draft-ietf-cose-rfc8152bis-struct-02.txt   draft-ietf-cose-rfc8152bis-struct-03.txt 
COSE Working Group J. Schaad COSE Working Group J. Schaad
Internet-Draft August Cellars Internet-Draft August Cellars
Obsoletes: 8152 (if approved) March 11, 2019 Obsoletes: 8152 (if approved) June 10, 2019
Intended status: Standards Track Intended status: Standards Track
Expires: September 12, 2019 Expires: December 12, 2019
CBOR CBOR Object Signing and Encryption (COSE): Structures and Process CBOR Object Signing and Encryption (COSE): Structures and Process
draft-ietf-cose-rfc8152bis-struct-02 draft-ietf-cose-rfc8152bis-struct-03
Abstract Abstract
Concise Binary Object Representation (CBOR) is a data format designed Concise Binary Object Representation (CBOR) is a 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 basic security services defined for this data format. ability to have basic security services defined for this data format.
This document defines the CBOR Object Signing and Encryption (COSE) This document defines the CBOR Object Signing and Encryption (COSE)
protocol. This specification describes how to create and process protocol. This specification describes how to create and process
signatures, message authentication codes, and encryption using CBOR signatures, message authentication codes, and encryption using CBOR
for serialization. This specification additionally describes how to for serialization. This specification additionally describes how to
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 12, 2019. This Internet-Draft will expire on December 12, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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1.5. CBOR-Related Terminology . . . . . . . . . . . . . . . . 7 1.5. CBOR-Related Terminology . . . . . . . . . . . . . . . . 7
1.6. Document Terminology . . . . . . . . . . . . . . . . . . 8 1.6. Document Terminology . . . . . . . . . . . . . . . . . . 8
2. Basic COSE Structure . . . . . . . . . . . . . . . . . . . . 8 2. Basic COSE Structure . . . . . . . . . . . . . . . . . . . . 8
3. Header Parameters . . . . . . . . . . . . . . . . . . . . . . 11 3. Header Parameters . . . . . . . . . . . . . . . . . . . . . . 11
3.1. Common COSE Headers Parameters . . . . . . . . . . . . . 13 3.1. Common COSE Headers Parameters . . . . . . . . . . . . . 13
4. Signing Objects . . . . . . . . . . . . . . . . . . . . . . . 17 4. Signing Objects . . . . . . . . . . . . . . . . . . . . . . . 17
4.1. Signing with One or More Signers . . . . . . . . . . . . 17 4.1. Signing with One or More Signers . . . . . . . . . . . . 17
4.2. Signing with One Signer . . . . . . . . . . . . . . . . . 19 4.2. Signing with One Signer . . . . . . . . . . . . . . . . . 19
4.3. Externally Supplied Data . . . . . . . . . . . . . . . . 20 4.3. Externally Supplied Data . . . . . . . . . . . . . . . . 20
4.4. Signing and Verification Process . . . . . . . . . . . . 21 4.4. Signing and Verification Process . . . . . . . . . . . . 21
4.5. Computing Counter Signatures . . . . . . . . . . . . . . 22 5. Counter Signatures . . . . . . . . . . . . . . . . . . . . . 22
5. Encryption Objects . . . . . . . . . . . . . . . . . . . . . 23 5.1. Full Countersignatures . . . . . . . . . . . . . . . . . 23
5.1. Enveloped COSE Structure . . . . . . . . . . . . . . . . 23 5.2. Abbreviated Countersignatures . . . . . . . . . . . . . . 24
5.1.1. Content Key Distribution Methods . . . . . . . . . . 25 6. Encryption Objects . . . . . . . . . . . . . . . . . . . . . 24
5.2. Single Recipient Encrypted . . . . . . . . . . . . . . . 25 6.1. Enveloped COSE Structure . . . . . . . . . . . . . . . . 25
5.3. How to Encrypt and Decrypt for AEAD Algorithms . . . . . 26 6.1.1. Content Key Distribution Methods . . . . . . . . . . 26
5.4. How to Encrypt and Decrypt for AE Algorithms . . . . . . 28 6.2. Single Recipient Encrypted . . . . . . . . . . . . . . . 27
6. MAC Objects . . . . . . . . . . . . . . . . . . . . . . . . . 30 6.3. How to Encrypt and Decrypt for AEAD Algorithms . . . . . 28
6.1. MACed Message with Recipients . . . . . . . . . . . . . . 30 6.4. How to Encrypt and Decrypt for AE Algorithms . . . . . . 30
6.2. MACed Messages with Implicit Key . . . . . . . . . . . . 31 7. MAC Objects . . . . . . . . . . . . . . . . . . . . . . . . . 31
6.3. How to Compute and Verify a MAC . . . . . . . . . . . . . 32 7.1. MACed Message with Recipients . . . . . . . . . . . . . . 32
7. Key Objects . . . . . . . . . . . . . . . . . . . . . . . . . 33 7.2. MACed Messages with Implicit Key . . . . . . . . . . . . 33
7.1. COSE Key Common Parameters . . . . . . . . . . . . . . . 34 7.3. How to Compute and Verify a MAC . . . . . . . . . . . . . 34
8. Signature Algorithms . . . . . . . . . . . . . . . . . . . . 37 8. Key Objects . . . . . . . . . . . . . . . . . . . . . . . . . 35
9. Message Authentication Code (MAC) Algorithms . . . . . . . . 38 8.1. COSE Key Common Parameters . . . . . . . . . . . . . . . 36
10. Content Encryption Algorithms . . . . . . . . . . . . . . . . 39 9. Signature Algorithms . . . . . . . . . . . . . . . . . . . . 38
11. Key Derivation Functions (KDFs) . . . . . . . . . . . . . . . 39 10. Message Authentication Code (MAC) Algorithms . . . . . . . . 39
12. Content Key Distribution Methods . . . . . . . . . . . . . . 40 11. Content Encryption Algorithms . . . . . . . . . . . . . . . . 40
12.1. Direct Encryption . . . . . . . . . . . . . . . . . . . 40 12. Key Derivation Functions (KDFs) . . . . . . . . . . . . . . . 40
12.2. Key Wrap . . . . . . . . . . . . . . . . . . . . . . . . 41 13. Content Key Distribution Methods . . . . . . . . . . . . . . 41
12.3. Key Transport . . . . . . . . . . . . . . . . . . . . . 41 13.1. Direct Encryption . . . . . . . . . . . . . . . . . . . 41
12.4. Direct Key Agreement . . . . . . . . . . . . . . . . . . 42 13.2. Key Wrap . . . . . . . . . . . . . . . . . . . . . . . . 42
12.5. Key Agreement with Key Wrap . . . . . . . . . . . . . . 43 13.3. Key Transport . . . . . . . . . . . . . . . . . . . . . 42
13. CBOR Encoder Restrictions . . . . . . . . . . . . . . . . . . 43 13.4. Direct Key Agreement . . . . . . . . . . . . . . . . . . 43
14. Application Profiling Considerations . . . . . . . . . . . . 44 13.5. Key Agreement with Key Wrap . . . . . . . . . . . . . . 44
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45 14. CBOR Encoding Restrictions . . . . . . . . . . . . . . . . . 44
15.1. CBOR Tag Assignment . . . . . . . . . . . . . . . . . . 45 15. Application Profiling Considerations . . . . . . . . . . . . 44
15.2. COSE Header Parameters Registry . . . . . . . . . . . . 45 16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46
15.3. COSE Header Algorithm Parameters Registry . . . . . . . 45 16.1. CBOR Tag Assignment . . . . . . . . . . . . . . . . . . 46
15.4. COSE Key Common Parameters Registry . . . . . . . . . . 46 16.2. COSE Header Parameters Registry . . . . . . . . . . . . 46
15.5. Media Type Registrations . . . . . . . . . . . . . . . . 46 16.3. COSE Header Algorithm Parameters Registry . . . . . . . 47
15.5.1. COSE Security Message . . . . . . . . . . . . . . . 46 16.4. COSE Key Common Parameters Registry . . . . . . . . . . 47
15.5.2. COSE Key Media Type . . . . . . . . . . . . . . . . 47 16.5. Media Type Registrations . . . . . . . . . . . . . . . . 47
15.6. CoAP Content-Formats Registry . . . . . . . . . . . . . 49 16.5.1. COSE Security Message . . . . . . . . . . . . . . . 47
15.7. Expert Review Instructions . . . . . . . . . . . . . . . 49 16.5.2. COSE Key Media Type . . . . . . . . . . . . . . . . 48
16. Security Considerations . . . . . . . . . . . . . . . . . . . 50 16.6. CoAP Content-Formats Registry . . . . . . . . . . . . . 50
17. Implementation Status . . . . . . . . . . . . . . . . . . . . 52 17. Security Considerations . . . . . . . . . . . . . . . . . . . 50
17.1. Author's Versions . . . . . . . . . . . . . . . . . . . 52 18. Implementation Status . . . . . . . . . . . . . . . . . . . . 52
17.2. Java Script Version . . . . . . . . . . . . . . . . . . 53 18.1. Author's Versions . . . . . . . . . . . . . . . . . . . 53
17.3. Python Version . . . . . . . . . . . . . . . . . . . . . 54 18.2. Java Script Version . . . . . . . . . . . . . . . . . . 53
17.4. COSE Testing Library . . . . . . . . . . . . . . . . . . 54 18.3. Python Version . . . . . . . . . . . . . . . . . . . . . 54
18. References . . . . . . . . . . . . . . . . . . . . . . . . . 54 18.4. COSE Testing Library . . . . . . . . . . . . . . . . . . 54
18.1. Normative References . . . . . . . . . . . . . . . . . . 54 19. References . . . . . . . . . . . . . . . . . . . . . . . . . 55
18.2. Informative References . . . . . . . . . . . . . . . . . 56 19.1. Normative References . . . . . . . . . . . . . . . . . . 55
19.2. Informative References . . . . . . . . . . . . . . . . . 56
Appendix A. Guidelines for External Data Authentication of Appendix A. Guidelines for External Data Authentication of
Algorithms . . . . . . . . . . . . . . . . . . . . . 58 Algorithms . . . . . . . . . . . . . . . . . . . . . 58
A.1. Algorithm Identification . . . . . . . . . . . . . . . . 58 Appendix B. Two Layers of Recipient Information . . . . . . . . 61
A.2. Counter Signature without Headers . . . . . . . . . . . . 61 Appendix C. Examples . . . . . . . . . . . . . . . . . . . . . . 63
Appendix B. Two Layers of Recipient Information . . . . . . . . 62 C.1. Examples of Signed Messages . . . . . . . . . . . . . . . 64
Appendix C. Examples . . . . . . . . . . . . . . . . . . . . . . 64 C.1.1. Single Signature . . . . . . . . . . . . . . . . . . 64
C.1. Examples of Signed Messages . . . . . . . . . . . . . . . 65 C.1.2. Multiple Signers . . . . . . . . . . . . . . . . . . 65
C.1.1. Single Signature . . . . . . . . . . . . . . . . . . 65 C.1.3. Counter Signature . . . . . . . . . . . . . . . . . . 66
C.1.2. Multiple Signers . . . . . . . . . . . . . . . . . . 66 C.1.4. Signature with Criticality . . . . . . . . . . . . . 67
C.1.3. Counter Signature . . . . . . . . . . . . . . . . . . 67 C.2. Single Signer Examples . . . . . . . . . . . . . . . . . 68
C.1.4. Signature with Criticality . . . . . . . . . . . . . 68 C.2.1. Single ECDSA Signature . . . . . . . . . . . . . . . 68
C.2. Single Signer Examples . . . . . . . . . . . . . . . . . 69 C.3. Examples of Enveloped Messages . . . . . . . . . . . . . 69
C.2.1. Single ECDSA Signature . . . . . . . . . . . . . . . 69 C.3.1. Direct ECDH . . . . . . . . . . . . . . . . . . . . . 69
C.3. Examples of Enveloped Messages . . . . . . . . . . . . . 70 C.3.2. Direct Plus Key Derivation . . . . . . . . . . . . . 70
C.3.1. Direct ECDH . . . . . . . . . . . . . . . . . . . . . 70 C.3.3. Counter Signature on Encrypted Content . . . . . . . 71
C.3.2. Direct Plus Key Derivation . . . . . . . . . . . . . 71 C.3.4. Encrypted Content with External Data . . . . . . . . 73
C.3.3. Counter Signature on Encrypted Content . . . . . . . 72 C.4. Examples of Encrypted Messages . . . . . . . . . . . . . 73
C.3.4. Encrypted Content with External Data . . . . . . . . 74 C.4.1. Simple Encrypted Message . . . . . . . . . . . . . . 73
C.4. Examples of Encrypted Messages . . . . . . . . . . . . . 74 C.4.2. Encrypted Message with a Partial IV . . . . . . . . . 74
C.4.1. Simple Encrypted Message . . . . . . . . . . . . . . 74
C.4.2. Encrypted Message with a Partial IV . . . . . . . . . 75 C.5. Examples of MACed Messages . . . . . . . . . . . . . . . 74
C.5. Examples of MACed Messages . . . . . . . . . . . . . . . 75 C.5.1. Shared Secret Direct MAC . . . . . . . . . . . . . . 74
C.5.1. Shared Secret Direct MAC . . . . . . . . . . . . . . 75 C.5.2. ECDH Direct MAC . . . . . . . . . . . . . . . . . . . 75
C.5.2. ECDH Direct MAC . . . . . . . . . . . . . . . . . . . 76 C.5.3. Wrapped MAC . . . . . . . . . . . . . . . . . . . . . 76
C.5.3. Wrapped MAC . . . . . . . . . . . . . . . . . . . . . 77 C.5.4. Multi-Recipient MACed Message . . . . . . . . . . . . 77
C.5.4. Multi-Recipient MACed Message . . . . . . . . . . . . 78 C.6. Examples of MAC0 Messages . . . . . . . . . . . . . . . . 78
C.6. Examples of MAC0 Messages . . . . . . . . . . . . . . . . 79 C.6.1. Shared Secret Direct MAC . . . . . . . . . . . . . . 78
C.6.1. Shared Secret Direct MAC . . . . . . . . . . . . . . 79 C.7. COSE Keys . . . . . . . . . . . . . . . . . . . . . . . . 79
C.7. COSE Keys . . . . . . . . . . . . . . . . . . . . . . . . 80 C.7.1. Public Keys . . . . . . . . . . . . . . . . . . . . . 79
C.7.1. Public Keys . . . . . . . . . . . . . . . . . . . . . 80 C.7.2. Private Keys . . . . . . . . . . . . . . . . . . . . 80
C.7.2. Private Keys . . . . . . . . . . . . . . . . . . . . 81 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 82
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 83 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 83
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 84
1. Introduction 1. Introduction
There has been an increased focus on small, constrained devices that There has been an increased focus on small, constrained devices that
make up the Internet of Things (IoT). One of the standards that has make up the Internet of Things (IoT). One of the standards that has
come out of this process is "Concise Binary Object Representation come out of this process is "Concise Binary Object Representation
(CBOR)" [RFC7049]. CBOR extended the data model of the JavaScript (CBOR)" [RFC7049]. CBOR extended the data model of the JavaScript
Object Notation (JSON) [RFC8259] by allowing for binary data, among Object Notation (JSON) [RFC8259] by allowing for binary data, among
other changes. CBOR has been adopted by several of the IETF working other changes. CBOR has been 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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directions and trimmed in others. directions and trimmed in others.
1.2. Changes from RFC8152 1.2. Changes from RFC8152
o Split the orignal document into this document and o Split the orignal document into this document and
[I-D.ietf-cose-rfc8152bis-algs]. [I-D.ietf-cose-rfc8152bis-algs].
o Add some text describing why there is no digest structure defined o Add some text describing why there is no digest structure defined
by COSE. by COSE.
o Rearrange the text around counter signatures and define a CBOR Tag
for a standalong countersignature.
1.3. Requirements Terminology 1.3. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
1.4. CBOR Grammar 1.4. CBOR Grammar
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//artwork[@type='CDDL']/text() //artwork[@type='CDDL']/text()
CDDL expects the initial non-terminal symbol to be the first symbol CDDL expects the initial non-terminal symbol to be the first symbol
in the file. For this reason, the first fragment of CDDL is in the file. For this reason, the first fragment of CDDL is
presented here. presented here.
start = COSE_Messages / COSE_Key / COSE_KeySet / Internal_Types start = COSE_Messages / COSE_Key / COSE_KeySet / Internal_Types
; This is defined to make the tool quieter: ; This is defined to make the tool quieter:
Internal_Types = Sig_structure / Enc_structure / MAC_structure / Internal_Types = Sig_structure / Enc_structure / MAC_structure
COSE_KDF_Context
The non-terminal Internal_Types is defined for dealing with the The non-terminal Internal_Types is defined for dealing with the
automated validation tools used during the writing of this document. automated validation tools used during the writing of this document.
It references those non-terminals that are used for security It references those non-terminals that are used for security
computations but are not emitted for transport. computations but are not emitted for transport.
1.5. CBOR-Related Terminology 1.5. CBOR-Related Terminology
In JSON, maps are called objects and only have one kind of map key: a In JSON, maps are called objects and only have one kind of map key: a
string. In COSE, we use strings, negative integers, and unsigned string. In COSE, we use strings, negative integers, and unsigned
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3. The content of the message. The content is either the plaintext 3. The content of the message. The content is either the plaintext
or the ciphertext as appropriate. The content may be detached or the ciphertext as appropriate. The content may be detached
(i.e. transported separately from the COSE structure), but the (i.e. transported separately from the COSE structure), but the
location is still used. The content is wrapped in a bstr when location is still used. The content is wrapped in a bstr when
present and is a nil value when detached. present and is a nil value when detached.
Elements after this point are dependent on the specific message type. Elements after this point are dependent on the specific message type.
COSE messages are built using the concept of layers to separate COSE messages are built using the concept of layers to separate
different types of cryptographic concepts. As an example of how this different types of cryptographic concepts. As an example of how this
works, consider the COSE_Encrypt message (Section 5.1). This message works, consider the COSE_Encrypt message (Section 6.1). This message
type is broken into two layers: the content layer and the recipient type is broken into two layers: the content layer and the recipient
layer. In the content layer, the plaintext is encrypted and layer. In the content layer, the plaintext is encrypted and
information about the encrypted message is placed. In the recipient information about the encrypted message is placed. In the recipient
layer, the content encryption key (CEK) is encrypted and information layer, the content encryption key (CEK) is encrypted and information
about how it is encrypted for each recipient is placed. A single about how it is encrypted for each recipient is placed. A single
layer version of the encryption message COSE_Encrypt0 (Section 5.2) layer version of the encryption message COSE_Encrypt0 (Section 6.2)
is provided for cases where the CEK is pre-shared. is provided for cases where the CEK is pre-shared.
Identification of which type of message has been presented is done by Identification of which type of message has been presented is done by
the following methods: the following methods:
1. The specific message type is known from the context. This may be 1. The specific message type is known from the context. This may be
defined by a marker in the containing structure or by defined by a marker in the containing structure or by
restrictions specified by the application protocol. restrictions specified by the application protocol.
2. The message type is identified by a CBOR tag. Messages with a 2. The message type is identified by a CBOR tag. Messages with a
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the untagged version of the structure is used. The value to use the untagged version of the structure is used. The value to use
with the parameter for each of the structures can be found in with the parameter for each of the structures can be found in
Table 1. Table 1.
4. When a COSE object is carried as a CoAP payload, the CoAP 4. When a COSE object is carried as a CoAP payload, the CoAP
Content-Format Option can be used to identify the message Content-Format Option can be used to identify the message
content. The CoAP Content-Format values can be found in Table 2. content. The CoAP Content-Format values can be found in Table 2.
The CBOR tag for the message structure is not required as each The CBOR tag for the message structure is not required as each
security message is uniquely identified. security message is uniquely identified.
+-------+---------------+---------------+---------------------------+ +-------+------------------+----------------+-----------------------+
| CBOR | cose-type | Data Item | Semantics | | CBOR | cose-type | Data Item | Semantics |
| Tag | | | | | Tag | | | |
+-------+---------------+---------------+---------------------------+ +-------+------------------+----------------+-----------------------+
| 98 | cose-sign | COSE_Sign | COSE Signed Data Object | | 98 | cose-sign | COSE_Sign | COSE Signed Data |
| 18 | cose-sign1 | COSE_Sign1 | COSE Single Signer Data | | | | | Object |
| | | | Object | | 18 | cose-sign1 | COSE_Sign1 | COSE Single Signer |
| 96 | cose-encrypt | COSE_Encrypt | COSE Encrypted Data | | | | | Data Object |
| | | | Object | | 96 | cose-encrypt | COSE_Encrypt | COSE Encrypted Data |
| 16 | cose-encrypt0 | COSE_Encrypt0 | COSE Single Recipient | | | | | Object |
| | | | Encrypted Data Object | | 16 | cose-encrypt0 | COSE_Encrypt0 | COSE Single Recipient |
| 97 | cose-mac | COSE_Mac | COSE MACed Data Object | | | | | Encrypted Data Object |
| 17 | cose-mac0 | COSE_Mac0 | COSE Mac w/o Recipients | | 97 | cose-mac | COSE_Mac | COSE MACed Data |
| | | | Object | | | | | Object |
+-------+---------------+---------------+---------------------------+ | 17 | cose-mac0 | COSE_Mac0 | COSE Mac w/o |
| | | | Recipients Object |
| TBD0 | cose-countersign | COSE_Signature | COSE standalone |
| | | | counter signature |
+-------+------------------+----------------+-----------------------+
Table 1: COSE Message Identification Table 1: COSE Message Identification
+--------------------------------------+----------+-----+-----------+ +--------------------------------------+----------+-----+-----------+
| Media Type | Encoding | ID | Reference | | Media Type | Encoding | ID | Reference |
+--------------------------------------+----------+-----+-----------+ +--------------------------------------+----------+-----+-----------+
| application/cose; cose-type="cose- | | 98 | [RFC8152] | | application/cose; cose-type="cose- | | 98 | [RFC8152] |
| sign" | | | | | sign" | | | |
| application/cose; cose-type="cose- | | 18 | [RFC8152] | | application/cose; cose-type="cose- | | 18 | [RFC8152] |
| sign1" | | | | | sign1" | | | |
skipping to change at page 11, line 9 skipping to change at page 11, line 9
Table 2: CoAP Content-Formats for COSE Table 2: CoAP Content-Formats for COSE
The following CDDL fragment identifies all of the top messages The following CDDL fragment identifies all of the top messages
defined in this document. Separate non-terminals are defined for the defined in this document. Separate non-terminals are defined for the
tagged and the untagged versions of the messages. tagged and the untagged versions of the messages.
COSE_Messages = COSE_Untagged_Message / COSE_Tagged_Message COSE_Messages = COSE_Untagged_Message / COSE_Tagged_Message
COSE_Untagged_Message = COSE_Sign / COSE_Sign1 / COSE_Untagged_Message = COSE_Sign / COSE_Sign1 /
COSE_Encrypt / COSE_Encrypt0 / COSE_Encrypt / COSE_Encrypt0 /
COSE_Mac / COSE_Mac0 COSE_Mac / COSE_Mac0 / COSE_Countersignature
COSE_Tagged_Message = COSE_Sign_Tagged / COSE_Sign1_Tagged / COSE_Tagged_Message = COSE_Sign_Tagged / COSE_Sign1_Tagged /
COSE_Encrypt_Tagged / COSE_Encrypt0_Tagged / COSE_Encrypt_Tagged / COSE_Encrypt0_Tagged /
COSE_Mac_Tagged / COSE_Mac0_Tagged COSE_Mac_Tagged / COSE_Mac0_Tagged / COSE_Countersignature_Tagged
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 content, algorithms, keys, but are used for holding information about content, algorithms, keys,
or evaluation hints for the processing of the layer. These two or evaluation hints for the processing of the layer. These two
buckets are available for use in all of the structures except for buckets are available for use in all of the structures except for
keys. While these buckets are present, they may not all be usable in keys. While these buckets are present, they may not all be usable in
all instances. For example, while the protected bucket is defined as all instances. For example, while the protected bucket is defined as
skipping to change at page 11, line 35 skipping to change at page 11, line 35
recipient structures do not provide for authenticated data. If this recipient structures do not provide for authenticated data. If this
is the case, the protected bucket is left empty. is the case, the protected bucket is left empty.
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 1.5). The value portion is dependent on the definition for (Section 1.5). 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 and string values for labels have been divided into several integer and string values for labels have been divided into several
sections including a standard range, a private range, and a range sections including a standard range, a private range, and a range
that is dependent on the algorithm selected. The defined labels can that is dependent on the algorithm selected. The defined labels can
be found in the "COSE Header Parameters" IANA registry be found in the "COSE Header Parameters" IANA registry
(Section 15.2). (Section 16.2).
Two buckets are provided for each layer: Two buckets are provided for each layer:
protected: Contains parameters about the current layer that are protected: Contains parameters about the current layer that are
cryptographically protected. This bucket MUST be empty if it is cryptographically protected. This bucket MUST be empty if it is
not going to be included in a cryptographic computation. This not going to be included in a cryptographic computation. This
bucket is encoded in the message as a binary object. This value bucket is encoded in the message as a binary object. This value
is obtained by CBOR encoding the protected map and wrapping it in is obtained by CBOR encoding the protected map and wrapping it in
a bstr object. Senders SHOULD encode a zero-length map as a zero- a bstr object. Senders SHOULD encode a zero-length map as a zero-
length byte string rather than as a zero-length map (encoded as length byte string rather than as a zero-length map (encoded as
skipping to change at page 12, line 27 skipping to change at page 12, line 27
not placed in the recipient or signature layers. In principle, one not placed in the recipient or signature layers. In principle, one
should be able to process any given layer without reference to any should be able to process any given layer without reference to any
other layer. With the exception of the COSE_Sign structure, the only other layer. With the exception of the COSE_Sign structure, the only
data that needs to cross layers is the cryptographic key. data that needs to cross layers is the cryptographic key.
The buckets are present in all of the security objects defined in The buckets are present in all of the security objects defined in
this document. The fields in order are the 'protected' bucket (as a this document. The fields in order are the 'protected' bucket (as a
CBOR 'bstr' type) and then the 'unprotected' bucket (as a CBOR 'map' CBOR 'bstr' type) and then the 'unprotected' bucket (as a CBOR 'map'
type). The presence of both buckets is required. The parameters type). The presence of both buckets is required. The parameters
that go into the buckets come from the IANA "COSE Header Parameters" that go into the buckets come from the IANA "COSE Header Parameters"
registry (Section 15.2). Some common parameters are defined in the registry (Section 16.2). Some common parameters are defined in the
next section, but a number of parameters are defined throughout this next section.
document.
Labels in each of the maps MUST be unique. When processing messages, Labels in each of the maps MUST be unique. When processing messages,
if a label appears multiple times, the message MUST be rejected as if a label appears multiple times, the message MUST be rejected as
malformed. Applications SHOULD verify that the same label does not malformed. Applications SHOULD verify that the same label does not
occur in both the protected and unprotected headers. If the message occur in both the protected and unprotected headers. If the message
is not rejected as malformed, attributes MUST be obtained from the is not rejected as malformed, attributes MUST be obtained from the
protected bucket before they are obtained from the unprotected protected bucket before they are obtained from the unprotected
bucket. bucket.
The following CDDL fragment represents the two header buckets. A The following CDDL fragment represents the two header buckets. A
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crit: The parameter is used to indicate which protected header crit: The parameter is used to indicate which protected header
labels an application that is processing a message is required to labels an application that is processing a message is required to
understand. Parameters defined in this document do not need to be understand. Parameters defined in this document do not need to be
included as they should be understood by all implementations. included as they should be understood by all implementations.
When present, this parameter MUST be placed in the protected When present, this parameter MUST be placed in the protected
header bucket. The array MUST have at least one value in it. header bucket. The array MUST have at least one value in it.
Not all labels need to be included in the 'crit' parameter. The Not all labels need to be included in the 'crit' parameter. The
rules for deciding which header labels are placed in the array rules for deciding which header labels are placed in the array
are: are:
* Integer labels in the range of 0 to 8 SHOULD be omitted. * Integer labels in the range of 0 to 7 SHOULD be omitted.
* Integer labels in the range -1 to -128 can be omitted as they * Integer labels in the range -1 to -128 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 common parameters associated with that process all of the common parameters associated with that
algorithm. Integer labels in the range -129 to -65536 SHOULD algorithm. Integer labels in the range -129 to -65536 SHOULD
be included as these would be less common parameters that might be included as these would be less common parameters that might
not be generally supported. not be generally supported.
* Labels for parameters required for an application MAY be * Labels for parameters required for an application MAY be
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2. XOR the padded Partial IV with the context IV. 2. XOR the padded Partial IV with the context IV.
counter signature: This parameter holds one or more counter counter signature: This parameter holds one or more counter
signature values. Counter signatures provide a method of having a signature values. Counter signatures provide a method of having a
second party sign some data. The counter signature parameter can second party sign some data. The counter signature parameter can
occur as an unprotected attribute in any of the following occur as an unprotected attribute in any of the following
structures: COSE_Sign1, COSE_Signature, COSE_Encrypt, structures: COSE_Sign1, COSE_Signature, COSE_Encrypt,
COSE_recipient, COSE_Encrypt0, COSE_Mac, and COSE_Mac0. These COSE_recipient, COSE_Encrypt0, COSE_Mac, and COSE_Mac0. These
structures all have the same beginning elements, so that a structures all have the same beginning elements, so that a
consistent calculation of the counter signature can be computed. consistent calculation of the counter signature can be computed.
Details on computing counter signatures are found in Section 4.5. Details on counter signatures are found in Section 5.
+-----------+-------+----------------+-------------+----------------+ +-----------+-------+----------------+-------------+----------------+
| Name | Label | Value Type | Value | Description | | Name | Label | Value Type | Value | Description |
| | | | Registry | | | | | | Registry | |
+-----------+-------+----------------+-------------+----------------+ +-----------+-------+----------------+-------------+----------------+
| alg | 1 | int / tstr | COSE | Cryptographic | | alg | 1 | int / tstr | COSE | Cryptographic |
| | | | Algorithms | algorithm to | | | | | Algorithms | algorithm to |
| | | | registry | use | | | | | registry | use |
| crit | 2 | [+ label] | COSE Header | Critical | | crit | 2 | [+ label] | COSE Header | Critical |
| | | | Parameters | headers to be | | | | | Parameters | headers to be |
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payload: This field contains the serialized content to be signed. payload: This field contains the serialized content to be signed.
If the payload is not present in the message, the application is If the payload is not present in the message, the application is
required to supply the payload separately. The payload is wrapped required to supply the payload separately. The payload is wrapped
in a bstr to ensure that it is transported without changes. If in a bstr to ensure that it is transported without changes. If
the payload is transported separately ("detached content"), then a the payload is transported separately ("detached content"), then a
nil CBOR object is placed in this location, and it is the nil CBOR object is placed in this location, and it is the
responsibility of the application to ensure that it will be responsibility of the application to ensure that it will be
transported without changes. transported without changes.
Note: When a signature with a message recovery algorithm is used Note: When a signature with a message recovery algorithm is used
(Section 8), the maximum number of bytes that can be recovered is (Section 9), the maximum number of bytes that can be recovered is
the length of the payload. The size of the payload is reduced by the length of the payload. The size of the payload is reduced by
the number of bytes that will be recovered. If all of the bytes the number of bytes that will be recovered. If all of the bytes
of the payload are consumed, then the payload is encoded as a of the payload are consumed, then the payload is encoded as a
zero-length binary string rather than as being absent. zero-length binary string rather than as being absent.
signatures: This field is an array of signatures. Each signature is signatures: This field is an array of signatures. Each signature is
represented as a COSE_Signature structure. represented as a COSE_Signature structure.
The CDDL fragment that represents the above text for COSE_Sign The CDDL fragment that represents the above text for COSE_Sign
follows. follows.
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1. A text string identifying the context of the signature. The 1. A text string identifying the context of the signature. The
context string is: context string is:
"Signature" for signatures using the COSE_Signature structure. "Signature" for signatures using the COSE_Signature structure.
"Signature1" for signatures using the COSE_Sign1 structure. "Signature1" for signatures using the COSE_Sign1 structure.
"CounterSignature" for signatures used as counter signature "CounterSignature" for signatures used as counter signature
attributes. attributes.
"CounterSignature0" for signatures used as CounterSignature0
attributes.
2. The protected attributes from the body structure encoded in a 2. The protected attributes from the body structure encoded in a
bstr type. If there are no protected attributes, a bstr of bstr type. If there are no protected attributes, a bstr of
length zero is used. length zero is used.
3. The protected attributes from the signer structure encoded in a 3. The protected attributes from the signer structure encoded in a
bstr type. If there are no protected attributes, a bstr of bstr type. If there are no protected attributes, a bstr of
length zero is used. This field is omitted for the COSE_Sign1 length zero is used. This field is omitted for the COSE_Sign1
signature structure. signature structure and CounterSignature0 attributes.
4. The protected attributes from the application encoded in a bstr 4. The protected attributes from the application encoded in a bstr
type. If this field is not supplied, it defaults to a zero- type. If this field is not supplied, it defaults to a zero-
length binary string. (See Section 4.3 for application guidance length binary string. (See Section 4.3 for application guidance
on constructing this field.) on constructing this field.)
5. The payload to be signed encoded in a bstr type. The payload is 5. The payload to be signed encoded in a bstr type. The payload is
placed here independent of how it is transported. placed here independent of how it is transported.
The CDDL fragment that describes the above text is: The CDDL fragment that describes the above text is:
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The CDDL fragment that describes the above text is: The CDDL fragment that describes the above text is:
Sig_structure = [ Sig_structure = [
context : "Signature" / "Signature1" / "CounterSignature", context : "Signature" / "Signature1" / "CounterSignature",
body_protected : empty_or_serialized_map, body_protected : empty_or_serialized_map,
? sign_protected : empty_or_serialized_map, ? sign_protected : empty_or_serialized_map,
external_aad : bstr, external_aad : bstr,
payload : bstr payload : bstr
] ]
How to compute a signature: How to compute a signature:
1. Create a Sig_structure and populate it with the appropriate 1. Create a Sig_structure and populate it with the appropriate
fields. fields.
2. Create the value ToBeSigned by encoding the Sig_structure to a 2. Create the value ToBeSigned by encoding the Sig_structure to a
byte string, using the encoding described in Section 13. byte string, using the encoding described in Section 14.
3. Call the signature creation algorithm passing in K (the key to 3. 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 4. Place the resulting signature value in the 'signature' field of
the array. the array.
The steps for verifying a signature are: The steps for verifying a signature are:
1. Create a Sig_structure object and populate it with the 1. Create a Sig_structure object and populate it with the
appropriate fields. appropriate fields.
2. Create the value ToBeSigned by encoding the Sig_structure to a 2. Create the value ToBeSigned by encoding the Sig_structure to a
byte string, using the encoding described in Section 13. byte string, using the encoding described in Section 14.
3. Call the signature verification algorithm passing in K (the key 3. Call the signature verification algorithm passing in K (the key
to verify with), alg (the algorithm used sign with), ToBeSigned to verify with), alg (the algorithm used 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, the application In addition to performing the signature verification, the application
performs the appropriate checks to ensure that the key is correctly performs the appropriate checks to ensure that the key is correctly
paired with the signing identity and that the signing identity is paired with the signing identity and that the signing identity is
authorized before performing actions. authorized before performing actions.
4.5. Computing Counter Signatures 5. Counter Signatures
Counter signatures provide a method of associating a different COSE supports two different forms for counter signatures. Full
signature generated by different signers with some piece of content. countersignatures use the structure COSE_Countersign. This is same
This is normally used to provide a signature on a signature allowing structure as COSE_Signature and thus it can have protected
for a proof that a signature existed at a given time (e.g., a attributes, chained countersignatures and information about
Timestamp). In this document, we allow for counter signatures to identifying the key. Abbreviated countersignatures use the structure
exist in a greater number of environments. As an example, it is COSE_Countersign1. This structure only contains the signature value
possible to place a counter signature in the unprotected attributes and nothing else. The structures cannot be converted between each
of a COSE_Encrypt object. This would allow for an intermediary to other; as the signature computation includes a parameter identifying
either verify that the encrypted byte string has not been modified, which structure is being used, the converted structure will fail
without being able to decrypt it, or assert that an encrypted byte signature validation.
string either existed at a given time or passed through it in terms
of routing (e.g., a proxy signature). COSE was designed for uniformity in how the data strutures are
specified. One result of this is that for COSE one can expand the
concept of countersignatures beyond just the idea of signing a
signature to being able to sign most of the structures without having
to create a new signing layer. When creating a countersignature, one
needs to be clear about the security properties that result. When
done on a COSE_Signature, the normal countersignature semantics are
preserved. That is the countersignature makes a statement about the
existance of a signature and, when used as a timestamp, a time point
at which the signature exists. When done on a COSE_Mac or a
COSE_Mac0, one effectively upgrades the MAC operation to a sginature
operation. When done on a COSE_Encrypt or COSE_Encrypt0, the
existance of the encrypted data is attested to. It should be noted
that there is a big difference between attesting to the enrypted data
as oppose to attesting to the unencrypted data. If the latter is
what is desired, then one needs to apply a signature to the data and
then encrypt that. It is always possible to construct cases where
the decryption is successful, while providing completely different
answers by using a different key. This situation is not detectable
by a countersignature on the encrypted data.
5.1. Full Countersignatures
The COSE_Countersignature structure allows for the same set of
capabilities of a COSE_Signature. This means that all of the
capabilities of a signature are duplicated with this structure.
Specifically, the countersigner does not need to be related to the
producer of what is being counter signed as key and algorithm
identification can be placed in the countersignature attributes.
This also means that the countersignature can itself be
countersigned. This is a feature required by protocols such as long-
term archiving services. More information on how this is used can be
found in the evidence record syntax described in [RFC4998].
The full countersignature structure can be encoded as either a tagged
or untagged depending on the context it is used in. A tagged
COSE_Countersign steruture is identified byt the CBOR tag TBD0. The
CDDL fragment for full countersignatures is:
COSE_CounterSignature_Tagged = #6.98(COSE_CounterSignature)
COSE_CounterSignature = COSE_Signature
The details of the fields of a countersignature can be found in
Section 4.1. The process of creating and validating abbreviated
countersignatures is defined in Section 4.4.
An example of a counter signature on a signature can be found in An example of a counter signature on a signature can be found in
Appendix C.1.3. An example of a counter signature in an encryption Appendix C.1.3. An example of a counter signature in an encryption
object can be found in Appendix C.3.3. object can be found in Appendix C.3.3.
The creation and validation of counter signatures over the different
items relies on the fact that the objects have the same structure.
The elements are a set of protected attributes, a set of unprotected
attributes, and a body, in that order. This means that the
Sig_structure can be used in a uniform manner to get the byte string
for processing a signature. If the counter signature is going to be
computed over a COSE_Encrypt structure, the body_protected and
payload items can be mapped into the Sig_structure in the same manner
as from the COSE_Sign structure.
It should be noted that only a signature algorithm with appendix (see It should be noted that only a signature algorithm with appendix (see
Section 8) can be used for counter signatures. This is because the Section 9) can be used for counter signatures. This is because the
body should be able to be processed without having to evaluate the body should be able to be processed without having to evaluate the
counter signature, and this is not possible for signature schemes counter signature, and this is not possible for signature schemes
with message recovery. with message recovery.
5. Encryption Objects 5.2. Abbreviated Countersignatures
Abbreviated countersignatures were designed primarily to deal with
the problem of having group encrypted messaging, but still needing to
know who orginated the message. The object was to keep the
countersignature as small as possible while still providing the
needed security. For abbreviated countersignatures, there is no
provision for any protected attributes related to the signing
operation. Instead, the context that was used to describe the
encryption processing is also assumed to describe the context that
was used to create the countersignature.
The byte string representing the signature value is placed in the
CounterSignature0 attribute. This attribute is then encoded as an
unprotected header. The attribute is defined below.
The process of creating and validating abbreviated countersignatures
is defined in Section 4.4.
+-------------------+-------+---------+-------+---------------------+
| Name | Label | Value | Value | Description |
| | | Type | | |
+-------------------+-------+---------+-------+---------------------+
| CounterSignature0 | 9 | bstr | | Abbreviated |
| | | | | Countersignature |
+-------------------+-------+---------+-------+---------------------+
Table 4: Header Parameter for CounterSignature0
6. Encryption Objects
COSE supports two different encryption structures. COSE_Encrypt0 is COSE supports two different encryption structures. COSE_Encrypt0 is
used when a recipient structure is not needed because the key to be used when a recipient structure is not needed because the key to be
used is known implicitly. COSE_Encrypt is used the rest of the time. used is known implicitly. COSE_Encrypt is used the rest of the time.
This includes cases where there are multiple recipients or a This includes cases where there are multiple recipients or a
recipient algorithm other than direct (i.e. pre-shared secret) is recipient algorithm other than direct (i.e. pre-shared secret) is
used. used.
5.1. Enveloped COSE Structure 6.1. Enveloped COSE Structure
The enveloped structure allows for one or more recipients of a The enveloped structure allows for one or more recipients of a
message. There are provisions for parameters about the content and message. There are provisions for parameters about the content and
parameters about the recipient information to be carried in the parameters about the recipient information to be carried in the
message. The protected parameters associated with the content are message. The protected parameters associated with the content are
authenticated by the content encryption algorithm. The protected authenticated by the content encryption algorithm. The protected
parameters associated with the recipient are authenticated by the parameters associated with the recipient are authenticated by the
recipient algorithm (when the algorithm supports it). Examples of recipient algorithm (when the algorithm supports it). Examples of
parameters about the content are the type of the content and the parameters about the content are the type of the content and the
content encryption algorithm. Examples of parameters about the content encryption algorithm. Examples of parameters about the
skipping to change at page 25, line 20 skipping to change at page 26, line 44
The CDDL fragment that corresponds to the above text for The CDDL fragment that corresponds to the above text for
COSE_recipient is: COSE_recipient is:
COSE_recipient = [ COSE_recipient = [
Headers, Headers,
ciphertext : bstr / nil, ciphertext : bstr / nil,
? recipients : [+COSE_recipient] ? recipients : [+COSE_recipient]
] ]
5.1.1. Content Key Distribution Methods 6.1.1. Content Key Distribution Methods
An encrypted message consists of an encrypted content and an An encrypted message consists of an encrypted content and an
encrypted CEK for one or more recipients. The CEK is encrypted for encrypted CEK for one or more recipients. The CEK is encrypted for
each recipient, using a key specific to that recipient. The details each recipient, using a key specific to that recipient. The details
of this encryption depend on which class the recipient algorithm of this encryption depend on which class the recipient algorithm
falls into. Specific details on each of the classes can be found in falls into. Specific details on each of the classes can be found in
Section 12. A short summary of the five content key distribution Section 13. A short summary of the five content key distribution
methods is: methods is:
direct: The CEK is the same as the identified previously distributed direct: The CEK is the same as the identified previously distributed
symmetric key or is derived from a previously distributed secret. symmetric key or is derived from a previously distributed secret.
No CEK is transported in the message. No CEK is transported in the message.
symmetric key-encryption keys (KEK): The CEK is encrypted using a symmetric key-encryption keys (KEK): The CEK is encrypted using a
previously distributed symmetric KEK. Also known as key wrap. previously distributed symmetric KEK. Also known as key wrap.
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 secret, a Key Derivation Function are used to generate a pairwise secret, a Key Derivation Function
(KDF) is applied to derive a key, and then the CEK is either the (KDF) is applied to derive a key, and then the CEK is either the
derived key or encrypted by the derived key. derived key or encrypted by the derived key.
key transport: The CEK is encrypted with the recipient's public key. key transport: The CEK is encrypted with the recipient's public key.
No key transport algorithms are defined in this document. No key transport algorithms are defined in this document.
passwords: The CEK is encrypted in a KEK that is derived from a passwords: The CEK is encrypted in a KEK that is derived from a
password. No password algorithms are defined in this document. password. No password algorithms are defined in this document.
5.2. Single Recipient Encrypted 6.2. Single Recipient Encrypted
The COSE_Encrypt0 encrypted structure does not have the ability to The COSE_Encrypt0 encrypted structure does not have the ability to
specify recipients of the message. The structure assumes that the specify recipients of the message. The structure assumes that the
recipient of the object will already know the identity of the key to recipient of the object will already know the identity of the key to
be used in order to decrypt the message. If a key needs to be be used in order to decrypt the message. If a key needs to be
identified to the recipient, the enveloped structure ought to be identified to the recipient, the enveloped structure ought to be
used. used.
Examples of encrypted messages can be found in Appendix C.3. Examples of encrypted messages can be found in Appendix C.3.
skipping to change at page 26, line 24 skipping to change at page 27, line 48
COSE_Encrypt0_Tagged = #6.16(COSE_Encrypt0) COSE_Encrypt0_Tagged = #6.16(COSE_Encrypt0)
The COSE_Encrypt0 structure is a CBOR array. The fields of the array The COSE_Encrypt0 structure is a CBOR array. The fields of the array
in order are: in order are:
protected: This is as described in Section 3. protected: This is as described in Section 3.
unprotected: This is as described in Section 3. unprotected: This is as described in Section 3.
ciphertext: This is as described in Section 5.1. ciphertext: This is as described in Section 6.1.
The CDDL fragment for COSE_Encrypt0 that corresponds to the above The CDDL fragment for COSE_Encrypt0 that corresponds to the above
text is: text is:
COSE_Encrypt0 = [ COSE_Encrypt0 = [
Headers, Headers,
ciphertext : bstr / nil, ciphertext : bstr / nil,
] ]
5.3. How to Encrypt and Decrypt for AEAD Algorithms 6.3. How to Encrypt and Decrypt for AEAD Algorithms
The encryption algorithm for AEAD algorithms is fairly simple. The The encryption algorithm for AEAD algorithms is fairly simple. The
first step is to create a consistent byte string for the first step is to create a consistent byte string for the
authenticated data structure. For this purpose, we use an authenticated data structure. For this purpose, we use an
Enc_structure. The Enc_structure is a CBOR array. The fields of the Enc_structure. The Enc_structure is a CBOR array. The fields of the
Enc_structure in order are: Enc_structure in order are:
1. A text string identifying the context of the authenticated data 1. A text string identifying the context of the authenticated data
structure. The context string is: structure. The context string is:
skipping to change at page 27, line 31 skipping to change at page 29, line 4
constructing this field.) constructing this field.)
The CDDL fragment that describes the above text is: The CDDL fragment that describes the above text is:
Enc_structure = [ Enc_structure = [
context : "Encrypt" / "Encrypt0" / "Enc_Recipient" / context : "Encrypt" / "Encrypt0" / "Enc_Recipient" /
"Mac_Recipient" / "Rec_Recipient", "Mac_Recipient" / "Rec_Recipient",
protected : empty_or_serialized_map, protected : empty_or_serialized_map,
external_aad : bstr external_aad : bstr
] ]
How to encrypt a message: How to encrypt a message:
1. Create an Enc_structure and populate it with the appropriate 1. Create an Enc_structure and populate it with the appropriate
fields. fields.
2. Encode the Enc_structure to a byte string (Additional 2. Encode the Enc_structure to a byte string (Additional
Authenticated Data (AAD)), using the encoding described in Authenticated Data (AAD)), using the encoding described in
Section 13. Section 14.
3. Determine the encryption key (K). This step is dependent on the 3. Determine the encryption key (K). This step is dependent on the
class of recipient algorithm being used. For: class of recipient algorithm being used. For:
No Recipients: The key to be used is determined by the algorithm No Recipients: The key to be used is determined by the algorithm
and key at the current layer. Examples are key transport keys and key at the current layer. Examples are key transport keys
(Section 12.3), key wrap keys (Section 12.2), or pre-shared (Section 13.3), key wrap keys (Section 13.2), or pre-shared
secrets. secrets.
Direct Encryption and Direct Key Agreement: The key is Direct Encryption and Direct Key Agreement: The key is
determined by the key and algorithm in the recipient determined by the key and algorithm in the recipient
structure. The encryption algorithm and size of the key to be structure. The encryption algorithm and size of the key to be
used are inputs into the KDF used for the recipient. (For used are inputs into the KDF used for the recipient. (For
direct, the KDF can be thought of as the identity operation.) direct, the KDF can be thought of as the identity operation.)
Examples of these algorithms are found in Sections !!! DIRECT- Examples of these algorithms are found in Sections 6.1.2 and
KDF !!! and !!! ECDH !!! of [I-D.ietf-cose-rfc8152bis-algs]. 6.3 of [I-D.ietf-cose-rfc8152bis-algs].
Other: The key is randomly or pseudorandomly generated. Other: The key is randomly or pseudorandomly generated.
4. Call the encryption algorithm with K (the encryption key), P (the 4. Call the encryption algorithm with K (the encryption key), P (the
plaintext), and AAD. Place the returned ciphertext into the plaintext), and AAD. Place the returned ciphertext into the
'ciphertext' field of the structure. '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 K (the encryption key) as the algorithm for that recipient, using K (the encryption key) as the
plaintext. plaintext.
How to decrypt a message: How to decrypt a message:
1. Create an Enc_structure and populate it with the appropriate 1. Create an Enc_structure and populate it with the appropriate
fields. fields.
2. Encode the Enc_structure to a byte string (AAD), using the 2. Encode the Enc_structure to a byte string (AAD), using the
encoding described in Section 13. encoding described in Section 14.
3. Determine the decryption key. This step is dependent on the 3. Determine the decryption key. This step is dependent on the
class of recipient algorithm being used. For: class of recipient algorithm being used. For:
No Recipients: The key to be used is determined by the algorithm No Recipients: The key to be used is determined by the algorithm
and key at the current layer. Examples are key transport keys and key at the current layer. Examples are key transport keys
(Section 12.3), key wrap keys (Section 12.2), or pre-shared (Section 13.3), key wrap keys (Section 13.2), or pre-shared
secrets. secrets.
Direct Encryption and Direct Key Agreement: The key is Direct Encryption and Direct Key Agreement: The key is
determined by the key and algorithm in the recipient determined by the key and algorithm in the recipient
structure. The encryption algorithm and size of the key to be structure. The encryption algorithm and size of the key to be
used are inputs into the KDF used for the recipient. (For used are inputs into the KDF used for the recipient. (For
direct, the KDF can be thought of as the identity operation.) direct, the KDF can be thought of as the identity operation.)
Other: The key is determined by decoding and decrypting one of Other: The key is determined by decoding and decrypting one of
the recipient structures. the recipient structures.
4. Call the decryption algorithm with K (the decryption key to use), 4. Call the decryption algorithm with K (the decryption key to use),
C (the ciphertext), and AAD. C (the ciphertext), and AAD.
5.4. How to Encrypt and Decrypt for AE Algorithms 6.4. How to Encrypt and Decrypt for AE Algorithms
How to encrypt a message: How to encrypt a message:
1. Verify that the 'protected' field is empty. 1. Verify that the 'protected' field is empty.
2. Verify that there was no external additional authenticated data 2. Verify that there was no external additional authenticated data
supplied for this operation. supplied for this operation.
3. Determine the encryption key. This step is dependent on the 3. Determine the encryption key. This step is dependent on the
class of recipient algorithm being used. For: class of recipient algorithm being used. For:
No Recipients: The key to be used is determined by the algorithm No Recipients: The key to be used is determined by the algorithm
and key at the current layer. Examples are key transport keys and key at the current layer. Examples are key transport keys
(Section 12.3), key wrap keys (Section 12.2), or pre-shared (Section 13.3), key wrap keys (Section 13.2), or pre-shared
secrets. secrets.
Direct Encryption and Direct Key Agreement: The key is Direct Encryption and Direct Key Agreement: The key is
determined by the key and algorithm in the recipient determined by the key and algorithm in the recipient
structure. The encryption algorithm and size of the key to be structure. The encryption algorithm and size of the key to be
used are inputs into the KDF used for the recipient. (For used are inputs into the KDF used for the recipient. (For
direct, the KDF can be thought of as the identity operation.) direct, the KDF can be thought of as the identity operation.)
Examples of these algorithms are found in Sections !!!DIRECT- Examples of these algorithms are found in Sections 6.1.2 and
KDF!!! and !!! ECDH !!! . 6.3 of [I-D.ietf-cose-rfc8152bis-algs].
Other: The key is randomly generated. Other: The key is randomly generated.
4. Call the encryption algorithm with K (the encryption key to use) 4. Call the encryption algorithm with K (the encryption key to use)
and P (the plaintext). Place the returned ciphertext into the and P (the plaintext). Place the returned ciphertext into the
'ciphertext' field of the structure. '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 K (the encryption key) as the algorithm for that recipient, using K (the encryption key) as the
plaintext. plaintext.
skipping to change at page 29, line 46 skipping to change at page 31, line 21
1. Verify that the 'protected' field is empty. 1. Verify that the 'protected' field is empty.
2. Verify that there was no external additional authenticated data 2. Verify that there was no external additional authenticated data
supplied for this operation. supplied for this operation.
3. Determine the decryption key. This step is dependent on the 3. Determine the decryption key. This step is dependent on the
class of recipient algorithm being used. For: class of recipient algorithm being used. For:
No Recipients: The key to be used is determined by the algorithm No Recipients: The key to be used is determined by the algorithm
and key at the current layer. Examples are key transport keys and key at the current layer. Examples are key transport keys
(Section 12.3), key wrap keys (Section 12.2), or pre-shared (Section 13.3), key wrap keys (Section 13.2), or pre-shared
secrets. secrets.
Direct Encryption and Direct Key Agreement: The key is Direct Encryption and Direct Key Agreement: The key is
determined by the key and algorithm in the recipient determined by the key and algorithm in the recipient
structure. The encryption algorithm and size of the key to be structure. The encryption algorithm and size of the key to be
used are inputs into the KDF used for the recipient. (For used are inputs into the KDF used for the recipient. (For
direct, the KDF can be thought of as the identity operation.) direct, the KDF can be thought of as the identity operation.)
Examples of these algorithms are found in Sections !!! DIRECT- Examples of these algorithms are found in Sections 6.1.2 and
KDF !!! and !!! ECDH !!! . 6.3 of [I-D.ietf-cose-rfc8152bis-algs].
Other: The key is determined by decoding and decrypting one of Other: The key is determined by decoding and decrypting one of
the recipient structures. the recipient structures.
4. Call the decryption algorithm with K (the decryption key to use) 4. Call the decryption algorithm with K (the decryption key to use)
and C (the ciphertext). and C (the ciphertext).
6. MAC Objects 7. MAC Objects
COSE supports two different MAC structures. COSE_MAC0 is used when a COSE supports two different MAC structures. COSE_MAC0 is used when a
recipient structure is not needed because the key to be used is recipient structure is not needed because the key to be used is
implicitly known. COSE_MAC is used for all other cases. These implicitly known. COSE_MAC is used for all other cases. These
include a requirement for multiple recipients, the key being unknown, include a requirement for multiple recipients, the key being unknown,
and a recipient algorithm of other than direct. and a recipient algorithm of other than direct.
In this section, we describe the structure and methods to be used In this section, we describe the structure and methods to be used
when doing MAC authentication in COSE. This document allows for the when doing MAC authentication in COSE. This document allows for the
use of all of the same classes of recipient algorithms as are allowed use of all of the same classes of recipient algorithms as are allowed
skipping to change at page 30, line 41 skipping to change at page 32, line 16
the content has not been changed since the MAC was computed and to the content has not been changed since the MAC was computed and to
use the recipient algorithm to verify who sent it. The classes of use the recipient algorithm to verify who sent it. The classes of
recipient algorithms that support this are those that use a pre- recipient algorithms that support this are those that use a pre-
shared secret or do static-static (SS) key agreement (without the key shared secret or do static-static (SS) key agreement (without the key
wrap step). In both of these cases, the entity that created and sent wrap step). In both of these cases, the entity that created and sent
the message MAC can be validated. (This knowledge of the sender the message MAC can be validated. (This knowledge of the sender
assumes that there are only two parties involved and that you did not assumes that there are only two parties involved and that you did not
send the message to yourself.) The origination property can be send the message to yourself.) The origination property can be
obtained with both of the MAC message structures. obtained with both of the MAC message structures.
6.1. MACed Message with Recipients 7.1. MACed Message with Recipients
The multiple recipient MACed message uses two structures: the The multiple recipient MACed message uses two structures: the
COSE_Mac structure defined in this section for carrying the body and COSE_Mac structure defined in this section for carrying the body and
the COSE_recipient structure (Section 5.1) to hold the key used for the COSE_recipient structure (Section 6.1) to hold the key used for
the MAC computation. Examples of MACed messages can be found in the MAC computation. Examples of MACed messages can be found in
Appendix C.5. Appendix C.5.
The MAC structure can be encoded as either tagged or untagged The MAC structure can be encoded as either tagged or untagged
depending on the context it will be used in. A tagged COSE_Mac depending on the context it will be used in. A tagged COSE_Mac
structure is identified by the CBOR tag 97. The CDDL fragment that structure is identified by the CBOR tag 97. The CDDL fragment that
represents this is: represents this is:
COSE_Mac_Tagged = #6.97(COSE_Mac) COSE_Mac_Tagged = #6.97(COSE_Mac)
skipping to change at page 31, line 27 skipping to change at page 32, line 49
the payload is not present in the message, the application is the payload is not present in the message, the application is
required to supply the payload separately. The payload is wrapped required to supply the payload separately. The payload is wrapped
in a bstr to ensure that it is transported without changes. If in a bstr to ensure that it is transported without changes. If
the payload is transported separately (i.e., detached content), the payload is transported separately (i.e., detached content),
then a nil CBOR value is placed in this location, and it is the then a nil CBOR value is placed in this location, and it is the
responsibility of the application to ensure that it will be responsibility of the application to ensure that it will be
transported without changes. transported without changes.
tag: This field contains the MAC value. tag: This field contains the MAC value.
recipients: This is as described in Section 5.1. recipients: This is as described in Section 6.1.
The CDDL fragment that represents the above text for COSE_Mac The CDDL fragment that represents the above text for COSE_Mac
follows. follows.
COSE_Mac = [ COSE_Mac = [
Headers, Headers,
payload : bstr / nil, payload : bstr / nil,
tag : bstr, tag : bstr,
recipients :[+COSE_recipient] recipients :[+COSE_recipient]
] ]
6.2. MACed Messages with Implicit Key 7.2. MACed Messages with Implicit Key
In this section, we describe the structure and methods to be used In this section, we describe the structure and methods to be used
when doing MAC authentication for those cases where the recipient is when doing MAC authentication for those cases where the recipient is
implicitly known. implicitly known.
The MACed message uses the COSE_Mac0 structure defined in this The MACed message uses the COSE_Mac0 structure defined in this
section for carrying the body. Examples of MACed messages with an section for carrying the body. Examples of MACed messages with an
implicit key can be found in Appendix C.6. implicit key can be found in Appendix C.6.
The MAC structure can be encoded as either tagged or untagged The MAC structure can be encoded as either tagged or untagged
skipping to change at page 32, line 16 skipping to change at page 33, line 39
COSE_Mac0_Tagged = #6.17(COSE_Mac0) COSE_Mac0_Tagged = #6.17(COSE_Mac0)
The COSE_Mac0 structure is a CBOR array. The fields of the array in The COSE_Mac0 structure is a CBOR array. The fields of the array in
order are: order are:
protected: This is as described in Section 3. protected: This is as described in Section 3.
unprotected: This is as described in Section 3. unprotected: This is as described in Section 3.
payload: This is as described in Section 6.1. payload: This is as described in Section 7.1.
tag: This field contains the MAC value. tag: This field contains the MAC value.
The CDDL fragment that corresponds to the above text is: The CDDL fragment that corresponds to the above text is:
COSE_Mac0 = [ COSE_Mac0 = [
Headers, Headers,
payload : bstr / nil, payload : bstr / nil,
tag : bstr, tag : bstr,
] ]
6.3. How to Compute and Verify a MAC 7.3. How to Compute and Verify a MAC
In order to get a consistent encoding of the data to be In order to get a consistent encoding of the data to be
authenticated, the MAC_structure is used to have a canonical form. authenticated, the MAC_structure is used to have a canonical form.
The MAC_structure is a CBOR array. The fields of the MAC_structure The MAC_structure is a CBOR array. The fields of the MAC_structure
in order are: in order are:
1. A text string that identifies the structure that is being 1. A text string that identifies the structure that is being
encoded. This string is "MAC" for the COSE_Mac structure. This encoded. This string is "MAC" for the COSE_Mac structure. This
string is "MAC0" for the COSE_Mac0 structure. string is "MAC0" for the COSE_Mac0 structure.
skipping to change at page 33, line 18 skipping to change at page 34, line 42
external_aad : bstr, external_aad : bstr,
payload : bstr payload : bstr
] ]
The steps to compute a MAC are: The steps to compute a MAC are:
1. Create a MAC_structure and populate it with the appropriate 1. Create a MAC_structure and populate it with the appropriate
fields. fields.
2. Create the value ToBeMaced by encoding the MAC_structure to a 2. Create the value ToBeMaced by encoding the MAC_structure to a
byte string, using the encoding described in Section 13. byte string, using the encoding described in Section 14.
3. Call the MAC creation algorithm passing in K (the key to use), 3. Call the MAC creation algorithm passing in K (the key to use),
alg (the algorithm to MAC with), and ToBeMaced (the value to alg (the algorithm to MAC with), and ToBeMaced (the value to
compute the MAC on). compute the MAC on).
4. Place the resulting MAC in the 'tag' field of the COSE_Mac or 4. Place the resulting MAC in the 'tag' field of the COSE_Mac or
COSE_Mac0 structure. COSE_Mac0 structure.
5. For COSE_Mac structures, encrypt and encode the MAC key for each 5. For COSE_Mac structures, encrypt and encode the MAC key for each
recipient of the message. recipient of the message.
The steps to verify a MAC are: The steps to verify a MAC are:
1. Create a MAC_structure object and populate it with the 1. Create a MAC_structure object and populate it with the
appropriate fields. appropriate fields.
2. Create the value ToBeMaced by encoding the MAC_structure to a 2. Create the value ToBeMaced by encoding the MAC_structure to a
byte string, using the encoding described in Section 13. byte string, using the encoding described in Section 14.
3. For COSE_Mac structures, obtain the cryptographic key from one of 3. For COSE_Mac structures, obtain the cryptographic key from one of
the recipients of the message. the recipients of the message.
4. Call the MAC creation algorithm passing in K (the key to use), 4. Call the MAC creation algorithm passing in K (the key to use),
alg (the algorithm to MAC with), and ToBeMaced (the value to alg (the algorithm to MAC with), and ToBeMaced (the value to
compute the MAC on). compute the MAC on).
5. Compare the MAC value to the 'tag' field of the COSE_Mac or 5. Compare the MAC value to the 'tag' field of the COSE_Mac or
COSE_Mac0 structure. COSE_Mac0 structure.
7. Key Objects 8. Key Objects
A COSE Key structure is built on a CBOR map object. The set of A COSE Key structure is built on a CBOR map object. The set of
common parameters that can appear in a COSE Key can be found in the common parameters that can appear in a COSE Key can be found in the
IANA "COSE Key Common Parameters" registry (Section 15.4). IANA "COSE Key Common Parameters" registry (Section 16.4).
Additional parameters defined for specific key types can be found in Additional parameters defined for specific key types can be found in
the IANA "COSE Key Type Parameters" registry ([COSE.KeyParameters]). the IANA "COSE Key Type Parameters" registry ([COSE.KeyParameters]).
A COSE Key Set uses a CBOR array object as its underlying type. The A COSE Key Set uses a CBOR array object as its underlying type. The
values of the array elements are COSE Keys. A COSE Key Set MUST have values of the array elements are COSE Keys. A COSE Key Set MUST have
at least one element in the array. Examples of COSE Key Sets can be at least one element in the array. Examples of COSE Key Sets can be
found in Appendix C.7. found in Appendix C.7.
Each element in a COSE Key Set MUST be processed independently. If Each element in a COSE Key Set MUST be processed independently. If
one element in a COSE Key Set is either malformed or uses a key that one element in a COSE Key Set is either malformed or uses a key that
skipping to change at page 34, line 33 skipping to change at page 36, line 16
1 => tstr / int, ; kty 1 => tstr / int, ; kty
? 2 => bstr, ; kid ? 2 => bstr, ; kid
? 3 => tstr / int, ; alg ? 3 => tstr / int, ; alg
? 4 => [+ (tstr / int) ], ; key_ops ? 4 => [+ (tstr / int) ], ; key_ops
? 5 => bstr, ; Base IV ? 5 => bstr, ; Base IV
* label => values * label => values
} }
COSE_KeySet = [+COSE_Key] COSE_KeySet = [+COSE_Key]
7.1. COSE Key Common Parameters 8.1. COSE Key Common Parameters
This document defines a set of common parameters for a COSE Key This document defines a set of common parameters for a COSE Key
object. Table 4 provides a summary of the parameters defined in this object. Table 5 provides a summary of the parameters defined in this
section. There are also parameters that are defined for specific key section. There are also parameters that are defined for specific key
types. Key-type-specific parameters can be found in types. Key-type-specific parameters can be found in
[I-D.ietf-cose-rfc8152bis-algs]. [I-D.ietf-cose-rfc8152bis-algs].
+---------+-------+----------------+------------+-------------------+ +---------+-------+----------------+------------+-------------------+
| Name | Label | CBOR Type | Value | Description | | Name | Label | CBOR Type | Value | Description |
| | | | Registry | | | | | | Registry | |
+---------+-------+----------------+------------+-------------------+ +---------+-------+----------------+------------+-------------------+
| kty | 1 | tstr / int | COSE Key | Identification of | | kty | 1 | tstr / int | COSE Key | Identification of |
| | | | Types | the key type | | | | | Types | the key type |
skipping to change at page 35, line 30 skipping to change at page 36, line 49
| | | | | | | | | | | |
| key_ops | 4 | [+ (tstr/int)] | | Restrict set of | | key_ops | 4 | [+ (tstr/int)] | | Restrict set of |
| | | | | permissible | | | | | | permissible |
| | | | | operations | | | | | | operations |
| | | | | | | | | | | |
| Base IV | 5 | bstr | | Base IV to be | | Base IV | 5 | bstr | | Base IV to be |
| | | | | xor-ed with | | | | | | xor-ed with |
| | | | | Partial IVs | | | | | | Partial IVs |
+---------+-------+----------------+------------+-------------------+ +---------+-------+----------------+------------+-------------------+
Table 4: Key Map Labels Table 5: Key Map Labels
kty: This parameter is used to identify the family of keys for this kty: This parameter is used to identify the family of keys for this
structure and, thus, the set of key-type-specific parameters to be structure and, thus, the set of key-type-specific parameters to be
found. The set of values defined in this document can be found in found. The set of values defined in this document can be found in
[COSE.KeyTypes]. This parameter MUST be present in a key object. [COSE.KeyTypes]. This parameter MUST be present in a key object.
Implementations MUST verify that the key type is appropriate for Implementations MUST verify that the key type is appropriate for
the algorithm being processed. The key type MUST be included as the algorithm being processed. The key type MUST be included as
part of the trust decision process. part of the trust decision process.
alg: This parameter is used to restrict the algorithm that is used alg: This parameter is used to restrict the algorithm that is used
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kid: This parameter is used to give an identifier for a key. The kid: This parameter is used to give an identifier for a key. The
identifier is not structured and can be anything from a user- identifier is not structured and can be anything from a user-
provided string to a value computed on the public portion of the provided string to a value computed on the public portion of the
key. This field is intended for matching against a 'kid' key. This field is intended for matching against a 'kid'
parameter in a message in order to filter down the set of keys parameter in a message in order to filter down the set of keys
that need to be checked. that need to be checked.
key_ops: This parameter is defined to restrict the set of operations key_ops: This parameter is defined to restrict the set of operations
that a key is to be used for. The value of the field is an array that a key is to be used for. The value of the field is an array
of values from Table 5. Algorithms define the values of key ops of values from Table 6. Algorithms define the values of key ops
that are permitted to appear and are required for specific that are permitted to appear and are required for specific
operations. The set of values matches that in [RFC7517] and operations. The set of values matches that in [RFC7517] and
[W3C.WebCrypto]. [W3C.WebCrypto].
Base IV: This parameter is defined to carry the base portion of an Base IV: This parameter is defined to carry the base portion of an
IV. It is designed to be used with the Partial IV header IV. It is designed to be used with the Partial IV header
parameter defined in Section 3.1. This field provides the ability parameter defined in Section 3.1. This field provides the ability
to associate a Partial IV with a key that is then modified on a to associate a Partial IV with a key that is then modified on a
per message basis with the Partial IV. per message basis with the Partial IV.
skipping to change at page 37, line 28 skipping to change at page 38, line 30
| derive | 7 | The key is used for deriving keys. Requires | | derive | 7 | The key is used for deriving keys. Requires |
| key | | private key fields. | | key | | private key fields. |
| derive | 8 | The key is used for deriving bits not to be | | derive | 8 | The key is used for deriving bits not to be |
| bits | | used as a key. Requires private key fields. | | bits | | used as a key. Requires private key fields. |
| MAC | 9 | The key is used for creating MACs. | | MAC | 9 | The key is used for creating MACs. |
| create | | | | create | | |
| MAC | 10 | The key is used for validating MACs. | | MAC | 10 | The key is used for validating MACs. |
| verify | | | | verify | | |
+---------+-------+-------------------------------------------------+ +---------+-------+-------------------------------------------------+
Table 5: Key Operation Values Table 6: Key Operation Values
8. Signature Algorithms 9. Signature Algorithms
There are two signature algorithm schemes. The first is signature There are two signature algorithm schemes. The first is signature
with appendix. In this scheme, the message content is processed and with appendix. In this scheme, the message content is processed and
a signature is produced; the signature is called the appendix. This a signature is produced; the signature is called the appendix. This
is the scheme used by algorithms such as ECDSA and the RSA is the scheme used by algorithms such as ECDSA and the RSA
Probabilistic Signature Scheme (RSASSA-PSS). (In fact, the SSA in Probabilistic Signature Scheme (RSASSA-PSS). (In fact, the SSA in
RSASSA-PSS stands for Signature Scheme with Appendix.) RSASSA-PSS stands for Signature Scheme with Appendix.)
The signature functions for this scheme are: The signature functions for this scheme are:
skipping to change at page 38, line 31 skipping to change at page 39, line 34
valid, message content = Verification(message sent, key, signature) valid, message content = Verification(message sent, key, signature)
Signature algorithms are used with the COSE_Signature and COSE_Sign1 Signature algorithms are used with the COSE_Signature and COSE_Sign1
structures. At this time, only signatures with appendixes are structures. At this time, only signatures with appendixes are
defined for use with COSE; however, considerable interest has been defined for use with COSE; however, considerable interest has been
expressed in using a signature with message recovery algorithm due to expressed in using a signature with message recovery algorithm due to
the effective size reduction that is possible. Implementations will the effective size reduction that is possible. Implementations will
need to keep this in mind for later possible integration. need to keep this in mind for later possible integration.
9. Message Authentication Code (MAC) Algorithms 10. Message Authentication Code (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. A MAC, for example, cannot be used to prove the origination. A MAC, for example, cannot be used to prove the
identity of the sender to a third party. identity of the sender to a third party.
MACs use the same scheme as signature with appendix algorithms. The MACs use the same scheme as signature with appendix algorithms. The
message content is processed and an authentication code is produced. message content is processed and an authentication code is produced.
The authentication code is frequently called a tag. The authentication code is frequently called a tag.
skipping to change at page 38, line 47 skipping to change at page 40, line 4
MACs use the same scheme as signature with appendix algorithms. The MACs use the same scheme as signature with appendix algorithms. The
message content is processed and an authentication code is produced. message content is processed and an authentication code is produced.
The authentication code is frequently called a tag. The authentication code is frequently called a tag.
The MAC functions are: The MAC functions are:
tag = MAC_Create(message content, key) tag = MAC_Create(message content, key)
valid = MAC_Verify(message content, key, tag) valid = MAC_Verify(message content, key, tag)
MAC algorithms can be based on either a block cipher algorithm (i.e., MAC algorithms can be based on either a block cipher algorithm (i.e.,
AES-MAC) or a hash algorithm (i.e., a Hash-based Message AES-MAC) or a hash algorithm (i.e., a Hash-based Message
Authentication Code (HMAC)). This document defines a MAC algorithm Authentication Code (HMAC)). This document defines a MAC algorithm
using each of these constructions. using each of these constructions.
MAC algorithms are used in the COSE_Mac and COSE_Mac0 structures. MAC algorithms are used in the COSE_Mac and COSE_Mac0 structures.
10. Content Encryption Algorithms 11. Content Encryption Algorithms
Content encryption algorithms provide data confidentiality for Content encryption algorithms provide data confidentiality for
potentially large blocks of data using a symmetric key. They provide potentially large blocks of data using a symmetric key. They provide
integrity on the data that was encrypted; however, they provide integrity on the data that was encrypted; however, they provide
either no or very limited data origination. (One cannot, for either no or very limited data origination. (One cannot, for
example, be used to prove the identity of the sender to a third example, be used to prove the identity of the sender to a third
party.) The ability to provide data origination is linked to how the party.) The ability to provide data origination is linked to how the
CEK is obtained. CEK is obtained.
COSE restricts the set of legal content encryption algorithms to COSE restricts the set of legal content encryption algorithms to
skipping to change at page 39, line 36 skipping to change at page 40, line 40
valid, message content = Decrypt(ciphertext, key, additional data) valid, message content = Decrypt(ciphertext, key, additional data)
Most AEAD algorithms are logically defined as returning the message Most AEAD algorithms are logically defined as returning the message
content only if the decryption is valid. Many but not all content only if the decryption is valid. Many but not all
implementations will follow this convention. The message content implementations will follow this convention. The message content
MUST NOT be used if the decryption does not validate. MUST NOT be used if the decryption does not validate.
These algorithms are used in COSE_Encrypt and COSE_Encrypt0. These algorithms are used in COSE_Encrypt and COSE_Encrypt0.
11. Key Derivation Functions (KDFs) 12. Key Derivation Functions (KDFs)
KDFs are used to take some secret value and generate a different one. KDFs are used to take some secret value and generate a different one.
The secret value comes in three flavors: The secret value comes in three flavors:
o Secrets that are uniformly random: This is the type of secret that o Secrets that are uniformly random: This is the type of secret that
is created by a good random number generator. is created by a good random number generator.
o Secrets that are not uniformly random: This is type of secret that o Secrets that are not uniformly random: This is type of secret that
is created by operations like key agreement. is created by operations like key agreement.
o Secrets that are not random: This is the type of secret that o Secrets that are not random: This is the type of secret that
people generate for things like passwords. people generate for things like passwords.
General KDFs work well with the first type of secret, can do General KDFs work well with the first type of secret, can do
reasonably well with the second type of secret, and generally do reasonably well with the second type of secret, and generally do
poorly with the last type of secret. Functions like PBES2 [RFC8018] poorly with the last type of secret. Functions like PBES2 [RFC8018]
need to be used for non-random secrets. need to be used for non-random secrets.
The same KDF can be set up to deal with the first two types of The same KDF can be set up to deal with the first two types of
secrets in a different way. The KDF defined in !!! HDKF !!! (section secrets in a different way. The KDF defined in section 5.1 of
XXXX of [I-D.ietf-cose-rfc8152bis-algs]) is such a function. This is [I-D.ietf-cose-rfc8152bis-algs] is such a function. This is
reflected in the set of algorithms defined around the HMAC-based reflected in the set of algorithms defined around the HMAC-based
Extract-and-Expand Key Derivation Function (HKDF). Extract-and-Expand Key Derivation Function (HKDF).
When using KDFs, one component that is included is context When using KDFs, one component that is included is context
information. Context information is used to allow for different information. Context information is used to allow for different
keying information to be derived from the same secret. The use of keying information to be derived from the same secret. The use of
context-based keying material is considered to be a good security context-based keying material is considered to be a good security
practice. practice.
12. Content Key Distribution Methods 13. Content Key Distribution Methods
Content key distribution methods (recipient algorithms) can be Content key distribution methods (recipient algorithms) can be
defined into a number of different classes. COSE has the ability to defined into a number of different classes. COSE has the ability to
support many classes of recipient algorithms. In this section, a support many classes of recipient algorithms. In this section, a
number of classes are listed. The names of the recipient algorithm number of classes are listed. The names of the recipient algorithm
classes used here are the same as those defined in [RFC7516]. Other classes used here are the same as those defined in [RFC7516]. Other
specifications use different terms for the recipient algorithm specifications use different terms for the recipient algorithm
classes or do not support some of the recipient algorithm classes. classes or do not support some of the recipient algorithm classes.
12.1. Direct Encryption 13.1. Direct Encryption
The direct encryption class algorithms share a secret between the The direct encryption class algorithms share a secret between the
sender and the recipient that is used either directly or after sender and the recipient that is used either directly or after
manipulation as the CEK. When direct encryption mode is used, it manipulation as the CEK. When direct encryption mode is used, it
MUST be the only mode used on the message. MUST be the only mode used on the message.
The COSE_Recipient structure for the recipient is organized as The COSE_Recipient structure for the recipient is organized as
follows: follows:
o The 'protected' field MUST be a zero-length item unless it is used o The 'protected' field MUST be a zero-length item unless it is used
in the computation of the content key. in the computation of the content key.
o The 'alg' parameter MUST be present. o The 'alg' parameter MUST be present.
o A parameter identifying the shared secret SHOULD be present. o A parameter identifying the shared secret SHOULD be present.
o The 'ciphertext' field MUST be a zero-length item. o The 'ciphertext' field MUST be a zero-length item.
o The 'recipients' field MUST be absent. o The 'recipients' field MUST be absent.
12.2. Key Wrap 13.2. Key Wrap
In key wrap mode, the CEK is randomly generated and that key is then In key wrap mode, the CEK is randomly generated and that key is then
encrypted by a shared secret between the sender and the recipient. encrypted by a shared secret between the sender and the recipient.
All of the currently defined key wrap algorithms for COSE are AE All of the currently defined key wrap algorithms for COSE are AE
algorithms. Key wrap mode is considered to be superior to direct algorithms. Key wrap mode is considered to be superior to direct
encryption if the system has any capability for doing random key encryption if the system has any capability for doing random key
generation. This is because the shared key is used to wrap random generation. This is because the shared key is used to wrap random
data rather than data that has some degree of organization and may in data rather than data that has some degree of organization and may in
fact be repeating the same content. The use of key wrap loses the fact be repeating the same content. The use of key wrap loses the
weak data origination that is provided by the direct encryption weak data origination that is provided by the direct encryption
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recipient is an acceptable way of dealing with it. Failing to recipient is an acceptable way of dealing with it. Failing to
process the message is not an acceptable way of dealing with it. process the message is not an acceptable way of dealing with it.
o The plaintext to be encrypted is the key from next layer down o The plaintext 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 shared parameter and SHOULD contain a parameter identifying the shared
secret. secret.
12.3. Key Transport 13.3. Key Transport
Key transport mode is also called key encryption mode in some Key transport mode is also called key encryption mode in some
standards. Key transport mode differs from key wrap mode in that it standards. Key transport 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. A set of key transport encryption algorithm to protect the key. A set of key transport
algorithms are defined in [RFC8230]. algorithms are defined in [RFC8230].
When using a key transport algorithm, the COSE_Encrypt structure for When using a key transport algorithm, the COSE_Encrypt structure for
the recipient is organized as follows: the recipient is organized as follows:
o The 'protected' field MUST be absent. o The 'protected' field MUST be absent.
o The plaintext to be encrypted is the key from the next layer down o The plaintext to be encrypted is the key from the 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.
12.4. Direct Key Agreement 13.4. Direct Key Agreement
The 'direct key agreement' class of recipient algorithms uses a key The 'direct key agreement' class of recipient algorithms uses a key
agreement method to create a shared secret. A KDF is then applied to agreement method to create a shared secret. A KDF is then applied to
the shared secret to derive a key to be used in protecting the data. 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, but could be used for 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 use (see Appendix B). other purposes if more than two layers are in use (see Appendix B).
The most commonly used key agreement algorithm is Diffie-Hellman, but The most commonly used key agreement algorithm is Diffie-Hellman, but
other variants exist. Since COSE is designed for a store and forward other variants exist. Since COSE is designed for a store and forward
environment rather than an online environment, many of the DH environment rather than an online environment, many of the DH
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The COSE_Encrypt structure for the recipient is organized as follows: The COSE_Encrypt structure for the recipient is organized as follows:
o At a minimum, headers MUST contain the 'alg' parameter and SHOULD o At a minimum, headers MUST contain the 'alg' parameter and SHOULD
contain a parameter identifying the recipient's asymmetric key. contain a parameter identifying the recipient's asymmetric key.
o The headers SHOULD identify the sender's key for the static-static o The headers SHOULD identify the sender's key for the static-static
versions and MUST contain the sender's ephemeral key for the versions and MUST contain the sender's ephemeral key for the
ephemeral-static versions. ephemeral-static versions.
12.5. Key Agreement with Key Wrap 13.5. Key Agreement with Key Wrap
Key Agreement with Key Wrap uses a randomly generated CEK. The CEK Key Agreement with Key Wrap uses a randomly generated CEK. The CEK
is then encrypted using a key wrap algorithm and a key derived from is then encrypted using a key wrap algorithm and a key derived from
the shared secret computed by the key agreement algorithm. The the shared secret computed by the key agreement algorithm. The
function for this would be: function for this would be:
encryptedKey = KeyWrap(KDF(DH-Shared, context), CEK) encryptedKey = KeyWrap(KDF(DH-Shared, context), CEK)
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 is fed into the KDF context structure. o The 'protected' field is fed into the KDF context structure.
o The plaintext to be encrypted is the key from the next layer down o The plaintext to be encrypted is the key from the next layer down
(usually the content layer). (usually the content layer).
o The 'alg' parameter MUST be present in the layer. o The 'alg' parameter MUST be present in the layer.
o A parameter identifying the recipient's key SHOULD be present. A o A parameter identifying the recipient's key SHOULD be present. A
parameter identifying the sender's key SHOULD be present. parameter identifying the sender's key SHOULD be present.
13. CBOR Encoder Restrictions 14. CBOR Encoding Restrictions
There has been an attempt to limit the number of places where the There has 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 of the COSE_KDF_Context, o The restriction applies to the encoding of the Sig_structure, the
the Sig_structure, the Enc_structure, and the MAC_structure. Enc_structure, and the MAC_structure.
o The rules for "Canonical CBOR" (Section 3.9 of RFC 7049) MUST be o Encoding MUST be done using definite lengths and the length of the
used in these locations. The main rule that needs to be enforced MUST be the minimum possible length. This means that the integer
is that all lengths in these structures MUST be encoded such that 1 is encoded as "0x01" and not "0x1801".
they are using definite lengths, and the minimum length encoding
is used.
o Applications MUST NOT generate messages with the same label used o Applications MUST NOT generate messages with the same label used
twice as a key in a single map. Applications MUST NOT parse and twice as a key in a single map. Applications MUST NOT parse and
process messages with the same label used twice as a key in a process messages with the same label used twice as a key in a
single map. Applications can enforce the parse and process single map. Applications can enforce the parse and process
requirement by using parsers that will fail the parse step or by requirement by using parsers that will fail the parse step or by
using parsers that will pass all keys to the application, and the using parsers that will pass all keys to the application, and the
application can perform the check for duplicate keys. application can perform the check for duplicate keys.
14. Application Profiling Considerations 15. Application Profiling Considerations
This document is designed to provide a set of security services, but This document is designed to provide a set of security services, but
not impose algorithm implementation requirements for specific usage. not impose algorithm implementation requirements for specific usage.
The interoperability requirements are provided for how each of the The interoperability requirements are provided for how each of the
individual services are used and how the algorithms are to be used individual services are used and how the algorithms are to be used
for interoperability. The requirements about which algorithms and for interoperability. The requirements about which algorithms and
which services are needed are deferred to each application. which services are needed are deferred to each application.
An example of a profile can be found in An example of a profile can be found in
[I-D.ietf-core-object-security] where a profiles was developed for [I-D.ietf-core-object-security] where a profiles was developed for
skipping to change at page 45, line 22 skipping to change at page 46, line 16
* Advertising in the message (S/MIME capabilities) [RFC5751]. * Advertising in the message (S/MIME capabilities) [RFC5751].
* Advertising in the certificate (capabilities extension) * Advertising in the certificate (capabilities extension)
[RFC4262]. [RFC4262].
* Minimum requirements for the S/MIME, which have been updated * Minimum requirements for the S/MIME, which have been updated
over time [RFC2633] [RFC5751] (note that [RFC2633] has been over time [RFC2633] [RFC5751] (note that [RFC2633] has been
obsoleted by [RFC5751]). obsoleted by [RFC5751]).
15. IANA Considerations 16. IANA Considerations
The registeries and registrations listed below were created during The registeries and registrations listed below were created during
processing of RFC 8152 [RFC8152]. The only known action at this time processing of RFC 8152 [RFC8152]. The only known action at this time
is to update the references. is to update the references.
15.1. CBOR Tag Assignment 16.1. CBOR Tag Assignment
IANA assigned tags in the "CBOR Tags" registry as part of processing IANA assigned tags in the "CBOR Tags" registry as part of processing
[RFC8152]. IANA is requested to update the references from [RFC8152] [RFC8152]. IANA is requested to update the references from [RFC8152]
to this document. to this document.
15.2. COSE Header Parameters Registry IANA is requested to register a new tag for the CounterSignature
type.
Tag: TBD0
Data Item: COSE_Signature
Semantics: COSE standalone counter signature
Reference: [[this document]]
16.2. COSE Header Parameters Registry
IANA created a registry titled "COSE Header Parameters" as part of IANA created a registry titled "COSE Header Parameters" as part of
processing [RFC8152]. The registry has been created to use the processing [RFC8152]. The registry has been created to use the
"Expert Review Required" registration procedure [RFC8126]. "Expert Review Required" registration procedure [RFC8126].
IANA is requested to update the reference for entries in the table IANA is requested to update the reference for entries in the table
from [RFC8152] to this document. This document does not update the from [RFC8152] to this document. This document does not update the
expert review guidelines provided in [RFC8152]. expert review guidelines provided in [RFC8152].
15.3. COSE Header Algorithm Parameters Registry 16.3. COSE Header Algorithm Parameters Registry
IANA created a registry titled "COSE Header Algorithm Parameters" as IANA created a registry titled "COSE Header Algorithm Parameters" as
part of processing [RFC8152]. The registry has been created to use part of processing [RFC8152]. The registry has been created to use
the "Expert Review Required" registration procedure [RFC8126]. the "Expert Review Required" registration procedure [RFC8126].
IANA is requested to update the references from [RFC8152] to this IANA is requested to update the references from [RFC8152] to this
document. This document does not update the expert review guidelines document. This document does not update the expert review guidelines
provided in [RFC8152]. provided in [RFC8152].
15.4. COSE Key Common Parameters Registry 16.4. COSE Key Common Parameters Registry
IANA created a registry titled "COSE Key Common Parameters" as part IANA created a registry titled "COSE Key Common Parameters" as part
of the processing of [RFC8152]. The registry has been created to use of the processing of [RFC8152]. The registry has been created to use
the "Expert Review Required" registration procedure [RFC8126]. the "Expert Review Required" registration procedure [RFC8126].
IANA is requested to update the reference for entries in the table IANA is requested to update the reference for entries in the table
from [RFC8152] to this document. This document does not update the from [RFC8152] to this document. This document does not update the
expert review guidelines provided in [RFC8152]. expert review guidelines provided in [RFC8152].
15.5. Media Type Registrations 16.5. Media Type Registrations
15.5.1. COSE Security Message 16.5.1. COSE Security Message
This section registers the 'application/cose' media type in the This section registers the 'application/cose' media type in the
"Media Types" registry. These media types are used to indicate that "Media Types" registry. These media types are used to indicate that
the content is a COSE message. the content is a COSE message.
Type name: application Type name: application
Subtype name: cose Subtype name: cose
Required parameters: N/A Required parameters: N/A
Optional parameters: cose-type Optional parameters: cose-type
Encoding considerations: binary Encoding considerations: binary
Security considerations: See the Security Considerations section Security considerations: See the Security Considerations section
of [[This Document]]. of [[This Document]].
Interoperability considerations: N/A Interoperability considerations: N/A
Published specification: RFC 8152 Published specification: [[this document]]
Applications that use this media type: IoT applications sending Applications that use this media type: IoT applications sending
security content over HTTP(S) transports. security content over HTTP(S) transports.
Fragment identifier considerations: N/A Fragment identifier considerations: N/A
Additional information: Additional information:
* Deprecated alias names for this type: N/A * Deprecated alias names for this type: N/A
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Intended usage: COMMON Intended usage: COMMON
Restrictions on usage: N/A Restrictions on usage: N/A
Author: Jim Schaad, ietf@augustcellars.com Author: Jim Schaad, ietf@augustcellars.com
Change Controller: IESG Change Controller: IESG
Provisional registration? No Provisional registration? No
15.5.2. COSE Key Media Type 16.5.2. COSE Key Media Type
This section registers the 'application/cose-key' and 'application/ This section registers the 'application/cose-key' and 'application/
cose-key-set' media types in the "Media Types" registry. These media cose-key-set' media types in the "Media Types" registry. These media
types are used to indicate, respectively, that content is a COSE_Key types are used to indicate, respectively, that content is a COSE_Key
or COSE_KeySet object. or COSE_KeySet object.
The template for registering 'application/cose-key' is: The template for registering 'application/cose-key' is:
Type name: application Type name: application
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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 [[This Document]]. of [[This Document]].
Interoperability considerations: N/A Interoperability considerations: N/A
Published specification: [[this document]]
Published specification: RFC 8152
Applications that use this media type: Distribution of COSE based Applications that use this media type: Distribution of COSE based
keys for IoT applications. keys for IoT applications.
Fragment identifier considerations: N/A Fragment identifier considerations: N/A
Additional information: Additional information:
* Deprecated alias names for this type: N/A * Deprecated alias names for this type: N/A
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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 [[This Document]]. of [[This Document]].
Interoperability considerations: N/A Interoperability considerations: N/A
Published specification: RFC 8152 Published specification: [[this document]]
Applications that use this media type: Distribution of COSE based Applications that use this media type: Distribution of COSE based
keys for IoT applications. keys for IoT applications.
Fragment identifier considerations: N/A Fragment identifier considerations: N/A
Additional information: Additional information:
* Deprecated alias names for this type: N/A * Deprecated alias names for this type: N/A
* Magic number(s): N/A * Magic number(s): N/A
* File extension(s): cbor * File extension(s): cbor
* Macintosh file type code(s): N/A * Macintosh file type code(s): N/A
Person & email address to contact for further information: Person & email address to contact for further information:
iesg@ietf.org iesg@ietf.org
Intended usage: COMMON Intended usage: COMMON
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Intended usage: COMMON Intended usage: COMMON
Restrictions on usage: N/A Restrictions on usage: N/A
Author: Jim Schaad, ietf@augustcellars.com Author: Jim Schaad, ietf@augustcellars.com
Change Controller: IESG Change Controller: IESG
Provisional registration? No Provisional registration? No
15.6. CoAP Content-Formats Registry 16.6. CoAP Content-Formats Registry
IANA added the following entries to the "CoAP Content-Formats" IANA added the following entries to the "CoAP Content-Formats"
registry while processing [RFC8152]. IANA is requested to update the registry while processing [RFC8152]. IANA is requested to update the
reference value from [RFC8152] to [[This Document]]. reference value from [RFC8152] to [[This Document]].
15.7. Expert Review Instructions 17. Security Considerations
All of the IANA registries established in this document are defined
as expert review. This section gives some general guidelines for
what the experts should be looking for, but they are being designated
as experts for a reason, so they should be given substantial
latitude.
Expert reviewers should take into consideration the following points:
o Point squatting should be discouraged. Reviewers are encouraged
to get sufficient information for registration requests to ensure
that the usage is not going to duplicate one that is already
registered, and that the point is likely to be used in
deployments. The zones tagged as private use are intended for
testing purposes and closed environments; code points in other
ranges should not be assigned for testing.
o Specifications are required for the standards track range of point
assignment. Specifications should exist for specification
required ranges, but early assignment before a specification is
available is considered to be permissible. Specifications are
needed for the first-come, first-serve range if they are expected
to be used outside of closed environments in an interoperable way.
When specifications are not provided, the description provided
needs to have sufficient information to identify what the point is
being used for.
o Experts should take into account the expected usage of fields when
approving point assignment. The fact that there is a range for
standards track documents does not mean that a standards track
document cannot have points assigned outside of that range. The
length of the encoded value should be weighed against how many
code points of that length are left, the size of device it will be
used on, and the number of code points left that encode to that
size.
o When algorithms are registered, vanity registrations should be
discouraged. One way to do this is to require registrations to
provide additional documentation on security analysis of the
algorithm. Another thing that should be considered is requesting
an opinion on the algorithm from the Crypto Forum Research Group
(CFRG). Algorithms that do not meet the security requirements of
the community and the messages structures should not be
registered.
16. Security Considerations
There are a number of security considerations that need to be taken There are a number of security considerations that need to be taken
into account by implementers of this specification. The security into account by implementers of this specification. The security
considerations that are specific to an individual algorithm are considerations that are specific to an individual algorithm are
placed next to the description of the algorithm. While some placed next to the description of the algorithm. While some
considerations have been highlighted here, additional considerations considerations have been highlighted here, additional considerations
may be found in the documents listed in the references. may be found in the documents listed in the references.
Implementations need to protect the private key material for any Implementations need to protect the private key material for any
individuals. There are some cases in this document that need to be individuals. There are some cases in this document that need to be
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analysis of encrypted messages based on the length of the message. analysis of encrypted messages based on the length of the message.
This specification does not provide for a uniform method of providing This specification does not provide for a uniform method of providing
padding as part of the message structure. An observer can padding as part of the message structure. An observer can
distinguish between two different strings (for example, 'YES' and distinguish between two different strings (for example, 'YES' and
'NO') based on the length for all of the content encryption 'NO') based on the length for all of the content encryption
algorithms that are defined in this document. This means that it is algorithms that are defined in this document. This means that it is
up to the applications to document how content padding is to be done up to the applications to document how content padding is to be done
in order to prevent or discourage such analysis. (For example, the in order to prevent or discourage such analysis. (For example, the
strings could be defined as 'YES' and 'NO '.) strings could be defined as 'YES' and 'NO '.)
17. Implementation Status 18. Implementation Status
This section records the status of known implementations of the This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942]. Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not supplied by IETF contributors. This is not intended as, and must not
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features. Readers are advised to note that other implementations may features. Readers are advised to note that other implementations may
exist. exist.
According to [RFC7942], "this will allow reviewers and working groups According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature. and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as It is up to the individual working groups to use this information as
they see fit". they see fit".
17.1. Author's Versions 18.1. Author's Versions
There are three different implementations that have been created by There are three different implementations that have been created by
the author of the document both to create the examples that are the author of the document both to create the examples that are
included in the document and to validate the structures and included in the document and to validate the structures and
methodology used in the design of COSE. methodology used in the design of COSE.
Implementation Location: https://github.com/cose-wg Implementation Location: https://github.com/cose-wg
Primary Maintainer: Jim Schaad Primary Maintainer: Jim Schaad
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libraries. All three libraries have tests to allow for the libraries. All three libraries have tests to allow for the
creating of the same messages that are in the example library creating of the same messages that are in the example library
followed by validating them. These are not compared against the followed by validating them. These are not compared against the
example library. The Java and C# libraries have unit testing example library. The Java and C# libraries have unit testing
included. Not all of the MUST statements in the document have included. Not all of the MUST statements in the document have
been implemented as part of the libraries. One such statement is been implemented as part of the libraries. One such statement is
the requirement that unique labels be present. the requirement that unique labels be present.
Licensing: Revised BSD License Licensing: Revised BSD License
17.2. Java Script Version 18.2. Java Script Version
Implementation Location: https://github.com/erdtman/cose-js Implementation Location: https://github.com/erdtman/cose-js
Primary Maintainer: Samuel Erdtman Primary Maintainer: Samuel Erdtman
Languages: JavaScript Languages: JavaScript
Cryptography: TBD Cryptography: TBD
Coverage: Full Encrypt, Signature and MAC objects are supported. Coverage: Full Encrypt, Signature and MAC objects are supported.
Testing: Basic testing against the common example library. Testing: Basic testing against the common example library.
Licensing: Apache License 2.0 Licensing: Apache License 2.0
17.3. Python Version 18.3. Python Version
Implementation Location: https://github.com/TimothyClaeys/COSE- Implementation Location: https://github.com/TimothyClaeys/COSE-
PYTHON PYTHON
Primary Maintainer: Timothy Claeys Primary Maintainer: Timothy Claeys
Languages: Python Languages: Python
Cryptography: pyecdsak, crypto python libraries Cryptography: pyecdsak, crypto python libraries
Coverage: TBD Coverage: TBD
Testing: Basic testing plus running against the common example Testing: Basic testing plus running against the common example
library. library.
Licensing: BSD 3-Clause License Licensing: BSD 3-Clause License
17.4. COSE Testing Library 18.4. COSE Testing Library
Implementation Location: https://github.com/cose-wg/Examples Implementation Location: https://github.com/cose-wg/Examples
Primary Maintainer: Jim Schaad Primary Maintainer: Jim Schaad
Description: A set of tests for the COSE library is provided as Description: A set of tests for the COSE library is provided as
part of the implementation effort. Both success and fail tests part of the implementation effort. Both success and fail tests
have been provided. All of the examples in this document are part have been provided. All of the examples in this document are part
of this example set. of this example set.
Coverage: An attempt has been made to have test cases for every Coverage: An attempt has been made to have test cases for every
message type and algorithm in the document. Currently examples message type and algorithm in the document. Currently examples
dealing with counter signatures, and ECDH with Curve24459 and dealing with counter signatures, and ECDH with Curve24459 and
Goldilocks are missing. Goldilocks are missing.
Licensing: Public Domain Licensing: Public Domain
18. References 19. References
18.1. Normative References 19.1. Normative References
[COAP.Formats] [COAP.Formats]
IANA, "CoAP Content-Formats", IANA, "CoAP Content-Formats",
<https://www.iana.org/assignments/core-parameters/ <https://www.iana.org/assignments/core-parameters/
core-parameters.xhtml#content-formats>. core-parameters.xhtml#content-formats>.
[COSE.Algorithms] [COSE.Algorithms]
IANA, "COSE Algorithms", IANA, "COSE Algorithms",
<https://www.iana.org/assignments/cose/ <https://www.iana.org/assignments/cose/
cose.xhtml#algorithms>. cose.xhtml#algorithms>.
skipping to change at page 55, line 27 skipping to change at page 55, line 36
<https://www.iana.org/assignments/cose/ <https://www.iana.org/assignments/cose/
cose.xhtml#algorithms>. cose.xhtml#algorithms>.
[DSS] National Institute of Standards and Technology, "Digital [DSS] National Institute of Standards and Technology, "Digital
Signature Standard (DSS)", FIPS PUB 186-4, Signature Standard (DSS)", FIPS PUB 186-4,
DOI 10.6028/NIST.FIPS.186-4, July 2013, DOI 10.6028/NIST.FIPS.186-4, July 2013,
<http://nvlpubs.nist.gov/nistpubs/FIPS/ <http://nvlpubs.nist.gov/nistpubs/FIPS/
NIST.FIPS.186-4.pdf>. NIST.FIPS.186-4.pdf>.
[I-D.ietf-cose-rfc8152bis-algs] [I-D.ietf-cose-rfc8152bis-algs]
Schaad, J., "CBOR Algorithms for Object Signing and Schaad, J., "CBOR Object Signing and Encryption (COSE):
Encryption (COSE)", draft-ietf-cose-rfc8152bis-algs-01 Initial Algorithms", draft-ietf-cose-rfc8152bis-algs-02
(work in progress), February 2019. (work in progress), March 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/info/rfc7049>. October 2013, <https://www.rfc-editor.org/info/rfc7049>.
[RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital [RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
Signature Algorithm (EdDSA)", RFC 8032, Signature Algorithm (EdDSA)", RFC 8032,
DOI 10.17487/RFC8032, January 2017, DOI 10.17487/RFC8032, January 2017,
<https://www.rfc-editor.org/info/rfc8032>. <https://www.rfc-editor.org/info/rfc8032>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
18.2. Informative References 19.2. Informative References
[I-D.ietf-cbor-cddl] [I-D.ietf-cbor-cddl]
Birkholz, H., Vigano, C., and C. Bormann, "Concise data Birkholz, H., Vigano, C., and C. Bormann, "Concise data
definition language (CDDL): a notational convention to definition language (CDDL): a notational convention to
express CBOR and JSON data structures", draft-ietf-cbor- express CBOR and JSON data structures", draft-ietf-cbor-
cddl-07 (work in progress), February 2019. cddl-08 (work in progress), March 2019.
[I-D.ietf-core-object-security] [I-D.ietf-core-object-security]
Selander, G., Mattsson, J., Palombini, F., and L. Seitz, Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments "Object Security for Constrained RESTful Environments
(OSCORE)", draft-ietf-core-object-security-15 (work in (OSCORE)", draft-ietf-core-object-security-16 (work in
progress), August 2018. progress), March 2019.
[PVSig] Brown, D. and D. Johnson, "Formal Security Proofs for a [PVSig] Brown, D. and D. Johnson, "Formal Security Proofs for a
Signature Scheme with Partial Message Recovery", Signature Scheme with Partial Message Recovery",
DOI 10.1007/3-540-45353-9_11, LNCS Volume 2020, June 2000. DOI 10.1007/3-540-45353-9_11, LNCS Volume 2020, June 2000.
[RFC2633] Ramsdell, B., Ed., "S/MIME Version 3 Message [RFC2633] Ramsdell, B., Ed., "S/MIME Version 3 Message
Specification", RFC 2633, DOI 10.17487/RFC2633, June 1999, Specification", RFC 2633, DOI 10.17487/RFC2633, June 1999,
<https://www.rfc-editor.org/info/rfc2633>. <https://www.rfc-editor.org/info/rfc2633>.
[RFC4262] Santesson, S., "X.509 Certificate Extension for Secure/ [RFC4262] Santesson, S., "X.509 Certificate Extension for Secure/
Multipurpose Internet Mail Extensions (S/MIME) Multipurpose Internet Mail Extensions (S/MIME)
Capabilities", RFC 4262, DOI 10.17487/RFC4262, December Capabilities", RFC 4262, DOI 10.17487/RFC4262, December
2005, <https://www.rfc-editor.org/info/rfc4262>. 2005, <https://www.rfc-editor.org/info/rfc4262>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", [RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>. <https://www.rfc-editor.org/info/rfc4949>.
[RFC4998] Gondrom, T., Brandner, R., and U. Pordesch, "Evidence
Record Syntax (ERS)", RFC 4998, DOI 10.17487/RFC4998,
August 2007, <https://www.rfc-editor.org/info/rfc4998>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008, Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/info/rfc5116>. <https://www.rfc-editor.org/info/rfc5116>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, [RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009, RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>. <https://www.rfc-editor.org/info/rfc5652>.
[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet [RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message Mail Extensions (S/MIME) Version 3.2 Message
skipping to change at page 58, line 25 skipping to change at page 58, line 35
Interchange Format", STD 90, RFC 8259, Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017, DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>. <https://www.rfc-editor.org/info/rfc8259>.
[W3C.WebCrypto] [W3C.WebCrypto]
Watson, M., "Web Cryptography API", W3C Recommendation, Watson, M., "Web Cryptography API", W3C Recommendation,
January 2017, <https://www.w3.org/TR/WebCryptoAPI/>. January 2017, <https://www.w3.org/TR/WebCryptoAPI/>.
Appendix A. Guidelines for External Data Authentication of Algorithms Appendix A. Guidelines for External Data Authentication of Algorithms
A portion of the working group has expressed a strong desire to relax During development of COSE, the requirement that the algorithm
the rule that the algorithm identifier be required to appear in each identifier be located in the protected attributes was relaxed from a
level of a COSE object. There are two basic reasons that have been must to a should. There were two basic reasons that have been
advanced to support this position. First, the resulting message will advanced to support this position. First, the resulting message will
be smaller if the algorithm identifier is omitted from the most be smaller if the algorithm identifier is omitted from the most
common messages in a CoAP environment. Second, there is a potential common messages in a CoAP environment. Second, there is a potential
bug that will arise if full checking is not done correctly between bug that will arise if full checking is not done correctly between
the different places that an algorithm identifier could be placed the different places that an algorithm identifier could be placed
(the message itself, an application statement, the key structure that (the message itself, an application statement, the key structure that
the sender possesses, and the key structure the recipient possesses). the sender possesses, and the key structure the recipient possesses).
This appendix lays out how such a change can be made and the details This appendix lays out how such a change can be made and the details
that an application needs to specify in order to use this option. that an application needs to specify in order to use this option.
Two different sets of details are specified: those needed to omit an Two different sets of details are specified: those needed to omit an
algorithm identifier and those needed to use a variant on the counter algorithm identifier and those needed to use a variant on the counter
signature attribute that contains no attributes about itself. signature attribute that contains no attributes about itself.
A.1. Algorithm Identification Three sets of recommendations are laid out. The first set of
recommendations apply to having an implicit algorithm identified for
In this section, three sets of recommendations are laid out. The a single layer of a COSE object. The second set of recommendations
first set of recommendations apply to having an implicit algorithm apply to having multiple implicit algorithms identified for multiple
identified for a single layer of a COSE object. The second set of layers of a COSE object. The third set of recommendations apply to
recommendations apply to having multiple implicit algorithms having implicit algorithms for multiple COSE object constructs.
identified for multiple layers of a COSE object. The third set of
recommendations apply to having implicit algorithms for multiple COSE
object constructs.
The key words from [RFC2119] are deliberately not used here. This The key words from [RFC2119] are deliberately not used here. This
specification can provide recommendations, but it cannot enforce specification can provide recommendations, but it cannot enforce
them. them.
This set of recommendations applies to the case where an application This set of recommendations applies to the case where an application
is distributing a fixed algorithm along with the key information for is distributing a fixed algorithm along with the key information for
use in a single COSE object. This normally applies to the smallest use in a single COSE object. This normally applies to the smallest
of the COSE objects, specifically COSE_Sign1, COSE_Mac0, and of the COSE objects, specifically COSE_Sign1, COSE_Mac0, and
COSE_Encrypt0, but could apply to the other structures as well. COSE_Encrypt0, but could apply to the other structures as well.
skipping to change at page 61, line 37 skipping to change at page 61, line 44
different types of messages that have different keys, but where different types of messages that have different keys, but where
the keys may be used in a coordinated manner. the keys may be used in a coordinated manner.
For these cases, the following additional items need to be For these cases, the following additional items need to be
considered: considered:
o Applications need to ensure that the multiple contexts stay o Applications need to ensure that the multiple contexts stay
associated. If one of the contexts is invalidated for any reason, associated. If one of the contexts is invalidated for any reason,
all of the contexts associated with it should also be invalidated. all of the contexts associated with it should also be invalidated.
A.2. Counter Signature without Headers
There is a group of people who want to have a counter signature
parameter that is directly tied to the value being signed, and thus
the authenticated and unauthenticated buckets can be removed from the
message being sent. The focus on this is an even smaller size, as
all of the information on the process of creating the counter
signature is implicit rather than being explicitly carried in the
message. This includes not only the algorithm identifier as
presented above, but also items such as the key identification, which
is always external to the signature structure. This means that the
entities that are doing the validation of the counter signature are
required to infer which key is to be used from context rather than
being explicit. One way of doing this would be to presume that all
data coming from a specific port (or to a specific URL) is to be
validated by a specific key. (Note that this does not require that
the key identifier be part of the value signed as it does not serve a
cryptographic purpose. If the key validates the counter signature,
then it should be presumed that the entity associated with that key
produced the signature.)
When computing the signature for the bare counter signature header,
the same Sig_structure defined in Section 4.4 is used. The
sign_protected field is omitted, as there is no protected header
field in this counter signature header. The value of
"CounterSignature0" is placed in the context field of the
Sig_stucture.
+-------------------+-------+-------+-------+-----------------------+
| Name | Label | Value | Value | Description |
| | | Type | | |
+-------------------+-------+-------+-------+-----------------------+
| CounterSignature0 | 9 | bstr | | Counter signature |
| | | | | with implied signer |
| | | | | and headers |
+-------------------+-------+-------+-------+-----------------------+
Table 6: Header Parameter for CounterSignature0
Appendix B. Two Layers of Recipient Information Appendix B. Two Layers of Recipient Information
All of the currently defined recipient algorithm classes only use two All of the currently defined recipient algorithm classes only use two
layers of the COSE_Encrypt structure. The first layer is the message layers of the COSE_Encrypt structure. The first layer is the message
content, and the second layer is the content key encryption. content, and the second layer is the content key encryption.
However, if one uses a recipient algorithm such as the RSA Key However, if one uses a recipient algorithm such as the RSA Key
Encapsulation Mechanism (RSA-KEM) (see Appendix A of RSA-KEM Encapsulation Mechanism (RSA-KEM) (see Appendix A of RSA-KEM
[RFC5990]), then it makes sense to have three layers of the [RFC5990]), then it makes sense to have three layers of the
COSE_Encrypt structure. COSE_Encrypt structure.
These layers would be: These layers would be:
o Layer 0: The content encryption layer. This layer contains the o Layer 0: The content encryption layer. This layer contains the
payload of the message. payload of the message.
o Layer 1: The encryption of the CEK by a KEK. o Layer 1: The encryption of the CEK by a KEK.
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