draft-ietf-cose-msg-02.txt   draft-ietf-cose-msg-03.txt 
COSE Working Group J. Schaad COSE Working Group J. Schaad
Internet-Draft August Cellars Internet-Draft August Cellars
Intended status: Informational July 20, 2015 Intended status: Informational August 9, 2015
Expires: January 21, 2016 Expires: February 10, 2016
CBOR Encoded Message Syntax CBOR Encoded Message Syntax
draft-ietf-cose-msg-02 draft-ietf-cose-msg-03
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
The source for this draft is being maintained in GitHub. Suggested The source for this draft is being maintained in GitHub. Suggested
changes should be submitted as pull requests at [1]. Instructions changes should be submitted as pull requests at <https://github.com/
are on that page as well. Editorial changes can be managed in cose-wg/cose-spec>. Instructions are on that page as well.
GitHub, but any substantial issues need to be discussed on the COSE Editorial changes can be managed in GitHub, but any substantial
mailing list. issues need to be discussed on the COSE mailing list.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 21, 2016. This Internet-Draft will expire on February 10, 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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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Design changes from JOSE . . . . . . . . . . . . . . . . 4 1.1. Design changes from JOSE . . . . . . . . . . . . . . . . 5
1.2. Requirements Terminology . . . . . . . . . . . . . . . . 5 1.2. Requirements Terminology . . . . . . . . . . . . . . . . 5
1.3. CBOR Grammar . . . . . . . . . . . . . . . . . . . . . . 5 1.3. CBOR Grammar . . . . . . . . . . . . . . . . . . . . . . 6
1.4. CBOR Related Terminology . . . . . . . . . . . . . . . . 6 1.4. CBOR Related Terminology . . . . . . . . . . . . . . . . 6
1.5. Document Terminology . . . . . . . . . . . . . . . . . . 6 1.5. Document Terminology . . . . . . . . . . . . . . . . . . 7
1.6. Mandatory to Implement Algorithms . . . . . . . . . . . . 6 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 . . . . . . . . . . . . . . . . . . . . . . 10
3.1. COSE Headers . . . . . . . . . . . . . . . . . . . . . . 11 3.1. COSE Headers . . . . . . . . . . . . . . . . . . . . . . 12
4. Signing Structure . . . . . . . . . . . . . . . . . . . . . . 14 4. Signing Structure . . . . . . . . . . . . . . . . . . . . . . 15
5. Encryption object . . . . . . . . . . . . . . . . . . . . . . 17 4.1. Externally Supplied Data . . . . . . . . . . . . . . . . 17
5.1. Key Management Methods . . . . . . . . . . . . . . . . . 18 4.2. Signing and Verification Process . . . . . . . . . . . . 17
5.2. Encryption Algorithm for AEAD algorithms . . . . . . . . 19 5. Encryption object . . . . . . . . . . . . . . . . . . . . . . 19
5.3. Encryption algorithm for AE algorithms . . . . . . . . . 20 5.1. Key Management Methods . . . . . . . . . . . . . . . . . 20
6. MAC objects . . . . . . . . . . . . . . . . . . . . . . . . . 21 5.2. Encryption Algorithm for AEAD algorithms . . . . . . . . 20
7. Key Structure . . . . . . . . . . . . . . . . . . . . . . . . 22 5.3. Encryption algorithm for AE algorithms . . . . . . . . . 21
7.1. COSE Key Map Labels . . . . . . . . . . . . . . . . . . . 23 6. MAC objects . . . . . . . . . . . . . . . . . . . . . . . . . 22
8. Signature Algorithms . . . . . . . . . . . . . . . . . . . . 26 7. Key Structure . . . . . . . . . . . . . . . . . . . . . . . . 23
8.1. ECDSA . . . . . . . . . . . . . . . . . . . . . . . . . . 27 7.1. COSE Key Common Parameters . . . . . . . . . . . . . . . 24
8.1.1. Security Considerations . . . . . . . . . . . . . . . 28 8. Signature Algorithms . . . . . . . . . . . . . . . . . . . . 27
8.2. RSASSA-PSS . . . . . . . . . . . . . . . . . . . . . . . 28 8.1. ECDSA . . . . . . . . . . . . . . . . . . . . . . . . . . 28
8.2.1. Security Considerations . . . . . . . . . . . . . . . 29 8.1.1. Security Considerations . . . . . . . . . . . . . . . 29
9. Message Authentication (MAC) Algorithms . . . . . . . . . . . 29 8.2. RSASSA-PSS . . . . . . . . . . . . . . . . . . . . . . . 30
9.1. Hash-based Message Authentication Codes (HMAC) . . . . . 29 8.2.1. Security Considerations . . . . . . . . . . . . . . . 30
9.1.1. Security Considerations . . . . . . . . . . . . . . . 30 9. Message Authentication (MAC) Algorithms . . . . . . . . . . . 31
9.2. AES Message Authentication Code (AES-MAC) . . . . . . . . 30 9.1. Hash-based Message Authentication Codes (HMAC) . . . . . 31
10. Content Encryption Algorithms . . . . . . . . . . . . . . . . 30 9.1.1. Security Considerations . . . . . . . . . . . . . . . 32
10.1. AES GCM . . . . . . . . . . . . . . . . . . . . . . . . 30 9.2. AES Message Authentication Code (AES-CBC-MAC) . . . . . . 32
10.2. AES CCM . . . . . . . . . . . . . . . . . . . . . . . . 31 9.2.1. Security Considerations . . . . . . . . . . . . . . . 33
10.2.1. Security Considerations . . . . . . . . . . . . . . 33 10. Content Encryption Algorithms . . . . . . . . . . . . . . . . 33
11. Key Derivation Functions (KDF) . . . . . . . . . . . . . . . 34 10.1. AES GCM . . . . . . . . . . . . . . . . . . . . . . . . 33
10.1.1. Security Considerations . . . . . . . . . . . . . . 34
10.2. AES CCM . . . . . . . . . . . . . . . . . . . . . . . . 34
10.2.1. Security Considerations . . . . . . . . . . . . . . 36
10.3. ChaCha20 and Poly1305 . . . . . . . . . . . . . . . . . 37
10.3.1. Security Considerations . . . . . . . . . . . . . . 37
11. Key Derivation Functions (KDF) . . . . . . . . . . . . . . . 38
11.1. HMAC-based Extract-and-Expand Key Derivation Function 11.1. HMAC-based Extract-and-Expand Key Derivation Function
(HKDF) . . . . . . . . . . . . . . . . . . . . . . . . . 34 (HKDF) . . . . . . . . . . . . . . . . . . . . . . . . . 38
11.2. Context Information Structure . . . . . . . . . . . . . 35 11.2. Context Information Structure . . . . . . . . . . . . . 39
12. Key Management Algorithms . . . . . . . . . . . . . . . . . . 38 12. Key Management Algorithms . . . . . . . . . . . . . . . . . . 42
12.1. Direct Encryption . . . . . . . . . . . . . . . . . . . 39 12.1. Direct Encryption . . . . . . . . . . . . . . . . . . . 43
12.1.1. Direct Key . . . . . . . . . . . . . . . . . . . . . 39 12.1.1. Direct Key . . . . . . . . . . . . . . . . . . . . . 43
12.2. Key Wrapping . . . . . . . . . . . . . . . . . . . . . . 40 12.1.2. Direct Key with KDF . . . . . . . . . . . . . . . . 44
12.2.1. AES Key Wrapping . . . . . . . . . . . . . . . . . . 40 12.2. Key Wrapping . . . . . . . . . . . . . . . . . . . . . . 45
12.3. Key Encryption . . . . . . . . . . . . . . . . . . . . . 41 12.2.1. AES Key Wrapping . . . . . . . . . . . . . . . . . . 46
12.3.1. RSA OAEP . . . . . . . . . . . . . . . . . . . . . . 41 12.3. Key Encryption . . . . . . . . . . . . . . . . . . . . . 47
12.4. Direct Key Agreement . . . . . . . . . . . . . . . . . . 42 12.3.1. RSAES-OAEP . . . . . . . . . . . . . . . . . . . . . 47
12.4.1. ECDH . . . . . . . . . . . . . . . . . . . . . . . . 43 12.4. Direct Key Agreement . . . . . . . . . . . . . . . . . . 48
12.5. Key Agreement with KDF . . . . . . . . . . . . . . . . . 46 12.4.1. ECDH . . . . . . . . . . . . . . . . . . . . . . . . 49
12.5.1. ECDH ES + HKDF . . . . . . . . . . . . . . . . . . . 46 12.5. Key Agreement with KDF . . . . . . . . . . . . . . . . . 52
12.6. Password . . . . . . . . . . . . . . . . . . . . . . . . 47 12.5.1. ECDH . . . . . . . . . . . . . . . . . . . . . . . . 52
12.6.1. PBES2 . . . . . . . . . . . . . . . . . . . . . . . 47 12.6. Password . . . . . . . . . . . . . . . . . . . . . . . . 52
13. Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 12.6.1. PBES2 . . . . . . . . . . . . . . . . . . . . . . . 53
13.1. Elliptic Curve Keys . . . . . . . . . . . . . . . . . . 48 13. Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
13.1.1. Single Coordinate Curves . . . . . . . . . . . . . . 48 13.1. Elliptic Curve Keys . . . . . . . . . . . . . . . . . . 54
13.1.2. Double Coordinate Curves . . . . . . . . . . . . . . 49 13.1.1. Single Coordinate Curves . . . . . . . . . . . . . . 54
13.2. RSA Keys . . . . . . . . . . . . . . . . . . . . . . . . 50 13.1.2. Double Coordinate Curves . . . . . . . . . . . . . . 55
13.3. Symmetric Keys . . . . . . . . . . . . . . . . . . . . . 51 13.2. RSA Keys . . . . . . . . . . . . . . . . . . . . . . . . 56
14. CBOR Encoder Restrictions . . . . . . . . . . . . . . . . . . 52 13.3. Symmetric Keys . . . . . . . . . . . . . . . . . . . . . 57
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 52 14. CBOR Encoder Restrictions . . . . . . . . . . . . . . . . . . 58
15.1. CBOR Tag assignment . . . . . . . . . . . . . . . . . . 52 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 58
15.2. COSE Object Labels Registry . . . . . . . . . . . . . . 52 15.1. CBOR Tag assignment . . . . . . . . . . . . . . . . . . 58
15.3. COSE Header Label Table . . . . . . . . . . . . . . . . 53 15.2. COSE Object Labels Registry . . . . . . . . . . . . . . 59
15.4. COSE Header Algorithm Label Table . . . . . . . . . . . 53 15.3. COSE Header Parameter Registry . . . . . . . . . . . . . 59
15.5. COSE Algorithm Registry . . . . . . . . . . . . . . . . 54 15.4. COSE Header Algorithm Label Table . . . . . . . . . . . 60
15.6. COSE Key Map Registry . . . . . . . . . . . . . . . . . 55 15.5. COSE Algorithm Registry . . . . . . . . . . . . . . . . 60
15.7. COSE Key Parameter Registry . . . . . . . . . . . . . . 56 15.6. COSE Key Common Parameter Registry . . . . . . . . . . . 61
15.8. Media Type Registration . . . . . . . . . . . . . . . . 56 15.7. COSE Key Type Parameter Registry . . . . . . . . . . . . 62
15.8.1. COSE Security Message . . . . . . . . . . . . . . . 56 15.8. Media Type Registration . . . . . . . . . . . . . . . . 62
15.8.2. COSE Key media type . . . . . . . . . . . . . . . . 58 15.8.1. COSE Security Message . . . . . . . . . . . . . . . 62
16. Security Considerations . . . . . . . . . . . . . . . . . . . 60 15.8.2. COSE Key media type . . . . . . . . . . . . . . . . 64
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 60 16. Security Considerations . . . . . . . . . . . . . . . . . . . 66
17.1. Normative References . . . . . . . . . . . . . . . . . . 60 17. References . . . . . . . . . . . . . . . . . . . . . . . . . 66
17.2. Informative References . . . . . . . . . . . . . . . . . 61 17.1. Normative References . . . . . . . . . . . . . . . . . . 66
Appendix A. AEAD and AE algorithms . . . . . . . . . . . . . . . 63 17.2. Informative References . . . . . . . . . . . . . . . . . 67
Appendix B. Three Levels of Recipient Information . . . . . . . 64 Appendix A. AEAD and AE algorithms . . . . . . . . . . . . . . . 69
Appendix C. Examples . . . . . . . . . . . . . . . . . . . . . . 65 Appendix B. Three Levels of Recipient Information . . . . . . . 70
C.1. Examples of MAC messages . . . . . . . . . . . . . . . . 66 Appendix C. Examples . . . . . . . . . . . . . . . . . . . . . . 72
C.1.1. Shared Secret Direct MAC . . . . . . . . . . . . . . 66 C.1. Examples of MAC messages . . . . . . . . . . . . . . . . 72
C.1.2. ECDH Direct MAC . . . . . . . . . . . . . . . . . . . 66 C.1.1. Shared Secret Direct MAC . . . . . . . . . . . . . . 72
C.1.3. Wrapped MAC . . . . . . . . . . . . . . . . . . . . . 67 C.1.2. ECDH Direct MAC . . . . . . . . . . . . . . . . . . . 73
C.1.4. Multi-recipient MAC message . . . . . . . . . . . . . 68 C.1.3. Wrapped MAC . . . . . . . . . . . . . . . . . . . . . 74
C.2. Examples of Encrypted Messages . . . . . . . . . . . . . 69 C.1.4. Multi-recipient MAC message . . . . . . . . . . . . . 74
C.2.1. Direct ECDH . . . . . . . . . . . . . . . . . . . . . 69 C.2. Examples of Encrypted Messages . . . . . . . . . . . . . 76
C.2.2. Direct plus Key Derivation . . . . . . . . . . . . . 70 C.2.1. Direct ECDH . . . . . . . . . . . . . . . . . . . . . 76
C.3. Examples of Signed Message . . . . . . . . . . . . . . . 71 C.2.2. Direct plus Key Derivation . . . . . . . . . . . . . 76
C.3.1. Single Signature . . . . . . . . . . . . . . . . . . 71 C.3. Examples of Signed Message . . . . . . . . . . . . . . . 77
C.3.2. Multiple Signers . . . . . . . . . . . . . . . . . . 72 C.3.1. Single Signature . . . . . . . . . . . . . . . . . . 77
C.3.2. Multiple Signers . . . . . . . . . . . . . . . . . . 78
Appendix D. COSE Header Algorithm Label Table . . . . . . . . . 72 C.4. COSE Keys . . . . . . . . . . . . . . . . . . . . . . . . 79
Appendix E. Document Updates . . . . . . . . . . . . . . . . . . 73 C.4.1. Public Keys . . . . . . . . . . . . . . . . . . . . . 79
E.1. Version -01 to -02 . . . . . . . . . . . . . . . . . . . 73 C.4.2. Private Keys . . . . . . . . . . . . . . . . . . . . 81
E.2. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 73 Appendix D. COSE Header Algorithm Label Table . . . . . . . . . 83
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 76 Appendix E. Document Updates . . . . . . . . . . . . . . . . . . 84
E.1. Version -02 to -03 . . . . . . . . . . . . . . . . . . . 84
E.2. Version -02 to -03 . . . . . . . . . . . . . . . . . . . 84
E.3. Version -01 to -2 . . . . . . . . . . . . . . . . . . . . 84
E.4. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 84
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
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examined, and where it seems to the author to be superior or examined, and where it seems to the author to be superior or
simpler, replaced. simpler, replaced.
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
attributes 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 Key management has been made to be more uniform. All key
management techniques are represented as a recipient rather than management techniques are represented as a recipient rather than
only have some of them be so. only have some of them be so.
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 key management on the MAC
authentication key. authentication key.
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are agumented in the text by the use of the CBOR Data Definition are agumented in the text by the use of the CBOR Data Definition
Language (CDDL) [I-D.greevenbosch-appsawg-cbor-cddl]. The use of Language (CDDL) [I-D.greevenbosch-appsawg-cbor-cddl]. The use of
CDDL is intended to be explanitory. In the event of a conflict CDDL is intended to be explanitory. In the event of a conflict
between the text and the CDDL grammar, the text is authorative. between the text and the CDDL grammar, the text is authorative.
(Problems may be introduced at a later point because the CDDL grammar (Problems may be introduced at a later point because the CDDL grammar
is not yet fixed.) is not yet fixed.)
CDDL productions that together define the grammar are interspersed in CDDL productions that together define the grammar are interspersed in
the document like this: the document like this:
start = COSE_MSG start = COSE_MSG / COSE_Key / COSE_KeySet
The collected CDDL can be extracted from the XML version of this The collected CDDL can be extracted from the XML version of this
document via the following XPath expression below. (Depending on the document via the following XPath expression below. (Depending on the
XPath evaluator one is using, it may be necessary to deal with &gt; XPath evaluator one is using, it may be necessary to deal with &gt;
as an entity.) as an entity.)
//artwork[@type='CDDL']/text() //artwork[@type='CDDL']/text()
1.4. CBOR Related Terminology 1.4. CBOR Related Terminology
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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 choice 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
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]
Byte is a synonym for octet. Byte is a synonym for octet.
Key management is used as a term to describe how a key at level n is Key management is used as a term to describe how a key at level n is
obtained from level n+1 in encrypted and MACed messages. The term is obtained from level n+1 in encrypted and MACed messages. The term is
also used to discuss key life cycle management, this document does also used to discuss key life cycle management, this document does
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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 algorithms, keys, or
evaluation hints for the processing of the layer. These two buckets evaluation hints for the processing of the layer. These two buckets
are available for use in all of the structures in this document are available for use in all of the structures in this document
except for keys. While these buckets can be present, they may not except for keys. While these buckets can be present, they may not
all be usable in all instances. For example, while the protected all be usable in all instances. For example, while the protected
bucket is present for recipient structures, most of the algorithms bucket is defined as part of recipient structures, most of the
that are used for recipients do not provide the necessary algorithms that are used for recipients do not provide the necessary
functionality to provide the needed protection and thus the element functionality to provide the needed protection and thus the bucket
is not used. 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 range for labels has been divided into several sections with
a standard range, a private range, and a range that is dependent on a standard range, a private range, and a range that is dependent on
the algorithm selected. The defined labels can be found in the 'COSE the algorithm selected. The defined labels can be found in the 'COSE
Header Labels' IANA registry (Section 15.3. Header Parameters' IANA registry (Section 15.3).
Two buckets are provided for each layer: [CREF7] Two buckets are provided for each layer: [CREF7]
protected contains attributes about the 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 NOT be used if it
is not going to be included in a cryptographic computation. This is 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. This 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 connical encoding.
unprotected contains attributes about the layer that are not unprotected contains parameters about the current layer that are not
cryptographically protected. cryptographically protected.
Both of the buckets are optional and are omitted if there are no Only parameters that deal with the current layer are to be placed at
items contained in the map. The CDDL fragment that describes the two that layer. As an example of this, the parameter 'content type'
buckets is: describes the content of the message being carried in the message.
As such this parameter is placed only the the content layer and is
not placed in the key managment or signature layers. In principle,
one should be able to process any given layer without reference to
any other layer. (The only data that should need to cross layers is
the cryptographic key.)
The presence of both buckets is optional, however the requirement
that the 'alg' parameter be present at each level effectively imposes
a requirement that one of the buckets will always be present. The
parameters that go into the buckets come from the IANA "COSE Header
Parameters" (Section 15.3). Some common parameters are defined in
the next section, but a number of parameters are defined throughout
this document.
The CDDL fragment that describes the two buckets is:
header_map = {+ label => any } header_map = {+ label => any }
Headers = ( Headers = (
? protected => bstr, ? protected => bstr, ; Contains a header_map
? unprotected => header_map ? unprotected => header_map
) )
3.1. COSE Headers 3.1. COSE Headers
The set of header fields defined in this document are: This document defines a set of common header parameters. A summary
of the parameters defined in this section can be found in Table 2.
This table should be consulted to determine the value of label used
as well as the type of the value.
alg This field is used to indicate the algorithm used for the The set of header parameters defined in this section are:
security processing. This field MUST be present at each level of
a signed, encrypted or authenticated message. This field using
the integer '1' for the label. The value is taken from the 'COSE
Algorithm Registry' (see Section 15.4).
crit This field is used to ensure that applications will take alg This parameter is used to indicate the algorithm used for the
appropriate action based on the values found. The field is used security processing. This parameter MUST be present at each level
to indicate which protected header labels an application that is of a signed, encrypted or authenticated message. The value is
processing a message is required to understand. This field uses taken from the 'COSE Algorithm Registry' (see Section 15.4).
the integer '2' for the label. The value is an array of COSE
Header Labels. When present, this MUST be placed in the protected crit This parameter is used to ensure that applications will take
header bucket. appropriate action based on the values found. The parameter is
used to indicate which protected header labels an application that
is processing a message is required to understand. The value is
an array of COSE Header Labels. When present, this parameter MUST
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.
* Integer labels in the range -1 to -255 can be omitted as they * Integer labels in the range -1 to -255 can be omitted as they
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 values indicated by 'crit' can be processed by either The header parameter values indicated by 'crit' can be processed
the security library code or by an application using a security by either the security library code or by an application using a
library, the only requirement is that the field is processed. security library, the only requirement is that the parameter is
processed.
cty This field is used to indicate the content type of the data in content type This parameter is used to indicate the content type of
the payload or ciphertext fields. The field uses the integer of the data in the payload or ciphertext fields. [CREF8] Integers
'3' for the label. The value can be either an integer or a are from the XXXXX[CREF9] IANA registry table. Strings are from
string. [CREF8] Integers are from the XXXXX[CREF9] IANA registry the IANA 'mime-content types' registry. Applications SHOULD
table. Strings are from the IANA 'mime-content types' registry. provide this parameter if the content structure is potentially
Applications SHOULD provide this field if the content structure is ambiguous.
potentially ambiguous.
kid This field one of the ways that can be used to find the key to kid This parameter one of the ways that can be used to find the key
be used. This value can be matched against the 'kid' field in a to be used. The value of this parameter is matched against the
COSE_Key structure. Applications MUST NOT assume that 'kid' 'kid' field in a COSE_Key structure. Applications MUST NOT assume
values are unique. There may be more than one key with the same that 'kid' values are unique. There may be more than one key with
'kid' value, it may be required that all of the keys need to be the same 'kid' value, it may be required that all of the keys need
checked to find the correct one. This field uses the integer to be checked to find the correct one. The internal structure of
value of '4' for the label. The value of field is the CBOR 'bstr' 'kid' values is not defined and generally cannot be relied on by
type. The internal structure of 'kid' is not defined and applications. Key identifier values are hints about which key to
generally cannot be relied on by applications. Key identifier use, they are not directly a security critical field, for this
values are hints about which key to use, they are not directly a reason they can normally be placed in the unprotected headers
security critical field, for this reason they can normally be bucket.
placed in the unprotected headers bucket.
nonce This field holds either a nonce or Initialization Vector nonce This parameter holds either a nonce or Initialization Vector
value. This 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. TODO: Talk about zero
extending the value in some cases. [CREF10] extending the value in some cases. [CREF10]
This table contains a list of all of the generic header parameters
defined in document. In the table is the data value type to be used
for CBOR as well as the integer value that can be used as a
replacement for the name in order to further decrease the size of the
sent item.
+----------+-------+----------+-------------+-----------------------+ +----------+-------+----------+-------------+-----------------------+
| name | label | value | registry | description | | name | label | value | value | description |
| | | type | registry | |
+----------+-------+----------+-------------+-----------------------+ +----------+-------+----------+-------------+-----------------------+
| alg | 1 | int / | COSE | Integers are taken | | alg | 1 | int / | COSE | Integers are taken |
| | | tstr | Algorithm | from table --POINT TO | | | | tstr | Algorithm | from table --POINT TO |
| | | | Registry | REGISTRY-- | | | | | Registry | REGISTRY-- |
| | | | | | | | | | | |
| crit | 2 | [+ | COSE Header | integer values are | | crit | 2 | [+ | COSE Header | integer values are |
| | | label] | Label | from -- POINT TO | | | | label] | Label | from -- POINT TO |
| | | | Registry | REGISTRY -- | | | | | Registry | REGISTRY -- |
| | | | | | | | | | | |
| cty | 3 | tstr / | media-types | Value is either a | | content | 3 | tstr / | media-types | Value is either a |
| | | int | registry | media-type or an | | type | | int | registry | media-type or an |
| | | | | integer from the | | | | | | integer from the |
| | | | | media-type registry | | | | | | media-type registry |
| | | | | | | | | | | |
| jku | * | tstr | | URL to COSE key | | jku | * | tstr | | URL to COSE key |
| | | | | object | | | | | | object |
| | | | | | | | | | | |
| jwk | * | COSE_Key | | contains a COSE key | | jwk | * | COSE_Key | | contains a COSE key |
| | | | | not a JWK key | | | | | | not a JWK key |
| | | | | | | | | | | |
| kid | 4 | bstr | | key identifier | | kid | 4 | bstr | | key identifier |
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| | | | | key | | | | | | key |
| | | | | | | | | | | |
| x5u | * | tstr | | URL for X.509 | | x5u | * | tstr | | URL for X.509 |
| | | | | certificate | | | | | | certificate |
| | | | | | | | | | | |
| zip | * | int / | | Integers are taken | | zip | * | int / | | Integers are taken |
| | | tstr | | from the table | | | | tstr | | from the table |
| | | | | --POINT TO REGISTRY-- | | | | | | --POINT TO REGISTRY-- |
+----------+-------+----------+-------------+-----------------------+ +----------+-------+----------+-------------+-----------------------+
Table 2: Header Labels Table 2: 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
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3. We might want to define some additional items. What are they? A 3. We might want to define some additional items. What are they? A
possible example would be a sequence number as this might be possible example would be a sequence number as this might be
common. On the other hand, this is the type of things that is common. On the other hand, this is the type of things that is
frequently used as the nonce in some places and thus should not frequently used as the nonce in some places and thus should not
be used in the same way. Other items might be challenge/response be used in the same way. Other items might be challenge/response
fields for freshness as these are likely to be common. fields for freshness as these are likely to be common.
4. Signing Structure 4. Signing Structure
The signature structure allows for one or more signatures to be The signature structure allows for one or more signatures to be
applied to a message payload. There are provisions for attributes applied to a message payload. There are provisions for parameters
about the content and attributes about the signature to be carried about the content and parameters about the signature to be carried
along with the signature itself. These attributes may be along with the signature itself. These parameters may be
authenticated by the signature, or just present. Examples of authenticated by the signature, or just present. Examples of
attributes about the content would be the type of content, when the parameters about the content would be the type of content, when the
content was created, and who created the content. Examples of content was created, and who created the content. Examples of
attributes about the signature would be the algorithm and key used to parameters about the signature would be the algorithm and key used to
create the signature, when the signature was created, and counter- create the signature, when the signature was created, and counter-
signatures. signatures.
When more than one signature is present, the successful validation of When more than one signature is present, the successful validation of
one signature associated with a given signer is usually treated as a one signature associated with a given signer is usually treated as a
successful signature by that signer. However, there are some successful signature by that signer. However, there are some
application environments where other rules are needed. An application environments where other rules are needed. An
application that employs a rule other than one valid signature for application that employs a rule other than one valid signature for
each signer must specify those rules. Also, where simple matching of each signer must specify those rules. Also, where simple matching of
the signer identifier is not sufficient to determine whether the the signer identifier is not sufficient to determine whether the
skipping to change at page 15, line 21 skipping to change at page 16, line 22
Headers, Headers,
? payload => bstr, ? payload => bstr,
signatures => [+ COSE_signature] signatures => [+ COSE_signature]
} }
The fields is the structure 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 contains attributes about the payload that are to be protected is described in Section 3.
protected by the signature. An example of such an attribute would
be the content type ('cty') attribute. The content is a CBOR map
of attributes that is encoded to a byte stream. This field MUST
NOT contain attributes about the signature, even if those
attributes are common across multiple signatures. The labels in
this map are typically taken from Table 2. [CREF11]
unprotected contains attributes about the payload that are not unprotected is described in Section 3.
protected by the signature. An example of such an attribute would
be the content type ('cty') attribute. This field MUST NOT
contain attributes about a signature, even if the attributes are
common across multiple signatures. The labels in this map are
typically taken from Table 2. [CREF12]
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.
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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 structure have the following semantics:
protected contains additional information to be authenticated by the protected is described in Section 3.
signature. The field holds data about the signature operation.
The field MUST NOT hold attributes about the payload being signed.
The content is a CBOR map of attributes that is encoded to a byte
stream. At least one of protected and unprotected MUST be
present.
unprotected contains attributes about the signature that are not unprotected is described in Section 3.
protected by the signature. This field MUST NOT contain
attributes about the payload being signed. At least one of
protected and unprotected MUST be present.
signature contains the computed signature value. signature contains the computed signature value.
4.1. Externally Supplied Data
One of the features that we supply in the COSE document is the
ability for applications to provide additional data to be
authenticated as part of the security, but that is not carried as
part of the COSE object. The primary reason for supporting this can
be seen by looking at the CoAP message struture [RFC7252] where the
facility exists for options to be carried before the payload. An
example of data that can be placed in this location would be
transaction ids and nonces to check for replay protection. If the
data is in the options section, then it is available for routers to
help in performing the replay detection and prevention. However, it
may also be desired to protect these values so that they cannot be
modified in transit. This is the purpose of the externally supplied
data field.
This document describes the process for using a byte array of
externally supplied authenticated data, however the method of
constructing the byte array is a function of the application.
Applications which use this feature need to define how the externally
supplied authenticated data is to be constructed. Such a
construction needs to take into account the following issues:
o If multiple items are included, care needs to be taken that data
cannot bleed between the items. This is usually addressed by
making fields fixed width and/or encoding the length of the field.
Using options from CoAP as an example, these fields use a TLV
structure so they can be concatenated without any problems.
o If multiple items are included, a defined order for the items
needs to be defined. Using options from CoAP as an example, an
application could state that the fields are to be ordered by the
option number.
4.2. Signing and Verification Process
The COSE structure used to create the byte stream to be signed uses The COSE structure used to create the byte stream to be signed uses
the following CDDL grammar structure: the following CDDL grammar structure:
Sig_structure = [ Sig_structure = [
body_protected: bstr, body_protected: bstr,
sign_protected: bstr, sign_protected: bstr,
external_aad: bstr,
payload: bstr payload: bstr
] ]
How to compute a signature: How to compute a signature:
1. Create a Sig_structure object and populate it with the 1. Create a Sig_structure object and populate it with the
appropriate fields. For body_protected and sign_protected, if appropriate fields. For body_protected and sign_protected, if
the fields are not present in their corresponding maps, an bstr the fields are not present in their corresponding maps, an bstr
of length zero is used. of length zero is used.
2. Create the value ToBeSigned by encoding the Sig_structure to a 2. If the application has supplied external additional authenticated
data to be included in the computation, then it is placed in the
'external_aad' field. If no data was supplied, then a zero
length binary value is used.
3. Create the value ToBeSigned by encoding the Sig_structure to a
byte string. byte string.
3. Call the signature creation algorithm passing in K (the key to 4. Call the signature creation algorithm passing in K (the key to
sign with), alg (the algorithm to sign with) and ToBeSigned (the sign with), alg (the algorithm to sign with) and ToBeSigned (the
value to sign). value to sign).
4. Place the resulting signature value in the 'signature' field of 5. Place the resulting signature value in the 'signature' field of
the map. the map.
How to verify a signature: How to verify a signature:
1. Create a Sig_structure object and populate it with the 1. Create a Sig_structure object and populate it with the
appropriate fields. For body_protected and sign_protected, if appropriate fields. For body_protected and sign_protected, if
the fields are not present in their corresponding maps, an bstr the fields are not present in their corresponding maps, an bstr
of length zero is used. of length zero is used.
2. Create the value ToBeSigned by encoding the Sig_structure to a 2. If the application has supplied external additional authenticated
data to be included in the computation, then it is placed in the
'external_aad' field. If no data was supplied, then a zero
length binary value is used.
3. Create the value ToBeSigned by encoding the Sig_structure to a
byte string. byte string.
3. Call the signature verification algorithm passing in K (the key 4. Call the signature verification algorithm passing in K (the key
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
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One of the byproducts of using the same technique for encrypting and One of the byproducts of using the same technique for encrypting and
encoding both the content and the keys using the various key encoding both the content and the keys using the various key
management techniques, is a requirement that all of the key management techniques, is a requirement that all of the key
management techniques use an Authenticated Encryption (AE) algorithm. management techniques use an Authenticated Encryption (AE) algorithm.
(For the purpose of this document we use a slightly loose definition (For the purpose of this document we use a slightly loose definition
of AE algorithms.) When encrypting the plain text, it is normal to of AE algorithms.) When encrypting the plain text, it is normal to
use an Authenticated Encryption with Additional Data (AEAD) use an Authenticated Encryption with Additional Data (AEAD)
algorithm. For key management, either AE or AEAD algorithms can be algorithm. For key management, either AE or AEAD algorithms can be
used. See Appendix A for more details about the different types of used. See Appendix A for more details about the different types of
algorithms. [CREF13] 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 contains the information about the plain text or protected is described in Section 3.
encryption process that is to be integrity protected. The field
is encoded in CBOR as a 'bstr'. The contents of the protected
field is a CBOR map of the protected data names and values. The
map is CBOR encoded before placing it into the bstr. Only values
associated with the current cipher text are to be placed in this
location even if the value would apply to multiple recipient
structures.
unprotected contains information about the plain text that is not unprotected is described in Section 3.
integrity protected. Only values associated with the current
cipher text are to be placed in this location even if the value
would apply to multiple recipient structures.
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.
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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 symmetric key, then the CEK is
either the derived key or encrypted by the derived key. 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 or other shared secret value.
Section 12 provides details on a number of different key management Section 12 provides details on a number of different key management
algorithms and discusses which elements need to be present for each algorithms and discusses which parameters need to be present for each
of the key management techniques. 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,
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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
] ]
1. Copy the protected header field from the message to be sent. 1. Copy the protected header field from the message to be sent.
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. length binary value is used. (See Section 4.1 for application
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 key
management method being used: For: management method 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.
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and the P (the plain text). Place the returned cipher text into and the P (the plain text). Place the returned cipher text into
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. JOSE used a variant of the doing MAC authentication in COSE. This document allows for the use
signature structure for doing MAC operations and it is restricted to of all of the same methods of key management as are allowed for
using a single pre-shared secret to do the authentication. [CREF14] encryption.
This document allows for the use of all of the same methods of key
management as are allowed for 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 of the key management
methods can be used for this purpose. The second mode is to both methods can be used for this purpose. The second mode is to both
check that the content has not been changed since the MAC was check that the content has not been changed since the MAC was
computed, and to use key management to verify who sent it. The key computed, and to use key management to verify who sent it. The key
management modes that support this are ones that either use a pre- management modes that support this are ones that either use a pre-
shared secret, or do static-static key agreement. In both of these shared secret, or do static-static key agreement. In both of these
cases the entity MACing the message can be validated by a key cases the entity MACing the message can be validated by a key
skipping to change at page 21, line 39 skipping to change at page 23, line 5
? 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 contains attributes about the payload that are to be protected is described in Section 3.
protected by the MAC. An example of such an attribute would be
the content type ('cty') attribute. The content is a CBOR map of
attributes that is encoded to a byte stream. This field MUST NOT
contain attributes about the recipient, even if those attributes
are common across multiple recipients. At least one of protected
and unprotected MUST be present.
unprotected contains attributes about the payload that are not unprotected is described in Section 3.
protected by the MAC. An example of such an attribute would be
the content type ('cty') attribute. This field MUST NOT contain
attributes about a recipient, even if the attributes are common
across multiple recipients. At least one of protected and
unprotected MUST be present.
payload contains the serialized content to be MACed. If the payload payload contains the serialized content to be MACed. If the payload
is not present in the message, the application is required to is not present in the message, the application is required to
supply the payload separately. The payload is wrapped in a bstr supply the payload separately. The payload is wrapped in a bstr
to ensure that it is transported without changes, if the payload to ensure that it is transported without changes, if the payload
is transported separately it is the responsibility of the 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.
tag contains the MAC value. tag contains the MAC value.
recipients contains the recipient information. See the description recipients contains the recipient information. See the description
under COSE_Encryption for more info. under COSE_Encryption for more info.
MAC_structure = [ MAC_structure = [
protected: bstr, protected: bstr,
external_aad: bstr, external_aad: bstr,
payload: bstr payload: bstr
] ]
How to compute a MAC: How to compute a MAC:
1. Create a MAC_structure and copy the protected and payload 1. Create a MAC_structure and copy the protected and payload fields
elements from the COSE_mac structure. from the COSE_mac structure.
2. If the application has supplied external authenticated data, 2. If the application has supplied external authenticated data,
encode it as a binary value and place in the MAC_structure. If encode it as a binary value and place in the MAC_structure. If
there is no external authenticated data, then use a zero length there is no external authenticated data, then use a zero length
'bstr'. 'bstr'. (See Section 4.1 for application guidance on
constructing this field.)
3. Encode the MAC_structure using a canonical CBOR encoder. The 3. Encode the MAC_structure using a canonical CBOR encoder. The
resulting bytes is the value to compute the MAC on. resulting bytes is the value to compute the MAC on.
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
There are only a few changes between JOSE and COSE for how keys are A COSE Key structure is built on a CBOR map object. The set of
formatted. As with JOSE, COSE uses a map to contain the elements of common parameters that can appear in a COSE Key can be found in the
a key. Those values, which in JOSE are base64url encoded because IANA registry 'COSE Key Common Parameter Registry' (Section 15.6).
they are binary values, are encoded as bstr values in COSE. Additional parameters defined for different key types can be found in
the IANA registry 'COSE Key Type Parameters' (Section 15.7).
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
least one element in the array. [CREF12]
The CDDL grammar describing a COSE_Key and COSE_KeySet is: [CREF13]
For COSE we use the same set of fields that were defined in
[RFC7517]. [CREF15] [CREF16]
COSE_Key = { COSE_Key = {
kty => tstr / int, key_kty => tstr / int,
? key_ops => [+ tstr / int ], ? key_ops => [+ (tstr / int) ],
? alg => tstr / int, ? key_alg => tstr / int,
? 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. All other The element "kty" is a required element in a COSE_Key map.
elements are optional and not all of the elements listed in [RFC7517]
or [RFC7518] have been listed here even though they can all appear in
a COSE_Key map.
7.1. COSE Key Map Labels 7.1. COSE Key Common Parameters
This document defines a set of common map elements for a COSE Key This document defines a set of common parameters for a COSE Key
object. Table 3 provides a summary of the elements defined in this object. Table 3 provides a summary of the parameters defined in this
section. There are also a set of map elements that are defined for a section. There are also a set of parameters that are defined for a
specific key type. Key specific elements can be found in Section 13. specific key type. Key type specific parameters can be found in
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 | |
| | | | | | | | | | | |
| key_ops | 4 | [* | | Restrict set of | | key_ops | 4 | [* | | Restrict set of |
| | | (tstr/int)] | | permissible | | | | (tstr/int)] | | permissible |
skipping to change at page 24, line 38 skipping to change at page 25, line 38
| 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 3: Key Map Labels
kty: This field 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 fields to be found. The set of structure, and thus the set of key type specific parameters to be
values can be found in Table 19. found. The set of values can be found in Table 21.
alg: This field is used to restrict the algorithms that are to be alg: This parameter is used to restrict the algorithms that are to
used with this key. If this field 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 field 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' field in key. This field is intended for matching against a 'kid'
a message in order to filter down the set of keys that need to be parameter in a message in order to filter down the set of keys
checked. that need to be checked.
key_ops: This field 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 4.
Only the 'kty' field MUST be present in a key object. All other Only the 'kty' field MUST be present in a key object. All other
members may be omitted if their behavior is not needed. 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 26 skipping to change at page 27, line 26
key_ops_wrap=5 key_ops_wrap=5
key_ops_unwrap=6 key_ops_unwrap=6
key_ops_agree=7 key_ops_agree=7
8. Signature Algorithms 8. Signature Algorithms
There are two basic signature algorithm structures that can be used. There are two basic signature algorithm structures that can be used.
The first is the common signature with appendix. In this structure, The first is the common signature with appendix. In this structure,
the message content is processed and a signature is produced, the the message content is processed and a signature is produced, the
signature is called the appendix. This is the message structure used signature is called the appendix. This is the message structure used
by our common algorithms such as ECDSA and RSASSA-PSS. (In fact two by our common algorithms such as ECDSA and RSASSA-PSS. (In fact the
of the letters in RSASSA-PSS are signature appendix.) The basic SSA in RSASSA-PSS stands for Signature Scheme with Appendix.) The
structure becomes: basic structure becomes:
signature = Sign(message content, key) signature = Sign(message content, key)
valid = Verification(message content, key, signature) valid = Verification(message content, key, signature)
The second is a signature with message recovery. (An example of such The second is a signature with message recovery. (An example of such
an algorithm is [TBD].) In this structure, the message content is an algorithm is [PVSig].) In this structure, the message content is
processed, but part of is included in the siguature. Moving bytes of processed, but part of is included in the signature. Moving bytes of
the message content into the signature allows for an effectively the message content into the signature allows for an effectively
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
skipping to change at page 27, line 21 skipping to change at page 28, line 21
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 security strength of the signature is no greater than the minimum The ECDSA signature algorithm is parameterized with a hash function
of the security strength associated with the bit length of the key (h. In the event that the length of the hash function output is
and the security strength of the hash function. When a hash function greater than group of the key, the left most bytes of the hash output
is used that has greater security than is provided by the length of are used.
the key, the signature algorithm uses the leftmost keyLength bits of
the hash function output. The algorithms defined in this document can be found in Table 5.
+-------+-------+---------+------------------+ +-------+-------+---------+------------------+
| 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 |
+-------+-------+---------+------------------+ +-------+-------+---------+------------------+
skipping to change at page 28, line 14 skipping to change at page 29, line 14
bits to get to the correct length. The two integers are then bits to get to the correct length. The two integers are then
concatenated together to form a byte string that is the resulting concatenated together to form a byte string that is the resulting
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
On of the issues that needs to be discussed is substitution attacks. The security strength of the signature is no greater than the minimum
There are two different things that can potentially be substituted in of the security strength associated with the bit length of the key
this algorithm. Both of these attacks are current theoretical only. and the security strength of the hash function. When a 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.
The first substitution attack is changing the curve used to validate System which have poor random number generation can leak their keys
the signature, the only requirement is that the order of the key by signing two messages with the same value of 'k'. [RFC6979]
match the length of R and S. It is theoretically possible to use a provides a method to deal with this problem by making 'k' be
different curve and get a different result. We current do not have deterministic based on the message content rather than randomly
any way to deal with this version of the attack except to restrict generated. Applications which specify ECDSA should evaluate the
the overall set of curves that can be used. ability to get good random number generation and recommend this when
it is not possible. Note: Use of this technique even when good
random number generation exists may still be a good idea.
The second substitution attack is to change the hash function that is There are two substitution that can theoretically be mounted against
used to verify the signature. This attack can be mitigated by the ECDSA signature algorithm.
including the signature algorithm identifier in the data to be
signed. o Changing the curve used to validate the signature: If one changes
the curve used to validate the signature, then potentially one
could have a two messages with the same signature each computed
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
the client. An example would be to change from using the curve
P-256 to using Curve25519. (Both are 256 bit curves.) We current
do not have any way to deal with this version of the attack except
to restrict the overall set of curves that can be used.
o Change the hash function used to validate the signature: If one
has either two different hash functions of the same length, or one
can truncate a hash function down, then one could potentially find
collisions between the hash functions rather than within a single
hash function. (For example, truncating SHA-512 to 256 bits might
collide with a SHA-256 bit hash value.) This attack can be
mitigated by including the signature algorithm identifier in the
data to be signed.
8.2. RSASSA-PSS 8.2. RSASSA-PSS
The RSASSA-PSS signature algorithm is defined in [RFC3447]. The RSASSA-PSS signature algorithm is defined in [RFC3447].
The RSASSA-PSS signature algorithm is parametized with a hash The RSASSA-PSS signature algorithm is parametized with a hash
function, a mask generation function and a salt length (sLen). For function (h), a mask generation function (mgf) and a salt length
this specification, the mask generation function is fixed to be MGF1 (sLen). For this specification, the mask generation function is
as defined in [RFC3447]. It has been recommended that the same hash fixed to be MGF1 as defined in [RFC3447]. It has been recommended
function be used for hashing the data as well as in the mask that the same hash function be used for hashing the data as well as
generation function, for this specification we following this in the mask generation function, for this specification we following
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.
Three algorithms are defined in this document. These algorithms are: The algorithms defined in this document can be found in Table 6.
PS256: This uses the hash algorithm SHA-256 for signature
processing. The value used for this algorithm is -10. The key
type used for this algorithm is 'RSA'.
PS384: This uses the hash algorithm SHA-384 for signature
processing. The value used for this algorithm is "PS384". The
key type used for this algorithm is 'RSA'.
PS512: This uses the hash algorithm SHA-512 for signature
processing. The value used for this algorithm is -11. The key
type used for this algorithm is 'RSA'.
There are no algorithm parameters defined for these signature
algorithms. A summary of the algorithm definitions can be found in
Table 6.
+-------+-------+---------+-------------+-----------------------+ +-------+-------+---------+-------------+-----------------------+
| name | value | hash | salt length | description | | name | value | hash | salt length | description |
+-------+-------+---------+-------------+-----------------------+ +-------+-------+---------+-------------+-----------------------+
| PS256 | -10 | SHA-256 | 32 | RSASSA-PSS w/ SHA-256 | | PS256 | -26 | SHA-256 | 32 | RSASSA-PSS w/ SHA-256 |
| | | | | | | | | | | |
| PS384 | * | SHA-384 | 48 | RSASSA-PSS w/ SHA-384 | | PS384 | -27 | SHA-384 | 48 | RSASSA-PSS w/ SHA-384 |
| | | | | | | | | | | |
| PS512 | -11 | SHA-512 | 64 | RSASSA-PSS w/ SHA-512 | | PS512 | -28 | SHA-512 | 64 | RSASSA-PSS w/ SHA-512 |
+-------+-------+---------+-------------+-----------------------+ +-------+-------+---------+-------------+-----------------------+
Table 6: RSA Algorithm Values Table 6: RSASSA-PSS Algorithm Values
8.2.1. Security Considerations 8.2.1. Security Considerations
Key size. is there a MUST for 2048? or do we need to specify a In addition to needing to worry about keys that are too small to
minimum here? provide the required security, there are issues with keys that are
too large. Denial of service attacks have been mounted with overly
large keys. This has the potential to consume resources with
potentially bad keys. There are two reasonable ways to address this
attack. First, a key should not be used for a cryptographic
operation until it has been matched back to an authorized user. This
approach means that no cryptography would be done except for
authorized users. Second, applications can impose maximum as well as
minimum length requirements on keys. This limits the resources
consumed even if the matching is not performed until the cryptography
has been done.
There is a theoretical hash substitution attack that can be mounted
against RSASSA-PSS. However, the requirement that the same hash
function be used consistently for all operations is an effective
mitigation against it. Unlike ECDSA, hash functions are not
truncated so that the full hash value is always signed. The internal
padding structure of RSASSA-PSS means that one needs to have multiple
collisions between the two hash functions in order to be successful
in producing a forgery based on changing the hash function. This is
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.)
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, in part, to deal with the birthday [RFC2104][RFC4231] was designed to deal with length extension
attacks on straight hash functions. The algorithm was also designed attacks. The algorithm was also designed to allow for new hash
to all for new hash algorithms to be directly plugged in without algorithms to be directly plugged in without changes to the hash
changes to the hash function. The HMAC design process has been function. The HMAC design process has been vindicated as, while the
vindicated as, while the security of hash algorithms such as MD5 has security of hash algorithms such as MD5 has decreased over time, the
decreased over time, the security of HMAC combined with MD5 has not security of HMAC combined with MD5 has not yet been shown to be
yet been shown to be compromised [RFC6151]. compromised [RFC6151].
For use in constrained environments, we define a set of HMAC The HMAC algorithm is parameterized by an inner and outer padding, a
algorithms that are truncated. There are currently no known issues hash function (h) and an authentication tag value length. For this
when truncating, however the security strength of the message tag is specification, the inner and outer padding are fixed to the values
correspondingly reduced in strength. When truncating, the left most set in [RFC2104]. The length of the authentication tag corresponds
tag length bits are kept and transmitted. to the difficulty of producing a forgery. For use in constrained
environments, we define a set of HMAC algorithms that are truncated.
There are currently no known issues when truncating, however the
security strength of the message tag is correspondingly reduced in
strength. When truncating, the left most tag length bits are kept
and transmitted.
The algorithm defined in this document can be found in Table 7.
+-----------+-------+---------+--------+----------------------------+ +-----------+-------+---------+--------+----------------------------+
| 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 8 bytes | | 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 7: HMAC Algorithm Values
For some key management methods, the length of the key is known or
determinable from the key management method. For example, if RSA-
OAEP is used then the key will be output at the correct length.
However, if any of the key derivation methods are used, then the size
of the key to be obtained is an input parameter to the key derivation
step. For all HMAC methods defined in this document, the key size
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
TBD. HMAC has proved to be resistant even when used with weakening hash
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
related to the security of an HMAC operation.
9.2. AES Message Authentication Code (AES-MAC) 9.2. AES Message Authentication Code (AES-CBC-MAC)
There are a set of different algorithms that we can specify here. AES-CBC-MAC is defined in [MAC].
Which should it be?
AES-MAC - Use standard CBC mode 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
fixed to all zeros. We provide an array of algorithms for various
key lengths and tag lengths. The algorithms defined in this document
are found in Table 8.
AES-CMAC - RFC 4493 - has improved security over AES-CBC. The +-------------+-------+----------+----------+-----------------------+
padding is different from CBC mode and requires one extra AES | name | value | key | tag | description |
block encryption step plus and xor operation. | | | length | length | |
+-------------+-------+----------+----------+-----------------------+
| AES-MAC | * | 128 | 64 | AES-MAC 128 bit key, |
| 128/64 | | | | 64-bit tag |
| | | | | |
| AES-MAC | * | 256 | 64 | AES-MAC 256 bit key, |
| 256/64 | | | | 64-bit tag |
| | | | | |
| AES-MAC | * | 128 | 128 | AES-MAC 128 bit key, |
| 128/128 | | | | 128-bit tag |
| | | | | |
| AES-MAC | * | 256 | 128 | AES-MAC 256 bit key, |
| 256/128 | | | | 128-bit tag |
+-------------+-------+----------+----------+-----------------------+
Table 8: AES-MAC Algorithm Values
9.2.1. Security Considerations
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
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.
This can be addressed by using different keys for different length
messages. (CMAC mode also addresses this issue.)
o If the same key is used for both encryption and authentication
operations, using CBC modes an attacker can produce messages with
a valid authentication code.
o If the IV can be modified, then messages can be forged. This is
addressed by fixing the IV to all zeros.
10. Content Encryption Algorithms 10. Content Encryption Algorithms
10.1. AES GCM 10.1. AES GCM
The GCM mode is is a generic authenticated encryption block cipher
mode defined in [AES-GCM]. The GCM mode is combined with the AES
block encryption algorithm to define a an AEAD cipher.
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
values. For this document however, the size of the authentication
tag is fixed at 128-bits.
The set of algorithms defined in this document are in Table 9.
+---------+-------+-----------------------------+ +---------+-------+-----------------------------+
| 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 8: Algorithm Value for AES-GCM Table 9: Algorithm Value for AES-GCM
10.1.1. Security Considerations
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 total amount of data encrypted MUST NOT exceed 2^39 - 256 bits
. An explicit check is required only in environments where it is
expected that it might be exceeded.
10.2. AES CCM 10.2. AES CCM
Counter with CBC-MAC (CCM) is a generic authentication encryption Counter with CBC-MAC (CCM) is a generic authentication encryption
block cipher mode defined in [RFC3610]. The CCM mode is combined block cipher mode defined in [RFC3610]. The CCM mode is combined
with the AES block encryption algorithm to define a commonly used with the AES block encryption algorithm to define a commonly used
content encryption algorithm used in constrainted devices. content encryption algorithm used in constrainted devices.
The CCM mode has two parameter choices. The first choice is M, the The CCM mode has two parameter choices. The first choice is M, the
size of the authentication field. The choice of the value for M size of the authentication field. The choice of the value for M
skipping to change at page 32, line 5 skipping to change at page 35, line 18
operations. This favors smaller values of M and larger values of L. operations. This favors smaller values of M and larger values of L.
Less constrained devices do will want to be able to user larger Less constrained devices do will want to be able to user larger
messages and are more willing to generate new keys for every messages and are more willing to generate new keys for every
operation. This favors larger values of M and smaller values of L. operation. This favors larger values of M and smaller values of L.
(The use of a large nonce means that random generation of both the (The use of a large nonce means that random generation of both the
key and the nonce will decrease the chances of repeating the pair on key and the nonce will decrease the chances of repeating the pair on
two different messages.) 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 in length. The nonce 16-bits (2) limits messages to 2^16 bytes (64Kbyte) in length. This
length is 13 bytes allowing for 2^(13*8) possible values of the sufficently long for messages in the constrainted world. The
nonce without repeating. nonce length is 13 bytes allowing for 2^(13*8) possible values of
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
without repeating. without repeating.
The following values are used for M: The following values are used for M:
64-bits (8) produces a 64-bit authentication tag. This implies that 64-bits (8) produces a 64-bit authentication tag. This implies that
there is a 1 in 2^64 chance that an modified message will there is a 1 in 2^64 chance that an modified message will
authenticate. authenticate.
128-bits (16) produces a 128-bit authentication tag. This implies 128-bits (16) produces a 128-bit authentication tag. This implies
that there is a 1 in 2^128 chance that an modified message will that there is a 1 in 2^128 chance that an modified message will
authenticate. authenticate.
+--------------------+--------+----+-----+-----+--------------------+ +--------------------+-------+----+-----+-----+---------------------+
| name | value | L | M | k | description | | name | value | L | M | k | description |
+--------------------+--------+----+-----+-----+--------------------+ +--------------------+-------+----+-----+-----+---------------------+
| AES-CCM-16-64-128 | A281C | 16 | 64 | 128 | AES-CCM mode | | AES-CCM-16-64-128 | 10 | 16 | 64 | 128 | AES-CCM mode |
| | | | | | 128-bit key, | | | | | | | 128-bit key, 64-bit |
| | | | | | 64-bit tag, | | | | | | | tag, 13-byte nonce |
| | | | | | 13-byte nonce | | | | | | | |
| | | | | | | | AES-CCM-16-64-256 | 11 | 16 | 64 | 256 | AES-CCM mode |
| AES-CCM-16-64-192 | A282C | 16 | 64 | 192 | AES-CCM mode | | | | | | | 256-bit key, 64-bit |
| | | | | | 192-bit key, | | | | | | | tag, 13-byte nonce |
| | | | | | 64-bit tag, | | | | | | | |
| | | | | | 13-byte nonce | | AES-CCM-64-64-128 | 30 | 64 | 64 | 128 | AES-CCM mode |
| | | | | | | | | | | | | 128-bit key, 64-bit |
| AES-CCM-16-64-256 | A283C | 16 | 64 | 256 | AES-CCM mode | | | | | | | tag, 7-byte nonce |
| | | | | | 256-bit key, | | | | | | | |
| | | | | | 64-bit tag, | | AES-CCM-64-64-256 | 31 | 64 | 64 | 256 | AES-CCM mode |
| | | | | | 13-byte nonce | | | | | | | 256-bit key, 64-bit |
| | | | | | | | | | | | | tag, 7-byte nonce |
| AES-CCM-64-64-128 | A881C | 64 | 64 | 128 | AES-CCM mode | | | | | | | |
| | | | | | 128-bit key, | | AES-CCM-16-128-128 | 12 | 16 | 128 | 128 | AES-CCM mode |
| | | | | | 64-bit tag, 7-byte | | | | | | | 128-bit key, |
| | | | | | nonce | | | | | | | 128-bit tag, |
| | | | | | | | | | | | | 13-byte nonce |
| AES-CCM-64-64-192 | A882C | 64 | 64 | 192 | AES-CCM mode | | | | | | | |
| | | | | | 192-bit key, | | AES-CCM-16-128-256 | 13 | 16 | 128 | 256 | AES-CCM mode |
| | | | | | 64-bit tag, 7-byte | | | | | | | 256-bit key, |
| | | | | | nonce | | | | | | | 128-bit tag, |
| | | | | | | | | | | | | 13-byte nonce |
| AES-CCM-64-64-256 | A883C | 64 | 64 | 256 | AES-CCM mode | | | | | | | |
| | | | | | 256-bit key, | | AES-CCM-64-128-128 | 32 | 64 | 128 | 128 | AES-CCM mode |
| | | | | | 64-bit tag, 7-byte | | | | | | | 128-bit key, |
| | | | | | nonce | | | | | | | 128-bit tag, 7-byte |
| | | | | | | | | | | | | nonce |
| AES-CCM-16-128-128 | A2161C | 16 | 128 | 128 | AES-CCM mode | | | | | | | |
| | | | | | 128-bit key, | | AES-CCM-64-128-256 | 33 | 64 | 128 | 256 | AES-CCM mode |
| | | | | | 128-bit tag, | | | | | | | 256-bit key, |
| | | | | | 13-byte nonce | | | | | | | 128-bit tag, 7-byte |
| | | | | | | | | | | | | nonce |
| AES-CCM-16-128-192 | A2162C | 16 | 128 | 192 | AES-CCM mode | +--------------------+-------+----+-----+-----+---------------------+
| | | | | | 192-bit key, |
| | | | | | 128-bit tag, |
| | | | | | 13-byte nonce |
| | | | | | |
| AES-CCM-16-128-256 | A2163C | 16 | 128 | 256 | AES-CCM mode |
| | | | | | 256-bit key, |
| | | | | | 128-bit tag, |
| | | | | | 13-byte nonce |
| | | | | | |
| AES-CCM-64-128-128 | A8161C | 64 | 128 | 128 | AES-CCM mode |
| | | | | | 128-bit key, |
| | | | | | 128-bit tag, |
| | | | | | 7-byte nonce |
| | | | | | |
| AES-CCM-64-128-192 | A8162C | 64 | 128 | 192 | AES-CCM mode |
| | | | | | 192-bit key, |
| | | | | | 128-bit tag, |
| | | | | | 7-byte nonce |
| | | | | | |
| AES-CCM-64-128-256 | A8163C | 64 | 128 | 256 | AES-CCM mode |
| | | | | | 256-bit key, |
| | | | | | 128-bit tag, |
| | | | | | 7-byte nonce |
+--------------------+--------+----+-----+-----+--------------------+
Table 9: Algorithm Values for AES-CCM
M00TODO: Make a determination of which ones get 1-, 2- or 3-byte Table 10: Algorithm Values for AES-CCM
identifiers. I.e. which ones are going to be popular.
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
skipping to change at page 34, line 18 skipping to change at page 37, line 22
is possible to do a pre-computation attack against the algorithm in is possible to do a pre-computation attack against the algorithm in
cases where the portions encryption content is highly predictable. cases where the portions encryption content is highly predictable.
This reduces the security of the key size by half. Ways to deal with This reduces the security of the key size by half. Ways to deal with
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
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
which is not AES and thus would not suffer from any future weaknesses
found in AES. These cryptographic functions are designed to be fast
in software only implementations.
The ChaCha20/Poly1305 AEAD construction defined in [RFC7539] has no
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
cipher text as an option. We define one algorithm identifier for
this algorithm in Table 11.
+-------------------+-------+----------------------------------+
| name | value | description |
+-------------------+-------+----------------------------------+
| ChaCha20/Poly1305 | 11 | ChaCha20/Poly1305 w/ 256-bit key |
+-------------------+-------+----------------------------------+
Table 11: Algorithm Value for AES-GCM
10.3.1. Security Considerations
The pair of key, nonce MUST be unique for every invocation of the
algorithm. Nonce counters are considered to be an acceptable way of
ensuring that they are unique.
11. Key Derivation Functions (KDF) 11. Key Derivation Functions (KDF)
11.1. HMAC-based Extract-and-Expand Key Derivation Function (HKDF) 11.1. HMAC-based Extract-and-Expand Key Derivation Function (HKDF)
See [RFC5869]. The HKDF key derivation algorithm is defined in [RFC5869].
Inputs: The HKDF algorithm is defined to take a number of inputs These inputs
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. The 'salt' parameter is different key values will be generated. A parameter to carry the
encoded as a binary string. This parameter is protected by being salt is defined in Table 13. 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 context information - Information that describes the context in
which the resulting value will be used. Making this information
specific to the context that the material is going to be used
ensures that the resulting material will always be unique. The
context structure used is encoded into the algorithm identifier.
hash function - The underlying hash function to be used in the hash function - The underlying hash function to be used in the
HKDF algorithm. The hash function is encoded into the HKDF HKDF algorithm. The hash function is encoded into the HKDF
algorithm selection. algorithm selection.
+----------+---------+---------+ HKDF is defined to use HMAC as the underlying PRF. However, it is
| name | hash | context | possible to use other functions in the same construct to provide a
+----------+---------+---------+ different KDF function that may be more appropriate in the
| HKDF-256 | SHA-256 | XXX | 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
| HKDF-512 | SHA-512 | XXX | random shared secret of the correct length, the extract step can be
+----------+---------+---------+ skipped. The extract cannot be skipped if the secret is not
uniformly random, for example if it is the result of a ECDH key
agreement step.
Table 10: HKDF algorithms The algorithms defined in this document are found in Table 12
+-------------+-------------+----------+----------------------------+
| name | hash | Skip | context |
| | | extract | |
+-------------+-------------+----------+----------------------------+
| HKDF | SHA-256 | no | XXX |
| SHA-256 | | | |
| | | | |
| HKDF | SHA-512 | no | XXX |
| SHA-512 | | | |
| | | | |
| HKDF AES- | AES-CBC-128 | yes | HKDF using AES-MAC as the |
| MAC-128 | | | PRF w/ 128-bit key |
| | | | |
| HKDF AES- | AES-CBC-128 | yes | HKDF using AES-MAC as the |
| MAC-256 | | | PRF w/ 256-bit key |
+-------------+-------------+----------+----------------------------+
Table 12: HKDF algorithms
+------+-------+------+-------------+ +------+-------+------+-------------+
| name | label | type | description | | name | label | type | description |
+------+-------+------+-------------+ +------+-------+------+-------------+
| salt | -20 | bstr | Random salt | | salt | -20 | bstr | Random salt |
+------+-------+------+-------------+ +------+-------+------+-------------+
Table 11: HKDF parameters Table 13: 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. stand alone store and forward messaging processes. In [SP800-56A],
PartyU is the initiator and PartyV is the responder. The
specification is written with the idea of on-line protocols rather
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 line without changing the role information.
Using the PartyU and PartyV fields is the easiest way to get
different keys in each direction. The use of a transaction
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
set of transactions. Combining nonce fields with the transaction
identifier provides a method so that a different key is used for each
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.
The fields in the array are: 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
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 uses a shorter key than algorithm B and thus can be if algorithm A is broken and thus can is easier to find, the key
found easier, the key derived for algorithm B will not contain the derived for algorithm B will not be the same as the key for
key for algorithm A as a prefix.) [CREF17] algorithm B.)
PartyUInfo This field holds information about party U. The PartyUInfo This field holds information about party U. The
ParytUInfo structure is divided into three pieces: ParytUInfo structure is divided into three pieces:
identity This contains the identity information for party U. The identity This contains the identity information for party U. The
identities can be assigned in one of two manners. Firstly, a identities can be assigned in one of two manners. Firstly, a
protocol can assign identities based on roles. For example, protocol can assign identities based on roles. For example,
the roles of "client" and "server" may be assigned to different the roles of "client" and "server" may be assigned to different
entities in the protocol. Each entity would then use the entities in the protocol. Each entity would then use the
correct label for the data they they send or receive. The correct label for the data they they send or receive. The
second way is for a protocol to assign identities is to use a second way is for a protocol to assign identities is to use a
name based on a naming system (i.e. DNS, X.509 names). name based on a naming system (i.e. DNS, X.509 names).
We define an algorithm parameter 'PartyU identity' that can be We define an algorithm parameter 'PartyU identity' that can be
used to carry identity information in the message. However, used to carry identity information in the message. However,
identity information is often known as part of the protocol and identity information is often known as part of the protocol and
can thus be inferred rather than made explicit. If identity can thus be inferred rather than made explicit. If identity
information is carried in the message, applications SHOULD have information is carried in the message, applications SHOULD have
a way of validating the supplied identity information. The a way of validating the supplied identity information. The
identity information does not need to be specified and can be identity information does not need to be specified and can be
left as absent. left as absent.
The identity value supplied will be validated as part of the
key derivation process. If the identity string is wrong, then The identity value supplied will be integrity checked as part
the wrong key will be created. of the key derivation process. If the identity string is
wrong, then the wrong key will be created.
nonce This contains a one time nonce value. The nonce can either nonce This contains a one time nonce value. The nonce can either
be implicit from the protocol or carried as a value in the be implicit from the protocol or carried as a value in the
unprotected headers. [CREF18] unprotected headers.
We define an algorithm parameter 'PartyU nonce' that can be We define an algorithm parameter 'PartyU nonce' that can be
used to carry this value in the message However, the nonce used to carry this value in the message However, the nonce
value could be determined by the application and the value value could be determined by the application and the value
determined from elsewhere. determined from elsewhere.
This item is optional and can be absent. This item is optional and can be absent.
other This contains other information that is defined by the other This contains other information that is defined by the
protocol. protocol.
This item is optional and can be absent. This item is optional and can be absent.
PartyVInfo M00TODO: Copy down from PartyUInfo when that text is PartyVInfo M00TODO: Copy down from PartyUInfo when that text is
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. output value. (This practice means if algorithm A can use two
different key lengths, the key derived for longer key size will
not contain the key for shorter key size as a prefix.)
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.
skipping to change at page 38, line 26 skipping to change at page 42, line 46
| 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 12: Context Algorithm Parameters Table 14: Context Algorithm Parameters
12. Key Management Algorithms 12. Key Management Algorithms
There are a number of different key management methods that can be There are a number of different key management methods that can be
used in the COSE encryption system. In this section we will discuss used in the COSE encryption system. In this section we will discuss
each of the key management methods, what fields need to be specified, each of the key management methods, what fields need to be specified,
and which algorithms are defined in this document to deal with each and which algorithms are defined in this document to deal with each
of them. of them.
The names of the key management methods used here are the same as are The names of the key management methods used here are the same as are
skipping to change at page 39, line 8 skipping to change at page 43, line 22
At the moment we do not have any key management methods that allow 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 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] if, for example, the AES-GCM Key wrap method defined in [RFC7518]
were extended to allow for authenticated data. In that event, the were extended to allow for authenticated data. In that event, the
use of the 'protected' field, which is current forbidden below, would use of the 'protected' field, which is current forbidden below, would
be permitted. be permitted.
12.1. Direct Encryption 12.1. Direct Encryption
In direct encryption mode, a shared secret between the sender and the In direct encryption mode, a shared secret between the sender and the
recipient is used as the key. [CREF19] When direct encryption mode recipient is used as the key. When direct encryption mode is used,
is used, it MUST be the only mode used on the message. It is a it MUST be the only mode used on the message. It is a massive
massive security leak to have both direct encryption and a different security leak to have both direct encryption and a different key
key management mode on the same message. management mode on the same message.
For JOSE, direct encryption key management is the only key management For JOSE, direct encryption key management is the only key management
method allowed for doing MACed messages. In COSE, all of the key method allowed for doing MACed messages. In COSE, all of the key
management methods can be used for MACed messages. 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', 'ciphertext' and 'recipients' fields MUST be
absent. 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 shared parameter and SHOULD contain a parameter identifying the shared
secret. secret.
12.1.1. Direct Key 12.1.1. Direct Key
We define two key agreement algorithms that function as direct key This key management technique is the simplest method, the supplied
algorithms. These algorithms are: key is directly used as the key for the next layer down in the
message. There are no algorithm parameters defined for this key
management methods. The algorithm identifier assignment can be found
in Table 15.
Direct: This key management technique is the simplest method, the +--------+-------+-------------------+
supplied key is directly used as the key for the next layer down | name | value | description |
in the message. There are no algorithm parameters defined for +--------+-------+-------------------+
this key management methods. | direct | -6 | Direct use of CEK |
+--------+-------+-------------------+
Direct KDF: This key managment takes a common shared secret between Table 15: Direct Key
the two parties and applies the HKDF function (Section 11.1) using
the context structure defined in Section 11.2 to transform the
shared secret into the necessary key. Either the 'salt' parameter
of HKDF or the partyU 'nonce' parameter of the context structure
MUST be present. This parameter can be generated either randomly
or deterministically, the requirement is that it be a unique value
for the key pair in question.
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 function underlying HKDF, i.e 256-bits. While there
is no way to guarantee that it will be unique, there is a high
probability that it will be unique. If the salt/nonce value is
generated deterministically, it can be guaranteed to be unique and
thus there is no length requirement.
+------------+-------+--------------+----------------------+ 12.1.1.1. Security Considerations
| name | value | KDF | description |
+------------+-------+--------------+----------------------+
| direct | -6 | N/A | Direct use of CEK |
| | | | |
| direct+KDF | * | HKDF SHA-256 | Shared secret w/ KDF |
+------------+-------+--------------+----------------------+
Table 13: Direct Key The direct key management technique has several potential problems
that need to be considered:
12.1.1.1. Security Considerations o These keys need to have some method to be regularly updated over
time. All of the content encryption algorithms specified in this
document have limits on how many times a key can be used without
significant loss of security.
Lifetime, Length, Compromise 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
used for multiple different algorithms. One example of this is
the use of a single key both for CBC encryption mode and CBC-MAC
authentication mode.
o Breaking one message means all messages are broken. If an
adversary succeeds in determining the key for a single message,
then the key for all messages is also determined.
12.1.2. Direct Key with KDF
This key managment takes a common shared secret between the two
parties and applies the HKDF function (Section 11.1) using the
context structure defined in Section 11.2 to transform the shared
secret into the necessary key. Either the 'salt' parameter of HKDF
or the partyU 'nonce' parameter of the context structure MUST be
present. This parameter can be generated either randomly or
deterministically, the requirement is that it be a unique value for
the key pair in question.
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
function underlying HKDF, i.e 256-bits. While there is no way to
guarantee that it will be unique, there is a high probability that it
will be unique. If the salt/nonce value is generated
deterministically, it can be guaranteed to be unique and thus there
is no length requirement.
Since with this technique a new key can be generated for every
message, the restrictions on IVs can frequently be relaxed. For the
content encryption algorithms used in this document IVs must be
unique for a specific key. If the key is altered then the IV can be
re-used. Alternatively, an application can be the IV be generated
from the same context as the key is by changing the algorithm
identifier to the string "IV-GENERATION".
The set of algorithms defined in this document can be found in
Table 16.
+--------------------+-------+-------------+------------------------+
| name | value | KDF | description |
+--------------------+-------+-------------+------------------------+
| direct+KDF-SHA-256 | * | HKDF | Shared secret w/ KDF |
| | | SHA-256 | |
| | | | |
| direct+KDF-SHA-512 | * | HKDF | Shared secret w/ KDF |
| | | SHA-512 | |
| | | | |
| direct+KDF-AES-128 | * | HKDF AES- | Shared secret w/ AES- |
| | | MAC-128 | MAC 128-bit key |
| | | | |
| direct+KDF-AES-256 | * | HKDF AES- | Shared secret w/ AES- |
| | | MAC-256 | MAC 256-bit key |
+--------------------+-------+-------------+------------------------+
Table 16: Direct Key
12.1.2.1. Security Considerations
The shared secret need to have some method to be regularly updated
over time. The shared secret is forming the basis of trust, although
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
then encrypted by a shared secret between the sender and the then encrypted by a shared secret between the sender and the
recipient. All of the currently defined key wrapping algorithms for recipient. All of the currently defined key wrapping algorithms for
JOSE (and thus for COSE) are AE algorithms. Key wrapping mode is JOSE (and thus for COSE) are AE algorithms. Key wrapping mode is
considered to be superior to direct encryption if the system has any considered to be superior to direct encryption if the system has any
capability for doing random key generation. This is because the capability for doing random key generation. This is because the
shared key is used to wrap random data rather than data has some shared key is used to wrap random data rather than data has some
skipping to change at page 41, line 4 skipping to change at page 46, line 26
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. [CREF20] The encryption algorithms defined in this document. [CREF14] The
algorithm requires a single fixed parameter, the initial value. This algorithm requires a single fixed parameter, the initial value. This
is fixed to the value specified in Section 2.2.3.1 of [RFC3394]. is fixed to the value specified in Section 2.2.3.1 of [RFC3394].
There are no public parameters that vary on a per invocation basis. There are no 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 14: AES Key Wrap Algorithm Values Table 17: AES Key Wrap Algorithm Values
12.2.1.1. Security Considerations for AES-KW 12.2.1.1. Security Considerations for AES-KW
There are no specific security considerations for this algorithm. The shared secret need to have some method to be regularly updated
over time. The shared secret is forming the basis of trust, although
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
standards. Key Encryption mode differs from Key Wrap mode in that it standards. Key Encryption mode differs from Key Wrap mode in that it
uses an asymmetric encryption algorithm rather than a symmetric uses an asymmetric encryption algorithm rather than a symmetric
encryption algorithm to protect the key. The only current Key encryption algorithm to protect the key. This document defines one
Encryption mode algorithm supported is RSAES-OAEP. Key Encryption mode algorithm.
The COSE_encrypt structure for the recipient is organized as follows: When using a key encryption algorithm, 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 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 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
asymmetric key. asymmetric key.
12.3.1. RSA OAEP 12.3.1. RSAES-OAEP
+----------+-------+-----------------------+
| name | value | description |
+----------+-------+-----------------------+
| RSA-OAEP | -2 | RSAES OAEP w/ SHA-256 |
+----------+-------+-----------------------+
Table 15: RSA OAEP Algorithm Values RSAES-OAEP is an asymmetric key encryption algorithm. The defintion
of RSAEA-OAEP can be find in Section 7.1 of [RFC3447]. The algorithm
is parameterized using a masking generation function (mgf), a hash
function (h) and encoding parameters (P). For the algorithm
identifiers defined in this section:
12.3.1.1. Security Considerations for RSA OAEP o mgf is always set to MFG1 from [RFC3447] and uses the same hash
function as h.
A key size of 2048 bits or larger MUST be used with this algorithm. o P is always set to the empty octet string.
Table 18 summarizes the rest of the values.
+----------------------+-------+---------+-----------------------+
| name | value | hash | description |
+----------------------+-------+---------+-----------------------+
| 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 |
+----------------------+-------+---------+-----------------------+
Table 18: RSAES-OAEP Algorithm Values
12.3.1.1. Security Considerations for RSAES-OAEP
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.[CREF21] Applications can impose additional restrictions on length.[CREF15] Applications can impose additional restrictions on
the length of the modulus. the 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 When using the 'Direct Key Agreement' key managment method, the two
parties use a key agreement method to create a shared secret. A KDF parties use a key agreement method to create a shared secret. A KDF
is then applied to the shared secret to derive a key to be used in is then applied to the shared secret to derive a key to be used in
protecting the data. This key is normally used as a CEK or MAC key, 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 but could be used for other purposes if more than two layers are in
use (see Appendix B). use (see Appendix B).
skipping to change at page 42, line 45 skipping to change at page 48, line 38
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:
Ephemeral-Static DH: where the sender of the message creates a one - Ephemeral-Static DH: where the sender of the message creates a
time DH key and uses a static key for the recipient. The use of one time DH key and uses a static key for the recipient. The use
the ephemeral sender key means that no additional random input is of the ephemeral sender key means that no additional random input
needed as this is randomly generated for each message. is needed as this is randomly generated for each message.
Static-Static DH: where a static key is used for both the sender Static-Static DH: where a static key is used for both the sender
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, it MUST be the only key
management mode used on the message and there MUST be only one management mode used on the message and there MUST be only one
recipient. This method creates the key directly and that makes it recipient. This method creates the key directly and that makes it
difficult to mix with additional recipients. If multiple recipients difficult to mix with additional recipients. If multiple recipients
are needed, then the version with key wrap (Section 12.5.1) needs to are needed, then the version with key wrap needs to be used.
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.
12.4.1. ECDH 12.4.1. ECDH
NOTE: Curves 25519 and Goldilocks are elements at risk. The basic mathematics for Elliptic Curve Diffie-Hellman can be found
in [RFC6090]. Two new curves have been defined in
We define one set of key agreement algorithms structured around [I-D.irtf-cfrg-curves].
Elliptic Curves Diffie-Hellman problem. [CREF22] We define both an
ephemeral-static and a static-static version of these algorithms. We
allow for multiple curves to be used, it needs to be noted that the
math required for the curves as well as the point representation is
going to be different. [CREF23]
We setup to use two different curve structures for the ECDH
algorithms.
Weierstrass Curves: These are the ones one is used to seeing from
NIST. We define three NIST curves for use with this document.
These curves are P-256, P-384 and P-512. (The mathematics can be
found in [RFC6090].) For these curves, the key type 'EC2' is used
(Section 13.1.2).
Montgomery Curves: These curves are Curve25519 and Goldilocks.
(The mathematics can be found in [I-D.irtf-cfrg-curves].) For
these curves, the key type 'EC1' is used (Section 13.1.1).
As shown in Table 16 we define two ECDH algorithm identifiers for EC
direct key agreement. These identifiers are:
ECDH-ES: This algorithm does a key agreement operation using a
static key for the recipient and an ephemeral key for the sender.
The ephemeral key MUST be generated fresh for every message. The
HKDF function (Section 11.1) is used with the context structure in
Section 11.2 to transform the key agreement secret into the
necessary key. Since the ephemeral key is generated freshly, the
'salt' parameter of HKDF is not needed and can be absent.
One new algorithm parameter is defined for use with this
algorithm. This parameter is:
ephemeral key: This parameter is used to hold and transport the ECDH is parameterized by the following:
ephemeral key generated by the sender of the message. This
parameter has a label of -1 and a type of COSE_Key. This
parameter can be placed in the unprotected bucket, if it is
changed then the correct key will not be able to be generated.
The parameter is summarized in Table 17. o Curve Type/Curve: The curve selected controls not only the size of
the shared secret, but the mathematics for computing the shared
secret. The curve selected also controls how a point in the curve
is represented and what happens for the identity points on the
curve. In this specification we allow for a number of different
curves to be used. The curves are defined in Table 22.
Since the only the math is changed by changing the curve, the
curve is not fixed for any of the algorithm identifiers we define,
instead it is defined by the points used.
ECDH-SS: This algorithm does a key agreement operation using two o Ephemeral-static or static-static: The key agreement process may
static keys, one for the recipient and one for the sender. The be done using either a static or an ephemeral key at the senders
HKDF function (Section 11.1) is used with the context structure in side. When using ephemeral keys, the sender MUST generate a new
Section 11.2 to transform the key agreement secret into the ephemeral key for every key agreement operation. The ephemeral
necessary key. Either the 'salt' parameter of HKDF or the partyU key is placed in in the 'ephemeral key' parameter and MUST be
'nonce' parameter of the context structure MUST be present. This present for all algorithm identifiers which use ephemeral keys.
parameter can be generated either randomly or deterministically, When using static keys, the sender MUST either generate a new
the requirement is that it be a unique value for the key pair in random value placed in either in the KDF parameters or the context
question. structure. For the KDF functions used, this means either in the
If the salt/nonce value is generated randomly, then it is 'salt' parameter for HKDF (Table 13) or in in the 'PartyU nonce'
suggested that the length of the random value be the same length parameter for the context struture (Table 14) MUST be present.
as the hash function underlying HKDF, i.e 256-bits. While there (Both may be present if desired.) The value in the parameter MUST
is no way to guarantee that it will be unique, there is a high be unique for the key pair being used. It is acceptable to use a
probability that it will be unique. If the salt/nonce value is global counter which is incremented for every static-static
generated deterministically, it can be guaranteed to be unique and operation and use the resulting value. When using static keys,
thus there is no length requirement. the static key needs to be identified to the recipient. The
Two new algorithm parameters are defined for use with this static key can be identified either by providing the key ('static
algorithm. These parameters are: key') or by providing a key identifier for the static key ('static
key id'). Both of these parameters are defined in Table 20
static key: This parameter is used to hold and transport the o Key derivation algorithm: The result of an ECDH key agreement
static key used by the sender of the message. This parameter process does not provide a uniformly random secret, as such it
has the label of -2 and a type of COSE_Key. The parameter can needs to be run through a KDF in order to produce a usable key.
be placed in the unprotected bucket, if it is changed then the Processing the secret through a KDF also allows for the
correct key will not be able to be generated. If the data introduction of both context material, how the key is going to be
origination service is desired, then the message recipient used, and one time material in the even to of a static-static key
needs to validate that the key in this field is associated with agreement.
the sender.
static key identifier: This parameter is used to hold a reference o Key Wrap algorithm: The key wrap algorithm can be 'none' if the
to the static key used by the sender of the message. The value result of the KDF is going to be used as the key directly. This
is expected to match the 'kid' member of a COSE_Key structure option, along with static-static, should be used if knowledge
published by the sender. The value in this field cannot be about the sender is desired. If 'none' is used then the content
assumed to uniquely identify a single key, multiple keys may layer encryption algorithm size is value fed to the context
need to be found and tested. Not all of the keys identified by structure. Support is also provided for any of the key wrap
a kid value may be associated with the sender of the message. algorithms defined in section Section 12.2.1. If one of these
If the data origination service is desired, then the message options is used, the input key size to the key wrap algorithm is
recipient needs to validate that the key in this field is the value fed into the context structure as the key size.
associated with the sender.
These parameters are summarized in Table 17. The set of algorithms direct ECDH defined in this document are found
in Table 19.
+---------+---------+--------------+--------------------------------+ +-------------+------+-------+----------------+--------+------------+
| name | value | KDF | description | | name | valu | KDF | Ephemeral- | Key | descriptio |
+---------+---------+--------------+--------------------------------+ | | e | | Static | Wrap | n |
| ECDH-ES | ECDH-ES | HKDF - | ECDH ES w/ HKDF - generate key | +-------------+------+-------+----------------+--------+------------+
| | | SHA-256 | directly | | ECDH-ES + | 50 | HKDF | yes | none | ECDH ES w/ |
| | | | | | HKDF-256 | | - SHA | | | HKDF - |
| ECDH-SS | ECDH-SS | HKDF - | ECDH SS w/ HKDF - generate key | | | | -256 | | | generate |
| | | SHA-256 | directly | | | | | | | key |
+---------+---------+--------------+--------------------------------+ | | | | | | directly |
| | | | | | |
| ECDH-ES + | 51 | HKDF | yes | none | ECDH ES w/ |
| HKDF-512 | | - SHA | | | HKDF - |
| | | -256 | | | generate |
| | | | | | key |
| | | | | | directly |
| | | | | | |
| ECDH-SS + | 52 | HKDF | no | none | ECDH ES w/ |
| HKDF-256 | | - SHA | | | HKDF - |
| | | -256 | | | generate |
| | | | | | key |
| | | | | | directly |
| | | | | | |
| ECDH-SS + | 53 | HKDF | no | none | ECDH ES w/ |
| HKDF-512 | | - SHA | | | HKDF - |
| | | -256 | | | generate |
| | | | | | key |
| | | | | | directly |
| | | | | | |
| ECDH- | 54 | HKDF | yes | A128KW | ECDH ES w/ |
| ES+A128KW | | - SHA | | | Concat KDF |
| | | -256 | | | and AES |
| | | | | | Key wrap |
| | | | | | w/ 128 bit |
| | | | | | key |
| | | | | | |
| ECDH- | 55 | HKDF | yes | A192KW | ECDH ES w/ |
| ES+A192KW | | - SHA | | | Concat KDF |
| | | -256 | | | and AES |
| | | | | | Key wrap |
| | | | | | w/ 192 bit |
| | | | | | key |
| | | | | | |
| ECDH- | 56 | HKDF | yes | A256KW | ECDH ES w/ |
| ES+A256KW | | - SHA | | | Concat KDF |
| | | -256 | | | and AES |
| | | | | | Key wrap |
| | | | | | w/ 256 bit |
| | | | | | key |
| | | | | | |
| ECDH- | 57 | HKDF | no | A128KW | ECDH SS w/ |
| SS+A128KW | | - SHA | | | Concat KDF |
| | | -256 | | | and AES |
| | | | | | Key wrap |
| | | | | | w/ 128 bit |
| | | | | | key |
| | | | | | |
| ECDH- | 58 | HKDF | no | A192KW | ECDH SS w/ |
| SS+A192KW | | - SHA | | | Concat KDF |
| | | -256 | | | and AES |
| | | | | | Key wrap |
| | | | | | w/ 192 bit |
| | | | | | key |
| | | | | | |
| ECDH- | 59 | HKDF | no | A256KW | ECDH SS w/ |
| SS+A256KW | | - SHA | | | Concat KDF |
| | | -256 | | | and AES |
| | | | | | Key wrap |
| | | | | | w/ 256 bit |
| | | | | | key |
+-------------+------+-------+----------------+--------+------------+
Table 16: ECDH Algorithm Values Table 19: 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 17: ECDH Algorithm Parameters Table 20: ECDH Algorithm Parameters
M00TODO: Talk about curves and point formats.
+------------+----------+-------+-------------------------------+
| name | key type | value | description |
+------------+----------+-------+-------------------------------+
| P-256 | EC2 | 1 | NIST P-256 also known as .... |
| | | | |
| P-384 | EC2 | 2 | NIST P-384 also known as .... |
| | | | |
| P-521 | EC2 | 3 | NIST P-512 also known as .... |
| | | | |
| Curve25519 | EC1 | 1 | Provide reference |
| | | | |
| Goldilocks | EC1 | 2 | Provide reference |
+------------+----------+-------+-------------------------------+
Table 18: EC Curves
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 MUST be absent if the key wrap algorithm is
an AE algorithm. [CREF24] 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 At a minimum, the 'unprotected' field MUST contain the 'alg'
parameter, a parameter identifying the recipient asymmetric key, parameter, a parameter identifying the recipient asymmetric key,
and a parameter with the sender's asymmetric public key. and a parameter with the sender's asymmetric public key.
12.5.1. ECDH ES + HKDF 12.5.1. ECDH
+----------------+-------+----------+-------------------------------+
| name | value | KDF | description | These algorithms are defined in Table 19.
+----------------+-------+----------+-------------------------------+
| ECDH-ES+A128KW | * | HKDF - | ECDH ES w/ Concat KDF and AES |
| | | SHA-256 | Key wrap w/ 128 bit key |
| | | | |
| ECDH-ES+A192KW | * | HKDF - | ECDH ES w/ Concat KDF and AES |
| | | SHA-256 | Key wrap w/ 192 bit key |
| | | | |
| ECDH-ES+A256KW | * | HKDF - | ECDH ES w/ Concat KDF and AES |
| | | SHA-256 | Key wrap w/ 256 bit key |
+----------------+-------+----------+-------------------------------+
12.6. Password 12.6. Password
[CREF25] [CREF17]
12.6.1. PBES2 12.6.1. PBES2
+--------------------+-------+--------------------------------------+ +--------------------+-------+--------------------------------------+
| name | value | description | | name | value | description |
+--------------------+-------+--------------------------------------+ +--------------------+-------+--------------------------------------+
| PBES2-HS256+A128KW | * | PBES2 w/ HMAC SHA-256 and AES Key | | PBES2-HS256+A128KW | * | PBES2 w/ HMAC SHA-256 and AES Key |
| | | wrap w/ 128 bit key | | | | wrap w/ 128 bit key |
| | | | | | | |
| PBES2-HS384+A192KW | * | PBES2 w/ HMAC SHA-384 and AES Key | | PBES2-HS384+A192KW | * | PBES2 w/ HMAC SHA-384 and AES Key |
skipping to change at page 48, line 20 skipping to change at page 53, line 52
+-----------+-------+--------------------------------------------+ +-----------+-------+--------------------------------------------+
| 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 |
+-----------+-------+--------------------------------------------+ +-----------+-------+--------------------------------------------+
Table 19: Key Type Values Table 21: 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].
+------------+----------+-------+-----------------------------------+
| name | key type | value | description |
+------------+----------+-------+-----------------------------------+
| P-256 | EC2 | 1 | NIST P-256 also known as |
| | | | secp256r1 |
| | | | |
| P-384 | EC2 | 2 | NIST P-384 also known as |
| | | | secp384r1 |
| | | | |
| P-521 | EC2 | 3 | NIST P-521 also known as |
| | | | secp521r1 |
| | | | |
| Curve25519 | EC1 | 1 | Provide reference |
| | | | |
| Goldilocks | EC1 | 2 | Provide reference |
+------------+----------+-------+-----------------------------------+
Table 22: 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 NOTE: This section represents at risk work depending on the ability
to get good references for Curve25519 and Goldilocks. to get good references for Curve25519 and Goldilocks.
New versions of ECC have been targeted at variants where only a New versions of ECC have been targeted at variants where only a
single value of the EC Point need to be transmitted. This work is single value of the EC Point need to be transmitted. This work is
currently going on in the IRTF CFRG group. 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 both coordinates, the 'kty' member is set to 1
(EC1). The members that are defined for this key type are: (EC1). 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.
[CREF26] The curves defined in this document for this key type can [CREF18] The curves defined in this document for this key type can
be found in Table 18. Other curves may be registered in the be found in Table 22. 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 integer is x contains the x coordinate for the EC point. The octet string
converted to an octet string use ???. Note that the octet string represents a little-endian encoding of x.
represents a little-endian encoding of x. [CREF27]
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. It is RECOMMENDED that 'x' also be
present, but it can be recomputed from the required elements and present, but it can be recomputed from the required elements and
omitting it saves on space. omitting it saves on space.
+------+-------+-------+--------+-----------------------------------+ +------+-------+-------+--------+-----------------------------------+
skipping to change at page 49, line 25 skipping to change at page 55, line 25
| | 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 20: EC Key Parameters Table 23: 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 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 18. Other curves may be registered in the future and in Table 22. 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. [CREF28] MUST NOT be removed from the front of the octet string. [CREF19]
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
skipping to change at page 50, line 28 skipping to change at page 56, line 28
| | | | 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 21: EC Key Parameters Table 24: EC Key Parameters
13.2. RSA Keys 13.2. RSA Keys
+-------+----------+-------+-------+----------------------------+
| name | key type | value | type | description |
+-------+----------+-------+-------+----------------------------+
| n | 3 | -1 | bstr | Modulus Parameter |
| | | | | |
| e | 3 | -2 | int | Exponent Parameter |
| | | | | |
| d | 3 | -3 | bstr | Private Exponent Parameter |
| | | | | |
| p | 3 | -4 | bstr | First Prime Factor |
| | | | | |
| q | 3 | -5 | bstr | Second Prime Factor |
| | | | | |
| dp | 3 | -6 | bstr | First Factor CRT Exponent |
| | | | | |
| dq | 3 | -7 | bstr | Second Factor CRT Exponent |
| | | | | |
| qi | 3 | -8 | bstr | First CRT Coefficient |
| | | | | |
| other | 3 | -9 | array | Other Primes Info |
| | | | | |
| r | 3 | -10 | bstr | Prime Factor |
| | | | | |
| d | 3 | -11 | bstr | Factor CRT Exponent |
| | | | | |
| t | 3 | -12 | bstr | Factor CRT Coefficient |
+-------+----------+-------+-------+----------------------------+
Table 22: RSA Key Parameters 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
key form an RSA key pair. [CREF20]
The document also provides support for the so-called "multi-prime"
RSA where the modulus may have more than two prime factors. The
benefit of multi-prime RSA is lower computational cost for the
decryption and signature primitives. For a discussion on how multi-
prime affects the security of RSA crypto-systems, the reader is
referred to [MultiPrimeRSA].
This document follows the naming convention of [RFC3447] for the
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
associated with each of those labels. The requirements for fields
for RSA keys are as follows:
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
other fields defined in Table 25 MUST be absent.
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.
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
represented as a map containing the fields 'r_i', 'd_i' and 't_i'.
The field 'other' is an array of those maps.
+-------+----------+-------+-------+--------------------------------+
| name | key type | value | type | description |
+-------+----------+-------+-------+--------------------------------+
| n | 3 | -1 | bstr | Modulus Parameter |
| | | | | |
| e | 3 | -2 | int | Exponent Parameter |
| | | | | |
| d | 3 | -3 | bstr | Private Exponent Parameter |
| | | | | |
| p | 3 | -4 | bstr | First Prime Factor |
| | | | | |
| q | 3 | -5 | bstr | Second Prime Factor |
| | | | | |
| dP | 3 | -6 | bstr | First Factor CRT Exponent |
| | | | | |
| dQ | 3 | -7 | bstr | Second Factor CRT Exponent |
| | | | | |
| qInv | 3 | -8 | bstr | First CRT Coefficient |
| | | | | |
| other | 3 | -9 | array | Other Primes Info |
| | | | | |
| r_i | 3 | -10 | bstr | i-th factor, Prime Factor |
| | | | | |
| d_i | 3 | -11 | bstr | i-th factor, Factor CRT |
| | | | | Exponent |
| | | | | |
| t_i | 3 | -12 | bstr | i-th factor, Factor CRT |
| | | | | Coefficient |
+-------+----------+-------+-------+--------------------------------+
Table 25: 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 52, line 11 skipping to change at page 58, line 18
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 23: Symmetric Key Parameters Table 26: 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 52, line 49 skipping to change at page 59, line 8
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 Object Labels Registry
It is requested that IANA create a new registry entitled "COSE Object It is requested that IANA create a new registry entitled "COSE Object
Labels Registry". [CREF29] Labels Registry". [CREF21]
This table is initially populated by the table in Table 1. This table is initially populated by the table in Table 1.
15.3. COSE Header Label Table 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
Labels". 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.
label This is the value used for the label. The label can be either label This is the value used for the label. The label can be either
an integer or a string. Registration in the table is based on the an integer or a string. Registration in the table is based on the
value of the label requested. Integer values between 1 and 255 value of the label requested. Integer values between 1 and 255
skipping to change at page 54, line 27 skipping to change at page 60, line 34
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 11, The initial contents of the registry can be found in: Table 13,
Table 12, Table 17, and Appendix D. The specification column for all Table 14, Table 20, and Appendix D. The specification column for all
rows in that table should be this document. rows in that table should be this document.
15.5. COSE Algorithm Registry 15.5. 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
skipping to change at page 55, line 9 skipping to change at page 61, line 14
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 9, Table 8, Table 5, Table 7, Table 13, Table 14, Table 15. Table 10, Table 9, Table 5, Table 7, Table 15, Table 17, Table 18.
The specification column for all rows in that table should be this The specification column for all rows in that table should be this
document. document.
15.6. COSE Key Map Registry 15.6. 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
Map 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
labels MUST be unique. The label can be a positive integer, a labels MUST be unique. The label 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 56, line 5 skipping to change at page 62, line 9
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 Parameter Registry 15.7. COSE Key Type Parameter Registry
It is requested that IANA create a new registry "COSE Key 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.
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.
skipping to change at page 56, line 30 skipping to change at page 62, line 34
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 20, This registry will be initially populated by the values in Table 23,
Table 21, Table 22, and Table 23. The specification column for all Table 24, Table 25, and Table 26. The specification column for all
of these entries will be this document. 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. [CREF30] These cose+cbor" media types in the "Media Types" registry. [CREF22] 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
Fragment identifier considerations: N/A Fragment identifier considerations: N/A
skipping to change at page 61, line 29 skipping to change at page 67, line 29
[I-D.irtf-cfrg-curves] [I-D.irtf-cfrg-curves]
Langley, A. and R. Salz, "Elliptic Curves for Security", Langley, A. and R. Salz, "Elliptic Curves for Security",
draft-irtf-cfrg-curves-02 (work in progress), March 2015. draft-irtf-cfrg-curves-02 (work in progress), March 2015.
[I-D.mcgrew-aead-aes-cbc-hmac-sha2] [I-D.mcgrew-aead-aes-cbc-hmac-sha2]
McGrew, D., Foley, J., and K. Paterson, "Authenticated McGrew, D., Foley, J., and K. Paterson, "Authenticated
Encryption with AES-CBC and HMAC-SHA", draft-mcgrew-aead- Encryption with AES-CBC and HMAC-SHA", draft-mcgrew-aead-
aes-cbc-hmac-sha2-05 (work in progress), July 2014. aes-cbc-hmac-sha2-05 (work in progress), July 2014.
[MAC] NiST, N., "FIPS PUB 113: Computer Data Authentication",
May 1985.
[MultiPrimeRSA]
Hinek, M. and D. Cheriton, "On the Security of Multi-prime
RSA", June 2006.
[PVSig] Brown, D. and D. Johnson, "Formal Security Proofs for a
Signature Scheme with Partial Message Recover", February
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.
[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.
skipping to change at page 62, line 35 skipping to change at page 68, line 46
Cryptographic Message Syntax (CMS)", RFC 5990, September Cryptographic Message Syntax (CMS)", RFC 5990, September
2010. 2010.
[RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic [RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
Curve Cryptography Algorithms", RFC 6090, February 2011. Curve Cryptography Algorithms", RFC 6090, February 2011.
[RFC6151] Turner, S. and L. Chen, "Updated Security Considerations [RFC6151] Turner, S. and L. Chen, "Updated Security Considerations
for the MD5 Message-Digest and the HMAC-MD5 Algorithms", for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
RFC 6151, March 2011. RFC 6151, March 2011.
[RFC6979] Pornin, T., "Deterministic Usage of the Digital Signature
Algorithm (DSA) and Elliptic Curve Digital Signature
Algorithm (ECDSA)", RFC 6979, DOI 10.17487/RFC6979, August
2013, <http://www.rfc-editor.org/info/rfc6979>.
[RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data [RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, March 2014. Interchange Format", RFC 7159, March 2014.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, DOI 10.17487/
RFC7252, June 2014,
<http://www.rfc-editor.org/info/rfc7252>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web [RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, May 2015. Signature (JWS)", RFC 7515, May 2015.
[RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)", [RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
RFC 7516, May 2015. RFC 7516, May 2015.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517, May 2015. [RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517, May 2015.
[RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518, May [RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518, May
2015. 2015.
[RFC7539] Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
Protocols", RFC 7539, DOI 10.17487/RFC7539, May 2015,
<http://www.rfc-editor.org/info/rfc7539>.
[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. AEAD and AE algorithms
skipping to change at page 65, line 5 skipping to change at page 71, line 15
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 3: 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
{ {
1: 2, 1: 2,
2: h'a10101', 2: h'a10101',
3: { 3: {
-1: h'02d1f7e6f26c43d4868d87ce' 5: h'02d1f7e6f26c43d4868d87ce'
}, },
4: h'64f84d913ba60a76070a9a48f26e97e863e285295a44320878caceb076 4: h'64f84d913ba60a76070a9a48f26e97e863e285295a44320878caceb076
3a334806857c67', 3a334806857c67',
9: [ 9: [
{ {
3: { 3: {
1: -3 1: -3
}, },
4: h'5a15dbf5b282ecb31a6074ee3815c252405dd7583e078188', 4: h'5a15dbf5b282ecb31a6074ee3815c252405dd7583e078188',
9: [ 9: [
{ {
3: { 3: {
1: "ECDH-ES", 1: 50,
5: h'6d65726961646f632e6272616e64796275636b406275636b 4: h'6d65726961646f632e6272616e64796275636b406275636b
6c616e642e6578616d706c65', 6c616e642e6578616d706c65',
4: { -1: {
1: 1, 1: 2,
-1: 4, -1: 1,
-2: h'b2add44368ea6d641f9ca9af308b4079aeb519f11e9b8 -2: h'b2add44368ea6d641f9ca9af308b4079aeb519f11e9b8
a55a600b21233e86e68', a55a600b21233e86e68',
-3: h'1a2cf118b9ee6895c8f415b686d4ca1cef362d4a7630a -3: h'1a2cf118b9ee6895c8f415b686d4ca1cef362d4a7630a
31ef6019c0c56d33de0' 31ef6019c0c56d33de0'
} }
} }
} }
] ]
} }
] ]
skipping to change at page 65, line 51 skipping to change at page 72, line 16
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. I
am currently still in the process of getting the examples up there am currently still in the process of getting the examples up there
along with some control information for people to be able to check along with some control information for people to be able to check
and reproduce the examples. 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. [CREF31] Using CBOR's diagnostic notation rather than a binary dump. [CREF23] Using
the Ruby based CBOR diagnostic tools at ????, the diagnostic notation the Ruby based CBOR diagnostic tools at ????, the diagnostic notation
can be converted into binary files using the following command line: can be converted into binary files using the following command line:
(install command is?...) (install command is?...)
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'.
skipping to change at page 66, line 25 skipping to change at page 72, line 39
C.1.1. Shared Secret Direct MAC C.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 Key management: direct shared secret
o File name: Mac-04 o File name: Mac-04
Size of binary file is 74 bytes
{ {
1: 3, 1: 3,
2: h'a1016f4145532d434d41432d3235362f3634', 2: h'a1016f4145532d434d41432d3235362f3634',
4: h'546869732069732074686520636f6e74656e742e', 4: h'546869732069732074686520636f6e74656e742e',
10: h'd9afa663dd740848', 10: h'd9afa663dd740848',
9: [ 9: [
{ {
3: { 3: {
1: -6, 1: -6,
5: h'6f75722d736563726574' 4: h'6f75722d736563726574'
} }
} }
] ]
} }
C.1.2. ECDH Direct MAC C.1.2. ECDH Direct MAC
This example uses the following: This example uses the following:
o MAC: HMAC w/SHA-256, 256-bit key [CREF32] o MAC: HMAC w/SHA-256, 256-bit key [CREF24]
o Key management: ECDH key agreement, two static keys, HKDF w/ o Key management: ECDH key agreement, two static keys, HKDF w/
context structure context structure
Size of binary file is 218 bytes
{ {
1: 3, 1: 3,
2: h'a10104', 2: h'a10104',
4: h'546869732069732074686520636f6e74656e742e', 4: h'546869732069732074686520636f6e74656e742e',
10: h'2ba937ca03d76c3dbad30cfcbaeef586f9c0f9ba616ad67e9205d3857 10: h'2ba937ca03d76c3dbad30cfcbaeef586f9c0f9ba616ad67e9205d3857
6ad9930', 6ad9930',
9: [ 9: [
{ {
3: { 3: {
1: "ECDH-SS", 1: 52,
5: h'6d65726961646f632e6272616e64796275636b406275636b6c61 4: h'6d65726961646f632e6272616e64796275636b406275636b6c61
6e642e6578616d706c65', 6e642e6578616d706c65',
"spk": { -3: h'706572656772696e2e746f6f6b407475636b626f726f7567682
"kid": "peregrin.took@tuckborough.example" e6578616d706c65',
},
"apu": h'4d8553e7e74f3c6a3a9dd3ef286a8195cbf8a23d19558ccf "apu": h'4d8553e7e74f3c6a3a9dd3ef286a8195cbf8a23d19558ccf
ec7d34b824f42d92bd06bd2c7f0271f0214e141fb779ae2856abf585a58368b01 ec7d34b824f42d92bd06bd2c7f0271f0214e141fb779ae2856abf585a58368b01
7e7f2a9e5ce4db5' 7e7f2a9e5ce4db5'
} }
} }
] ]
} }
C.1.3. Wrapped MAC C.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 Key management: AES keywrap w/ a pre-shared 256-bit key
Size of binary file is 127 bytes
{ {
1: 3, 1: 3,
2: h'a1016e4145532d3132382d4d41432d3634', 2: h'a1016e4145532d3132382d4d41432d3634',
4: h'546869732069732074686520636f6e74656e742e', 4: h'546869732069732074686520636f6e74656e742e',
10: h'6d1fa77b2dd9146a', 10: h'6d1fa77b2dd9146a',
9: [ 9: [
{ {
3: { 3: {
1: -5, 1: -5,
5: h'30313863306165352d346439622d343731622d626664362d6565 4: h'30313863306165352d346439622d343731622d626664362d6565
66333134626337303337' 66333134626337303337'
}, },
4: h'711ab0dc2fc4585dce27effa6781c8093eba906f227b6eb0' 4: h'711ab0dc2fc4585dce27effa6781c8093eba906f227b6eb0'
} }
] ]
} }
C.1.4. Multi-recipient MAC message C.1.4. Multi-recipient MAC message
This example uses the following: This example uses the following:
skipping to change at page 68, line 20 skipping to change at page 74, line 47
o Key management: Uses three different methods o Key management: 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
{ {
1: 3, 1: 3,
2: h'a10104', 2: h'a10104',
4: h'546869732069732074686520636f6e74656e742e', 4: h'546869732069732074686520636f6e74656e742e',
10: h'7aaa6e74546873061f0a7de21ff0c0658d401a68da738dd8937486519 10: h'7aaa6e74546873061f0a7de21ff0c0658d401a68da738dd8937486519
83ce1d0', 83ce1d0',
9: [ 9: [
{ {
3: { 3: {
1: "ECDH-ES+A128KW", 1: 55,
5: h'62696c626f2e62616767696e7340686f626269746f6e2e657861 4: h'62696c626f2e62616767696e7340686f626269746f6e2e657861
6d706c65', 6d706c65',
4: { -1: {
1: 1, 1: 2,
-1: 5, -1: 3,
-2: h'43b12669acac3fd27898ffba0bcd2e6c366d53bc4db71f909 -2: h'43b12669acac3fd27898ffba0bcd2e6c366d53bc4db71f909
a759304acfb5e18cdc7ba0b13ff8c7636271a6924b1ac63c02688075b55ef2d61 a759304acfb5e18cdc7ba0b13ff8c7636271a6924b1ac63c02688075b55ef2d61
3574e7dc242f79c3', 3574e7dc242f79c3',
-3: h'812dd694f4ef32b11014d74010a954689c6b6e8785b333d1a -3: h'812dd694f4ef32b11014d74010a954689c6b6e8785b333d1a
b44f22b9d1091ae8fc8ae40b687e5cfbe7ee6f8b47918a07bb04e9f5b1a51a334 b44f22b9d1091ae8fc8ae40b687e5cfbe7ee6f8b47918a07bb04e9f5b1a51a334
a16bc09777434113' a16bc09777434113'
} }
}, },
4: h'1b120c848c7f2f8943e402cbdbdb58efb281753af4169c70d0126c 4: h'f20ad9c96134f3c6be4f75e7101c0ecc5efa071ff20a87fd1ac285
0d16436277160821790ef4fe3f' 10941ee0376573e2b384b56b99'
}, },
{ {
3: { 3: {
1: -2, 1: -26,
5: h'62696c626f2e62616767696e7340686f626269746f6e2e657861 4: h'62696c626f2e62616767696e7340686f626269746f6e2e657861
6d706c65' 6d706c65'
}, },
4: h'46c4f88069b650909a891e84013614cd58a3668f88fa18f3852940 4: h'46c4f88069b650909a891e84013614cd58a3668f88fa18f3852940
a20b35098591d3aacf91c125a2595cda7bee75a490579f0e2f20fd6bc956623bf a20b35098591d3aacf91c125a2595cda7bee75a490579f0e2f20fd6bc956623bf
de3029c318f82c426dac3463b261c981ab18b72fe9409412e5c7f2d8f2b5abaf7 de3029c318f82c426dac3463b261c981ab18b72fe9409412e5c7f2d8f2b5abaf7
80df6a282db033b3a863fa957408b81741878f466dcc437006ca21407181a016c 80df6a282db033b3a863fa957408b81741878f466dcc437006ca21407181a016c
a608ca8208bd3c5a1ddc828531e30b89a67ec6bb97b0c3c3c92036c0cb84aa0f0 a608ca8208bd3c5a1ddc828531e30b89a67ec6bb97b0c3c3c92036c0cb84aa0f0
ce8c3e4a215d173bfa668f116ca9f1177505afb7629a9b0b5e096e81d37900e06 ce8c3e4a215d173bfa668f116ca9f1177505afb7629a9b0b5e096e81d37900e06
f561a32b6bc993fc6d0cb5d4bb81b74e6ffb0958dac7227c2eb8856303d989f93 f561a32b6bc993fc6d0cb5d4bb81b74e6ffb0958dac7227c2eb8856303d989f93
b4a051830706a4c44e8314ec846022eab727e16ada628f12ee7978855550249cc b4a051830706a4c44e8314ec846022eab727e16ada628f12ee7978855550249cc
b58' b58'
}, },
{ {
skipping to change at page 69, line 17 skipping to change at page 75, line 45
80df6a282db033b3a863fa957408b81741878f466dcc437006ca21407181a016c 80df6a282db033b3a863fa957408b81741878f466dcc437006ca21407181a016c
a608ca8208bd3c5a1ddc828531e30b89a67ec6bb97b0c3c3c92036c0cb84aa0f0 a608ca8208bd3c5a1ddc828531e30b89a67ec6bb97b0c3c3c92036c0cb84aa0f0
ce8c3e4a215d173bfa668f116ca9f1177505afb7629a9b0b5e096e81d37900e06 ce8c3e4a215d173bfa668f116ca9f1177505afb7629a9b0b5e096e81d37900e06
f561a32b6bc993fc6d0cb5d4bb81b74e6ffb0958dac7227c2eb8856303d989f93 f561a32b6bc993fc6d0cb5d4bb81b74e6ffb0958dac7227c2eb8856303d989f93
b4a051830706a4c44e8314ec846022eab727e16ada628f12ee7978855550249cc b4a051830706a4c44e8314ec846022eab727e16ada628f12ee7978855550249cc
b58' b58'
}, },
{ {
3: { 3: {
1: -5, 1: -5,
5: h'30313863306165352d346439622d343731622d626664362d6565 4: h'30313863306165352d346439622d343731622d626664362d6565
66333134626337303337' 66333134626337303337'
}, },
4: h'0b2c7cfce04e98276342d6476a7723c090dfdd15f9a518e7736549 4: h'0b2c7cfce04e98276342d6476a7723c090dfdd15f9a518e7736549
e998370695e6d6a83b4ae507bb' e998370695e6d6a83b4ae507bb'
} }
] ]
} }
C.2. Examples of Encrypted Messages C.2. Examples of Encrypted Messages
C.2.1. Direct ECDH C.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
skipping to change at page 70, line 4 skipping to change at page 76, line 16
C.2. Examples of Encrypted Messages C.2. Examples of Encrypted Messages
C.2.1. Direct ECDH C.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 Key managment: ECDH Ephemeral-Static, Curve P-256
Size of binary file is 186 bytes
{ {
1: 2, 1: 2,
2: h'a10101', 2: h'a10101',
3: { 3: {
-1: h'c9cf4df2fe6c632bf7886413' 5: h'c9cf4df2fe6c632bf7886413'
}, },
4: h'45fce2814311024d3a479e7d3eed063850f3f0b9f3f948677e3ae9869b 4: h'45fce2814311024d3a479e7d3eed063850f3f0b9f3f948677e3ae9869b
cf9ff4e1763812', cf9ff4e1763812',
9: [ 9: [
{ {
3: { 3: {
1: "ECDH-ES", 1: 50,
5: h'6d65726961646f632e6272616e64796275636b406275636b6c61 4: h'6d65726961646f632e6272616e64796275636b406275636b6c61
6e642e6578616d706c65', 6e642e6578616d706c65',
4: { -1: {
1: 1, 1: 2,
-1: 4, -1: 1,
-2: h'98f50a4ff6c05861c8860d13a638ea56c3f5ad7590bbfbf05 -2: h'98f50a4ff6c05861c8860d13a638ea56c3f5ad7590bbfbf05
4e1c7b4d91d6280', 4e1c7b4d91d6280',
-3: h'f01400b089867804b8e9fc96c3932161f1934f4223069170d -3: h'f01400b089867804b8e9fc96c3932161f1934f4223069170d
924b7e03bf822bb' 924b7e03bf822bb'
} }
} }
} }
] ]
} }
skipping to change at page 70, line 36 skipping to change at page 77, line 4
} }
} }
] ]
} }
C.2.2. Direct plus Key Derivation C.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 Key managment: 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
{ {
1: 2, 1: 2,
2: h'a1016e4145532d43434d2d3132382f3634', 2: h'a1010a',
3: { 3: {
-1: h'8f2720f78dce2737ae61a4fa' 5: h'89f52f65a1c580933b5261a7'
}, },
4: h'0159973c5d790041cf54be80412b3d12a7be30f6b64193d3bb51dfec', 4: h'7b9dcfa42c4e1d3182c402dc18ef8b5637de4fb62cf1dd156ea6e6e0',
9: [ 9: [
{ {
3: { 3: {
1: "dir+kdf", 1: "dir+kdf",
5: h'6f75722d736563726574', 4: h'6f75722d736563726574',
-10: h'61616262636364646565666667676868' -20: h'61616262636364646565666667676868'
} }
} }
] ]
} }
C.3. Examples of Signed Message C.3. Examples of Signed Message
C.3.1. Single Signature C.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
{ {
1: 1, 1: 1,
4: h'546869732069732074686520636f6e74656e742e', 4: h'546869732069732074686520636f6e74656e742e',
5: [ 5: [
{ {
2: h'a20165505333383405581e62696c626f2e62616767696e7340686f 2: h'a20165505333383404581e62696c626f2e62616767696e7340686f
626269746f6e2e6578616d706c65', 626269746f6e2e6578616d706c65',
6: h'1b22515f96fd798a331c7b156e90bfea7f558ec6de840e05a8e5f4 6: h'0144e54a23b35cba9f9477beda0578c56653a3642fa64095ab71e2
b7be44ea1451c48517da7fd216c6143898673c232a96937ebcfb88264a58f5995 9527fef410ab3626005267f9c5d75cba5377ab3c46ded94236c77ebfcdea8a71d
82d89cf8a4f20ef35fbfcfd2aad46ad8b99ea6425367afd898de1b712d558b0d2 9b1d5c6faeb870733993267b0ab40569870602b903a518a273c303f78c129f14c
49d6d180d0b1fb7256140ec3553556f3b5b95a49931a75998dfc23ca905efc7d8 fdc49f3d1de8be8599c861ddefdfc8f0e8037a3acf195e0da2cc287ce0945e98b
e04deeb92d5936c0824e535aa344396f73913d8a65de0010600270ae5df7f5c8d e7b3666ace2183f77c313b45e9488a1dae5925f01a4e7c5ef1622abe9cd678eaa
52ae525a7642d4c4ff9e219acaa52fd933df003be36b9e3c77ced37129d66745e 02f501d950f24161cd7ef9458c13bfc96fb787fcd3e07ff47f1d7e37c9cc50d29
2a42baa3d0b3f2675cd51ae8a64fd024d126be5396c91b9236fb5f8548d09881b 023d0e310c7c36c1a0e44b2c7347136c1ad6a0664c3697919eda6e3af813e1c3b
b5d40a61c0d342bed9fe8058f36b8722b9e8465dc3b8bfa4f2fd138ce186b73e4 ef846513d8ff8bd761d4ea979e9a2a2b6d2de57bb26d92220f4188cc0fdd68020
082' 874'
} }
] ]
} }
C.3.2. Multiple Signers C.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
{ {
1: 1, 1: 1,
4: h'546869732069732074686520636f6e74656e742e', 4: h'546869732069732074686520636f6e74656e742e',
5: [ 5: [
{ {
2: h'a10129', 2: h'a1013819',
3: { 3: {
5: h'62696c626f2e62616767696e7340686f626269746f6e2e657861 4: h'62696c626f2e62616767696e7340686f626269746f6e2e657861
6d706c65' 6d706c65'
}, },
6: h'028947ac3521f66f2506013007e2cd7b0cb09a209e76ab5b95f751 6: h'2f5e3809c370d409ffb7600b66b15bd597b10ca326da04fdaeedb5
eb63f5730f1672a282419c49b9653d742577fb6a6cea9ab2e1d4d5d9e786e2240 bfc3cdfd289593347bb06fe1fc50f6eed18588d90c270c9dc9613be89b4e043f0
4760663cc74a1c2c90160af92628e1ebbc3eeba552f757054b691ab17271396b7 4c1845d1b7ff10c49ebe8e5f373ab3d5b058117b4b5b9a08c7f9b0ae3f5f0debf
ff2d86c100b94a2fce0438c0b50ca70bcdd3074a0f8dc40c2e44e9b26e9093287 03a5b917b5270ccb211765e961b6476542ceaab36d4f994e313f1ffc092ee83ad
b7245ee13171b28ea0f3e291c2cca64aa17f7094aee2be02b5fe5cd2cf343e18c bf51c2c9ea06ec0be349f453ef0a64c3831c5709fe8627de1bf47b586b941e0d1
eec0c763cb76a128df9a9cbfc37b835f6467d98d74505eee1dccc9e6ebf2405ea dd8e261c71be0aa28ea288835c4d62e4b56b24eed369483eb3bf8abea00cfc873
1329b41a33eeb13f1bbef3a272e42b3df96cdaea9016663e31ddff4603eb66a88 8afd86698d7076ba2f6fb1f59936c60668d9d43acef17d1b5eae6bccc9896b0d4
5c583b53977c1fb9707550717d7387f84616a6670e27d4007b08879109aaf3720 d4ffbc41e2c25011e15a0093c76b9b7d68655216835d467ce4188c107a1093855
f33' 7ea'
}, },
{ {
3: { 3: {
1: -9, 1: -9,
5: h'62696c626f2e62616767696e7340686f626269746f6e2e657861 4: h'62696c626f2e62616767696e7340686f626269746f6e2e657861
6d706c65' 6d706c65'
}, },
6: h'0195345953742c6725352a13cdc55402c895133525c9a3b16bb47d 6: h'0118eaa7d62778b5a9525a583f06b115d80cd246bc930f0c285058
02ca5f57f8a34aebf47298c602a8feb1dd71d1936886f21029a4142abf38c3aa3 8eec85186b427026e096a076bfab738215f354be59f57643a7f6b2c92535cf3c3
94b3597c2f35c01987c801edc7022c8fddacbf25bc8794b9ffb7cb27f9f346ba4 7ee2746a908ab1fec618a3f8965b66d426fd1e6604e164d12eb29734a045c4110
4db6f5c9b60406530f62b378c5da3e7e2259327f4e55f48271873496497724492 c76867438cbe86d4f8e14b95427722667aeeed9b4a3efac04ad0b2ee260db759a
d90ba67a4b65112' e17226cc25501'
} }
] ]
} }
C.4. COSE Keys
C.4.1. Public Keys
This is an example of a COSE Key set. This example includes the
public keys for all of the previous examples.
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 "peregrin.took@tuckborough.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"
Size of binary file is 703 bytes
[
{
-1: 1,
-2: h'65eda5a12577c2bae829437fe338701a10aaa375e1bb5b5de108de4
39c08551d',
-3: h'1e52ed75701163f7f9e40ddf9f341b3dc9ba860af7e0ca7ca7e9eec
d0084d19c',
1: 2,
2: h'6d65726961646f632e6272616e64796275636b406275636b6c616e64
2e6578616d706c65'
},
{
-1: 1,
-2: h'98f50a4ff6c05861c8860d13a638ea56c3f5ad7590bbfbf054e1c7b
4d91d6280',
-3: h'f01400b089867804b8e9fc96c3932161f1934f4223069170d924b7e
03bf822bb',
1: 2,
2: h'706572656772696e2e746f6f6b407475636b626f726f7567682e6578
616d706c65'
},
{
-1: 3,
-2: h'0072992cb3ac08ecf3e5c63dedec0d51a8c1f79ef2f82f94f3c737b
f5de7986671eac625fe8257bbd0394644caaa3aaf8f27a4585fbbcad0f2457620
085e5c8f42ad',
-3: h'01dca6947bce88bc5790485ac97427342bc35f887d86d65a089377e
247e60baa55e4e8501e2ada5724ac51d6909008033ebc10ac999b9d7f5cc2519f
3fe1ea1d9475',
1: 2,
2: h'62696c626f2e62616767696e7340686f626269746f6e2e6578616d70
6c65'
},
{
-2: h'9f810fb4038273d02591e4073f31d2b6001b82cedb4d92f050165d4
7cfcab8a3c41cb778ac7553793f8ef975768d1a2374d8712564c3bcd77b9ea434
544899407cff0099920a931a24c4414852ab29bdb0a95c0653f36c60e60bf90b6
258dda56f37047ba5c2d1d029af9c9d40bac7aa41c78a0dd1068add699e808fea
011ea1441d8a4f7bb4e97be39f55f1ddd44e9c4ba335159703d4d34b603e65147
a4f23d6d3c0996c75edee846a82d190ae10783c961cf0387aed2106d2d0555b6f
d937fad5535387e0ff72ffbe78941402b0b822ea2a74b6058c1dabf9b34a76cb6
3b87faa2c6847b8e2837fff91186e6b1c14911cf989a89092a81ce601ddacd3f9
cf',
-1: h'010001',
1: 3,
2: h'62696c626f2e62616767696e7340686f626269746f6e2e6578616d70
6c65'
}
]
C.4.2. Private Keys
This is an example of a COSE Key set. This example includes the
private keys for all of the previous examples.
In order the keys are:
o An EC key with a kid of "meriadoc.brandybuck@buckland.example"
o A shared-secret key with a kid of "our-secret"
o An EC key with a kid of "peregrin.took@tuckborough.example"
o A shared-secret key with a kid of "018c0ae5-4d9b-471b-
bfd6-eef314bc7037"
o An EC 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 1884 bytes
[
{
1: 2,
2: h'6d65726961646f632e6272616e64796275636b406275636b6c616e64
2e6578616d706c65',
-1: 1,
-2: h'65eda5a12577c2bae829437fe338701a10aaa375e1bb5b5de108de4
39c08551d',
-3: h'1e52ed75701163f7f9e40ddf9f341b3dc9ba860af7e0ca7ca7e9eec
d0084d19c',
-4: h'aff907c99f9ad3aae6c4cdf21122bce2bd68b5283e6907154ad9118
40fa208cf'
},
{
1: 4,
2: h'6f75722d736563726574',
-1: h'849b57219dae48de646d07dbb533566e976686457c1491be3a76dce
a6c427188'
},
{
1: 2,
-1: 1,
2: h'706572656772696e2e746f6f6b407475636b626f726f7567682e6578
616d706c65',
-2: h'98f50a4ff6c05861c8860d13a638ea56c3f5ad7590bbfbf054e1c7b
4d91d6280',
-3: h'f01400b089867804b8e9fc96c3932161f1934f4223069170d924b7e
03bf822bb',
-4: h'02d1f7e6f26c43d4868d87ceb2353161740aacf1f7163647984b522
a848df1c3'
},
{
1: 4,
2: h'30313863306165352d346439622d343731622d626664362d65656633
3134626337303337',
-1: h'849b57219dae48de646d07dbb533566e976686457c1491be3a76dce
a6c427188'
},
{
1: 2,
2: h'62696c626f2e62616767696e7340686f626269746f6e2e6578616d70
6c65',
-1: 3,
-2: h'0072992cb3ac08ecf3e5c63dedec0d51a8c1f79ef2f82f94f3c737b
f5de7986671eac625fe8257bbd0394644caaa3aaf8f27a4585fbbcad0f2457620
085e5c8f42ad',
-3: h'01dca6947bce88bc5790485ac97427342bc35f887d86d65a089377e
247e60baa55e4e8501e2ada5724ac51d6909008033ebc10ac999b9d7f5cc2519f
3fe1ea1d9475',
-4: h'00085138ddabf5ca975f5860f91a08e91d6d5f9a76ad4018766a476
680b55cd339e8ab6c72b5facdb2a2a50ac25bd086647dd3e2e6e99e84ca2c3609
fdf177feb26d'
},
{
1: 3,
2: h'62696c626f2e62616767696e7340686f626269746f6e2e6578616d70
6c65',
-2: h'9f810fb4038273d02591e4073f31d2b6001b82cedb4d92f050165d4
7cfcab8a3c41cb778ac7553793f8ef975768d1a2374d8712564c3bcd77b9ea434
544899407cff0099920a931a24c4414852ab29bdb0a95c0653f36c60e60bf90b6
258dda56f37047ba5c2d1d029af9c9d40bac7aa41c78a0dd1068add699e808fea
011ea1441d8a4f7bb4e97be39f55f1ddd44e9c4ba335159703d4d34b603e65147
a4f23d6d3c0996c75edee846a82d190ae10783c961cf0387aed2106d2d0555b6f
d937fad5535387e0ff72ffbe78941402b0b822ea2a74b6058c1dabf9b34a76cb6
3b87faa2c6847b8e2837fff91186e6b1c14911cf989a89092a81ce601ddacd3f9
cf',
-1: h'010001',
-3: h'6d6502f41f84151228f24a467e1d19bb218fbcc34abd858db41fe29
221fd936d1e4fe3b5abf23bf1e8999295f15d0d144c4b362ec3514bef2e25bbd0
f80d62ae4c0c48c90ad49dd74c681dae10a4bbd81195d63bb0d03f00a64687e43
aeb5ff8dab20d2d109ef16fa7677e2e8bfa8e7e42e72bd4160c3aa9688b00f9b3
3059648316ed8c5016309074cc1332d81aa39ed389e8a9eab5844c414c704e05d
90c5e2b85854ab5054ea5f83a84896c6a83cdac5edda1f8b3274f7d38e8039826
8462a33ef9b525107c60ac8564c19cfe6e0e3775f242a1cafd3b9617d225dacf7
4ce4f972976d61b057f82ff9870aea056aeee076c3df1cfc718d539c3a906b433
c1',
-4: h'dd297183f0f04d725c6fad3de51a17ca0402019e519c0bd9967a35c
a11ed9d47b1fdfa7b019ffd9d168eec75fff9215f1907aeb5aa364c38c3016538
56ea64f2bc3d251d00cd9d0dd9fbee2009abfd60ac986a5e36a4277afd53ec8c8
4b2787c50cb7e9f909a7e1922933844b2b9a7747e8bc4eaef44996c3e9e99bfc6
d4ab49',
-5: h'b8a136761f9c4dfe84445e24e1efe3cbbf067cf61421a532a12489b
81ce9dc2b9b937382aacea0ad3f1b47f72ed039b5319c169ad76a0f223de47ad4
7aadcc3f5e6f30c38df251d3799bb69662afc2a5bb6a757953384cd6267bcf8c8
c92e530156a01bf263cf7c117bd10fe85da91c47952a80675f76cc1de9545274b
3ba457',
-6: h'07c3d5bd792f26b8f62fe19843bbf7cbdafa2b0e60f526a15c1c2c5
94ce9d7d4d596023e615f39ab53486f5af142d0fe22c5d7477f936a77afb913d1
b7938139d88c190a7ca5bb76ea096361f294fc4f719fe4542c7cf4f9e77d13d81
72ca0f85469e0a73f8f7d0feadbda64e71587a09a74d3d41fd47bc2862c515f9f
5e8629',
-7: h'08b0e60c676e87295cf68eebf38ac45159fba7343a3c5f3763e8816
71e4d4fe4e99ce64a175a44ac031578acc5125e350e51c7aaa04b48cd16d6c385
6f04f16166439bab08ea88398936f0406202de09c929b8bfee4fef260187c07c6
03da5f63e7bcffb3c84903111b9ffabcb873f675d42abd02a0b6c9e2fa91d293d
5c605f',
-8: h'dcf8aabd740dd33c0c784fac06f6608b6f3d5cff57090177556a8fc
cc2a7220429eff4ee828ebe35904a090b0c7f71da1060634d526cfe370af3e4d1
5ef68a7beed931a423f157c175892cb1bbb434a0c386327e1ad8ac79a0d55aded
d707d1c7f0c601541e9421ec5a02ae3149ea1e99129305eb19ae8ece2a3293f3f
1a688e'
}
]
Appendix D. COSE Header Algorithm Label Table Appendix D. COSE Header Algorithm Label Table
This section disappears when we make a decision on password based key This section disappears when we make a decision on password based key
management. management.
+------+-----------+-------+-----------+-------------+ +------+-----------+-------+-----------+-------------+
| name | algorithm | label | CBOR type | description | | name | algorithm | label | CBOR type | description |
+------+-----------+-------+-----------+-------------+ +------+-----------+-------+-----------+-------------+
| p2c | PBE | -1 | int | | | p2c | PBE | -1 | int | |
| | | | | | | | | | | |
| p2s | PBE | -2 | bstr | | | p2s | PBE | -2 | bstr | |
+------+-----------+-------+-----------+-------------+ +------+-----------+-------+-----------+-------------+
Appendix E. Document Updates Appendix E. Document Updates
E.1. Version -01 to -02 E.1. Version -02 to -03
o Make a pass over all of the algorithm text.
o Alter the CDDL so that Keys and KeySets are top level items and
the key examples validate.
o Add sample key structures.
o Expand text on dealing with Externally Supplied Data.
o Update the examples to match some of the renumbering of fields.
E.2. 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.
E.2. Version -00 to -01 o Provide guidance on use of externally supplied authenticated data.
o Add external authenticated data to signing structure.
E.3. Version -01 to -2
o Add first pass of algorithm information
o Add direct key derivation example.
E.4. 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 74, line 32 skipping to change at page 86, line 7
should be: [int int]/[int tstr] so that we can keep the major/ should be: [int int]/[int tstr] so that we can keep the major/
minor difference of media-types. This does cost a couple of minor difference of media-types. This does cost a couple of
bytes in the message. bytes in the message.
[CREF9] JLS: Need to figure out how we are going to go about creating [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- this registry -or are we going to modify the current mime-
content table? content table?
[CREF10] JLS: Open to do. [CREF10] JLS: Open to do.
[CREF11] JLS: Should be able to move much of this text into the headers [CREF11] Ilari: I don't follow/understand this text
section and just do a refer to that text from here.
[CREF12] JLS: Should be able to move much of this text into the headers
section and just do a refer to that text from here.
[CREF13] Ilari: I don't follow/understand this text
[CREF14] JLS: Should this sentence be removed?
[CREF15] JLS: Do we remove this line and just define them ourselves? [CREF12] JLS: Is there a reason to assign a CBOR tag to identify keys
and/or key sets?
[CREF16] JLS: We can really simplify the grammar for COSE_Key to be just [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 the kty (the one required field) and the generic item. The
reason to do this is that it makes things simpler. The reason 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 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 so that a grammar check can be done that is more tightly
enforced. enforced.
[CREF17] JLS: Unless key material is being derived for multiple items [CREF14] JLS: Do we also want to document the use of RFC 5649 as well?
(i.e both a key and an IV) this will be the COSE algorithm
value. Even then it might still be the COSE algorithm value,
it is just a requirement for a new algorithm. Do we want to
have the ability to derive both the key and a partial IV for
CCM?
[CREF18] JLS: I need to get a better justification for this item. It
has to do with generating new keys for each message in a series
of messages that have the same salt value.
[CREF19] JLS: It would be reasonable to support a shared-secret + KDF
that is not PBE for when one has good randomness in the shared-
secret.
[CREF20] 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 - 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 i.e. a 200 bit key. The algorithm exists, but I do not
personally know of any standard uses of it. personally know of any standard uses of it.
[CREF21] JLS: Is this range we want to specify? [CREF15] JLS: Is this range we want to specify?
[CREF22] JLS: Does anybody need pure DH?
[CREF23] JLS: This could just as easily be done by specifying two
different set of algorithm identifiers, one for each of the key
formats. I don't believe that we need to set things up by
having two different sets of algorithm identifiers for the
different keys as the structure of what is represented is going
to be the same, just the math and point formats are going to be
different. The other "difference" is the question of how the
octet string of the shared secret is defined. However, since
we don't need to specify either in this document we can defer
both of them into their respective documents.
[CREF24] JLS: It would be possible to include the protected field in the [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 KDF rather than the key wrap algorithm if we wanted to. This
would provide the same level of security, it would not be would provide the same level of security, it would not be
possible to get the same key if they are different. possible to get the same key if they are different.
[CREF25] JLS: Do we want/need to support this? JOSE did it mainly to [CREF17] JLS: Do we want/need to support this? JOSE did it mainly to
support the encryption of private keys. support the encryption of private keys.
[CREF26] JLS: Do we create a registry for curves? Is is the same [CREF18] JLS: Do we create a registry for curves? Is is the same
registry for both EC1 and EC2? registry for both EC1 and EC2?
[CREF27] JLS: Should we use the integer encoding for x and d instead of [CREF19] JLS: Should we use the integer encoding for x, y and d instead
bstr?
[CREF28] JLS: Should we use the integer encoding for x, y and d instead
of bstr? of bstr?
[CREF29] JLS: Finish the registration process. [CREF20] JLS: Looking at the CBOR specification, the bstr that we are
looking in our table below should most likely be specified as
big numbers rather than as binary strings. This means that we
would use the tag 6.2 instead. From my reading of the
specification, there is no difference in the encoded size of
the resulting output. The specification of bignum does
explicitly allow for integers encoded with leading zeros.
[CREF30] JLS: Should we register both or just the cose+cbor one? [CREF21] JLS: Finish the registration process.
[CREF31] JLS: Do we want to keep this as diagnostic notation or should [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? we switch to having "binary" examples instead?
[CREF32] JLS: Need to examine how this is worked out. In this case the [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. 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 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 length, however it means that when the key is derived, there is
currently nothing to state how long the derived key needs to currently nothing to state how long the derived key needs to
be. be.
Author's Address Author's Address
Jim Schaad Jim Schaad
August Cellars August Cellars
 End of changes. 228 change blocks. 
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