
The CDDL grammar for a signature message is: The CDDL grammar for a signature message is:
COSE_Sign = { COSE_Sign = [
msg_type => msg_type_signed, msg_type: msg_type_signed,
Headers, Headers,
? payload => bstr, payload : bstr,
signatures => [+ COSE_signature] signatures : [+ COSE_signature]
} ]
The fields in the array have the following semantics:
The fields is the structure have the following semantics:
msg_type identifies this as providing the signed security service. msg_type identifies this as providing the signed security service.
The value MUST be msg_type_signed (1). The value MUST be msg_type_signed (1).
protected is described in Section 3. protected is described in Section 3.
unprotected is described in Section 3. unprotected is described in Section 3.
payload contains the serialized content to be signed. If the payload contains the serialized content to be signed. If the
payload is not present in the message, the application is required payload is not present in the message, the application is required
to supply the payload separately. The payload is wrapped in a to supply the payload separately. The payload is wrapped in a
bstr to ensure that it is transported without changes. If the bstr to ensure that it is transported without changes. If the
payload is transported separately, it is the responsibility of the payload is transported separately, it is the responsibility of the
application to ensure that it will be transported without changes. application to ensure that it will be transported without changes.
signatures is an array of signature items. Each of these items uses signatures is an array of signature items. Each of these items uses
the COSE_signature structure for its representation. the COSE_signature structure for its representation.
We use the values in Table 1 as the labels in the COSE_Sign map.
While other labels can be present in the map, it is not generally a
recommended practice. The other labels can be either of integer or
string type, use of other types SHOULD be treated as an error.
The CDDL grammar structure for a signature is: The CDDL grammar structure for a signature is:
COSE_signature = { COSE_signature = [
Headers, Headers,
signature => bstr signature : bstr
} ]
The fields in the structure have the following semantics: The fields in the array have the following semantics:
protected is described in Section 3. protected is described in Section 3.
unprotected is described in Section 3. unprotected is described in Section 3.
signature contains the computed signature value. signature contains the computed signature value.
4.1. Externally Supplied Data 4.1. Externally Supplied Data
One of the features that we supply in the COSE document is the One of the features that we supply in the COSE document is the
skipping to change at page 19, line 12 skipping to change at page 16, line 38
to verify with), alg (the algorithm to sign with), ToBeSigned to verify with), alg (the algorithm to sign with), ToBeSigned
(the value to sign), and sig (the signature to be verified). (the value to sign), and sig (the signature to be verified).
In addition to performing the signature verification, one must also In addition to performing the signature verification, one must also
perform the appropriate checks to ensure that the key is correctly perform the appropriate checks to ensure that the key is correctly
paired with the signing identity and that the appropriate paired with the signing identity and that the appropriate
authorization is done. authorization is done.
5. Encryption object 5. Encryption object
In this section we describe the structure and methods to be used when The encryption structure allows for one or more recipients of a
doing an encryption in COSE. In COSE, we use the same techniques and message. There are provisions for parameters about the content and
structures for encrypting both the plain text and the keys used to parameters about the recipient information to be carried in the
protect the text. This is different from the approach used by both message. The parameters associated with the content can be
[RFC5652] and [RFC7516] where different structures are used for the authenticated by the content encryption algorithm. The parameters
plain text and for the different key management techniques. associated with the recipient can be authenticated by the recipient
algorithm (when the algorithm supports it). Examples of parameters
about the content are the type of the content, when the content was
created, and the content encryption algorithm. Examples of
parameters about the recipient are the recipients key identifier, the
recipient encryption algorithm.
One of the byproducts of using the same technique for encrypting and In COSE, the same techniques and structures for encrypting both the
encoding both the content and the keys using the various key plain text and the keys used to protect the text. This is different
management techniques, is a requirement that all of the key from the approach used by both [RFC5652] and [RFC7516] where
management techniques use an Authenticated Encryption (AE) algorithm. different structures are used for the content layer and for the
(For the purpose of this document we use a slightly loose definition recipient layer.
of AE algorithms.) When encrypting the plain text, it is normal to
use an Authenticated Encryption with Additional Data (AEAD)
algorithm. For key management, either AE or AEAD algorithms can be
used. See Appendix A for more details about the different types of
algorithms. [CREF11]
The CDDL grammar structure for encryption is: The CDDL grammar structure for encryption is:
COSE_encrypt = { COSE_encrypt = [
msg_type=>msg_type_encrypted, msg_type: msg_type_encrypted,
COSE_encrypt_fields COSE_encrypt_fields
} ]
COSE_encrypt_fields = ( COSE_encrypt_fields = (
Headers, Headers,
? ciphertext => bstr, ciphertext: bstr,
? recipients => [+{COSE_encrypt_fields}] ? recipients: [+[COSE_encrypt_fields]]
) )
Description of the fields: Description of the fields:
msg_type identifies this as providing the encrypted security msg_type identifies this as providing the encrypted security
service. The value MUST be msg_type_encrypted (2). service. The value MUST be msg_type_encrypted (2).
protected is described in Section 3. protected is described in Section 3.
unprotected is described in Section 3. unprotected is described in Section 3.
ciphertext contains the encrypted plain text. If the ciphertext is ciphertext contains the encrypted plain text. If the ciphertext is
to be transported independently of the control information about to be transported independently of the control information about
the encryption process (i.e. detached content) then the field is the encryption process (i.e. detached content) then the field is
omitted. omitted.
recipients contains the recipient information. It is required that recipients contains the recipient information. It is required that
at least one recipient MUST be present for the content encryption at least one recipient MUST be present for the content encryption
layer. layer.
5.1. Key Management Methods 5.1. Recipient Algorithm Classes
A typical encrypted message consists of an encrypted content and an A typical encrypted message consists of an encrypted content and an
encrypted CEK for one or more recipients. The content-encryption key encrypted CEK for one or more recipients. The content-encryption key
is encrypted for each recipient. The details of this encryption is encrypted for each recipient, using a key specific to that
depends on the key management technique used, but the six generally recipient. The details of this encryption depends on which class the
techniques are: recipient algorithm falls into. Specific details on each of the
classes can be found in Section 12. A short summary of the six
recipient algorithm classes is:
none: The CEK is the same as as the identified previously none: The CEK is the same as as the identified previously
distributed symmetric key. distributed symmetric key or derived from a previously distributed
secret.
symmetric key-encryption keys: The CEK is encrypted using a symmetric key-encryption keys: The CEK is encrypted using a
previously distributed symmetric key-encryption key. previously distributed symmetric key-encryption key.
key agreement: the recipient's public key and a sender's private key key agreement: the recipient's public key and a sender's private key
are used to generate a pairwise symmetric key, then the CEK is are used to generate a pairwise secret, a KDF is applied to derive
either the derived key or encrypted by the derived key. a key, and then the CEK is either the derived key or encrypted by
the derived key.
key transport: the CEK is encrypted in the recipient's public key key transport: the CEK is encrypted in the recipient's public key
passwords: the CEK is encrypted in a key-encryption key that is passwords: the CEK is encrypted in a key-encryption key that is
derived from a password or other shared secret value. derived from a password.
Section 12 provides details on a number of different key management
algorithms and discusses which parameters need to be present for each
of the key management techniques.
5.2. Encryption Algorithm for AEAD algorithms 5.2. Encryption Algorithm for AEAD algorithms
The encryption algorithm for AEAD algorithms is fairly simple. In The encryption algorithm for AEAD algorithms is fairly simple. In
order to get a consistent encoding of the data to be authenticated, order to get a consistent encoding of the data to be authenticated,
the Enc_structure is used to have canonical form of the AAD. the Enc_structure is used to have canonical form of the AAD.
Enc_structure = [ Enc_structure = [
protected: bstr, protected: bstr,
external_aad: bstr external_aad: bstr
skipping to change at page 21, line 15 skipping to change at page 18, line 40
2. If the application has supplied external additional authenticated 2. If the application has supplied external additional authenticated
data to be included in the computation, then it is placed in the data to be included in the computation, then it is placed in the
'external_aad' field. If no data was supplied, then a zero 'external_aad' field. If no data was supplied, then a zero
length binary value is used. (See Section 4.1 for application length binary value is used. (See Section 4.1 for application
guidance on constructing this field.) guidance on constructing this field.)
3. Encode the Enc_structure using a CBOR Canonical encoding 3. Encode the Enc_structure using a CBOR Canonical encoding
Section 14 to get the AAD value. Section 14 to get the AAD value.
4. Determine the encryption key. This step is dependent on the key 4. Determine the encryption key. This step is dependent on the
management method being used: For: class of recipient algorithm being used. For:
No Recipients: The key to be used is determined by the algorithm No Recipients: The key to be used is determined by the algorithm
and key at the current level. and key at the current level.
Direct and Direct Key Agreement: The key is determined by the Direct and Direct Key Agreement: The key is determined by the
key and algorithm in the recipient structure. The encryption key and algorithm in the recipient structure. The encryption
algorithm and size of the key to be used are inputs into the algorithm and size of the key to be used are inputs into the
KDF used for the recipient. (For direct, the KDF can be KDF used for the recipient. (For direct, the KDF can be
thought of as the identity operation.) thought of as the identity operation.)
skipping to change at page 21, line 45 skipping to change at page 19, line 23
algorithm for that recipient using the encryption key as the algorithm for that recipient using the encryption key as the
plain text. plain text.
5.3. Encryption algorithm for AE algorithms 5.3. Encryption algorithm for AE algorithms
1. Verify that the 'protected' field is absent. 1. Verify that the 'protected' field is absent.
2. Verify that there was no external additional authenticated data 2. Verify that there was no external additional authenticated data
supplied for this operation. supplied for this operation.
3. Determine the encryption key. This step is dependent on the key 3. Determine the encryption key. This step is dependent on the
management method being used: For: class of recipient algorithm being used. For:
No Recipients: The key to be used is determined by the algorithm No Recipients: The key to be used is determined by the algorithm
and key at the current level. and key at the current level.
Direct and Direct Key Agreement: The key is determined by the Direct and Direct Key Agreement: The key is determined by the
key and algorithm in the recipient structure. The encryption key and algorithm in the recipient structure. The encryption
algorithm and size of the key to be used are inputs into the algorithm and size of the key to be used are inputs into the
KDF used for the recipient. (For direct, the KDF can be KDF used for the recipient. (For direct, the KDF can be
thought of as the identity operation.) thought of as the identity operation.)
skipping to change at page 22, line 25 skipping to change at page 19, line 49
the 'ciphertext' field of the structure. the 'ciphertext' field of the structure.
5. For recipients of the message, recursively perform the encryption 5. For recipients of the message, recursively perform the encryption
algorithm for that recipient using the encryption key as the algorithm for that recipient using the encryption key as the
plain text. plain text.
6. MAC objects 6. MAC objects
In this section we describe the structure and methods to be used when In this section we describe the structure and methods to be used when
doing MAC authentication in COSE. This document allows for the use doing MAC authentication in COSE. This document allows for the use
of all of the same methods of key management as are allowed for of all of the same classes of recipient algorithms as are allowed for
encryption. encryption.
When using MAC operations, there are two modes in which it can be When using MAC operations, there are two modes in which it can be
used. The first is just a check that the content has not been used. The first is just a check that the content has not been
changed since the MAC was computed. Any of the key management changed since the MAC was computed. Any class of recipient algorithm
methods can be used for this purpose. The second mode is to both can be used for this purpose. The second mode is to both check that
check that the content has not been changed since the MAC was the content has not been changed since the MAC was computed, and to
computed, and to use key management to verify who sent it. The key use recipient algorithm to verify who sent it. The classes of
management modes that support this are ones that either use a pre- recipient algorithms that support this are those that use a pre-
shared secret, or do static-static key agreement. In both of these shared secret or do static-static key agreement (without the key wrap
cases the entity MACing the message can be validated by a key step). In both of these cases the entity MACing the message can be
binding. (The binding of identity assumes that there are only two validated by a key binding. (The binding of identity assumes that
parties involved and you did not send the message yourself.) there are only two parties involved and you did not send the message
yourself.)
COSE_mac = { COSE_mac = [
msg_type=>msg_type_mac, msg_type: msg_type_mac,
Headers, Headers,
? payload => bstr, payload: bstr,
tag => bstr, tag: bstr,
recipients => [+{COSE_encrypt_fields}] recipients: [+[COSE_encrypt_fields]]
} ]
Field descriptions: Field descriptions:
msg_type identifies this as providing the encrypted security msg_type identifies this as providing the encrypted security
service. The value MUST be msg_type_mac (3). service. The value MUST be msg_type_mac (3).
protected is described in Section 3. protected is described in Section 3.
unprotected is described in Section 3. unprotected is described in Section 3.
skipping to change at page 23, line 50 skipping to change at page 21, line 27
4. Compute the MAC and place the result in the 'tag' field of the 4. Compute the MAC and place the result in the 'tag' field of the
COSE_mac structure. COSE_mac structure.
5. Encrypt and encode the MAC key for each recipient of the message. 5. Encrypt and encode the MAC key for each recipient of the message.
7. Key Structure 7. Key Structure
A COSE Key structure is built on a CBOR map object. The set of A COSE Key structure is built on a CBOR map object. The set of
common parameters that can appear in a COSE Key can be found in the common parameters that can appear in a COSE Key can be found in the
IANA registry 'COSE Key Common Parameter Registry' (Section 15.6). IANA registry 'COSE Key Common Parameter Registry' (Section 15.5).
Additional parameters defined for different key types can be found in Additional parameters defined for specific key types can be found in
the IANA registry 'COSE Key Type Parameters' (Section 15.7). the IANA registry 'COSE Key Type Parameters' (Section 15.6).
A COSE Key Set uses a CBOR array object as it's underlying type. The A COSE Key Set uses a CBOR array object as it's underlying type. The
values of the array elements are COSE Keys. A Key Set MUST have at values of the array elements are COSE Keys. A Key Set MUST have at
least one element in the array. [CREF12] least one element in the array. [CREF8]
The CDDL grammar describing a COSE_Key and COSE_KeySet is: [CREF13] The CDDL grammar describing a COSE_Key and COSE_KeySet is: [CREF9]
COSE_Key = { COSE_Key = {
key_kty => tstr / int, key_kty => tstr / int,
? key_ops => [+ (tstr / int) ], ? key_ops => [+ (tstr / int) ],
? key_alg => tstr / int, ? key_alg => tstr / int,
? key_kid => bstr, ? key_kid => bstr,
* label => values * label => values
} }
COSE_KeySet = [+COSE_Key] COSE_KeySet = [+COSE_Key]
The element "kty" is a required element in a COSE_Key map. The element "kty" is a required element in a COSE_Key map.
7.1. COSE Key Common Parameters 7.1. COSE Key Common Parameters
This document defines a set of common parameters for a COSE Key This document defines a set of common parameters for a COSE Key
object. Table 3 provides a summary of the parameters defined in this object. Table 2 provides a summary of the parameters defined in this
section. There are also a set of parameters that are defined for a section. There are also a set of parameters that are defined for a
specific key type. Key type specific parameters can be found in specific key type. Key type specific parameters can be found in
Section 13. Section 13.
+----------+-------+-------------+------------+---------------------+ +----------+-------+-------------+------------+---------------------+
| name | label | CBOR type | registry | description | | name | label | CBOR type | registry | description |
+----------+-------+-------------+------------+---------------------+ +----------+-------+-------------+------------+---------------------+
| kty | 1 | tstr / int | COSE | Identification of | | kty | 1 | tstr / int | COSE | Identification of |
| | | | General | the key type | | | | | General | the key type |
| | | | Values | | | | | | Values | |
skipping to change at page 25, line 36 skipping to change at page 22, line 44
| x5c | * | bstr* | | | | x5c | * | bstr* | | |
| | | | | | | | | | | |
| x5t | * | bstr | | | | x5t | * | bstr | | |
| | | | | | | | | | | |
| x5t#S256 | * | bstr | | | | x5t#S256 | * | bstr | | |
| | | | | | | | | | | |
| use | * | tstr | | deprecated - don't | | use | * | tstr | | deprecated - don't |
| | | | | use | | | | | | use |
+----------+-------+-------------+------------+---------------------+ +----------+-------+-------------+------------+---------------------+
Table 3: Key Map Labels Table 2: Key Map Labels
kty: This parameter is used to identify the family of keys for this kty: This parameter is used to identify the family of keys for this
structure, and thus the set of key type specific parameters to be structure, and thus the set of key type specific parameters to be
found. The set of values can be found in Table 21. found. The set of values can be found in Table 20. This
parameter MUST be present in a key object.
alg: This parameter is used to restrict the algorithms that are to alg: This parameter is used to restrict the algorithms that are to
be used with this key. If this parameter is present in the key be used with this key. If this parameter is present in the key
structure, the application MUST verify that this algorithm matches structure, the application MUST verify that this algorithm matches
the algorithm for which the key is being used. If the algorthms the algorithm for which the key is being used. If the algorthms
do not match, then this key object MUST NOT be used to perform the do not match, then this key object MUST NOT be used to perform the
cryptographic operation. Note that the same key can be in a cryptographic operation. Note that the same key can be in a
different key structure with a different or no algorithm different key structure with a different or no algorithm
specified, however this is considered to be a poor security specified, however this is considered to be a poor security
practice. practice.
kid: This parameter is used to give an identifier for a key. The kid: This parameter is used to give an identifier for a key. The
identifier is not structured and can be anything from a user identifier is not structured and can be anything from a user
provided string to a value computed on the public portion of the provided string to a value computed on the public portion of the
key. This field is intended for matching against a 'kid' key. This field is intended for matching against a 'kid'
parameter in a message in order to filter down the set of keys parameter in a message in order to filter down the set of keys
that need to be checked. that need to be checked.
key_ops: This parameter is defined to restrict the set of operations key_ops: This parameter is defined to restrict the set of operations
that a key is to be used for. The value of the field is an array that a key is to be used for. The value of the field is an array
of values from Table 4. of values from Table 3.
Only the 'kty' field MUST be present in a key object. All other
parameters can be omitted if their behavior is not needed.
+---------+-------+-------------------------------------------------+ +---------+-------+-------------------------------------------------+
| name | value | description | | name | value | description |
+---------+-------+-------------------------------------------------+ +---------+-------+-------------------------------------------------+
| sign | 1 | The key is used to create signatures. Requires | | sign | 1 | The key is used to create signatures. Requires |
| | | private key fields. | | | | private key fields. |
| | | | | | | |
| verify | 2 | The key is used for verification of signatures. | | verify | 2 | The key is used for verification of signatures. |
| | | | | | | |
| encrypt | 3 | The key is used for key transport encryption. | | encrypt | 3 | The key is used for key transport encryption. |
skipping to change at page 26, line 42 skipping to change at page 23, line 46
| wrap | 5 | The key is used for key wrapping. | | wrap | 5 | The key is used for key wrapping. |
| key | | | | key | | |
| | | | | | | |
| unwrap | 6 | The key is used for key unwrapping. Requires | | unwrap | 6 | The key is used for key unwrapping. Requires |
| key | | private key fields. | | key | | private key fields. |
| | | | | | | |
| key | 7 | The key is used for key agreement. | | key | 7 | The key is used for key agreement. |
| agree | | | | agree | | |
+---------+-------+-------------------------------------------------+ +---------+-------+-------------------------------------------------+
Table 4: Key Operation Values Table 3: Key Operation Values
The following provides a CDDL fragment which duplicates the The following provides a CDDL fragment which duplicates the
assignment labels from Table 3 and Table 4. assignment labels from Table 2 and Table 3.
;key_labels ;key_labels
key_kty=1 key_kty=1
key_kid=2 key_kid=2
key_alg=3 key_alg=3
key_ops=4 key_ops=4
;key_ops values ;key_ops values
key_ops_sign=1 key_ops_sign=1
key_ops_verify=2 key_ops_verify=2
skipping to change at page 27, line 48 skipping to change at page 24, line 48
smaller signature, the signature size is still potentially large, but smaller signature, the signature size is still potentially large, but
the message content is shrunk. This has implications for systems the message content is shrunk. This has implications for systems
implementing these algoritms and for applications that use them. The implementing these algoritms and for applications that use them. The
first is that the message content is not fully available until after first is that the message content is not fully available until after
a signature has been validated. Until that point the part of the a signature has been validated. Until that point the part of the
message contained inside of the signature is unrecoverable. The message contained inside of the signature is unrecoverable. The
second is that the security analysis of the strength of the signature second is that the security analysis of the strength of the signature
is very much based on the structure of the message content. Messages is very much based on the structure of the message content. Messages
which are highly predictable require additional randomness to be which are highly predictable require additional randomness to be
supplied as part of the signature process, in the worst case it supplied as part of the signature process, in the worst case it
because the same as doing a singature with appendix. Thirdly, in the becomes the same as doing a signature with appendix. Thirdly, in the
event that multple signatures are applied to a message, all of the event that multple signatures are applied to a message, all of the
signature algorithms are going to be required to consume the same signature algorithms are going to be required to consume the same
number of bytes of message content. number of bytes of message content.
signature, message sent = Sign(message content, key) signature, message sent = Sign(message content, key)
valid, message content = Verification(message sent, key, signature) valid, message content = Verification(message sent, key, signature)
At this time, only signatures with appendixes are defined for use At this time, only signatures with appendixes are defined for use
with COSE, however considerable interest has been expressed in using with COSE, however considerable interest has been expressed in using
a signature with message recovery algorithm due to the effective size a signature with message recovery algorithm due to the effective size
reduction that is possible. Implementations will need to keep this reduction that is possible. Implementations will need to keep this
in mind for later possible integration. in mind for later possible integration.
8.1. ECDSA 8.1. ECDSA
ECDSA [DSS] defines a signature algorithm using ECC. ECDSA [DSS] defines a signature algorithm using ECC.
The ECDSA signature algorithm is parameterized with a hash function The ECDSA signature algorithm is parameterized with a hash function
(h. In the event that the length of the hash function output is (h). In the event that the length of the hash function output is
greater than group of the key, the left most bytes of the hash output greater than group of the key, the left most bytes of the hash output
are used. are used.
The algorithms defined in this document can be found in Table 5. The algorithms defined in this document can be found in Table 4.
+-------+-------+---------+------------------+ +-------+-------+---------+------------------+
| name | value | hash | description | | name | value | hash | description |
+-------+-------+---------+------------------+ +-------+-------+---------+------------------+
| ES256 | -7 | SHA-256 | ECDSA w/ SHA-256 | | ES256 | -7 | SHA-256 | ECDSA w/ SHA-256 |
| | | | | | | | | |
| ES384 | -8 | SHA-384 | ECDSA w/ SHA-384 | | ES384 | -8 | SHA-384 | ECDSA w/ SHA-384 |
| | | | | | | | | |
| ES512 | -9 | SHA-512 | ECDSA w/ SHA-512 | | ES512 | -9 | SHA-512 | ECDSA w/ SHA-512 |
+-------+-------+---------+------------------+ +-------+-------+---------+------------------+
Table 5: ECDSA Algorithm Values Table 4: ECDSA Algorithm Values
In order to promote interoperability, it is suggested that SHA-256 be In order to promote interoperability, it is suggested that SHA-256 be
used only with keys of length 256, SHA-384 be used only with keys of used only with keys of length 256, SHA-384 be used only with keys of
length 384 and SHA-512 be used only with keys of length 521. This is length 384 and SHA-512 be used only with keys of length 521. This is
aligned with the recommendation in Section 4 of [RFC5480]. aligned with the recommendation in Section 4 of [RFC5480].
The signature algorithm results in a pair of integers (R, S). These The signature algorithm results in a pair of integers (R, S). These
integers will be of the same order as length of the key used for the integers will be of the same order as length of the key used for the
signature process. The signature is encoded by converting the signature process. The signature is encoded by converting the
integers into byte strings of the same length as the key size. The integers into byte strings of the same length as the key size. The
skipping to change at page 29, line 16 skipping to change at page 26, line 16
signature. signature.
Using the function defined in [RFC3447] the signature is: Using the function defined in [RFC3447] the signature is:
Signature = I2OSP(R, n) | I2OSP(S, n) Signature = I2OSP(R, n) | I2OSP(S, n)
where n = ceiling(key_length / 8) where n = ceiling(key_length / 8)
8.1.1. Security Considerations 8.1.1. Security Considerations
The security strength of the signature is no greater than the minimum The security strength of the signature is no greater than the minimum
of the security strength associated with the bit length of the key of the security strength associated with the bit length of the key
and the security strength of the hash function. When a hash function and the security strength of the hash function.
is used that has greater security than is provided by the length of
the key, the signature algorithm uses the leftmost key length bits of
the hash function output.
System which have poor random number generation can leak their keys System which have poor random number generation can leak their keys
by signing two messages with the same value of 'k'. [RFC6979] by signing two different messages with the same value of 'k'.
provides a method to deal with this problem by making 'k' be [RFC6979] provides a method to deal with this problem by making 'k'
deterministic based on the message content rather than randomly be deterministic based on the message content rather than randomly
generated. Applications which specify ECDSA should evaluate the generated. Applications which specify ECDSA should evaluate the
ability to get good random number generation and recommend this when ability to get good random number generation and require this when it
it is not possible. Note: Use of this technique even when good is not possible. Note: Use of this technique a good idea even when
random number generation exists may still be a good idea. good random number generation exists. Doing so both reduces the
possiblity of having the same value of 'k' in two signature
operations, but allows for reproducable signature values which helps
testing.
There are two substitution that can theoretically be mounted against There are two substitution that can theoretically be mounted against
the ECDSA signature algorithm. the ECDSA signature algorithm.
o Changing the curve used to validate the signature: If one changes o Changing the curve used to validate the signature: If one changes
the curve used to validate the signature, then potentially one the curve used to validate the signature, then potentially one
could have a two messages with the same signature each computed could have a two messages with the same signature each computed
under a different curve. The only requirement on the new curve is under a different curve. The only requirement on the new curve is
that it's order be the same as the old one and it be acceptable to that it's order be the same as the old one and it be acceptable to
the client. An example would be to change from using the curve the client. An example would be to change from using the curve
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The RSASSA-PSS signature algorithm is parametized with a hash The RSASSA-PSS signature algorithm is parametized with a hash
function (h), a mask generation function (mgf) and a salt length function (h), a mask generation function (mgf) and a salt length
(sLen). For this specification, the mask generation function is (sLen). For this specification, the mask generation function is
fixed to be MGF1 as defined in [RFC3447]. It has been recommended fixed to be MGF1 as defined in [RFC3447]. It has been recommended
that the same hash function be used for hashing the data as well as that the same hash function be used for hashing the data as well as
in the mask generation function, for this specification we following in the mask generation function, for this specification we following
this recommendation. The salt length is the same length as the hash this recommendation. The salt length is the same length as the hash
function output. function output.
The algorithms defined in this document can be found in Table 6. The algorithms defined in this document can be found in Table 5.
+-------+-------+---------+-------------+-----------------------+ +-------+-------+---------+-------------+-----------------------+
| name | value | hash | salt length | description | | name | value | hash | salt length | description |
+-------+-------+---------+-------------+-----------------------+ +-------+-------+---------+-------------+-----------------------+
| PS256 | -26 | SHA-256 | 32 | RSASSA-PSS w/ SHA-256 | | PS256 | -26 | SHA-256 | 32 | RSASSA-PSS w/ SHA-256 |
| | | | | | | | | | | |
| PS384 | -27 | SHA-384 | 48 | RSASSA-PSS w/ SHA-384 | | PS384 | -27 | SHA-384 | 48 | RSASSA-PSS w/ SHA-384 |
| | | | | | | | | | | |
| PS512 | -28 | SHA-512 | 64 | RSASSA-PSS w/ SHA-512 | | PS512 | -28 | SHA-512 | 64 | RSASSA-PSS w/ SHA-512 |
+-------+-------+---------+-------------+-----------------------+ +-------+-------+---------+-------------+-----------------------+
Table 6: RSASSA-PSS Algorithm Values Table 5: RSASSA-PSS Algorithm Values
8.2.1. Security Considerations 8.2.1. Security Considerations
In addition to needing to worry about keys that are too small to In addition to needing to worry about keys that are too small to
provide the required security, there are issues with keys that are provide the required security, there are issues with keys that are
too large. Denial of service attacks have been mounted with overly too large. Denial of service attacks have been mounted with overly
large keys. This has the potential to consume resources with large keys. This has the potential to consume resources with
potentially bad keys. There are two reasonable ways to address this potentially bad keys. There are two reasonable ways to address this
attack. First, a key should not be used for a cryptographic attack. First, a key should not be used for a cryptographic
operation until it has been matched back to an authorized user. This operation until it has been matched back to an authorized user. This
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in producing a forgery based on changing the hash function. This is in producing a forgery based on changing the hash function. This is
highly unlikely. highly unlikely.
9. Message Authentication (MAC) Algorithms 9. Message Authentication (MAC) Algorithms
Message Authentication Codes (MACs) provide data authentication and Message Authentication Codes (MACs) provide data authentication and
integrity protection. They provide either no or very limited data integrity protection. They provide either no or very limited data
origination. (One cannot, for example, be used to prove the identity origination. (One cannot, for example, be used to prove the identity
of the sender to a third party.) of the sender to a third party.)
MACs are designed in the same basic structure as signature with
appendix algorithms. The message content is processed and an
authentication code is produced, the authentication code is
frequently called a tag. The basic structure becomes:
tag = MAC_Create(message content, key)
valid = MAC_Verify(message content, key, tag)
MAC algorithms can be based on either a block cipher algorithm (i.e. MAC algorithms can be based on either a block cipher algorithm (i.e.
AES-MAC) or a hash algorithm (i.e. HMAC). This document defines a AES-MAC) or a hash algorithm (i.e. HMAC). This document defines a
MAC algorithm for each of these two constructions. MAC algorithm for each of these two constructions.
9.1. Hash-based Message Authentication Codes (HMAC) 9.1. Hash-based Message Authentication Codes (HMAC)
The Hash-base Message Authentication Code algorithm (HMAC) The Hash-base Message Authentication Code algorithm (HMAC)
[RFC2104][RFC4231] was designed to deal with length extension [RFC2104][RFC4231] was designed to deal with length extension
attacks. The algorithm was also designed to allow for new hash attacks. The algorithm was also designed to allow for new hash
algorithms to be directly plugged in without changes to the hash algorithms to be directly plugged in without changes to the hash
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hash function (h) and an authentication tag value length. For this hash function (h) and an authentication tag value length. For this
specification, the inner and outer padding are fixed to the values specification, the inner and outer padding are fixed to the values
set in [RFC2104]. The length of the authentication tag corresponds set in [RFC2104]. The length of the authentication tag corresponds
to the difficulty of producing a forgery. For use in constrained to the difficulty of producing a forgery. For use in constrained
environments, we define a set of HMAC algorithms that are truncated. environments, we define a set of HMAC algorithms that are truncated.
There are currently no known issues when truncating, however the There are currently no known issues when truncating, however the
security strength of the message tag is correspondingly reduced in security strength of the message tag is correspondingly reduced in
strength. When truncating, the left most tag length bits are kept strength. When truncating, the left most tag length bits are kept
and transmitted. and transmitted.
The algorithm defined in this document can be found in Table 7. The algorithm defined in this document can be found in Table 6.
+-----------+-------+---------+--------+----------------------------+ +-----------+-------+---------+--------+----------------------------+
| name | value | Hash | Length | description | | name | value | Hash | Length | description |
+-----------+-------+---------+--------+----------------------------+ +-----------+-------+---------+--------+----------------------------+
| HMAC | * | SHA-256 | 64 | HMAC w/ SHA-256 truncated | | HMAC | * | SHA-256 | 64 | HMAC w/ SHA-256 truncated |
| 256/64 | | | | to 64 bits | | 256/64 | | | | to 64 bits |
| | | | | | | | | | | |
| HMAC | 4 | SHA-256 | 256 | HMAC w/ SHA-256 | | HMAC | 4 | SHA-256 | 256 | HMAC w/ SHA-256 |
| 256/256 | | | | | | 256/256 | | | | |
| | | | | | | | | | | |
| HMAC | 5 | SHA-384 | 384 | HMAC w/ SHA-384 | | HMAC | 5 | SHA-384 | 384 | HMAC w/ SHA-384 |
| 384/384 | | | | | | 384/384 | | | | |
| | | | | | | | | | | |
| HMAC | 6 | SHA-512 | 512 | HMAC w/ SHA-512 | | HMAC | 6 | SHA-512 | 512 | HMAC w/ SHA-512 |
| 512/512 | | | | | | 512/512 | | | | |
+-----------+-------+---------+--------+----------------------------+ +-----------+-------+---------+--------+----------------------------+
Table 7: HMAC Algorithm Values Table 6: HMAC Algorithm Values
For some key management methods, the length of the key is known or Some recipient algorithms carry the key while others derive a key
determinable from the key management method. For example, if RSA- from secret data. For those algorithms which carry the key (i.e.
OAEP is used then the key will be output at the correct length. RSA-OAEP and AES-KeyWrap), the size of the HMAC key SHOULD be the
However, if any of the key derivation methods are used, then the size same size as the underlying hash function. For those algorithms
of the key to be obtained is an input parameter to the key derivation which derive the key, the derived key MUST be the same size as the
step. For all HMAC methods defined in this document, the key size underlying hash function.
for a key derivation methods MUST be the same size as the hash
function used. It is RECOMMENDED that the key size be the same size
as the hash function for all other key management methods.
9.1.1. Security Considerations 9.1.1. Security Considerations
HMAC has proved to be resistant even when used with weakening hash HMAC has proved to be resistant even when used with weakening hash
algorithms. The current best method appears to be a brute force algorithms. The current best method appears to be a brute force
attack on the key. This means that key size is going to be directly attack on the key. This means that key size is going to be directly
related to the security of an HMAC operation. related to the security of an HMAC operation.
9.2. AES Message Authentication Code (AES-CBC-MAC) 9.2. AES Message Authentication Code (AES-CBC-MAC)
AES-CBC-MAC is defined in [MAC]. AES-CBC-MAC is defined in [MAC].
AES-CBC-MAC is parameterized by the key length, the authentication AES-CBC-MAC is parameterized by the key length, the authentication
tag length and the IV used. For all of these algorithms, the IV is tag length and the IV used. For all of these algorithms, the IV is
fixed to all zeros. We provide an array of algorithms for various fixed to all zeros. We provide an array of algorithms for various
key lengths and tag lengths. The algorithms defined in this document key lengths and tag lengths. The algorithms defined in this document
are found in Table 8. are found in Table 7.
+-------------+-------+----------+----------+-----------------------+ +-------------+-------+----------+----------+-----------------------+
| name | value | key | tag | description | | name | value | key | tag | description |
| | | length | length | | | | | length | length | |
+-------------+-------+----------+----------+-----------------------+ +-------------+-------+----------+----------+-----------------------+
| AES-MAC | * | 128 | 64 | AES-MAC 128 bit key, | | AES-MAC | * | 128 | 64 | AES-MAC 128 bit key, |
| 128/64 | | | | 64-bit tag | | 128/64 | | | | 64-bit tag |
| | | | | | | | | | | |
| AES-MAC | * | 256 | 64 | AES-MAC 256 bit key, | | AES-MAC | * | 256 | 64 | AES-MAC 256 bit key, |
| 256/64 | | | | 64-bit tag | | 256/64 | | | | 64-bit tag |
| | | | | | | | | | | |
| AES-MAC | * | 128 | 128 | AES-MAC 128 bit key, | | AES-MAC | * | 128 | 128 | AES-MAC 128 bit key, |
| 128/128 | | | | 128-bit tag | | 128/128 | | | | 128-bit tag |
| | | | | | | | | | | |
| AES-MAC | * | 256 | 128 | AES-MAC 256 bit key, | | AES-MAC | * | 256 | 128 | AES-MAC 256 bit key, |
| 256/128 | | | | 128-bit tag | | 256/128 | | | | 128-bit tag |
+-------------+-------+----------+----------+-----------------------+ +-------------+-------+----------+----------+-----------------------+
Table 8: AES-MAC Algorithm Values Table 7: AES-MAC Algorithm Values
9.2.1. Security Considerations 9.2.1. Security Considerations
A number of attacks exist against CBC-MAC that need to be considered. A number of attacks exist against CBC-MAC that need to be considered.
o A single key must only be used for messages of a fixed and known o A single key must only be used for messages of a fixed and known
length. If this is not the case, an attacker will be able to length. If this is not the case, an attacker will be able to
generated a message with a valid tag given two message, tag pairs. generated a message with a valid tag given two message, tag pairs.
This can be addressed by using different keys for different length This can be addressed by using different keys for different length
messages. (CMAC mode also addresses this issue.) messages. (CMAC mode also addresses this issue.)
o If the same key is used for both encryption and authentication o If the same key is used for both encryption and authentication
operations, using CBC modes an attacker can produce messages with operations, using CBC modes an attacker can produce messages with
a valid authentication code. a valid authentication code.
o If the IV can be modified, then messages can be forged. This is o If the IV can be modified, then messages can be forged. This is
addressed by fixing the IV to all zeros. addressed by fixing the IV to all zeros.
10. Content Encryption Algorithms 10. Content Encryption Algorithms
Content Encryption Algorithms provide data confidentialty for
potentially large blocks of data using a symmetric key. They provide
either no or very limited data origination. (One cannot, for
example, be used to prove the identity of the sender to a third
party.) The ability to provide data origination is linked to how the
symmetric key is obtained.
We restrict the set of legal content encryption algorithms to those
which support authentication both of the content and additional data.
The encryption process will generate some type of authentication
value, but that value may be either explicit or implicit in terms of
the algorithm definition. For simplicity sake, the authentication
code will normally be defined as being appended to the cipher text
stream. The basic structure becomes:
ciphertext = Encrypt(message content, key, additional data)
valid, message content = Decrypt(cipher text, key, additional data)
Most AEAD algorithms are logically defined as returning the message
content only if the decryption is valid. Many but not all
implementations will follow this convention. The message content
MUST NOT be used if the decryption does not validate.
10.1. AES GCM 10.1. AES GCM
The GCM mode is is a generic authenticated encryption block cipher The GCM mode is is a generic authenticated encryption block cipher
mode defined in [AES-GCM]. The GCM mode is combined with the AES mode defined in [AES-GCM]. The GCM mode is combined with the AES
block encryption algorithm to define a an AEAD cipher. block encryption algorithm to define a an AEAD cipher.
The GCM mode is parameterized with by the size of the authentication The GCM mode is parameterized with by the size of the authentication
tag. The size of the authentication tag is limited to a small set of tag. The size of the authentication tag is limited to a small set of
values. For this document however, the size of the authentication values. For this document however, the size of the authentication
tag is fixed at 128-bits. tag is fixed at 128-bits.
The set of algorithms defined in this document are in Table 9. The set of algorithms defined in this document are in Table 8.
+---------+-------+-----------------------------+ +---------+-------+-----------------------------+
| name | value | description | | name | value | description |
+---------+-------+-----------------------------+ +---------+-------+-----------------------------+
| A128GCM | 1 | AES-GCM mode w/ 128-bit key | | A128GCM | 1 | AES-GCM mode w/ 128-bit key |
| | | | | | | |
| A192GCM | 2 | AES-GCM mode w/ 192-bit key | | A192GCM | 2 | AES-GCM mode w/ 192-bit key |
| | | | | | | |
| A256GCM | 3 | AES-GCM mode w/ 256-bit key | | A256GCM | 3 | AES-GCM mode w/ 256-bit key |
+---------+-------+-----------------------------+ +---------+-------+-----------------------------+
Table 9: Algorithm Value for AES-GCM Table 8: Algorithm Value for AES-GCM
10.1.1. Security Considerations 10.1.1. Security Considerations
When using AES-CCM the following restrictions MUST be enforced: When using AES-CCM the following restrictions MUST be enforced:
o The key and nonce pair MUST be unique for every message encrypted. o The key and nonce pair MUST be unique for every message encrypted.
o The total amount of data encrypted MUST NOT exceed 2^39 - 256 bits o The total amount of data encrypted MUST NOT exceed 2^39 - 256 bits
. An explicit check is required only in environments where it is . An explicit check is required only in environments where it is
expected that it might be exceeded. expected that it might be exceeded.
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a count of bytes rather than a count of bits. This leads to possible a count of bytes rather than a count of bits. This leads to possible
misunderstandings where AES-CCM-8 is frequently used to refer to a misunderstandings where AES-CCM-8 is frequently used to refer to a
version of CCM mode where the size of the authentication is 64-bits version of CCM mode where the size of the authentication is 64-bits
and not 8-bits. These values have traditionally been specified as and not 8-bits. These values have traditionally been specified as
bit counts rather than byte counts. This document will follow the bit counts rather than byte counts. This document will follow the
tradition of using bit counts so that it is easier to compare the tradition of using bit counts so that it is easier to compare the
different algorithms presented in this document. different algorithms presented in this document.
We define a matrix of algorithms in this document over the values of We define a matrix of algorithms in this document over the values of
L and M. Constrained devices are usually operating in situations L and M. Constrained devices are usually operating in situations
where they use short messages and want to avoid doing key management where they use short messages and want to avoid doing recipient
operations. This favors smaller values of M and larger values of L. specific cryptographic operations. This favors smaller values of M
Less constrained devices do will want to be able to user larger and larger values of L. Less constrained devices do will want to be
messages and are more willing to generate new keys for every able to user larger messages and are more willing to generate new
operation. This favors larger values of M and smaller values of L. keys for every operation. This favors larger values of M and smaller
(The use of a large nonce means that random generation of both the values of L. (The use of a large nonce means that random generation
key and the nonce will decrease the chances of repeating the pair on of both the key and the nonce will decrease the chances of repeating
two different messages.) the pair on two different messages.)
The following values are used for L: The following values are used for L:
16-bits (2) limits messages to 2^16 bytes (64Kbyte) in length. This 16-bits (2) limits messages to 2^16 bytes (64Kbyte) in length. This
sufficently long for messages in the constrainted world. The sufficently long for messages in the constrainted world. The
nonce length is 13 bytes allowing for 2^(13*8) possible values of nonce length is 13 bytes allowing for 2^(13*8) possible values of
the nonce without repeating. the nonce without repeating.
64-bits (8) limits messages to 2^64 byes in length. The nonce 64-bits (8) limits messages to 2^64 byes in length. The nonce
length is 7 bytes allowing for 2^56 possible values of the nonce length is 7 bytes allowing for 2^56 possible values of the nonce
skipping to change at page 36, line 45 skipping to change at page 34, line 45
| | | | | | 128-bit key, | | | | | | | 128-bit key, |
| | | | | | 128-bit tag, 7-byte | | | | | | | 128-bit tag, 7-byte |
| | | | | | nonce | | | | | | | nonce |
| | | | | | | | | | | | | |
| AES-CCM-64-128-256 | 33 | 64 | 128 | 256 | AES-CCM mode | | AES-CCM-64-128-256 | 33 | 64 | 128 | 256 | AES-CCM mode |
| | | | | | 256-bit key, | | | | | | | 256-bit key, |
| | | | | | 128-bit tag, 7-byte | | | | | | | 128-bit tag, 7-byte |
| | | | | | nonce | | | | | | | nonce |
+--------------------+-------+----+-----+-----+---------------------+ +--------------------+-------+----+-----+-----+---------------------+
Table 10: Algorithm Values for AES-CCM Table 9: Algorithm Values for AES-CCM
10.2.1. Security Considerations 10.2.1. Security Considerations
When using AES-CCM the following restrictions MUST be enforced: When using AES-CCM the following restrictions MUST be enforced:
o The key and nonce pair MUST be unique for every message encrypted. o The key and nonce pair MUST be unique for every message encrypted.
o The total number of times the AES block cipher is used MUST NOT o The total number of times the AES block cipher is used MUST NOT
exceed 2^61 operations. This limitation is the sum of times the exceed 2^61 operations. This limitation is the sum of times the
block cipher is used in computing the MAC value and in performing block cipher is used in computing the MAC value and in performing
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this attack include adding a random portion to the nonce value and/or this attack include adding a random portion to the nonce value and/or
increasing the key size used. Using a portion of the nonce for a increasing the key size used. Using a portion of the nonce for a
random value will decrease the number of messages that a single key random value will decrease the number of messages that a single key
can be used for. Increasing the key size may require more resources can be used for. Increasing the key size may require more resources
in the constrained device. See sections 5 and 10 of [RFC3610] for in the constrained device. See sections 5 and 10 of [RFC3610] for
more information. more information.
10.3. ChaCha20 and Poly1305 10.3. ChaCha20 and Poly1305
ChaCha20 and Poly1305 combined together is a new AEAD mode that is ChaCha20 and Poly1305 combined together is a new AEAD mode that is
defined in [RFC7539]. This is a new mode defined to be a cipher defined in [RFC7539]. This is a new algorithm defined to be a cipher
which is not AES and thus would not suffer from any future weaknesses which is not AES and thus would not suffer from any future weaknesses
found in AES. These cryptographic functions are designed to be fast found in AES. These cryptographic functions are designed to be fast
in software only implementations. in software only implementations.
The ChaCha20/Poly1305 AEAD construction defined in [RFC7539] has no The ChaCha20/Poly1305 AEAD construction defined in [RFC7539] has no
parameterization. It takes a 256-bit key and an a 96-bit nonce as parameterization. It takes a 256-bit key and an a 96-bit nonce as
well as the plain text and additional data as inputs and produces the well as the plain text and additional data as inputs and produces the
cipher text as an option. We define one algorithm identifier for cipher text as an option. We define one algorithm identifier for
this algorithm in Table 11. this algorithm in Table 10.
+-------------------+-------+----------------------------------+ +-------------------+-------+----------------------------------+
| name | value | description | | name | value | description |
+-------------------+-------+----------------------------------+ +-------------------+-------+----------------------------------+
| ChaCha20/Poly1305 | 11 | ChaCha20/Poly1305 w/ 256-bit key | | ChaCha20/Poly1305 | 11 | ChaCha20/Poly1305 w/ 256-bit key |
+-------------------+-------+----------------------------------+ +-------------------+-------+----------------------------------+
Table 11: Algorithm Value for AES-GCM Table 10: Algorithm Value for AES-GCM
10.3.1. Security Considerations 10.3.1. Security Considerations
The pair of key, nonce MUST be unique for every invocation of the The pair of key, nonce MUST be unique for every invocation of the
algorithm. Nonce counters are considered to be an acceptable way of algorithm. Nonce counters are considered to be an acceptable way of
ensuring that they are unique. ensuring that they are unique.
11. Key Derivation Functions (KDF) 11. Key Derivation Functions (KDF)
Key Derivation Functions (KDFs) are used to take some secret value
and generate a different one. The original secret values come in
three basic flavors:
o Secrets which are uniformly random: This is the type of secret
which is created by a good random number generator.
o Secrets which are not uniformly random: This is type of secret
which is created by operations like key agreement.
o Secrets which are not random: This is the type of secret that
people generate for things like passwords.
General KDF functions work well with the first type of secret, can do
reasonable well with the second type of secret and generally do
poorly with the last type of secret. None of the KDF functions in
this section are designed to deal with the type of secrets that are
used for passwords. Functions like PBSE2 [RFC2898] need to be used
for that type of secret.
Many functions are going to handle the first two type of secrets
differently. The KDF function defined in Section 11.1 can use
different underlying constructions if the secret is uniformly random
than if the secret is not uniformly random. This is reflected in the
set of algorithms defined for HKDF.
When using KDF functions, one component that is generally included is
context information. Context information is used to allow for
different keying information to be derived from the same secret. The
use of context based keying material is considered to be a good
security practice. This document defines a single context structure
and a single KDF function.
11.1. HMAC-based Extract-and-Expand Key Derivation Function (HKDF) 11.1. HMAC-based Extract-and-Expand Key Derivation Function (HKDF)
The HKDF key derivation algorithm is defined in [RFC5869]. The HKDF key derivation algorithm is defined in [RFC5869].
The HKDF algorithm is defined to take a number of inputs These inputs The HKDF algorithm is defined to take a number of inputs These inputs
are: are:
secret - a shared value that is secret. Secrets may be either secret - a shared value that is secret. Secrets may be either
previously shared or derived from operations like a DH key previously shared or derived from operations like a DH key
agreement. agreement.
salt - an optional public value that is used to change the salt - an optional public value that is used to change the
generation process. If specified, the salt is carried using the generation process. If specified, the salt is carried using the
'salt' algorithm parameter. While [RFC5869] suggests that the 'salt' algorithm parameter. While [RFC5869] suggests that the
length of the salt be the same as the length of the underlying length of the salt be the same as the length of the underlying
hash value, any amount of salt will improve the security as hash value, any amount of salt will improve the security as
different key values will be generated. A parameter to carry the different key values will be generated. A parameter to carry the
salt is defined in Table 13. This parameter is protected by being salt is defined in Table 12. This parameter is protected by being
included in the key computation and does not need to be separately included in the key computation and does not need to be separately
authenticated. authenticated.
length - the number of bytes of output that need to be generated. length - the number of bytes of output that need to be generated.
context information - Information that describes the context in context information - Information that describes the context in
which the resulting value will be used. Making this information which the resulting value will be used. Making this information
specific to the context that the material is going to be used specific to the context that the material is going to be used
ensures that the resulting material will always be unique. The ensures that the resulting material will always be unique. The
context structure used is encoded into the algorithm identifier. context structure used is encoded into the algorithm identifier.
skipping to change at page 38, line 50 skipping to change at page 37, line 34
HKDF is defined to use HMAC as the underlying PRF. However, it is HKDF is defined to use HMAC as the underlying PRF. However, it is
possible to use other functions in the same construct to provide a possible to use other functions in the same construct to provide a
different KDF function that may be more appropriate in the different KDF function that may be more appropriate in the
constrained world. Specifically, one can use AES-CBC-MAC as the PRF constrained world. Specifically, one can use AES-CBC-MAC as the PRF
for the expand step, but not for the extract step. When using a good for the expand step, but not for the extract step. When using a good
random shared secret of the correct length, the extract step can be random shared secret of the correct length, the extract step can be
skipped. The extract cannot be skipped if the secret is not skipped. The extract cannot be skipped if the secret is not
uniformly random, for example if it is the result of a ECDH key uniformly random, for example if it is the result of a ECDH key
agreement step. agreement step.
The algorithms defined in this document are found in Table 12 The algorithms defined in this document are found in Table 11
+-------------+-------------+----------+----------------------------+ +-------------+-------------+----------+----------------------------+
| name | hash | Skip | context | | name | hash | Skip | context |
| | | extract | | | | | extract | |
+-------------+-------------+----------+----------------------------+ +-------------+-------------+----------+----------------------------+
| HKDF | SHA-256 | no | XXX | | HKDF | SHA-256 | no | XXX |
| SHA-256 | | | | | SHA-256 | | | |
| | | | | | | | | |
| HKDF | SHA-512 | no | XXX | | HKDF | SHA-512 | no | XXX |
| SHA-512 | | | | | SHA-512 | | | |
| | | | | | | | | |
| HKDF AES- | AES-CBC-128 | yes | HKDF using AES-MAC as the | | HKDF AES- | AES-CBC-128 | yes | HKDF using AES-MAC as the |
| MAC-128 | | | PRF w/ 128-bit key | | MAC-128 | | | PRF w/ 128-bit key |
| | | | | | | | | |
| HKDF AES- | AES-CBC-128 | yes | HKDF using AES-MAC as the | | HKDF AES- | AES-CBC-128 | yes | HKDF using AES-MAC as the |
| MAC-256 | | | PRF w/ 256-bit key | | MAC-256 | | | PRF w/ 256-bit key |
+-------------+-------------+----------+----------------------------+ +-------------+-------------+----------+----------------------------+
Table 12: HKDF algorithms Table 11: HKDF algorithms
+------+-------+------+-------------+ +------+-------+------+-------------+
| name | label | type | description | | name | label | type | description |
+------+-------+------+-------------+ +------+-------+------+-------------+
| salt | -20 | bstr | Random salt | | salt | -20 | bstr | Random salt |
+------+-------+------+-------------+ +------+-------+------+-------------+
Table 13: HKDF Algorithm Parameters Table 12: HKDF Algorithm Parameters
11.2. Context Information Structure 11.2. Context Information Structure
The context information structure is used to ensure that the derived The context information structure is used to ensure that the derived
keying material is "bound" to the context of the transaction. The keying material is "bound" to the context of the transaction. The
context information structure used here is based on that defined in context information structure used here is based on that defined in
[SP800-56A]. By using CBOR for the encoding of the context [SP800-56A]. By using CBOR for the encoding of the context
information structure, we automatically get the same type of type and information structure, we automatically get the same type of type and
length separation of fields that is obtained by the use of ASN.1. length separation of fields that is obtained by the use of ASN.1.
This means that there is no need to encode the lengths for the base This means that there is no need to encode the lengths for the base
elements as it is done by the CBOR encoding. elements as it is done by the CBOR encoding.
The context information structure refers to PartyU and PartyV as the The context information structure refers to PartyU and PartyV as the
two parties which are doing the key derivation. Unless the two parties which are doing the key derivation. Unless the
application protocol defines differently, we assign PartyU to the application protocol defines differently, we assign PartyU to the
entity that is creating the message and PartyV to the entity that is entity that is creating the message and PartyV to the entity that is
receiving the message. This is because we are assuming a set of receiving the message. This is because we are assuming a set of
stand alone store and forward messaging processes. In [SP800-56A], standalone store and forward messaging processes. In [SP800-56A],
PartyU is the initiator and PartyV is the responder. The PartyU is the initiator and PartyV is the responder. The
specification is written with the idea of on-line protocols rather specification is written with the idea of on-line protocols rather
than store and forward protocols as the main consumer. than store and forward protocols as the main consumer.
Application protocols are free to define the roles differently. For Application protocols are free to define the roles differently. For
example, they could assign the PartyU role to the entity that example, they could assign the PartyU role to the entity that
initiates the connection and allow directly sending multiple messages initiates the connection and allow directly sending multiple messages
over the line without changing the role information. over the connection in both directions without changing the role
information.
Using the PartyU and PartyV fields is the easiest way to get Using the PartyU and PartyV fields is the easiest way to get
different keys in each direction. The use of a transaction different keys in each direction. The use of a transaction
identifier, either in one of the supplemental fields or as the salt identifier, either in one of the supplemental fields or as the salt
if one is using HKDF, ensures that a unique key is generated for each if one is using HKDF, ensures that a unique key is generated for each
set of transactions. Combining nonce fields with the transaction set of transactions. Combining nonce fields with the transaction
identifier provides a method so that a different key is used for each identifier provides a method so that a different key is used for each
message in each direction. message in each direction.
We encode the context specific information using a CBOR array type. We encode the context specific information using a CBOR array type.
For the fields that we define an algorithm parameter, the details of For the fields that we define an algorithm parameter, the details of
the parameters can be found in Table 14. The fields in the array the parameters can be found in Table 13. The fields in the array
are: are:
AlgorithmID This field indicates the algorithm for which the key AlgorithmID This field indicates the algorithm for which the key
material will be used. This field is required to be present and material will be used. This field is required to be present and
is a copy of the algorithm identifier in the message. The field is a copy of the algorithm identifier in the message. The field
exists in the context information so that if the same environment exists in the context information so that if the same environment
is used for different algorithms, then completely different keys is used for different algorithms, then completely different keys
will be generated each of those algorithms. (This practice means will be generated each of those algorithms. (This practice means
if algorithm A is broken and thus can is easier to find, the key if algorithm A is broken and thus can is easier to find, the key
derived for algorithm B will not be the same as the key for derived for algorithm B will not be the same as the key for
skipping to change at page 41, line 33 skipping to change at page 40, line 33
ready. ready.
SuppPubInfo This field contains public information that is mutually SuppPubInfo This field contains public information that is mutually
known to both parties. known to both parties.
keyDataLength This is set to the number of bits of the desired keyDataLength This is set to the number of bits of the desired
output value. (This practice means if algorithm A can use two output value. (This practice means if algorithm A can use two
different key lengths, the key derived for longer key size will different key lengths, the key derived for longer key size will
not contain the key for shorter key size as a prefix.) not contain the key for shorter key size as a prefix.)
protected This field contains the protected parameter field.
other The field other is for free form data defined by the other The field other is for free form data defined by the
application. An example is that an application could defined application. An example is that an application could defined
two different strings to be placed here to generate different two different strings to be placed here to generate different
keys for a data stream vs a control stream. This field is keys for a data stream vs a control stream. This field is
optional and will only be present if the application defines a optional and will only be present if the application defines a
structure for this information. Applications that define this structure for this information. Applications that define this
SHOULD use CBOR to encode the data so that types and lengths SHOULD use CBOR to encode the data so that types and lengths
are correctly include. are correctly include.
SuppPrivInfo This field contains private information that is SuppPrivInfo This field contains private information that is
skipping to change at page 42, line 19 skipping to change at page 41, line 19
? identity : bstr, ? identity : bstr,
? other : bstr ? other : bstr
], ],
PartyVInfo : [ PartyVInfo : [
? nonce : bstr, ? nonce : bstr,
? identity : bstr / tstr, ? identity : bstr / tstr,
? other : bstr ? other : bstr
], ],
SuppPubInfo : [ SuppPubInfo : [
keyDataLength : uint, keyDataLength : uint,
protected : bstr,
? other : bstr ? other : bstr
], ],
? SuppPrivInfo : bstr ? SuppPrivInfo : bstr
] ]
+---------------+-------+-----------+-------------------------------+ +---------------+-------+-----------+-------------------------------+
| name | label | type | description | | name | label | type | description |
+---------------+-------+-----------+-------------------------------+ +---------------+-------+-----------+-------------------------------+
| PartyU | -21 | bstr | Party U identity Information | | PartyU | -21 | bstr | Party U identity Information |
| identity | | | | | identity | | | |
skipping to change at page 42, line 46 skipping to change at page 41, line 47
| PartyV | -24 | bstr | Party V identity Information | | PartyV | -24 | bstr | Party V identity Information |
| identity | | | | | identity | | | |
| | | | | | | | | |
| PartyV nonce | -25 | bstr / | Party V provided nonce | | PartyV nonce | -25 | bstr / | Party V provided nonce |
| | | int | | | | | int | |
| | | | | | | | | |
| PartyV other | -26 | bstr | Party V other provided | | PartyV other | -26 | bstr | Party V other provided |
| | | | information | | | | | information |
+---------------+-------+-----------+-------------------------------+ +---------------+-------+-----------+-------------------------------+
Table 14: Context Algorithm Parameters Table 13: Context Algorithm Parameters
12. Key Management Algorithms
There are a number of different key management methods that can be 12. Recipient Algorithm Classes
used in the COSE encryption system. In this section we will discuss
each of the key management methods, what fields need to be specified,
and which algorithms are defined in this document to deal with each
of them.
The names of the key management methods used here are the same as are Recipient algorithms can be defined into a number of different
classes. COSE has the ability to support many classes of recipient
algorithms. In this section, a number of classes are listed and then
a set of algorithms are specified for each of the classes. The names
of the recipient algorithm classes used here are the same as are
defined in [RFC7517]. Other specifications use different terms for defined in [RFC7517]. Other specifications use different terms for
the key management methods or do not support some of the key the recipient algorithm classes or do not support some of our
management methods. recipient algorithm classes.
At the moment we do not have any key management methods that allow
for the use of protected headers. This may be changed in the future
if, for example, the AES-GCM Key wrap method defined in [RFC7518]
were extended to allow for authenticated data. In that event, the
use of the 'protected' field, which is current forbidden below, would
be permitted.
12.1. Direct Encryption 12.1. Direct Encryption
In direct encryption mode, a shared secret between the sender and the The direct encryption class algorithms share a secret between the
recipient is used as the key. When direct encryption mode is used, sender and the recipient that is used either directly or after
it MUST be the only mode used on the message. It is a massive manipulation as the content key. When direct encryption mode is
security leak to have both direct encryption and a different key used, it MUST be the only mode used on the message.
management mode on the same message.
For JOSE, direct encryption key management is the only key management
method allowed for doing MACed messages. In COSE, all of the key
management methods can be used for MACed messages.
The COSE_encrypt structure for the recipient is organized as follows: The COSE_encrypt structure for the recipient is organized as follows:
o The 'protected', 'ciphertext' and 'recipients' fields MUST be o The 'protected' field MUST be a zero length item if it is not used
absent. in the computation of the content key.
o At a minimum, the 'unprotected' field MUST contain the 'alg' o The 'alg' parameter MUST be present.
parameter and SHOULD contain a parameter identifying the shared
secret. o A parameter identifying the shared secret SHOULD be present.
o The 'ciphertext' field MUST be a zero length item.
o The 'recipients' field MUST be absent.
12.1.1. Direct Key 12.1.1. Direct Key
This key management technique is the simplest method, the supplied This recipient algorithm is the simplest, the supplied key is
key is directly used as the key for the next layer down in the directly used as the key for the next layer down in the message.
message. There are no algorithm parameters defined for this key There are no algorithm parameters defined for this algorithm. The
management methods. The algorithm identifier assignment can be found algorithm identifier value is assigned in Table 14.
in Table 15.
When this algorithm is used, the protected field MUST be zero length.
+--------+-------+-------------------+ +--------+-------+-------------------+
| name | value | description | | name | value | description |
+--------+-------+-------------------+ +--------+-------+-------------------+
| direct | -6 | Direct use of CEK | | direct | -6 | Direct use of CEK |
+--------+-------+-------------------+ +--------+-------+-------------------+
Table 15: Direct Key Table 14: Direct Key
12.1.1.1. Security Considerations 12.1.1.1. Security Considerations
The direct key management technique has several potential problems This recipient algorithm has several potential problems that need to
that need to be considered: be considered:
o These keys need to have some method to be regularly updated over o These keys need to have some method to be regularly updated over
time. All of the content encryption algorithms specified in this time. All of the content encryption algorithms specified in this
document have limits on how many times a key can be used without document have limits on how many times a key can be used without
significant loss of security. significant loss of security.
o These keys need to be dedicated to a single algorithm. There have o These keys need to be dedicated to a single algorithm. There have
been a number of attacks developed over time when a single key is been a number of attacks developed over time when a single key is
used for multiple different algorithms. One example of this is used for multiple different algorithms. One example of this is
the use of a single key both for CBC encryption mode and CBC-MAC the use of a single key both for CBC encryption mode and CBC-MAC
authentication mode. authentication mode.
o Breaking one message means all messages are broken. If an o Breaking one message means all messages are broken. If an
adversary succeeds in determining the key for a single message, adversary succeeds in determining the key for a single message,
then the key for all messages is also determined. then the key for all messages is also determined.
12.1.2. Direct Key with KDF 12.1.2. Direct Key with KDF
This key managment takes a common shared secret between the two These recipient algorithms take a common shared secret between the
parties and applies the HKDF function (Section 11.1) using the two parties and applies the HKDF function (Section 11.1) using the
context structure defined in Section 11.2 to transform the shared context structure defined in Section 11.2 to transform the shared
secret into the necessary key. Either the 'salt' parameter of HKDF secret into the necessary key. Either the 'salt' parameter of HKDF
or the partyU 'nonce' parameter of the context structure MUST be or the partyU 'nonce' parameter of the context structure MUST be
present. This parameter can be generated either randomly or present. This parameter can be generated either randomly or
deterministically, the requirement is that it be a unique value for deterministically, the requirement is that it be a unique value for
the key pair in question. the key pair in question.
If the salt/nonce value is generated randomly, then it is suggested If the salt/nonce value is generated randomly, then it is suggested
that the length of the random value be the same length as the hash that the length of the random value be the same length as the hash
function underlying HKDF, i.e 256-bits. While there is no way to function underlying HKDF. While there is no way to guarantee that it
guarantee that it will be unique, there is a high probability that it will be unique, there is a high probability that it will be unique.
will be unique. If the salt/nonce value is generated If the salt/nonce value is generated deterministically, it can be
deterministically, it can be guaranteed to be unique and thus there guaranteed to be unique and thus there is no length requirement.
is no length requirement.
Since with this technique a new key can be generated for every A new IV must be used if the same key is used in more than one
message, the restrictions on IVs can frequently be relaxed. For the message. The IV can be modified in a predictable manner, a random
content encryption algorithms used in this document IVs must be manner or an unpredictable manner. One unpredictable manner that can
unique for a specific key. If the key is altered then the IV can be be used is to use the HKDF function to generate the IV. If HKDF is
re-used. Alternatively, an application can be the IV be generated used for generating the IV, the algorithm identifier is set to "IV-
from the same context as the key is by changing the algorithm GENERATION".
identifier to the string "IV-GENERATION".
The set of algorithms defined in this document can be found in The set of algorithms defined in this document can be found in
Table 16. Table 15.
+--------------------+-------+-------------+------------------------+ +---------------------+-------+-------------+-----------------------+
| name | value | KDF | description | | name | value | KDF | description |
+--------------------+-------+-------------+------------------------+ +---------------------+-------+-------------+-----------------------+
| direct+KDF-SHA-256 | * | HKDF | Shared secret w/ KDF | | direct+HKDF-SHA-256 | * | HKDF | Shared secret w/ HKDF |
| | | SHA-256 | | | | | SHA-256 | and SHA-256 |
| | | | | | | | | |
| direct+KDF-SHA-512 | * | HKDF | Shared secret w/ KDF | | direct+HKDF-SHA-512 | * | HKDF | Shared secret w/ HKDF |
| | | SHA-512 | | | | | SHA-512 | and SHA-512 |
| | | | | | | | | |
| direct+KDF-AES-128 | * | HKDF AES- | Shared secret w/ AES- | | direct+HKDF-AES-128 | * | HKDF AES- | Shared secret w/ AES- |
| | | MAC-128 | MAC 128-bit key | | | | MAC-128 | MAC 128-bit key |
| | | | | | | | | |
| direct+KDF-AES-256 | * | HKDF AES- | Shared secret w/ AES- | | direct+HKDF-AES-256 | * | HKDF AES- | Shared secret w/ AES- |
| | | MAC-256 | MAC 256-bit key | | | | MAC-256 | MAC 256-bit key |
+--------------------+-------+-------------+------------------------+ +---------------------+-------+-------------+-----------------------+
Table 16: Direct Key Table 15: Direct Key
12.1.2.1. Security Considerations 12.1.2.1. Security Considerations
The shared secret need to have some method to be regularly updated The shared secret need to have some method to be regularly updated
over time. The shared secret is forming the basis of trust, although over time. The shared secret is forming the basis of trust, although
not used directly it should still be subject to scheduled rotation. not used directly it should still be subject to scheduled rotation.
12.2. Key Wrapping 12.2. Key Wrapping
In key wrapping mode, the CEK is randomly generated and that key is In key wrapping mode, the CEK is randomly generated and that key is
skipping to change at page 46, line 26 skipping to change at page 45, line 14
o At a minimum, the 'unprotected' field MUST contain the 'alg' o At a minimum, the 'unprotected' field MUST contain the 'alg'
parameter and SHOULD contain a parameter identifying the shared parameter and SHOULD contain a parameter identifying the shared
secret. secret.
12.2.1. AES Key Wrapping 12.2.1. AES Key Wrapping
The AES Key Wrapping algorithm is defined in [RFC3394]. This The AES Key Wrapping algorithm is defined in [RFC3394]. This
algorithm uses an AES key to wrap a value that is a multiple of algorithm uses an AES key to wrap a value that is a multiple of
64-bits, as such it can be used to wrap a key for any of the content 64-bits, as such it can be used to wrap a key for any of the content
encryption algorithms defined in this document. [CREF14] The encryption algorithms defined in this document. The algorithm
algorithm requires a single fixed parameter, the initial value. This requires a single fixed parameter, the initial value. This is fixed
is fixed to the value specified in Section 2.2.3.1 of [RFC3394]. to the value specified in Section 2.2.3.1 of [RFC3394]. There are no
There are no public parameters that vary on a per invocation basis. public parameters that vary on a per invocation basis.
+--------+-------+----------+-----------------------------+ +--------+-------+----------+-----------------------------+
| name | value | key size | description | | name | value | key size | description |
+--------+-------+----------+-----------------------------+ +--------+-------+----------+-----------------------------+
| A128KW | -3 | 128 | AES Key Wrap w/ 128-bit key | | A128KW | -3 | 128 | AES Key Wrap w/ 128-bit key |
| | | | | | | | | |
| A192KW | -4 | 192 | AES Key Wrap w/ 192-bit key | | A192KW | -4 | 192 | AES Key Wrap w/ 192-bit key |
| | | | | | | | | |
| A256KW | -5 | 256 | AES Key Wrap w/ 256-bit key | | A256KW | -5 | 256 | AES Key Wrap w/ 256-bit key |
+--------+-------+----------+-----------------------------+ +--------+-------+----------+-----------------------------+
Table 17: AES Key Wrap Algorithm Values Table 16: AES Key Wrap Algorithm Values
12.2.1.1. Security Considerations for AES-KW 12.2.1.1. Security Considerations for AES-KW
The shared secret need to have some method to be regularly updated The shared secret need to have some method to be regularly updated
over time. The shared secret is forming the basis of trust, although over time. The shared secret is forming the basis of trust, although
not used directly it should still be subject to scheduled rotation. not used directly it should still be subject to scheduled rotation.
12.3. Key Encryption 12.3. Key Encryption
Key Encryption mode is also called key transport mode in some Key Encryption mode is also called key transport mode in some
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of RSAEA-OAEP can be find in Section 7.1 of [RFC3447]. The algorithm of RSAEA-OAEP can be find in Section 7.1 of [RFC3447]. The algorithm
is parameterized using a masking generation function (mgf), a hash is parameterized using a masking generation function (mgf), a hash
function (h) and encoding parameters (P). For the algorithm function (h) and encoding parameters (P). For the algorithm
identifiers defined in this section: identifiers defined in this section:
o mgf is always set to MFG1 from [RFC3447] and uses the same hash o mgf is always set to MFG1 from [RFC3447] and uses the same hash
function as h. function as h.
o P is always set to the empty octet string. o P is always set to the empty octet string.
Table 18 summarizes the rest of the values. Table 17 summarizes the rest of the values.
+----------------------+-------+---------+-----------------------+ +----------------------+-------+---------+-----------------------+
| name | value | hash | description | | name | value | hash | description |
+----------------------+-------+---------+-----------------------+ +----------------------+-------+---------+-----------------------+
| RSAES-OAEP w/SHA-256 | -25 | SHA-256 | RSAES OAEP w/ SHA-256 | | RSAES-OAEP w/SHA-256 | -25 | SHA-256 | RSAES OAEP w/ SHA-256 |
| | | | | | | | | |
| RSAES-OAEP w/SHA-512 | -26 | SHA-512 | RSAES OAEP w/ SHA-512 | | RSAES-OAEP w/SHA-512 | -26 | SHA-512 | RSAES OAEP w/ SHA-512 |
+----------------------+-------+---------+-----------------------+ +----------------------+-------+---------+-----------------------+
Table 18: RSAES-OAEP Algorithm Values Table 17: RSAES-OAEP Algorithm Values
12.3.1.1. Security Considerations for RSAES-OAEP 12.3.1.1. Security Considerations for RSAES-OAEP
A key size of 2048 bits or larger MUST be used with these algorithms. A key size of 2048 bits or larger MUST be used with these algorithms.
This key size corresponds roughly to the same strength as provided by This key size corresponds roughly to the same strength as provided by
a 128-bit symmetric encryption algorithm. a 128-bit symmetric encryption algorithm.
It is highly recommended that checks on the key length be done before It is highly recommended that checks on the key length be done before
starting a decryption operation. One potential denial of service starting a decryption operation. One potential denial of service
operation is to provide encrypted objects using either abnormally operation is to provide encrypted objects using either abnormally
long or oddly sized RSA modulus values. Implementations SHOULD be long or oddly sized RSA modulus values. Implementations SHOULD be
able to encrypt and decrypt with modulus between 2048 and 16K bits in able to encrypt and decrypt with modulus between 2048 and 16K bits in
length.[CREF15] Applications can impose additional restrictions on length. Applications can impose additional restrictions on the
the length of the modulus. length of the modulus.
12.4. Direct Key Agreement 12.4. Direct Key Agreement
When using the 'Direct Key Agreement' key managment method, the two The 'direct key agreement' class of recipient algorithms uses a key
parties use a key agreement method to create a shared secret. A KDF agreement method to create a shared secret. A KDF is then applied to
is then applied to the shared secret to derive a key to be used in the shared secret to derive a key to be used in protecting the data.
protecting the data. This key is normally used as a CEK or MAC key,
but could be used for other purposes if more than two layers are in This key is normally used as a CEK or MAC key, but could be used for
use (see Appendix B). other purposes if more than two layers are in use (see Appendix A).
The most commonly used key agreement algorithm used is Diffie- The most commonly used key agreement algorithm used is Diffie-
Hellman, but other variants exist. Since COSE is designed for a Hellman, but other variants exist. Since COSE is designed for a
store and forward environment rather than an on-line environment, store and forward environment rather than an on-line environment,
many of the DH variants cannot be used as the receiver of the message many of the DH variants cannot be used as the receiver of the message
cannot provide any key material. One side-effect of this is that cannot provide any key material. One side-effect of this is that
perfect forward security is not achievable, a static key will always perfect forward security is not achievable, a static key will always
be used for the receiver of the COSE message. be used for the receiver of the COSE message.
Two variants of DH that are easily supported are: Two variants of DH that are easily supported are:
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and the recipient. The use of static keys allows for recipient to and the recipient. The use of static keys allows for recipient to
get a weak version of data origination for the message. When get a weak version of data origination for the message. When
static-static key agreement is used, then some piece of unique static-static key agreement is used, then some piece of unique
data is require to ensure that a different key is created for each data is require to ensure that a different key is created for each
message message
In this specification, both variants are specified. This has been In this specification, both variants are specified. This has been
done to provide the weak data origination option for use with MAC done to provide the weak data origination option for use with MAC
operations. operations.
When direct key agreement mode is used, it MUST be the only key When direct key agreement mode is used, there MUST be only one
management mode used on the message and there MUST be only one recipient in the message. This method creates the key directly and
recipient. This method creates the key directly and that makes it that makes it difficult to mix with additional recipients. If
difficult to mix with additional recipients. If multiple recipients multiple recipients are needed, then the version with key wrap needs
are needed, then the version with key wrap needs to be used. to be used.
The COSE_encrypt structure for the recipient is organized as follows: The COSE_encrypt structure for the recipient is organized as follows:
o The 'protected' field MUST be absent. o The 'protected' field MUST be absent.
o At a minimum, the 'unprotected' field MUST contain the 'alg' o At a minimum, the 'unprotected' field MUST contain the 'alg'
parameter and SHOULD contain a parameter identifying the parameter and SHOULD contain a parameter identifying the
recipient's asymmetric key. recipient's asymmetric key.
o The 'unprotected' field MUST contain the 'epk' parameter. o The 'unprotected' field MUST contain the 'epk' parameter.
skipping to change at page 49, line 34 skipping to change at page 48, line 18
in [RFC6090]. Two new curves have been defined in in [RFC6090]. Two new curves have been defined in
[I-D.irtf-cfrg-curves]. [I-D.irtf-cfrg-curves].
ECDH is parameterized by the following: ECDH is parameterized by the following:
o Curve Type/Curve: The curve selected controls not only the size of o Curve Type/Curve: The curve selected controls not only the size of
the shared secret, but the mathematics for computing the shared the shared secret, but the mathematics for computing the shared
secret. The curve selected also controls how a point in the curve secret. The curve selected also controls how a point in the curve
is represented and what happens for the identity points on the is represented and what happens for the identity points on the
curve. In this specification we allow for a number of different curve. In this specification we allow for a number of different
curves to be used. The curves are defined in Table 22. curves to be used. The curves are defined in Table 21.
Since the only the math is changed by changing the curve, the Since the only the math is changed by changing the curve, the
curve is not fixed for any of the algorithm identifiers we define, curve is not fixed for any of the algorithm identifiers we define,
instead it is defined by the points used. instead it is defined by the points used.
o Ephemeral-static or static-static: The key agreement process may o Ephemeral-static or static-static: The key agreement process may
be done using either a static or an ephemeral key at the senders be done using either a static or an ephemeral key at the senders
side. When using ephemeral keys, the sender MUST generate a new side. When using ephemeral keys, the sender MUST generate a new
ephemeral key for every key agreement operation. The ephemeral ephemeral key for every key agreement operation. The ephemeral
key is placed in in the 'ephemeral key' parameter and MUST be key is placed in in the 'ephemeral key' parameter and MUST be
present for all algorithm identifiers which use ephemeral keys. present for all algorithm identifiers which use ephemeral keys.
When using static keys, the sender MUST either generate a new When using static keys, the sender MUST either generate a new
random value placed in either in the KDF parameters or the context random value placed in either in the KDF parameters or the context
structure. For the KDF functions used, this means either in the structure. For the KDF functions used, this means either in the
'salt' parameter for HKDF (Table 13) or in in the 'PartyU nonce' 'salt' parameter for HKDF (Table 12) or in in the 'PartyU nonce'
parameter for the context struture (Table 14) MUST be present. parameter for the context struture (Table 13) MUST be present.
(Both may be present if desired.) The value in the parameter MUST (Both may be present if desired.) The value in the parameter MUST
be unique for the key pair being used. It is acceptable to use a be unique for the key pair being used. It is acceptable to use a
global counter which is incremented for every static-static global counter which is incremented for every static-static
operation and use the resulting value. When using static keys, operation and use the resulting value. When using static keys,
the static key needs to be identified to the recipient. The the static key needs to be identified to the recipient. The
static key can be identified either by providing the key ('static static key can be identified either by providing the key ('static
key') or by providing a key identifier for the static key ('static key') or by providing a key identifier for the static key ('static
key id'). Both of these parameters are defined in Table 20 key id'). Both of these parameters are defined in Table 19
o Key derivation algorithm: The result of an ECDH key agreement o Key derivation algorithm: The result of an ECDH key agreement
process does not provide a uniformly random secret, as such it process does not provide a uniformly random secret, as such it
needs to be run through a KDF in order to produce a usable key. needs to be run through a KDF in order to produce a usable key.
Processing the secret through a KDF also allows for the Processing the secret through a KDF also allows for the
introduction of both context material, how the key is going to be introduction of both context material, how the key is going to be
used, and one time material in the even to of a static-static key used, and one time material in the even to of a static-static key
agreement. agreement.
o Key Wrap algorithm: The key wrap algorithm can be 'none' if the o Key Wrap algorithm: The key wrap algorithm can be 'none' if the
result of the KDF is going to be used as the key directly. This result of the KDF is going to be used as the key directly. This
option, along with static-static, should be used if knowledge option, along with static-static, should be used if knowledge
about the sender is desired. If 'none' is used then the content about the sender is desired. If 'none' is used then the content
layer encryption algorithm size is value fed to the context layer encryption algorithm size is value fed to the context
structure. Support is also provided for any of the key wrap structure. Support is also provided for any of the key wrap
algorithms defined in section Section 12.2.1. If one of these algorithms defined in section Section 12.2.1. If one of these
options is used, the input key size to the key wrap algorithm is options is used, the input key size to the key wrap algorithm is
the value fed into the context structure as the key size. the value fed into the context structure as the key size.
The set of algorithms direct ECDH defined in this document are found The set of algorithms direct ECDH defined in this document are found
in Table 19. in Table 18.
+-------------+------+-------+----------------+--------+------------+ +-------------+------+-------+----------------+--------+------------+
| name | valu | KDF | Ephemeral- | Key | descriptio | | name | valu | KDF | Ephemeral- | Key | descriptio |
| | e | | Static | Wrap | n | | | e | | Static | Wrap | n |
+-------------+------+-------+----------------+--------+------------+ +-------------+------+-------+----------------+--------+------------+
| ECDH-ES + | 50 | HKDF | yes | none | ECDH ES w/ | | ECDH-ES + | 50 | HKDF | yes | none | ECDH ES w/ |
| HKDF-256 | | - SHA | | | HKDF - | | HKDF-256 | | - SHA | | | HKDF - |
| | | -256 | | | generate | | | | -256 | | | generate |
| | | | | | key | | | | | | | key |
| | | | | | directly | | | | | | | directly |
skipping to change at page 52, line 6 skipping to change at page 50, line 38
| | | | | | key | | | | | | | key |
| | | | | | | | | | | | | |
| ECDH- | 59 | HKDF | no | A256KW | ECDH SS w/ | | ECDH- | 59 | HKDF | no | A256KW | ECDH SS w/ |
| SS+A256KW | | - SHA | | | Concat KDF | | SS+A256KW | | - SHA | | | Concat KDF |
| | | -256 | | | and AES | | | | -256 | | | and AES |
| | | | | | Key wrap | | | | | | | Key wrap |
| | | | | | w/ 256 bit | | | | | | | w/ 256 bit |
| | | | | | key | | | | | | | key |
+-------------+------+-------+----------------+--------+------------+ +-------------+------+-------+----------------+--------+------------+
Table 19: ECDH Algorithm Values Table 18: ECDH Algorithm Values
+-----------+-------+----------+-----------+------------------------+ +-----------+-------+----------+-----------+------------------------+
| name | label | type | algorithm | description | | name | label | type | algorithm | description |
+-----------+-------+----------+-----------+------------------------+ +-----------+-------+----------+-----------+------------------------+
| ephemeral | -1 | COSE_Key | ECDH-ES | Ephemeral Public key | | ephemeral | -1 | COSE_Key | ECDH-ES | Ephemeral Public key |
| key | | | | for the sender | | key | | | | for the sender |
| | | | | | | | | | | |
| static | -2 | COSE_Key | ECDH-ES | Static Public key for | | static | -2 | COSE_Key | ECDH-ES | Static Public key for |
| key | | | | the sender | | key | | | | the sender |
| | | | | | | | | | | |
| static | -3 | bstr | ECDH-SS | Static Public key | | static | -3 | bstr | ECDH-SS | Static Public key |
| key id | | | | identifier for the | | key id | | | | identifier for the |
| | | | | sender | | | | | | sender |
+-----------+-------+----------+-----------+------------------------+ +-----------+-------+----------+-----------+------------------------+
Table 20: ECDH Algorithm Parameters Table 19: ECDH Algorithm Parameters
12.5. Key Agreement with KDF 12.5. Key Agreement with KDF
Key Agreement with Key Wrapping uses a randomly generated CEK. The Key Agreement with Key Wrapping uses a randomly generated CEK. The
CEK is then encrypted using a Key Wrapping algorithm and a key CEK is then encrypted using a Key Wrapping algorithm and a key
derived from the shared secret computed by the key agreement derived from the shared secret computed by the key agreement
algorithm. algorithm.
The COSE_encrypt structure for the recipient is organized as follows: The COSE_encrypt structure for the recipient is organized as follows:
o The 'protected' field MUST be absent if the key wrap algorithm is o The 'protected' field is fed into the KDF context structure.
an AE algorithm. [CREF16]
o The plain text to be encrypted is the key from next layer down o The plain text to be encrypted is the key from next layer down
(usually the content layer). (usually the content layer).
o At a minimum, the 'unprotected' field MUST contain the 'alg' o The 'alg' parameter MUST be present in the layer.
parameter, a parameter identifying the recipient asymmetric key,
and a parameter with the sender's asymmetric public key.
12.5.1. ECDH
These algorithms are defined in Table 19.
12.6. Password
[CREF17] o A parameter identifying the recipient's key SHOULD be present. A
parameter identifying the senders key SHOULD be present.
12.6.1. PBES2 12.5.1. ECDH
+--------------------+-------+--------------------------------------+ These algorithms are defined in Table 18.
| name | value | description |
+--------------------+-------+--------------------------------------+
| PBES2-HS256+A128KW | * | PBES2 w/ HMAC SHA-256 and AES Key |
| | | wrap w/ 128 bit key |
| | | |
| PBES2-HS384+A192KW | * | PBES2 w/ HMAC SHA-384 and AES Key |
| | | wrap w/ 192 bit key |
| | | |
| PBES2-HS512+A256KW | * | PBES2 w/ HMAC SHA-512 and AES Key |
| | | wrap w/ 256 bit key |
+--------------------+-------+--------------------------------------+
13. Keys 13. Keys
The COSE_Key object defines a way to hold a single key object, it is The COSE_Key object defines a way to hold a single key object, it is
still required that the members of individual key types be defined. still required that the members of individual key types be defined.
This section of the document is where we define an initial set of This section of the document is where we define an initial set of
members for specific key types. members for specific key types.
For each of the key types, we define both public and private members. For each of the key types, we define both public and private members.
The public members are what is transmitted to others for their usage. The public members are what is transmitted to others for their usage.
skipping to change at page 53, line 29 skipping to change at page 52, line 4
13. Keys 13. Keys
The COSE_Key object defines a way to hold a single key object, it is The COSE_Key object defines a way to hold a single key object, it is
still required that the members of individual key types be defined. still required that the members of individual key types be defined.
This section of the document is where we define an initial set of This section of the document is where we define an initial set of
members for specific key types. members for specific key types.
For each of the key types, we define both public and private members. For each of the key types, we define both public and private members.
The public members are what is transmitted to others for their usage. The public members are what is transmitted to others for their usage.
We define private members mainly for the purpose of archival of keys We define private members mainly for the purpose of archival of keys
by individuals. However, there are some circumstances where private by individuals. However, there are some circumstances where private
keys may be distributed by various entities in a protocol. Examples keys may be distributed by various entities in a protocol. Examples
include: Entities which have poor random number generation. include: Entities which have poor random number generation.
Centralized key creation for multi-cast type operations. Protocols Centralized key creation for multi-cast type operations. Protocols
where a shared secret is used as a bearer token for authorization where a shared secret is used as a bearer token for authorization
purposes. purposes.
Keys are identified by the 'kty' member of the COSE_Key object. In Key types are identified by the 'kty' member of the COSE_Key object.
this document we define four values for the member. In this document we define four values for the member.
+-----------+-------+--------------------------------------------+ +-----------+-------+--------------------------------------------+
| name | value | description | | name | value | description |
+-----------+-------+--------------------------------------------+ +-----------+-------+--------------------------------------------+
| EC1 | 1 | Elliptic Curve Keys w/ X Coordinate only | | EC1 | 1 | Elliptic Curve Keys w/ X Coordinate only |
| | | | | | | |
| EC2 | 2 | Elliptic Curve Keys w/ X,Y Coordinate pair | | EC2 | 2 | Elliptic Curve Keys w/ X,Y Coordinate pair |
| | | | | | | |
| RSA | 3 | RSA Keys | | RSA | 3 | RSA Keys |
| | | | | | | |
| Symmetric | 4 | Symmetric Keys | | Symmetric | 4 | Symmetric Keys |
| | | |
| Reserved | 0 | This value is reserved |
+-----------+-------+--------------------------------------------+ +-----------+-------+--------------------------------------------+
Table 21: Key Type Values Table 20: Key Type Values
13.1. Elliptic Curve Keys 13.1. Elliptic Curve Keys
Two different key structures are being defined for Elliptic Curve Two different key structures are being defined for Elliptic Curve
keys. One version uses both an x and a y coordinate, potentially keys. One version uses both an x and a y coordinate, potentially
with point compression. This is the traditional EC point with point compression. This is the traditional EC point
representation that is used in [RFC5480]. The other version uses representation that is used in [RFC5480]. The other version uses
only the x coordinate as the y coordinate is either to be recomputed only the x coordinate as the y coordinate is either to be recomputed
or not needed for the key agreement operation. An example of this is or not needed for the key agreement operation. An example of this is
Curve25519 [I-D.irtf-cfrg-curves]. Curve25519 [I-D.irtf-cfrg-curves].
skipping to change at page 54, line 27 skipping to change at page 53, line 17
+------------+----------+-------+-----------------------------------+ +------------+----------+-------+-----------------------------------+
| P-256 | EC2 | 1 | NIST P-256 also known as | | P-256 | EC2 | 1 | NIST P-256 also known as |
| | | | secp256r1 | | | | | secp256r1 |
| | | | | | | | | |
| P-384 | EC2 | 2 | NIST P-384 also known as | | P-384 | EC2 | 2 | NIST P-384 also known as |
| | | | secp384r1 | | | | | secp384r1 |
| | | | | | | | | |
| P-521 | EC2 | 3 | NIST P-521 also known as | | P-521 | EC2 | 3 | NIST P-521 also known as |
| | | | secp521r1 | | | | | secp521r1 |
| | | | | | | | | |
| Curve25519 | EC1 | 1 | Provide reference | | Curve25519 | EC1 | 1 | Curve 25519 |
| | | | | | | | | |
| Goldilocks | EC1 | 2 | Provide reference | | Curve448 | EC1 | 2 | Curve 448 |
+------------+----------+-------+-----------------------------------+ +------------+----------+-------+-----------------------------------+
Table 22: EC Curves Table 21: EC Curves
13.1.1. Single Coordinate Curves 13.1.1. Single Coordinate Curves
NOTE: This section represents at risk work depending on the ability One class of Elliptic Curve mathematics allows for a point to be
to get good references for Curve25519 and Goldilocks. completely defined using the curve and the x coordinate of the point
on the curve. The two curves that are initially setup to use is
New versions of ECC have been targeted at variants where only a point format are Curve 25519 and Curve 448 which are defined in
single value of the EC Point need to be transmitted. This work is [I-D.irtf-cfrg-curves].
currently going on in the IRTF CFRG group.
For EC keys with both coordinates, the 'kty' member is set to 1 For EC keys with only the x coordinates, the 'kty' member is set to 1
(EC1). The members that are defined for this key type are: (EC1). The key parameters defined in this section are summarized in
Table 22. The members that are defined for this key type are:
crv contains an identifier of the curve to be used with the key. crv contains an identifier of the curve to be used with the key.
[CREF18] The curves defined in this document for this key type can [CREF10] The curves defined in this document for this key type can
be found in Table 22. Other curves may be registered in the be found in Table 21. Other curves may be registered in the
future and private curves can be used as well. future and private curves can be used as well.
x contains the x coordinate for the EC point. The octet string x contains the x coordinate for the EC point. The octet string
represents a little-endian encoding of x. represents a little-endian encoding of x.
d contains the private key. d contains the private key.
For public keys, it is REQUIRED that 'crv' and 'x' be present in the For public keys, it is REQUIRED that 'crv' and 'x' be present in the
structure. For private keys, it is REQUIRED that 'crv' and 'd' be structure. For private keys, it is REQUIRED that 'crv' and 'd' be
present in the structure. It is RECOMMENDED that 'x' also be present in the structure. For private keys, it is RECOMMENDED that
present, but it can be recomputed from the required elements and 'x' also be present, but it can be recomputed from the required
omitting it saves on space. elements and omitting it saves on space.
+------+-------+-------+--------+-----------------------------------+ +------+-------+-------+--------+-----------------------------------+
| name | key | value | type | description | | name | key | value | type | description |
| | type | | | | | | type | | | |
+------+-------+-------+--------+-----------------------------------+ +------+-------+-------+--------+-----------------------------------+
| crv | 1 | -1 | int / | EC Curve identifier - Taken from | | crv | 1 | -1 | int / | EC Curve identifier - Taken from |
| | | | tstr | the COSE General Registry | | | | | tstr | the COSE General Registry |
| | | | | | | | | | | |
| x | 1 | -2 | bstr | X Coordinate | | x | 1 | -2 | bstr | X Coordinate |
| | | | | | | | | | | |
| d | 1 | -4 | bstr | Private key | | d | 1 | -4 | bstr | Private key |
+------+-------+-------+--------+-----------------------------------+ +------+-------+-------+--------+-----------------------------------+
Table 23: EC Key Parameters Table 22: EC Key Parameters
13.1.2. Double Coordinate Curves 13.1.2. Double Coordinate Curves
The traditional way of sending EC curves has been to send either both The traditional way of sending EC curves has been to send either both
the x and y coordinates, or the x coordinate and a sign bit for the y the x and y coordinates, or the x coordinate and a sign bit for the y
coordinate. The latter encoding has not been recommend in the IETF coordinate. The latter encoding has not been recommend in the IETF
due to potential IPR issues with Certicom. However, for operations due to potential IPR issues with Certicom. However, for operations
in constrained environments, the ability to shrink a message by not in constrained environments, the ability to shrink a message by not
sending the y coordinate is potentially useful. sending the y coordinate is potentially useful.
For EC keys with both coordinates, the 'kty' member is set to 2 For EC keys with both coordinates, the 'kty' member is set to 2
(EC2). The members that are defined for this key type are: (EC2). The key parameters defined in this section are summarized in
Table 23. The members that are defined for this key type are:
crv contains an identifier of the curve to be used with the key. crv contains an identifier of the curve to be used with the key.
The curves defined in this document for this key type can be found The curves defined in this document for this key type can be found
in Table 22. Other curves may be registered in the future and in Table 21. Other curves may be registered in the future and
private curves can be used as well. private curves can be used as well.
x contains the x coordinate for the EC point. The integer is x contains the x coordinate for the EC point. The integer is
converted to an octet string as defined in [SEC1]. Zero octets converted to an octet string as defined in [SEC1]. Zero octets
MUST NOT be removed from the front of the octet string. [CREF19] MUST NOT be removed from the front of the octet string. [CREF11]
y contains either the sign bit or the value of y coordinate for the y contains either the sign bit or the value of y coordinate for the
EC point. For the value, the integer is converted to an octet EC point. For the value, the integer is converted to an octet
string as defined in [SEC1]. Zero octets MUST NOT be removed from string as defined in [SEC1]. Zero octets MUST NOT be removed from
the front of the octet string. For the sign bit, the value is the front of the octet string. For the sign bit, the value is
true if the value of y is positive. true if the value of y is positive.
d contains the private key. d contains the private key.
For public keys, it is REQUIRED that 'crv', 'x' and 'y' be present in For public keys, it is REQUIRED that 'crv', 'x' and 'y' be present in
the structure. For private keys, it is REQUIRED that 'crv' and 'd' the structure. For private keys, it is REQUIRED that 'crv' and 'd'
be present in the structure. It is RECOMMENDED that 'x' and 'y' also be present in the structure. For private keys, it is RECOMMENDED
be present, but they can be recomputed from the required elements and that 'x' and 'y' also be present, but they can be recomputed from the
omitting them saves on space. required elements and omitting them saves on space.
+------+-------+-------+---------+----------------------------------+ +------+-------+-------+---------+----------------------------------+
| name | key | value | type | description | | name | key | value | type | description |
| | type | | | | | | type | | | |
+------+-------+-------+---------+----------------------------------+ +------+-------+-------+---------+----------------------------------+
| crv | 2 | -1 | int / | EC Curve identifier - Taken from | | crv | 2 | -1 | int / | EC Curve identifier - Taken from |
| | | | tstr | the COSE General Registry | | | | | tstr | the COSE General Registry |
| | | | | | | | | | | |
| x | 2 | -2 | bstr | X Coordinate | | x | 2 | -2 | bstr | X Coordinate |
| | | | | | | | | | | |
| y | 2 | -3 | bstr / | Y Coordinate | | y | 2 | -3 | bstr / | Y Coordinate |
| | | | bool | | | | | | bool | |
| | | | | | | | | | | |
| d | 2 | -4 | bstr | Private key | | d | 2 | -4 | bstr | Private key |
+------+-------+-------+---------+----------------------------------+ +------+-------+-------+---------+----------------------------------+
Table 24: EC Key Parameters Table 23: EC Key Parameters
13.2. RSA Keys 13.2. RSA Keys
This document defines a key structure for both the public and private This document defines a key structure for both the public and private
halves of RSA keys. Together, an RSA public key and an RSA private halves of RSA keys. Together, an RSA public key and an RSA private
key form an RSA key pair. [CREF20] key form an RSA key pair. [CREF12]
The document also provides support for the so-called "multi-prime" The document also provides support for the so-called "multi-prime"
RSA where the modulus may have more than two prime factors. The RSA where the modulus may have more than two prime factors. The
benefit of multi-prime RSA is lower computational cost for the benefit of multi-prime RSA is lower computational cost for the
decryption and signature primitives. For a discussion on how multi- decryption and signature primitives. For a discussion on how multi-
prime affects the security of RSA crypto-systems, the reader is prime affects the security of RSA crypto-systems, the reader is
referred to [MultiPrimeRSA]. referred to [MultiPrimeRSA].
This document follows the naming convention of [RFC3447] for the This document follows the naming convention of [RFC3447] for the
naming of the fields of an RSA public or private key. The table naming of the fields of an RSA public or private key. The table
Table 25 provides a summary of the label values and the types Table 24 provides a summary of the label values and the types
associated with each of those labels. The requirements for fields associated with each of those labels. The requirements for fields
for RSA keys are as follows: for RSA keys are as follows:
o For all keys, 'kty' MUST be present and MUST have a value of 3. o For all keys, 'kty' MUST be present and MUST have a value of 3.
o For public keys, the fields 'n' and 'e' MUST be present. All o For public keys, the fields 'n' and 'e' MUST be present. All
other fields defined in Table 25 MUST be absent. other fields defined in Table 24 MUST be absent.
o For private keys with two primes, the fields 'other', 'r_i', 'd_i' o For private keys with two primes, the fields 'other', 'r_i', 'd_i'
and 't_i' MUST be absent, all other fields MUST be present. and 't_i' MUST be absent, all other fields MUST be present.
o For private keys with more than two primes, all fields MUST be o For private keys with more than two primes, all fields MUST be
present. For the third to nth primes, each of the primes is present. For the third to nth primes, each of the primes is
represented as a map containing the fields 'r_i', 'd_i' and 't_i'. represented as a map containing the fields 'r_i', 'd_i' and 't_i'.
The field 'other' is an array of those maps. The field 'other' is an array of those maps.
+-------+----------+-------+-------+--------------------------------+ +-------+----------+-------+-------+--------------------------------+
skipping to change at page 57, line 43 skipping to change at page 56, line 40
| | | | | | | | | | | |
| r_i | 3 | -10 | bstr | i-th factor, Prime Factor | | r_i | 3 | -10 | bstr | i-th factor, Prime Factor |
| | | | | | | | | | | |
| d_i | 3 | -11 | bstr | i-th factor, Factor CRT | | d_i | 3 | -11 | bstr | i-th factor, Factor CRT |
| | | | | Exponent | | | | | | Exponent |
| | | | | | | | | | | |
| t_i | 3 | -12 | bstr | i-th factor, Factor CRT | | t_i | 3 | -12 | bstr | i-th factor, Factor CRT |
| | | | | Coefficient | | | | | | Coefficient |
+-------+----------+-------+-------+--------------------------------+ +-------+----------+-------+-------+--------------------------------+
Table 25: RSA Key Parameters Table 24: RSA Key Parameters
13.3. Symmetric Keys 13.3. Symmetric Keys
Occasionally it is required that a symmetric key be transported Occasionally it is required that a symmetric key be transported
between entities. This key structure allows for that to happen. between entities. This key structure allows for that to happen.
For symmetric keys, the 'kty' member is set to 3 (Symmetric). The For symmetric keys, the 'kty' member is set to 3 (Symmetric). The
member that is defined for this key type is: member that is defined for this key type is:
k contains the value of the key. k contains the value of the key.
skipping to change at page 58, line 18 skipping to change at page 57, line 16
be taken that it is never transmitted accidentally. For public keys, be taken that it is never transmitted accidentally. For public keys,
there are no required fields. For private keys, it is REQUIRED that there are no required fields. For private keys, it is REQUIRED that
'k' be present in the structure. 'k' be present in the structure.
+------+----------+-------+------+-------------+ +------+----------+-------+------+-------------+
| name | key type | value | type | description | | name | key type | value | type | description |
+------+----------+-------+------+-------------+ +------+----------+-------+------+-------------+
| k | 4 | -1 | bstr | Key Value | | k | 4 | -1 | bstr | Key Value |
+------+----------+-------+------+-------------+ +------+----------+-------+------+-------------+
Table 26: Symmetric Key Parameters Table 25: Symmetric Key Parameters
14. CBOR Encoder Restrictions 14. CBOR Encoder Restrictions
There as been an attempt to limit the number of places where the There as been an attempt to limit the number of places where the
document needs to impose restrictions on how the CBOR Encoder needs document needs to impose restrictions on how the CBOR Encoder needs
to work. We have managed to narrow it down to the following to work. We have managed to narrow it down to the following
restrictions: restrictions:
o The restriction applies to the encoding the Sig_structure, the o The restriction applies to the encoding the Sig_structure, the
Enc_structure, and the MAC_structure. Enc_structure, and the MAC_structure.
skipping to change at page 59, line 5 skipping to change at page 58, line 5
It is requested that IANA assign a new tag from the "Concise Binary It is requested that IANA assign a new tag from the "Concise Binary
Object Representation (CBOR) Tags" registry. It is requested that Object Representation (CBOR) Tags" registry. It is requested that
the tag be assigned in the 0 to 23 value range. the tag be assigned in the 0 to 23 value range.
Tag Value: TBD1 Tag Value: TBD1
Data Item: COSE_Msg Data Item: COSE_Msg
Semantics: COSE security message. Semantics: COSE security message.
15.2. COSE Object Labels Registry 15.2. COSE Header Parameter Registry
It is requested that IANA create a new registry entitled "COSE Object
Labels Registry". [CREF21]
This table is initially populated by the table in Table 1.
15.3. COSE Header Parameter Registry
It is requested that IANA create a new registry entitled "COSE Header It is requested that IANA create a new registry entitled "COSE Header
Parameters". Parameters".
The columns of the registry are: The columns of the registry are:
name The name is present to make it easier to refer to and discuss name The name is present to make it easier to refer to and discuss
the registration entry. The value is not used in the protocol. the registration entry. The value is not used in the protocol.
Names are to be unique in the table. Names are to be unique in the table.
skipping to change at page 59, line 46 skipping to change at page 58, line 39
label. label.
value registry This contains a pointer to the registry used to value registry This contains a pointer to the registry used to
contain values where the set is limited. contain values where the set is limited.
description This contains a brief description of the header field. description This contains a brief description of the header field.
specification This contains a pointer to the specification defining specification This contains a pointer to the specification defining
the header field (where public). the header field (where public).
The initial contents of the registry can be found in Table 2. The The initial contents of the registry can be found in Table 1. The
specification column for all rows in that table should be this specification column for all rows in that table should be this
document. document.
Additionally, the label of 0 is to be marked as 'Reserved'. Additionally, the label of 0 is to be marked as 'Reserved'.
15.4. COSE Header Algorithm Label Table 15.3. COSE Header Algorithm Label Table
It is requested that IANA create a new registry entitled "COSE Header It is requested that IANA create a new registry entitled "COSE Header
Algorithm Labels". Algorithm Labels".
The columns of the registry are: The columns of the registry are:
name The name is present to make it easier to refer to and discuss name The name is present to make it easier to refer to and discuss
the registration entry. The value is not used in the protocol. the registration entry. The value is not used in the protocol.
algorithm The algorithm(s) that this registry entry is used for. algorithm The algorithm(s) that this registry entry is used for.
skipping to change at page 60, line 34 skipping to change at page 59, line 27
label. label.
value registry This contains a pointer to the registry used to value registry This contains a pointer to the registry used to
contain values where the set is limited. contain values where the set is limited.
description This contains a brief description of the header field. description This contains a brief description of the header field.
specification This contains a pointer to the specification defining specification This contains a pointer to the specification defining
the header field (where public). the header field (where public).
The initial contents of the registry can be found in: Table 13, The initial contents of the registry can be found in: Table 12,
Table 14, Table 20, and Appendix D. The specification column for all Table 13, Table 19. The specification column for all rows in that
rows in that table should be this document. table should be this document.
15.5. COSE Algorithm Registry 15.4. COSE Algorithm Registry
It is requested that IANA create a new registry entitled "COSE It is requested that IANA create a new registry entitled "COSE
Algorithm Registry". Algorithm Registry".
The columns of the registry are: The columns of the registry are:
value The value to be used to identify this algorithm. Algorithm value The value to be used to identify this algorithm. Algorithm
values MUST be unique. The value can be a positive integer, a values MUST be unique. The value can be a positive integer, a
negative integer or a string. Integer values between 0 and 255 negative integer or a string. Integer values between 0 and 255
and strings of length 1 are designated as Standards Track Document and strings of length 1 are designated as Standards Track Document
skipping to change at page 61, line 14 skipping to change at page 60, line 9
range -1 to -65536 are delegated to the "COSE Header Algorithm range -1 to -65536 are delegated to the "COSE Header Algorithm
Label" registry. Integer values beyond -65536 are marked as Label" registry. Integer values beyond -65536 are marked as
private use. private use.
description A short description of the algorithm. description A short description of the algorithm.
specification A document where the algorithm is defined (if publicly specification A document where the algorithm is defined (if publicly
available). available).
The initial contents of the registry can be found in the following: The initial contents of the registry can be found in the following:
Table 10, Table 9, Table 5, Table 7, Table 15, Table 17, Table 18. Table 9, Table 8, Table 10, Table 4, Table 5, Table 6, Table 7,
The specification column for all rows in that table should be this Table 14, Table 15, Table 16, Table 17, Table 18. The specification
document. column for all rows in that table should be this document.
15.6. COSE Key Common Parameter Registry 15.5. COSE Key Common Parameter Registry
It is requested that IANA create a new registry entitled "COSE Key It is requested that IANA create a new registry entitled "COSE Key
Common Parameter" Registry. Common Parameter" Registry.
The columns of the registry are: The columns of the registry are:
name This is a descriptive name that enables easier reference to the name This is a descriptive name that enables easier reference to the
item. It is not used in the encoding. item. It is not used in the encoding.
label The value to be used to identify this algorithm. Key map label The value to be used to identify this algorithm. Key map
skipping to change at page 62, line 9 skipping to change at page 61, line 5
description This field contains a brief description for the field description This field contains a brief description for the field
specification This contains a pointer to the public specification specification This contains a pointer to the public specification
for the field if one exists for the field if one exists
This registry will be initially populated by the values in This registry will be initially populated by the values in
Section 7.1. The specification column for all of these entries will Section 7.1. The specification column for all of these entries will
be this document. be this document.
15.7. COSE Key Type Parameter Registry 15.6. COSE Key Type Parameter Registry
It is requested that IANA create a new registry "COSE Key Type It is requested that IANA create a new registry "COSE Key Type
Parameters". Parameters".
The columns of the table are: The columns of the table are:
key type This field contains a descriptive string of a key type. key type This field contains a descriptive string of a key type.
This should be a value that is in the COSE General Values table This should be a value that is in the COSE General Values table
and is placed in the 'kty' field of a COSE Key structure. and is placed in the 'kty' field of a COSE Key structure.
skipping to change at page 62, line 34 skipping to change at page 61, line 30
range of values is from -256 to -1. Labels are expected to be range of values is from -256 to -1. Labels are expected to be
reused for different keys. reused for different keys.
CBOR type This field contains the CBOR type for the field CBOR type This field contains the CBOR type for the field
description This field contains a brief description for the field description This field contains a brief description for the field
specification This contains a pointer to the public specification specification This contains a pointer to the public specification
for the field if one exists for the field if one exists
This registry will be initially populated by the values in Table 23, This registry will be initially populated by the values in Table 22,
Table 24, Table 25, and Table 26. The specification column for all Table 23, Table 24, and Table 25. The specification column for all
of these entries will be this document. of these entries will be this document.
15.7. COSE Elliptic Curve Registry
It is requested that IANA create a new registry "COSE Elliptic Curve
Parameters".
The columns of the table are:
name This is a descriptive name that enables easier reference to the
item. It is not used in the encoding.
value This is the value used to identify the curve. These values
MUST be unique. The integer values from -256 to 255 are
designated as Standards Track Document Required. The the integer
values from 256 to 65535 and -65536 to -257 are designated as
Specification Required. Integer values over 65535 are designated
as first come first serve. Integer values less than -65536 are
marked as private use.
key type This designates the key type(s) that can be used with this
curve.
description This field contains a brief description of the curve.
specification This contains a pointer to the public specification
for the curve if one exists.
This registry will be initially populated by the values in Table 20.
The specification column for all of these entries will be this
document.
15.8. Media Type Registration 15.8. Media Type Registration
15.8.1. COSE Security Message 15.8.1. COSE Security Message
This section registers the "application/cose" and "application/ This section registers the "application/cose" and "application/
cose+cbor" media types in the "Media Types" registry. [CREF22] These cose+cbor" media types in the "Media Types" registry. [CREF13] These
media types are used to indicate that the content is a COSE_MSG. media types are used to indicate that the content is a COSE_MSG.
Type name: application Type name: application
Subtype name: cose Subtype name: cose
Required parameters: N/A Required parameters: N/A
Optional parameters: N/A Optional parameters: N/A
Encoding considerations: binary Encoding considerations: binary
Security considerations: See the Security Considerations section Security considerations: See the Security Considerations section
of RFC TBD. of RFC TBD.
Interoperability considerations: N/A Interoperability considerations: N/A
Published specification: RFC TBD Published specification: RFC TBD
Applications that use this media type: To be identified Applications that use this media type: To be identified
skipping to change at page 67, line 47 skipping to change at page 67, line 28
Signature Scheme with Partial Message Recover", February Signature Scheme with Partial Message Recover", February
2000. 2000.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, February Hashing for Message Authentication", RFC 2104, February
1997. 1997.
[RFC2633] Ramsdell, B., "S/MIME Version 3 Message Specification", [RFC2633] Ramsdell, B., "S/MIME Version 3 Message Specification",
RFC 2633, June 1999. RFC 2633, June 1999.
[RFC2898] Kaliski, B., "PKCS #5: Password-Based Cryptography
Specification Version 2.0", RFC 2898, DOI 10.17487/
RFC2898, September 2000,
<http://www.rfc-editor.org/info/rfc2898>.
[RFC3394] Schaad, J. and R. Housley, "Advanced Encryption Standard [RFC3394] Schaad, J. and R. Housley, "Advanced Encryption Standard
(AES) Key Wrap Algorithm", RFC 3394, September 2002. (AES) Key Wrap Algorithm", RFC 3394, September 2002.
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography [RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications Standards (PKCS) #1: RSA Cryptography Specifications
Version 2.1", RFC 3447, February 2003. Version 2.1", RFC 3447, February 2003.
[RFC3610] Whiting, D., Housley, R., and N. Ferguson, "Counter with [RFC3610] Whiting, D., Housley, R., and N. Ferguson, "Counter with
CBC-MAC (CCM)", RFC 3610, September 2003. CBC-MAC (CCM)", RFC 3610, September 2003.
skipping to change at page 69, line 34 skipping to change at page 69, line 23
[SEC1] Standards for Efficient Cryptography Group, "SEC 1: [SEC1] Standards for Efficient Cryptography Group, "SEC 1:
Elliptic Curve Cryptography", May 2009. Elliptic Curve Cryptography", May 2009.
[SP800-56A] [SP800-56A]
Barker, E., Chen, L., Roginsky, A., and M. Smid, "NIST Barker, E., Chen, L., Roginsky, A., and M. Smid, "NIST
Special Publication 800-56A: Recommendation for Pair-Wise Special Publication 800-56A: Recommendation for Pair-Wise
Key Establishment Schemes Using Discrete Logarithm Key Establishment Schemes Using Discrete Logarithm
Cryptography", May 2013. Cryptography", May 2013.
Appendix A. AEAD and AE algorithms Appendix A. Three Levels of Recipient Information
The set of encryption algorithms that can be used with this
specification is restricted to authenticated encryption (AE) and
authenticated encryption with additional data (AEAD) algorithms.
This means that there is a strong check that the data decrypted by
the recipient is the same as what was encrypted by the sender.
Encryption modes such as counter have no check on this at all. The
CBC encryption mode had a weak check that the data is correct, given
a random key and random data, the CBC padding check will pass one out
of 256 times. There have been several times that a normal encryption
mode has been combined with an integrity check to provide a content
encryption mode that does provide the necessary authentication. AES-
GCM [AES-GCM], AES-CCM [RFC3610], AES-CBC-HMAC
[I-D.mcgrew-aead-aes-cbc-hmac-sha2] are examples of these composite
modes.
PKCS v1.5 RSA key transport does not qualify as an AE algorithm.
There are only three bytes in the encoding that can be checked as
having decrypted correctly, the rest of the content can only be
probabilistically checked as having decrypted correctly. For this
reason, PKCS v1.5 RSA key transport MUST NOT be used with this
specification. RSA-OAEP was designed to have the necessary checks
that that content correctly decrypted and does qualify as an AE
algorithm.
When dealing with authenticated encryption algorithms, there is
always some type of value that needs to be checked to see if the
authentication level has passed. This authentication value may be:
o A separately generated tag computed by both the encrypter and
decrypter and then compared by the decryptor. This tag value may
be either placed at the end of the cipher text (the decision we
made) or kept separately (the decision made by the JOSE working
group). This is the approach followed by AES-GCM [AES-GCM] and
AES-CCM [RFC3610].
o A fixed value that is part of the encoded plain text. This is the
approach followed by the AES key wrap algorithm [RFC3394].
o A computed value is included as part of the encoded plain text.
The computed value is then checked by the decryptor using the same
computation path. This is the approach followed by RSAES-OAEP
[RFC3447].
Appendix B. Three Levels of Recipient Information
All of the currently defined Key Management methods only use two All of the currently defined recipient algorithms classes only use
levels of the COSE_Encrypt structure. The first level is the message two levels of the COSE_Encrypt structure. The first level is the
content and the second level is the content key encryption. However, message content and the second level is the content key encryption.
if one uses a key management technique such as RSA-KEM (see However, if one uses a recipient algorithm such as RSA-KEM (see
Appendix A of RSA-KEM [RFC5990], then it make sense to have three Appendix A of RSA-KEM [RFC5990], then it make sense to have three
levels of the COSE_Encrypt structure. levels of the COSE_Encrypt structure.
These levels would be: These levels would be:
o Level 0: The content encryption level. This level contains the o Level 0: The content encryption level. This level contains the
payload of the message. payload of the message.
o Level 1: The encryption of the CEK by a KEK. o Level 1: The encryption of the CEK by a KEK.
o Level 2: The encryption of a long random secret using an RSA key o Level 2: The encryption of a long random secret using an RSA key
and a key derivation function to convert that secret into the KEK. and a key derivation function to convert that secret into the KEK.
This is an example of what a triple layer message would look like. This is an example of what a triple layer message would look like.
The message has the following layers: The message has the following layers:
o Level 0: Has a content encrypted with AES-GCM using a 128-bit key. o Level 0: Has a content encrypted with AES-GCM using a 128-bit key.
o Level 1: Uses the AES Key wrap algorithm with a 128-bit key. o Level 1: Uses the AES Key wrap algorithm with a 128-bit key.
o Level 3: Uses ECDH Ephemeral-Static direct to generate the level 1 o Level 2: Uses ECDH Ephemeral-Static direct to generate the level 1
key. key.
In effect this example is a decomposed version of using the ECDH- In effect this example is a decomposed version of using the ECDH-
ES+A128KW algorithm. ES+A128KW algorithm.
Size of binary file is 220 bytes Size of binary file is 214 bytes
{ [
1: 2, 2,
2: h'a10101', h'a10101',
3: { {
5: h'02d1f7e6f26c43d4868d87ce' 5: h'02d1f7e6f26c43d4868d87ce'
}, },
4: h'64f84d913ba60a76070a9a48f26e97e863e285295a44320878caceb076 h'64f84d913ba60a76070a9a48f26e97e863e285295a44320878caceb0763a3
3a334806857c67', 34806857c67',
9: [ [
{ [
3: { h'',
{
1: -3 1: -3
}, },
4: h'5a15dbf5b282ecb31a6074ee3815c252405dd7583e078188', h'5a15dbf5b282ecb31a6074ee3815c252405dd7583e078188',
9: [ [
{ [
3: { h'',
{
1: 50, 1: 50,
4: h'6d65726961646f632e6272616e64796275636b406275636b 4: h'6d65726961646f632e6272616e64796275636b406275636b
6c616e642e6578616d706c65', 6c616e642e6578616d706c65',
-1: { -1: {
1: 2, 1: 2,
-1: 1, -1: 1,
-2: h'b2add44368ea6d641f9ca9af308b4079aeb519f11e9b8 -2: h'b2add44368ea6d641f9ca9af308b4079aeb519f11e9b8
a55a600b21233e86e68', a55a600b21233e86e68',
-3: h'1a2cf118b9ee6895c8f415b686d4ca1cef362d4a7630a -3: h'1a2cf118b9ee6895c8f415b686d4ca1cef362d4a7630a
31ef6019c0c56d33de0' 31ef6019c0c56d33de0'
} }
} },
} h''
]
] ]
} ]
] ]
} ]
Appendix C. Examples Appendix B. Examples
The examples can be found at https://github.com/cose-wg/Examples. I The examples can be found at https://github.com/cose-wg/Examples.
am currently still in the process of getting the examples up there The file names in each section correspond the the same file names in
along with some control information for people to be able to check the repository. I am currently still in the process of getting the
and reproduce the examples. examples up there along with some control information for people to
be able to check and reproduce the examples.
Examples may have some features that are in questions but not yet Examples may have some features that are in questions but not yet
incorporated in the document. incorporated in the document.
To make it easier to read, the examples are presented using the To make it easier to read, the examples are presented using the
CBOR's diagnostic notation rather than a binary dump. [CREF23] Using CBOR's diagnostic notation rather than a binary dump. A ruby based
the Ruby based CBOR diagnostic tools at ????, the diagnostic notation tool exists to convert between a number of formats. This tool can be
can be converted into binary files using the following command line: installed with the command line:
(install command is?...)
gem install cbor-diag
The diagnostic notation can be converted into binary files using the
following command line:
diag2cbor < inputfile > outputfile diag2cbor < inputfile > outputfile
The examples can be extracted from the XML version of this docuent The examples can be extracted from the XML version of this docuent
via an XPath expression as all of the artwork is tagged with the via an XPath expression as all of the artwork is tagged with the
attribute type='CBORdiag'. attribute type='CBORdiag'.
C.1. Examples of MAC messages B.1. Examples of MAC messages
C.1.1. Shared Secret Direct MAC B.1.1. Shared Secret Direct MAC
This example users the following: This example users the following:
o MAC: AES-CMAC, 256-bit key, trucated to 64 bits o MAC: AES-CMAC, 256-bit key, trucated to 64 bits
o Key management: direct shared secret o Recipient class: direct shared secret
o File name: Mac-04 o File name: Mac-04
Size of binary file is 74 bytes Size of binary file is 71 bytes
{
1: 3, [
2: h'a1016f4145532d434d41432d3235362f3634', 3,
4: h'546869732069732074686520636f6e74656e742e', h'a1016f4145532d434d41432d3235362f3634',
10: h'd9afa663dd740848', {
9: [ },
{ h'546869732069732074686520636f6e74656e742e',
3: { h'd9afa663dd740848',
[
[
h'',
{
1: -6, 1: -6,
4: h'6f75722d736563726574' 4: h'6f75722d736563726574'
} },
} h''
]
] ]
} ]
C.1.2. ECDH Direct MAC B.1.2. ECDH Direct MAC
This example uses the following: This example uses the following:
o MAC: HMAC w/SHA-256, 256-bit key [CREF24] o MAC: HMAC w/SHA-256, 256-bit key
o Key management: ECDH key agreement, two static keys, HKDF w/ o Recipient class: ECDH key agreement, two static keys, HKDF w/
context structure context structure
Size of binary file is 218 bytes Size of binary file is 215 bytes
{ [
1: 3, 3,
2: h'a10104', h'a10104',
4: h'546869732069732074686520636f6e74656e742e', {
10: h'2ba937ca03d76c3dbad30cfcbaeef586f9c0f9ba616ad67e9205d3857 },
6ad9930', h'546869732069732074686520636f6e74656e742e',
9: [ h'2ba937ca03d76c3dbad30cfcbaeef586f9c0f9ba616ad67e9205d38576ad9
{ 930',
3: { [
[
h'',
{
1: 52, 1: 52,
4: h'6d65726961646f632e6272616e64796275636b406275636b6c61 4: h'6d65726961646f632e6272616e64796275636b406275636b6c61
6e642e6578616d706c65', 6e642e6578616d706c65',
-3: h'706572656772696e2e746f6f6b407475636b626f726f7567682 -3: h'706572656772696e2e746f6f6b407475636b626f726f7567682
e6578616d706c65', e6578616d706c65',
"apu": h'4d8553e7e74f3c6a3a9dd3ef286a8195cbf8a23d19558ccf "apu": h'4d8553e7e74f3c6a3a9dd3ef286a8195cbf8a23d19558ccf
ec7d34b824f42d92bd06bd2c7f0271f0214e141fb779ae2856abf585a58368b01 ec7d34b824f42d92bd06bd2c7f0271f0214e141fb779ae2856abf585a58368b01
7e7f2a9e5ce4db5' 7e7f2a9e5ce4db5'
} },
} h''
]
] ]
} ]
C.1.3. Wrapped MAC B.1.3. Wrapped MAC
This example uses the following: This example uses the following:
o MAC: AES-MAC, 128-bit key, truncated to 64 bits o MAC: AES-MAC, 128-bit key, truncated to 64 bits
o Key management: AES keywrap w/ a pre-shared 256-bit key o Recipient class: AES keywrap w/ a pre-shared 256-bit key
Size of binary file is 127 bytes Size of binary file is 122 bytes
{ [
1: 3, 3,
2: h'a1016e4145532d3132382d4d41432d3634', h'a1016e4145532d3132382d4d41432d3634',
4: h'546869732069732074686520636f6e74656e742e', {
10: h'6d1fa77b2dd9146a', },
9: [ h'546869732069732074686520636f6e74656e742e',
{ h'6d1fa77b2dd9146a',
3: { [
[
h'',
{
1: -5, 1: -5,
4: h'30313863306165352d346439622d343731622d626664362d6565 4: h'30313863306165352d346439622d343731622d626664362d6565
66333134626337303337' 66333134626337303337'
}, },
4: h'711ab0dc2fc4585dce27effa6781c8093eba906f227b6eb0' h'711ab0dc2fc4585dce27effa6781c8093eba906f227b6eb0'
} ]
] ]
} ]
C.1.4. Multi-recipient MAC message B.1.4. Multi-recipient MAC message
This example uses the following: This example uses the following:
o MAC: HMAC w/ SHA-256, 128-bit key o MAC: HMAC w/ SHA-256, 128-bit key
o Key management: Uses three different methods o Recipient class: Uses three different methods
1. ECDH Ephemeral-Static, Curve P-521, AES-Key Wrap w/ 128-bit 1. ECDH Ephemeral-Static, Curve P-521, AES-Key Wrap w/ 128-bit
key key
2. RSA-OAEP w/ SHA-256 2. RSA-OAEP w/ SHA-256
3. AES-Key Wrap w/ 256-bit key 3. AES-Key Wrap w/ 256-bit key
Size of binary file is 677 bytes Size of binary file is 670 bytes
{ [
1: 3, 3,
2: h'a10104', h'a10104',
4: h'546869732069732074686520636f6e74656e742e', {
10: h'7aaa6e74546873061f0a7de21ff0c0658d401a68da738dd8937486519 },
83ce1d0', h'546869732069732074686520636f6e74656e742e',
9: [ h'7aaa6e74546873061f0a7de21ff0c0658d401a68da738dd893748651983ce
{ 1d0',
3: { [
[
h'',
{
1: 55, 1: 55,
4: h'62696c626f2e62616767696e7340686f626269746f6e2e657861 4: h'62696c626f2e62616767696e7340686f626269746f6e2e657861
6d706c65', 6d706c65',
-1: { -1: {
1: 2, 1: 2,
-1: 3, -1: 3,
-2: h'43b12669acac3fd27898ffba0bcd2e6c366d53bc4db71f909 -2: h'43b12669acac3fd27898ffba0bcd2e6c366d53bc4db71f909
a759304acfb5e18cdc7ba0b13ff8c7636271a6924b1ac63c02688075b55ef2d61 a759304acfb5e18cdc7ba0b13ff8c7636271a6924b1ac63c02688075b55ef2d61
3574e7dc242f79c3', 3574e7dc242f79c3',
-3: h'812dd694f4ef32b11014d74010a954689c6b6e8785b333d1a -3: h'812dd694f4ef32b11014d74010a954689c6b6e8785b333d1a
b44f22b9d1091ae8fc8ae40b687e5cfbe7ee6f8b47918a07bb04e9f5b1a51a334 b44f22b9d1091ae8fc8ae40b687e5cfbe7ee6f8b47918a07bb04e9f5b1a51a334
a16bc09777434113' a16bc09777434113'
} }
}, },
4: h'f20ad9c96134f3c6be4f75e7101c0ecc5efa071ff20a87fd1ac285 h'f20ad9c96134f3c6be4f75e7101c0ecc5efa071ff20a87fd1ac285109
10941ee0376573e2b384b56b99' 41ee0376573e2b384b56b99'
}, ],
{ [
3: { h'',
{
1: -26, 1: -26,
4: h'62696c626f2e62616767696e7340686f626269746f6e2e657861 4: h'62696c626f2e62616767696e7340686f626269746f6e2e657861
6d706c65' 6d706c65'
}, },
4: h'46c4f88069b650909a891e84013614cd58a3668f88fa18f3852940 h'46c4f88069b650909a891e84013614cd58a3668f88fa18f3852940a20
a20b35098591d3aacf91c125a2595cda7bee75a490579f0e2f20fd6bc956623bf b35098591d3aacf91c125a2595cda7bee75a490579f0e2f20fd6bc956623bfde3
de3029c318f82c426dac3463b261c981ab18b72fe9409412e5c7f2d8f2b5abaf7 029c318f82c426dac3463b261c981ab18b72fe9409412e5c7f2d8f2b5abaf780d
80df6a282db033b3a863fa957408b81741878f466dcc437006ca21407181a016c f6a282db033b3a863fa957408b81741878f466dcc437006ca21407181a016ca60
a608ca8208bd3c5a1ddc828531e30b89a67ec6bb97b0c3c3c92036c0cb84aa0f0 8ca8208bd3c5a1ddc828531e30b89a67ec6bb97b0c3c3c92036c0cb84aa0f0ce8
ce8c3e4a215d173bfa668f116ca9f1177505afb7629a9b0b5e096e81d37900e06 c3e4a215d173bfa668f116ca9f1177505afb7629a9b0b5e096e81d37900e06f56
f561a32b6bc993fc6d0cb5d4bb81b74e6ffb0958dac7227c2eb8856303d989f93 1a32b6bc993fc6d0cb5d4bb81b74e6ffb0958dac7227c2eb8856303d989f93b4a
b4a051830706a4c44e8314ec846022eab727e16ada628f12ee7978855550249cc 051830706a4c44e8314ec846022eab727e16ada628f12ee7978855550249ccb58
b58' '
}, ],
{ [
3: { h'',
{
1: -5, 1: -5,
4: h'30313863306165352d346439622d343731622d626664362d6565 4: h'30313863306165352d346439622d343731622d626664362d6565
66333134626337303337' 66333134626337303337'
}, },
4: h'0b2c7cfce04e98276342d6476a7723c090dfdd15f9a518e7736549 h'0b2c7cfce04e98276342d6476a7723c090dfdd15f9a518e7736549e99
e998370695e6d6a83b4ae507bb' 8370695e6d6a83b4ae507bb'
} ]
] ]
]
} B.2. Examples of Encrypted Messages
C.2. Examples of Encrypted Messages
C.2.1. Direct ECDH B.2.1. Direct ECDH
This example uses the following: This example uses the following:
o CEK: AES-GCM w/ 128-bit key o CEK: AES-GCM w/ 128-bit key
o Key managment: ECDH Ephemeral-Static, Curve P-256 o Recipient class: ECDH Ephemeral-Static, Curve P-256
Size of binary file is 186 bytes Size of binary file is 182 bytes
{ [
1: 2, 2,
2: h'a10101', h'a10101',
3: { {
5: h'c9cf4df2fe6c632bf7886413' 5: h'c9cf4df2fe6c632bf7886413'
}, },
4: h'45fce2814311024d3a479e7d3eed063850f3f0b9f3f948677e3ae9869b h'45fce2814311024d3a479e7d3eed063850f3f0b9f3f948677e3ae9869bcf9
cf9ff4e1763812', ff4e1763812',
9: [ [
{ [
3: { h'',
{
1: 50, 1: 50,
4: h'6d65726961646f632e6272616e64796275636b406275636b6c61 4: h'6d65726961646f632e6272616e64796275636b406275636b6c61
6e642e6578616d706c65', 6e642e6578616d706c65',
-1: { -1: {
1: 2, 1: 2,
-1: 1, -1: 1,
-2: h'98f50a4ff6c05861c8860d13a638ea56c3f5ad7590bbfbf05 -2: h'98f50a4ff6c05861c8860d13a638ea56c3f5ad7590bbfbf05
4e1c7b4d91d6280', 4e1c7b4d91d6280',
-3: h'f01400b089867804b8e9fc96c3932161f1934f4223069170d -3: h'f01400b089867804b8e9fc96c3932161f1934f4223069170d
924b7e03bf822bb' 924b7e03bf822bb'
} }
} },
} h''
]
] ]
} ]
C.2.2. Direct plus Key Derivation B.2.2. Direct plus Key Derivation
This example uses the following: This example uses the following:
o CEK: AES-CCM w/128-bit key, trucate the tag to 64-bits o CEK: AES-CCM w/128-bit key, trucate the tag to 64-bits
o Key managment: Use HKDF on a shared secret with the following o Recipient class: Use HKDF on a shared secret with the following
implicit fields as part of the context. implicit fields as part of the context.
* APU identity: "lighting-client" * APU identity: "lighting-client"
* APV identity: "lighting-server" * APV identity: "lighting-server"
* Supplimentary Public Other: "Encryption Example 02" * Supplimentary Public Other: "Encryption Example 02"
Size of binary file is 99 bytes Size of binary file is 95 bytes
{ [
1: 2, 2,
2: h'a1010a', h'a1010a',
3: { {
5: h'89f52f65a1c580933b5261a7' 5: h'89f52f65a1c580933b5261a7'
}, },
4: h'7b9dcfa42c4e1d3182c402dc18ef8b5637de4fb62cf1dd156ea6e6e0', h'7b9dcfa42c4e1d3182c402dc18ef8b5637de4fb62cf1dd156ea6e6e0',
9: [ [
{ [
3: { h'',
{
1: "dir+kdf", 1: "dir+kdf",
4: h'6f75722d736563726574', 4: h'6f75722d736563726574',
-20: h'61616262636364646565666667676868' -20: h'61616262636364646565666667676868'
} },
} h''
]
] ]
} ]
C.3. Examples of Signed Message B.3. Examples of Signed Message
C.3.1. Single Signature B.3.1. Single Signature
This example uses the following: This example uses the following:
o Signature Algorithm: RSA-PSS w/ SHA-384, MGF-1 o Signature Algorithm: RSA-PSS w/ SHA-384, MGF-1
Size of binary file is 332 bytes Size of binary file is 330 bytes
{
1: 1, [
4: h'546869732069732074686520636f6e74656e742e', 1,
5: [ h'',
{ {
2: h'a20165505333383404581e62696c626f2e62616767696e7340686f },
626269746f6e2e6578616d706c65', h'546869732069732074686520636f6e74656e742e',
6: h'0144e54a23b35cba9f9477beda0578c56653a3642fa64095ab71e2 [
9527fef410ab3626005267f9c5d75cba5377ab3c46ded94236c77ebfcdea8a71d [
9b1d5c6faeb870733993267b0ab40569870602b903a518a273c303f78c129f14c h'a20165505333383404581e62696c626f2e62616767696e7340686f626
fdc49f3d1de8be8599c861ddefdfc8f0e8037a3acf195e0da2cc287ce0945e98b 269746f6e2e6578616d706c65',
e7b3666ace2183f77c313b45e9488a1dae5925f01a4e7c5ef1622abe9cd678eaa {
02f501d950f24161cd7ef9458c13bfc96fb787fcd3e07ff47f1d7e37c9cc50d29 },
023d0e310c7c36c1a0e44b2c7347136c1ad6a0664c3697919eda6e3af813e1c3b h'6d9d88a90ef4d6d7c0079fb11a33c855e2274c773f358df43b68f7873
ef846513d8ff8bd761d4ea979e9a2a2b6d2de57bb26d92220f4188cc0fdd68020 eeda210692a61d70cd6a24ba0e3d82e359384be09faafea496bb0ed16f02091c4
874' 8c02f33574edab5b3e334bae68d19580021327cc131fbee38eb0b28289dbce118
} 3f9067891b17fe752674b80437da02e9928ab7a155fef707b11d2bd38a71f224f
53170480116d96cc3f7266487b268679a13cdedffa93252a550371acc19971369
b58039056b308cc4e158bebe7c55db7874442d4321fd27f17dbb820ef19f43dcc
16cd50ccdd1b7dfd7cdde239a9245af41d949cdbbf1337ca254af20eeb167a62d
a5a51c83899c6f6e7c7e01dc3db21a250092a69fc635b74a2e54f5c98cb955d83
'
]
] ]
} ]
C.3.2. Multiple Signers B.3.2. Multiple Signers
This example uses the following: This example uses the following:
o Signature Algorithm: RSA-PSS w/ SHA-256, MGF-1 o Signature Algorithm: RSA-PSS w/ SHA-256, MGF-1
o Signature Algorithm: ECDSA w/ SHA-512, Curve P-521 o Signature Algorithm: ECDSA w/ SHA-512, Curve P-521
Size of binary file is 501 bytes Size of binary file is 496 bytes
{
1: 1, [
4: h'546869732069732074686520636f6e74656e742e', 1,
5: [ h'',
{ {
2: h'a1013819', },
3: { h'546869732069732074686520636f6e74656e742e',
[
[
h'a1013819',
{
4: h'62696c626f2e62616767696e7340686f626269746f6e2e657861 4: h'62696c626f2e62616767696e7340686f626269746f6e2e657861
6d706c65' 6d706c65'
}, },
6: h'2f5e3809c370d409ffb7600b66b15bd597b10ca326da04fdaeedb5 h'0ee972d931c7ab906e4bb71b80da0cc99c104fa53ebbf1f2cf7b668b9
bfc3cdfd289593347bb06fe1fc50f6eed18588d90c270c9dc9613be89b4e043f0 3d766d3d2da28299f074675bb0db3cd0792ba83050c23c96795d58f9c7d68f66a
4c1845d1b7ff10c49ebe8e5f373ab3d5b058117b4b5b9a08c7f9b0ae3f5f0debf bbb8f35af8a0b5df369517b6db85e2cb62d852b666bc135c9022e46b538f78c26
03a5b917b5270ccb211765e961b6476542ceaab36d4f994e313f1ffc092ee83ad adc2668963e74a019de718254385bb9cb137926ad6a88d1ff70043f85e555fb57
bf51c2c9ea06ec0be349f453ef0a64c3831c5709fe8627de1bf47b586b941e0d1 84107ce6e9de7c89c4fbadf8eca363a35f415f7a23523a8331b1aa2dfbac59a06
dd8e261c71be0aa28ea288835c4d62e4b56b24eed369483eb3bf8abea00cfc873 3e4357bde8e53fe34195d59bcda37d2c604804fffe60362e81476436aaa677129
8afd86698d7076ba2f6fb1f59936c60668d9d43acef17d1b5eae6bccc9896b0d4 f34b26639fc41b8e758e5edf273079c61b30130f0f83c57aa6856347e2556f718
d4ffbc41e2c25011e15a0093c76b9b7d68655216835d467ce4188c107a1093855 eaf79a1fee1397a4f0b16b1b34db946eaaff10c793e5d1e681cb21c4fd20c5fdf
7ea' '
}, ],
{ [
3: { h'',
{
1: -9, 1: -9,
4: h'62696c626f2e62616767696e7340686f626269746f6e2e657861 4: h'62696c626f2e62616767696e7340686f626269746f6e2e657861
6d706c65' 6d706c65'
}, },
6: h'0118eaa7d62778b5a9525a583f06b115d80cd246bc930f0c285058 h'0118eaa7d62778b5a9525a583f06b115d80cd246bc930f0c2850588ee
8eec85186b427026e096a076bfab738215f354be59f57643a7f6b2c92535cf3c3 c85186b427026e096a076bfab738215f354be59f57643a7f6b2c92535cf3c37ee
7ee2746a908ab1fec618a3f8965b66d426fd1e6604e164d12eb29734a045c4110 2746a908ab1dcc673a63f327d9eff852b874f7a98b6638c7054fdeeaa3dce6542
c76867438cbe86d4f8e14b95427722667aeeed9b4a3efac04ad0b2ee260db759a 4a21bd5dc728acedda7fcae6df6fc3298ff51ac911603a0f26d066935dccb85ea
e17226cc25501' eb0ae6d0e6'
} ]
] ]
} ]
C.4. COSE Keys B.4. COSE Keys
C.4.1. Public Keys B.4.1. Public Keys
This is an example of a COSE Key set. This example includes the This is an example of a COSE Key set. This example includes the
public keys for all of the previous examples. public keys for all of the previous examples.
In order the keys are: In order the keys are:
o An EC key with a kid of "meriadoc.brandybuck@buckland.example" o An EC key with a kid of "meriadoc.brandybuck@buckland.example"
o An EC key with a kid of "peregrin.took@tuckborough.example" o An EC key with a kid of "peregrin.took@tuckborough.example"
o An EC key with a kid of "bilbo.baggins@hobbiton.example" o An EC key with a kid of "bilbo.baggins@hobbiton.example"
o An RSA key with a kid of "bilbo.baggins@hobbiton.example" o An RSA key with a kid of "bilbo.baggins@hobbiton.example"
Size of binary file is 703 bytes Size of binary file is 703 bytes
[ [
{ {
-1: 1, -1: 1,
-2: h'65eda5a12577c2bae829437fe338701a10aaa375e1bb5b5de108de4 -2: h'65eda5a12577c2bae829437fe338701a10aaa375e1bb5b5de108de4
skipping to change at page 81, line 12 skipping to change at page 81, line 16
d937fad5535387e0ff72ffbe78941402b0b822ea2a74b6058c1dabf9b34a76cb6 d937fad5535387e0ff72ffbe78941402b0b822ea2a74b6058c1dabf9b34a76cb6
3b87faa2c6847b8e2837fff91186e6b1c14911cf989a89092a81ce601ddacd3f9 3b87faa2c6847b8e2837fff91186e6b1c14911cf989a89092a81ce601ddacd3f9
cf', cf',
-1: h'010001', -1: h'010001',
1: 3, 1: 3,
2: h'62696c626f2e62616767696e7340686f626269746f6e2e6578616d70 2: h'62696c626f2e62616767696e7340686f626269746f6e2e6578616d70
6c65' 6c65'
} }
] ]
C.4.2. Private Keys B.4.2. Private Keys
This is an example of a COSE Key set. This example includes the This is an example of a COSE Key set. This example includes the
private keys for all of the previous examples. private keys for all of the previous examples.
In order the keys are: In order the keys are:
o An EC key with a kid of "meriadoc.brandybuck@buckland.example" o An EC key with a kid of "meriadoc.brandybuck@buckland.example"
o A shared-secret key with a kid of "our-secret" o A shared-secret key with a kid of "our-secret"
skipping to change at page 83, line 42 skipping to change at page 83, line 46
03da5f63e7bcffb3c84903111b9ffabcb873f675d42abd02a0b6c9e2fa91d293d 03da5f63e7bcffb3c84903111b9ffabcb873f675d42abd02a0b6c9e2fa91d293d
5c605f', 5c605f',
-8: h'dcf8aabd740dd33c0c784fac06f6608b6f3d5cff57090177556a8fc -8: h'dcf8aabd740dd33c0c784fac06f6608b6f3d5cff57090177556a8fc
cc2a7220429eff4ee828ebe35904a090b0c7f71da1060634d526cfe370af3e4d1 cc2a7220429eff4ee828ebe35904a090b0c7f71da1060634d526cfe370af3e4d1
5ef68a7beed931a423f157c175892cb1bbb434a0c386327e1ad8ac79a0d55aded 5ef68a7beed931a423f157c175892cb1bbb434a0c386327e1ad8ac79a0d55aded
d707d1c7f0c601541e9421ec5a02ae3149ea1e99129305eb19ae8ece2a3293f3f d707d1c7f0c601541e9421ec5a02ae3149ea1e99129305eb19ae8ece2a3293f3f
1a688e' 1a688e'
} }
] ]
Appendix D. COSE Header Algorithm Label Table Appendix C. Document Updates
C.1. Version -03 to -04
This section disappears when we make a decision on password based key o Change top level from map to array.
management.
+------+-----------+-------+-----------+-------------+ o Eliminate the term "key managment" from the document.
| name | algorithm | label | CBOR type | description |
+------+-----------+-------+-----------+-------------+
| p2c | PBE | -1 | int | |
| | | | | |
| p2s | PBE | -2 | bstr | |
+------+-----------+-------+-----------+-------------+
Appendix E. Document Updates o Point to content registries for the 'content type' attribute
E.1. Version -02 to -03 o Push protected field into the KDF functions for recipients.
o Remove password based recipient information.
o Create EC Curve Registry.
C.2. Version -02 to -03
o Make a pass over all of the algorithm text. o Make a pass over all of the algorithm text.
o Alter the CDDL so that Keys and KeySets are top level items and o Alter the CDDL so that Keys and KeySets are top level items and
the key examples validate. the key examples validate.
o Add sample key structures. o Add sample key structures.
o Expand text on dealing with Externally Supplied Data. o Expand text on dealing with Externally Supplied Data.
o Update the examples to match some of the renumbering of fields. o Update the examples to match some of the renumbering of fields.
E.2. Version -02 to -03 C.3. Version -02 to -03
o Add a set of straw man proposals for algorithms. It is possible/ o Add a set of straw man proposals for algorithms. It is possible/
expected that this text will be moved to a new document. expected that this text will be moved to a new document.
o Add a set of straw man proposals for key structures. It is o Add a set of straw man proposals for key structures. It is
possible/expected that this text will be moved to a new document. possible/expected that this text will be moved to a new document.
o Provide guidance on use of externally supplied authenticated data. o Provide guidance on use of externally supplied authenticated data.
o Add external authenticated data to signing structure. o Add external authenticated data to signing structure.
E.3. Version -01 to -2 C.4. Version -01 to -2
o Add first pass of algorithm information o Add first pass of algorithm information
o Add direct key derivation example. o Add direct key derivation example.
E.4. Version -00 to -01 C.5. Version -00 to -01
o Add note on where the document is being maintained and o Add note on where the document is being maintained and
contributing notes. contributing notes.
o Put in proposal on MTI algorithms. o Put in proposal on MTI algorithms.
o Changed to use labels rather than keys when talking about what o Changed to use labels rather than keys when talking about what
indexes a map. indexes a map.
o Moved nonce/IV to be a common header item. o Moved nonce/IV to be a common header item.
skipping to change at page 85, line 29 skipping to change at page 85, line 36
[CREF1] JLS: Need to check this list for correctness before publishing. [CREF1] JLS: Need to check this list for correctness before publishing.
[CREF2] JLS: I have not gone through the document to determine what [CREF2] JLS: I have not gone through the document to determine what
needs to be here yet. We mostly want to grab terms which are needs to be here yet. We mostly want to grab terms which are
used in unusual ways or are not generally understood. used in unusual ways or are not generally understood.
[CREF3] JLS: It would be possible to extend this section to talk about [CREF3] JLS: It would be possible to extend this section to talk about
those decisions which an application needs to think about rather those decisions which an application needs to think about rather
than just talking about MTI algoithms. than just talking about MTI algoithms.
[CREF4] JLS: I have moved msg_type into the individual structures. [CREF4] Hannes: I would remove references to CMS and S/MIME since they
are most likely only helpful to a very small audience.
[CREF5] JLS: I have moved msg_type into the individual structures.
However, they would not be necessary in the cases where a) the However, they would not be necessary in the cases where a) the
security service is known and b) security libraries can setup to security service is known and b) security libraries can setup to
take individual structures. Should they be moved back to just take individual structures. Should they be moved back to just
appearing if used in a COSE_MSG rather than on the individual appearing if used in a COSE_MSG rather than on the individual
structure? structure? This would make things shorter if one was using just
a signed message because the msg_type field can be omitted as
well as the COSE_Tagged_MSG tag field. One the other hand, it
will complicated the code if one is doing general purpose
library type things.
[CREF5] JLS: Should we create an IANA registries for the values of [CREF6] JLS: Should we create an IANA registries for the values of
msg_type? msg_type?
[CREF6] JLS: OPEN ISSUE
[CREF7] JLS: A completest version of this grammar would list the options [CREF7] JLS: A completest version of this grammar would list the options
available in the protected and unprotected headers. Do we want available in the protected and unprotected headers. Do we want
to head that direction? to head that direction?
[CREF8] JLS: After looking at this, I am wondering if the type for this [CREF8] JLS: Is there a reason to assign a CBOR tag to identify keys
should be: [int int]/[int tstr] so that we can keep the major/ and/or key sets?
minor difference of media-types. This does cost a couple of
bytes in the message.
[CREF9] JLS: Need to figure out how we are going to go about creating
this registry -or are we going to modify the current mime-
content table?
[CREF10] JLS: Open to do.
[CREF11] Ilari: I don't follow/understand this text
[CREF12] JLS: Is there a reason to assign a CBOR tag to identify keys
and/or key sets?
[CREF13] JLS: We can really simplify the grammar for COSE_Key to be just
the kty (the one required field) and the generic item. The
reason to do this is that it makes things simpler. The reason
not to do this says that we really need to add a lot more items
so that a grammar check can be done that is more tightly
enforced.
[CREF14] JLS: Do we also want to document the use of RFC 5649 as well?
It allows for other sizes of keys that might be used for HMAC -
i.e. a 200 bit key. The algorithm exists, but I do not
personally know of any standard uses of it.
[CREF15] JLS: Is this range we want to specify?
[CREF16] JLS: It would be possible to include the protected field in the
KDF rather than the key wrap algorithm if we wanted to. This
would provide the same level of security, it would not be
possible to get the same key if they are different.
[CREF17] JLS: Do we want/need to support this? JOSE did it mainly to [CREF9] JLS: We can really simplify the grammar for COSE_Key to be just
support the encryption of private keys. the kty (the one required field) and the generic item. The
reason to do this is that it makes things simpler. The reason
not to do this says that we really need to add a lot more items
so that a grammar check can be done that is more tightly
enforced.
[CREF18] JLS: Do we create a registry for curves? Is is the same [CREF10] JLS: Do we create a registry for curves? Is is the same
registry for both EC1 and EC2? registry for both EC1 and EC2?
[CREF19] JLS: Should we use the integer encoding for x, y and d instead [CREF11] JLS: Should we use the bignum encoding for x, y and d instead
of bstr? of bstr?
[CREF20] JLS: Looking at the CBOR specification, the bstr that we are [CREF12] JLS: Looking at the CBOR specification, the bstr that we are
looking in our table below should most likely be specified as looking in our table below should most likely be specified as
big numbers rather than as binary strings. This means that we big numbers rather than as binary strings. This means that we
would use the tag 6.2 instead. From my reading of the would use the tag 6.2 instead. From my reading of the
specification, there is no difference in the encoded size of specification, there is no difference in the encoded size of
the resulting output. The specification of bignum does the resulting output. The specification of bignum does
explicitly allow for integers encoded with leading zeros. explicitly allow for integers encoded with leading zeros.
[CREF21] JLS: Finish the registration process. [CREF13] JLS: Should we register both or just the cose+cbor one?
[CREF22] JLS: Should we register both or just the cose+cbor one?
[CREF23] JLS: Do we want to keep this as diagnostic notation or should
we switch to having "binary" examples instead?
[CREF24] JLS: Need to examine how this is worked out. In this case the
length of the key to be used is implicit rather than explicit.
This needs to be the case because a direct key could be any
length, however it means that when the key is derived, there is
currently nothing to state how long the derived key needs to
be.
Author's Address Authors' Addresses
Jim Schaad Jim Schaad
August Cellars August Cellars
Email: ietf@augustcellars.com Email: ietf@augustcellars.com
Brian Campbell
Ping Identity
Email: brian.d.campbell@gmail.com
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