--- 1/draft-ietf-cose-rfc8152bis-struct-10.txt 2020-07-01 21:13:34.932988388 -0700 +++ 2/draft-ietf-cose-rfc8152bis-struct-11.txt 2020-07-01 21:13:35.084992229 -0700 @@ -1,19 +1,19 @@ COSE Working Group J. Schaad Internet-Draft August Cellars -Obsoletes: 8152 (if approved) 2 June 2020 +Obsoletes: 8152 (if approved) 1 July 2020 Intended status: Standards Track -Expires: 4 December 2020 +Expires: 2 January 2021 CBOR Object Signing and Encryption (COSE): Structures and Process - draft-ietf-cose-rfc8152bis-struct-10 + draft-ietf-cose-rfc8152bis-struct-11 Abstract Concise Binary Object Representation (CBOR) is a data format designed 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. This document defines the CBOR Object Signing and Encryption (COSE) protocol. This specification describes how to create and process signatures, message authentication codes, and encryption using CBOR for serialization. This specification additionally describes how to @@ -39,21 +39,21 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on 4 December 2020. + This Internet-Draft will expire on 2 January 2021. Copyright Notice Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights @@ -72,112 +72,112 @@ 1.5. CBOR-Related Terminology . . . . . . . . . . . . . . . . 8 1.6. Document Terminology . . . . . . . . . . . . . . . . . . 9 2. Basic COSE Structure . . . . . . . . . . . . . . . . . . . . 9 3. Header Parameters . . . . . . . . . . . . . . . . . . . . . . 13 3.1. Common COSE Header Parameters . . . . . . . . . . . . . . 15 4. Signing Objects . . . . . . . . . . . . . . . . . . . . . . . 18 4.1. Signing with One or More Signers . . . . . . . . . . . . 18 4.2. Signing with One Signer . . . . . . . . . . . . . . . . . 20 4.3. Externally Supplied Data . . . . . . . . . . . . . . . . 21 4.4. Signing and Verification Process . . . . . . . . . . . . 22 - 5. Counter Signatures . . . . . . . . . . . . . . . . . . . . . 24 - 5.1. Full Counter Signatures . . . . . . . . . . . . . . . . . 25 + 5. Counter Signatures . . . . . . . . . . . . . . . . . . . . . 25 + 5.1. Full Counter Signatures . . . . . . . . . . . . . . . . . 26 5.2. Abbreviated Counter Signatures . . . . . . . . . . . . . 26 - 6. Encryption Objects . . . . . . . . . . . . . . . . . . . . . 26 - 6.1. Enveloped COSE Structure . . . . . . . . . . . . . . . . 26 - 6.1.1. Content Key Distribution Methods . . . . . . . . . . 28 - 6.2. Single Recipient Encrypted . . . . . . . . . . . . . . . 29 - 6.3. How to Encrypt and Decrypt for AEAD Algorithms . . . . . 29 - 6.4. How to Encrypt and Decrypt for AE Algorithms . . . . . . 32 - 7. MAC Objects . . . . . . . . . . . . . . . . . . . . . . . . . 33 - 7.1. MACed Message with Recipients . . . . . . . . . . . . . . 34 - 7.2. MACed Messages with Implicit Key . . . . . . . . . . . . 35 - 7.3. How to Compute and Verify a MAC . . . . . . . . . . . . . 35 - 8. Key Objects . . . . . . . . . . . . . . . . . . . . . . . . . 37 - 8.1. COSE Key Common Parameters . . . . . . . . . . . . . . . 37 + 6. Encryption Objects . . . . . . . . . . . . . . . . . . . . . 27 + 6.1. Enveloped COSE Structure . . . . . . . . . . . . . . . . 27 + 6.1.1. Content Key Distribution Methods . . . . . . . . . . 29 + 6.2. Single Recipient Encrypted . . . . . . . . . . . . . . . 30 + 6.3. How to Encrypt and Decrypt for AEAD Algorithms . . . . . 30 + 6.4. How to Encrypt and Decrypt for AE Algorithms . . . . . . 33 + 7. MAC Objects . . . . . . . . . . . . . . . . . . . . . . . . . 34 + 7.1. MACed Message with Recipients . . . . . . . . . . . . . . 35 + 7.2. MACed Messages with Implicit Key . . . . . . . . . . . . 36 + 7.3. How to Compute and Verify a MAC . . . . . . . . . . . . . 36 + 8. Key Objects . . . . . . . . . . . . . . . . . . . . . . . . . 38 + 8.1. COSE Key Common Parameters . . . . . . . . . . . . . . . 38 - 9. Taxonomy of Algorithms used by COSE . . . . . . . . . . . . . 40 - 9.1. Signature Algorithms . . . . . . . . . . . . . . . . . . 41 - 9.2. Message Authentication Code (MAC) Algorithms . . . . . . 42 - 9.3. Content Encryption Algorithms . . . . . . . . . . . . . . 42 - 9.4. Key Derivation Functions (KDFs) . . . . . . . . . . . . . 43 - 9.5. Content Key Distribution Methods . . . . . . . . . . . . 44 - 9.5.1. Direct Encryption . . . . . . . . . . . . . . . . . . 44 - 9.5.2. Key Wrap . . . . . . . . . . . . . . . . . . . . . . 44 - 9.5.3. Key Transport . . . . . . . . . . . . . . . . . . . . 45 - 9.5.4. Direct Key Agreement . . . . . . . . . . . . . . . . 45 - 9.5.5. Key Agreement with Key Wrap . . . . . . . . . . . . . 46 - 10. CBOR Encoding Restrictions . . . . . . . . . . . . . . . . . 47 - 11. Application Profiling Considerations . . . . . . . . . . . . 47 - 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 49 - 12.1. CBOR Tag Assignment . . . . . . . . . . . . . . . . . . 49 - 12.2. COSE Header Parameters Registry . . . . . . . . . . . . 49 - 12.3. COSE Header Algorithm Parameters Registry . . . . . . . 49 - 12.4. COSE Key Common Parameters Registry . . . . . . . . . . 49 - 12.5. Media Type Registrations . . . . . . . . . . . . . . . . 50 - 12.5.1. COSE Security Message . . . . . . . . . . . . . . . 50 - 12.5.2. COSE Key Media Type . . . . . . . . . . . . . . . . 51 - 12.6. CoAP Content-Formats Registry . . . . . . . . . . . . . 53 - 13. Security Considerations . . . . . . . . . . . . . . . . . . . 53 - 14. Implementation Status . . . . . . . . . . . . . . . . . . . . 55 - 14.1. Author's Versions . . . . . . . . . . . . . . . . . . . 55 - 14.2. JavaScript Version . . . . . . . . . . . . . . . . . . . 56 - 14.3. Python Version . . . . . . . . . . . . . . . . . . . . . 56 - 14.4. COSE Testing Library . . . . . . . . . . . . . . . . . . 57 - 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 57 - 15.1. Normative References . . . . . . . . . . . . . . . . . . 57 - 15.2. Informative References . . . . . . . . . . . . . . . . . 58 + 9. Taxonomy of Algorithms used by COSE . . . . . . . . . . . . . 41 + 9.1. Signature Algorithms . . . . . . . . . . . . . . . . . . 42 + 9.2. Message Authentication Code (MAC) Algorithms . . . . . . 43 + 9.3. Content Encryption Algorithms . . . . . . . . . . . . . . 43 + 9.4. Key Derivation Functions (KDFs) . . . . . . . . . . . . . 44 + 9.5. Content Key Distribution Methods . . . . . . . . . . . . 45 + 9.5.1. Direct Encryption . . . . . . . . . . . . . . . . . . 45 + 9.5.2. Key Wrap . . . . . . . . . . . . . . . . . . . . . . 45 + 9.5.3. Key Transport . . . . . . . . . . . . . . . . . . . . 46 + 9.5.4. Direct Key Agreement . . . . . . . . . . . . . . . . 46 + 9.5.5. Key Agreement with Key Wrap . . . . . . . . . . . . . 47 + 10. CBOR Encoding Restrictions . . . . . . . . . . . . . . . . . 48 + 11. Application Profiling Considerations . . . . . . . . . . . . 48 + 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 50 + 12.1. CBOR Tag Assignment . . . . . . . . . . . . . . . . . . 50 + 12.2. COSE Header Parameters Registry . . . . . . . . . . . . 50 + 12.3. COSE Key Common Parameters Registry . . . . . . . . . . 50 + 12.4. Media Type Registrations . . . . . . . . . . . . . . . . 50 + 12.4.1. COSE Security Message . . . . . . . . . . . . . . . 51 + 12.4.2. COSE Key Media Type . . . . . . . . . . . . . . . . 52 + 12.5. CoAP Content-Formats Registry . . . . . . . . . . . . . 54 + 12.6. Expert Review Instructions . . . . . . . . . . . . . . . 54 + 13. Security Considerations . . . . . . . . . . . . . . . . . . . 55 + 14. Implementation Status . . . . . . . . . . . . . . . . . . . . 56 + 14.1. Author's Versions . . . . . . . . . . . . . . . . . . . 57 + 14.2. JavaScript Version . . . . . . . . . . . . . . . . . . . 58 + 14.3. Python Version . . . . . . . . . . . . . . . . . . . . . 58 + 14.4. COSE Testing Library . . . . . . . . . . . . . . . . . . 58 + 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 59 + 15.1. Normative References . . . . . . . . . . . . . . . . . . 59 + 15.2. Informative References . . . . . . . . . . . . . . . . . 59 Appendix A. Guidelines for External Data Authentication of - Algorithms . . . . . . . . . . . . . . . . . . . . . . . 61 - Appendix B. Two Layers of Recipient Information . . . . . . . . 65 - Appendix C. Examples . . . . . . . . . . . . . . . . . . . . . . 66 - C.1. Examples of Signed Messages . . . . . . . . . . . . . . . 67 - C.1.1. Single Signature . . . . . . . . . . . . . . . . . . 67 - C.1.2. Multiple Signers . . . . . . . . . . . . . . . . . . 68 - C.1.3. Counter Signature . . . . . . . . . . . . . . . . . . 69 - C.1.4. Signature with Criticality . . . . . . . . . . . . . 70 - C.2. Single Signer Examples . . . . . . . . . . . . . . . . . 71 - C.2.1. Single ECDSA Signature . . . . . . . . . . . . . . . 71 - C.3. Examples of Enveloped Messages . . . . . . . . . . . . . 72 - C.3.1. Direct ECDH . . . . . . . . . . . . . . . . . . . . . 72 - C.3.2. Direct Plus Key Derivation . . . . . . . . . . . . . 73 - C.3.3. Counter Signature on Encrypted Content . . . . . . . 74 - C.3.4. Encrypted Content with External Data . . . . . . . . 75 - C.4. Examples of Encrypted Messages . . . . . . . . . . . . . 76 - C.4.1. Simple Encrypted Message . . . . . . . . . . . . . . 76 - C.4.2. Encrypted Message with a Partial IV . . . . . . . . . 77 - C.5. Examples of MACed Messages . . . . . . . . . . . . . . . 77 - C.5.1. Shared Secret Direct MAC . . . . . . . . . . . . . . 77 - C.5.2. ECDH Direct MAC . . . . . . . . . . . . . . . . . . . 78 - C.5.3. Wrapped MAC . . . . . . . . . . . . . . . . . . . . . 79 - C.5.4. Multi-Recipient MACed Message . . . . . . . . . . . . 80 - C.6. Examples of MAC0 Messages . . . . . . . . . . . . . . . . 81 - C.6.1. Shared Secret Direct MAC . . . . . . . . . . . . . . 81 - C.7. COSE Keys . . . . . . . . . . . . . . . . . . . . . . . . 82 - C.7.1. Public Keys . . . . . . . . . . . . . . . . . . . . . 82 - C.7.2. Private Keys . . . . . . . . . . . . . . . . . . . . 83 - Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 85 - Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 86 + Algorithms . . . . . . . . . . . . . . . . . . . . . . . 63 + Appendix B. Two Layers of Recipient Information . . . . . . . . 66 + Appendix C. Examples . . . . . . . . . . . . . . . . . . . . . . 68 + C.1. Examples of Signed Messages . . . . . . . . . . . . . . . 69 + C.1.1. Single Signature . . . . . . . . . . . . . . . . . . 69 + C.1.2. Multiple Signers . . . . . . . . . . . . . . . . . . 70 + C.1.3. Counter Signature . . . . . . . . . . . . . . . . . . 71 + C.1.4. Signature with Criticality . . . . . . . . . . . . . 72 + C.2. Single Signer Examples . . . . . . . . . . . . . . . . . 73 + C.2.1. Single ECDSA Signature . . . . . . . . . . . . . . . 73 + C.3. Examples of Enveloped Messages . . . . . . . . . . . . . 74 + C.3.1. Direct ECDH . . . . . . . . . . . . . . . . . . . . . 74 + C.3.2. Direct Plus Key Derivation . . . . . . . . . . . . . 75 + C.3.3. Counter Signature on Encrypted Content . . . . . . . 76 + C.3.4. Encrypted Content with External Data . . . . . . . . 77 + C.4. Examples of Encrypted Messages . . . . . . . . . . . . . 78 + C.4.1. Simple Encrypted Message . . . . . . . . . . . . . . 78 + C.4.2. Encrypted Message with a Partial IV . . . . . . . . . 79 + C.5. Examples of MACed Messages . . . . . . . . . . . . . . . 79 + C.5.1. Shared Secret Direct MAC . . . . . . . . . . . . . . 79 + C.5.2. ECDH Direct MAC . . . . . . . . . . . . . . . . . . . 80 + C.5.3. Wrapped MAC . . . . . . . . . . . . . . . . . . . . . 81 + C.5.4. Multi-Recipient MACed Message . . . . . . . . . . . . 82 + C.6. Examples of MAC0 Messages . . . . . . . . . . . . . . . . 83 + C.6.1. Shared Secret Direct MAC . . . . . . . . . . . . . . 83 + C.7. COSE Keys . . . . . . . . . . . . . . . . . . . . . . . . 84 + C.7.1. Public Keys . . . . . . . . . . . . . . . . . . . . . 84 + C.7.2. Private Keys . . . . . . . . . . . . . . . . . . . . 85 + Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 87 + Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 88 1. Introduction There has been an increased focus on small, constrained devices that make up the Internet of Things (IoT). One of the standards that has come out of this process is "Concise Binary Object Representation (CBOR)" [RFC7049]. CBOR extended the data model of the JavaScript - Object Notation (JSON) [RFC8259] by allowing for binary data, among + Object Notation (JSON) [STD90] by allowing for binary data, among other changes. CBOR has been adopted by several of the IETF working groups dealing with the IoT world as their encoding of data structures. CBOR was designed specifically both to be small in terms - of messages transported and implementation size and be a schema-free - decoder. A need exists to provide message security services for IoT, - and using CBOR as the message-encoding format makes sense. + of messages transported and implementation size and to be a schema- + free decoder. A need exists to provide message security services for + IoT, and using CBOR as the message-encoding format makes sense. The JOSE working group produced a set of documents [RFC7515] [RFC7516] [RFC7517] [RFC7518] that specified how to process encryption, signatures, and Message Authentication Code (MAC) operations and how to encode keys using JSON. This document along with [I-D.ietf-cose-rfc8152bis-algs] defines the CBOR Object Signing and Encryption (COSE) standard, which does the same thing for the CBOR encoding format. While there is a strong attempt to keep the flavor of the original JSON Object Signing and Encryption (JOSE) documents, two considerations are taken into account: @@ -188,63 +188,62 @@ into a base64-encoded text string. * COSE is not a direct copy of the JOSE specification. In the process of creating COSE, decisions that were made for JOSE were re-examined. In many cases, different results were decided on as the criteria were not always the same. This document contains: * The description of the structure for the CBOR objects which are - transmitted over the wire. Two objects are defined for + transmitted over the wire. Two objects are defined for each of encryption, signing and message authentication. One object is defined for transporting keys and one for transporting groups of keys. * The procedures used to build the inputs to the cryptographic functions required for each of the structures. - * A starting set of attributes that apply to the different security - objects. + * A set of attributes that apply to the different security objects. This document does not contain the rules and procedures for using specific cryptographic algorithms. Details on specific algorithms can be found in [I-D.ietf-cose-rfc8152bis-algs] and [RFC8230]. Details for additional algorithms are expected to be defined in future documents. COSE was initially designed as part of a solution to provide security to Constrained RESTful Environments (CoRE), and this is done using [RFC8613] and [I-D.ietf-core-groupcomm-bis]. However, COSE is not restricted to just these cases and can be used in any place where one would consider either JOSE or CMS [RFC5652] for the purpose of providing security services. The use of COSE, like JOSE and CMS, is - only in store and forward or offline protocols, different solutions - would be appropriate for online protocols although one can use COSE - in an online protocol after having done some type of online key - establishment process. Any application which uses COSE for security - services first needs to determine what security services are required - and then select the appropriate COSE structures and cryptographic - algorithms based on those needs. Section 11 provides additional - information on what applications need to specify when using COSE. + only for use in store and forward or offline protocols. The use of + COSE in online protocols needing encryption, require that an online + key establishment process be done before sending objects back and + forth. Any application which uses COSE for security services first + needs to determine what security services are required and then + select the appropriate COSE structures and cryptographic algorithms + based on those needs. Section 11 provides additional information on + what applications need to specify when using COSE. One feature that is present in CMS that is not present in this standard is a digest structure. This omission is deliberate. It is better for the structure to be defined in each protocol as different protocols will want to include a different set of fields as part of the structure. While an algorithm identifier and the digest value are going to be common to all applications, the two values may not always be adjacent as the algorithm could be defined once with multiple values. Applications may additionally want to define - additional data fields as part of the structure. A common structure - is going to include a URI or other pointer to where the data that is - being hashed is kept, allowing this to be application-specific. + additional data fields as part of the structure. A one such + application-specific element would be to include a URI or other + pointer to where the data that is being hashed can be obtained. [I-D.ietf-cose-hash-algs] contains one such possible structure along with defining a set of digest algorithms. 1.1. Requirements Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. @@ -257,27 +256,27 @@ * Add some text describing why there is no digest structure defined by COSE. * Rearrange the text around counter signatures and define a CBOR Tag for a standalone counter signature. * Text clarifications and changes in terminology. 1.3. Design Changes from JOSE - * Define a single top message structure so that encrypted, signed, - and MACed messages can easily be identified and still have a - consistent view. + * Define a single overall message structure so that encrypted, + signed, and MACed messages can easily be identified and still have + a consistent view. * Signed messages distinguish between the protected and unprotected - header parameters that relate to the content from those that - relate to the signature. + header parameters that relate to the content and those that relate + to the signature. * MACed messages are separated from signed messages. * MACed messages have the ability to use the same set of recipient algorithms as enveloped messages for obtaining the MAC authentication key. * Use binary encodings, rather than base64url encodings, to encode binary data. @@ -367,91 +366,96 @@ In JSON, maps are called objects and only have one kind of map key: a text string. In COSE, we use text strings, negative integers, and unsigned integers as map keys. The integers are used for compactness of encoding and easy comparison. The inclusion of text strings allows for an additional range of short encoded values to be used as well. Since the word "key" is mainly used in its other meaning, as a cryptographic key, we use the term "label" for this usage as a map key. - The presence in a CBOR map of a label that is not a text string or an - integer is an error. Applications can either fail processing or - process messages by ignoring incorrect labels; however, they MUST NOT - create messages with incorrect labels. + The presence a label that is neither a a text string bor an integer, + in a CBOR map, is an error. Applications can either fail processing + or process messages by ignoring incorrect labels; however, they MUST + NOT create messages with incorrect labels. A CDDL grammar fragment defines the non-terminal 'label', as in the previous paragraph, and 'values', which permits any value to be used. label = int / tstr values = any 1.6. Document Terminology In this document, we use the following terminology: Byte is a synonym for octet. Constrained Application Protocol (CoAP) is a specialized web transfer protocol for use in constrained systems. It is defined in [RFC7252]. - Authenticated Encryption (AE) [RFC5116] algorithms are those - encryption algorithms that provide an authentication check of the - contents algorithm with the encryption service. + Authenticated Encryption (AE) [RFC5116] algorithms are encryption + algorithms that provide an authentication check of the contents with + the encryption service. An example of an AE algorithm used in COSE + is AES Key Wrap [RFC3394]. These algorithms are used for key + encryption algorithms, but AEAD algorithms would be preferred. Authenticated Encryption with Associated Data (AEAD) [RFC5116] - algorithms provide the same content authentication service as AE - algorithms, but they additionally provide for authentication of non- - encrypted data as well. + algorithms provide the same authentication service of the content as + AE algorithms do. They also allow for associated data to be included + in the authentication service, but which is not part of the encrypted + body. An example of an AEAD algorithm used in COSE is AES-GCM + [RFC5116]. These algorithms are used for content encryption and can + be used for key encryption as well. Context is used throughout the document to represent information that is not part of the COSE message. Information which is part of the context can come from several different sources including: Protocol - interactions, associated key structures and program configuration. + interactions, associated key structures, and program configuration. The context to use can be implicit, identified using the 'kid context' header parameter defined in [RFC8613], or identified by a protocol-specific identifier. Context should generally be included - in the cryptographic configuration; for more details see Section 4.3. + in the cryptographic construction; for more details see Section 4.3. The term 'byte string' is used for sequences of bytes, while the term 'text string' is used for sequences of characters. 2. Basic COSE Structure The COSE object structure is designed so that there can be a large amount of common code when parsing and processing the different types of security messages. All of the message structures are built on the CBOR array type. The first three elements of the array always contain the same information: - 1. The protected header parameters encoded and wrapped in a bstr. + 1. The protected header parameters, encoded and wrapped in a bstr. 2. The unprotected header parameters as a map. 3. The content of the message. The content is either the plaintext or the ciphertext as appropriate. The content may be detached (i.e. transported separately from the COSE structure), but the location is still used. The content is wrapped in a bstr when present and is a nil value when detached. Elements after this point are dependent on the specific message type. COSE messages are built using the concept of layers to separate different types of cryptographic concepts. As an example of how this works, consider the COSE_Encrypt message (Section 6.1). This message type is broken into two layers: the content layer and the recipient - layer. In the content layer, the plaintext is encrypted and - information about the encrypted message is placed. In the recipient - layer, the content encryption key (CEK) is encrypted and information - about how it is encrypted for each recipient is placed. A single - layer version of the encryption message COSE_Encrypt0 (Section 6.2) - is provided for cases where the CEK is pre-shared. + layer. The content layer contains the plaintext is encrypted and + information about the encrypted message. The recipient layer contins + the content encryption key (CEK) is encrypted and information about + how it is encrypted for each recipient. A single layer version of + the encryption message COSE_Encrypt0 (Section 6.2) is provided for + cases where the CEK is pre-shared. Identification of which type of message has been presented is done by the following methods: 1. The specific message type is known from the context. This may be defined by a marker in the containing structure or by restrictions specified by the application protocol. 2. The message type is identified by a CBOR tag. Messages with a CBOR tag are known in this specification as tagged messages, @@ -466,57 +470,57 @@ the untagged version of the structure is used. The value to use with the parameter for each of the structures can be found in Table 1. 4. When a COSE object is carried as a CoAP payload, the CoAP Content-Format Option can be used to identify the message content. The CoAP Content-Format values can be found in Table 2. The CBOR tag for the message structure is not required as each security message is uniquely identified. - +------+------------------+-----------------------+-------------+ + +=======+==================+=======================+=============+ | CBOR | cose-type | Data Item | Semantics | | Tag | | | | - +======+==================+=======================+=============+ + +=======+==================+=======================+=============+ | 98 | cose-sign | COSE_Sign | COSE Signed | | | | | Data Object | - +------+------------------+-----------------------+-------------+ + +-------+------------------+-----------------------+-------------+ | 18 | cose-sign1 | COSE_Sign1 | COSE Single | | | | | Signer Data | | | | | Object | - +------+------------------+-----------------------+-------------+ + +-------+------------------+-----------------------+-------------+ | 96 | cose-encrypt | COSE_Encrypt | COSE | | | | | Encrypted | | | | | Data Object | - +------+------------------+-----------------------+-------------+ + +-------+------------------+-----------------------+-------------+ | 16 | cose-encrypt0 | COSE_Encrypt0 | COSE Single | | | | | Recipient | | | | | Encrypted | | | | | Data Object | - +------+------------------+-----------------------+-------------+ + +-------+------------------+-----------------------+-------------+ | 97 | cose-mac | COSE_Mac | COSE MACed | | | | | Data Object | - +------+------------------+-----------------------+-------------+ + +-------+------------------+-----------------------+-------------+ | 17 | cose-mac0 | COSE_Mac0 | COSE Mac w/ | | | | | o | | | | | Recipients | | | | | Object | - +------+------------------+-----------------------+-------------+ - | TBD0 | cose-countersign | COSE_Countersignature | COSE | + +-------+------------------+-----------------------+-------------+ + | TBD00 | cose-countersign | COSE_Countersignature | COSE | | | | | standalone | | | | | counter | | | | | signature | - +------+------------------+-----------------------+-------------+ + +-------+------------------+-----------------------+-------------+ Table 1: COSE Message Identification - +---------------------------+----------+-----+------------+ + +===========================+==========+=====+============+ | Media Type | Encoding | ID | Reference | +===========================+==========+=====+============+ | application/cose; cose- | | 98 | [[THIS | | type="cose-sign" | | | DOCUMENT]] | +---------------------------+----------+-----+------------+ | application/cose; cose- | | 18 | [[THIS | | type="cose-sign1" | | | DOCUMENT]] | +---------------------------+----------+-----+------------+ | application/cose; cose- | | 96 | [[THIS | | type="cose-encrypt" | | | DOCUMENT]] | @@ -553,23 +557,23 @@ COSE_Encrypt_Tagged / COSE_Encrypt0_Tagged / COSE_Mac_Tagged / COSE_Mac0_Tagged / COSE_Countersignature_Tagged 3. Header Parameters The structure of COSE has been designed to have two buckets of information that are not considered to be part of the payload itself, but are used for holding information about content, algorithms, keys, or evaluation hints for the processing of the layer. These two 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 - all instances. For example, while the protected bucket is defined as - part of the recipient structure, some of the algorithms used for + keys. While these buckets are present, they may not always be usable + in all instances. For example, while the protected bucket is defined + as part of the recipient structure, some of the algorithms used for recipient structures do not provide for authenticated data. If this is the case, the protected bucket is left empty. 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 the label. Both maps use the same set of label/value pairs. The integer and text string values for labels have been divided into several sections including a standard range, a private range, and a range that is dependent on the algorithm selected. The defined labels can be found in the "COSE Header Parameters" IANA registry @@ -579,61 +583,61 @@ protected: Contains parameters about the current layer that are cryptographically protected. This bucket MUST be empty if it is not going to be included in a cryptographic computation. This bucket is encoded in the message as a binary object. This value 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- length byte string rather than as a zero-length map (encoded as h'a0'). The zero-length binary encoding is preferred because it is both shorter and the version used in the serialization - structures for cryptographic computation. After encoding the map, - the value is wrapped in the binary object. Recipients MUST accept - both a zero-length byte string and a zero-length map encoded in - the binary value. + structures for cryptographic computation. Recipients MUST accept + both a zero-length byte string and a zero-length map encoded in a + byte string. Wrapping the encoding with a byte string allows for the protected map to be transported with a greater chance that it will not be altered accidentally in transit. (Badly behaved intermediates could decode and re-encode, but this will result in a failure to verify unless the re-encoded byte string is identical to the decoded byte string.) This avoids the problem of all parties - needing to be able to do a common canonical encoding. + needing to be able to do a common canonical encoding of the map + for input to cyprtographic operations. unprotected: Contains parameters about the current layer that are not cryptographically protected. Only header parameters that deal with the current layer are to be placed at that layer. As an example of this, the header parameter 'content type' describes the content of the message being carried in the message. As such, this header parameter is placed only in the content layer and is not placed in the recipient or signature layers. In principle, one should be able to process any given layer without reference to any other layer. With the exception of the COSE_Sign structure, the only data that needs to cross layers is the cryptographic key. The buckets are present in all of the security objects defined in this document. The fields in order are the 'protected' bucket (as a CBOR 'bstr' type) and then the 'unprotected' bucket (as a CBOR 'map' type). The presence of both buckets is required. The header parameters that go into the buckets come from the IANA "COSE Header - Parameters" registry (Section 12.2). Some common header parameters - are defined in the next section. + Parameters" registry (Section 12.2). Some header parameters are + defined in the next section. Labels in each of the maps MUST be unique. When processing messages, if a label appears multiple times, the message MUST be rejected as malformed. Applications SHOULD verify that the same label does not occur in both the protected and unprotected header parameters. If the message is not rejected as malformed, attributes MUST be obtained - from the protected bucket before they are obtained from the - unprotected bucket. + from the protected bucket, and only if not found are attributes + obtained from the unprotected bucket. The following CDDL fragment represents the two header parameter buckets. A group "Headers" is defined in CDDL that represents the two buckets in which attributes are placed. This group is used to provide these two fields consistently in all locations. A type is also defined that represents the map of common header parameters. Headers = ( protected : empty_or_serialized_map, unprotected : header_map @@ -651,48 +655,50 @@ This section defines a set of common header parameters. A summary of these header parameters can be found in Table 3. This table should be consulted to determine the value of label and the type of the value. The set of header parameters defined in this section are: alg: This header parameter is used to indicate the algorithm used for the security processing. This header parameter MUST be authenticated where the ability to do so exists. This support is - provided by AEAD algorithms or construction (COSE_Sign, - COSE_Sign1, COSE_Mac, and COSE_Mac0). This authentication can be - done either by placing the header parameter in the protected - header parameter bucket or as part of the externally supplied - data. The value is taken from the "COSE Algorithms" registry (see - [COSE.Algorithms]). + provided by AEAD algorithms or construction (e.g. COSE_Sign and + COSE_Mac0). This authentication can be done either by placing the + header parameter in the protected header parameter bucket or as + part of the externally supplied data Section 4.3). The value is + taken from the "COSE Algorithms" registry (see [COSE.Algorithms]). crit: This header parameter is used to indicate which protected header parameters an application that is processing a message is required to understand. Header parameters defined in this document do not need to be included as they should be understood by all implementations. When present, this the 'crit' header parameter MUST be placed in the protected header parameter bucket. The array MUST have at least one value in it. Not all header parameter labels need to be included in the 'crit' header parameter. The rules for deciding which header parameters are placed in the array are: * 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 - are algorithm dependent. If an application can correctly - process an algorithm, it can be assumed that it will correctly - process all of the common header parameters associated with - that algorithm. Integer labels in the range -129 to -65536 - SHOULD be included as these would be less common header - parameters that might not be generally supported. + * Integer labels in the range -1 to -128 can be omitted. + Algorithms can assign labels in this range where the ability to + process the content of the label is considered to be core to + implementing the algorithm. Algorithms can assign labels + outside of this range where the ability to process the content + of the label is not considered to be core, but needs to be + understood to correctly process this instance. Integer labels + in the range -129 to -65536 SHOULD be included as these would + be less common header parameters that might not be generally + supported. * Labels for header parameters required for an application MAY be omitted. Applications should have a statement if the label can be omitted. The header parameters indicated by 'crit' can be processed by either the security library code or an application using a security library; the only requirement is that the header parameter is processed. If the 'crit' value list includes a label for which the header parameter is not in the protected header @@ -735,35 +741,36 @@ portion can be changed with each message (Partial IV). This field is used to carry a value that causes the IV to be changed for each message. The Partial IV can be placed in the unprotected bucket as modifying the value will cause the decryption to yield plaintext that is readily detectable as garbled. The 'Initialization Vector' and 'Partial Initialization Vector' header parameters MUST NOT both be present in the same security layer. The message IV is generated by the following steps: - 1. Left-pad the Partial IV with zeros to the length of IV. + 1. Left-pad the Partial IV with zeros to the length of IV + (determined by the algorithm). 2. XOR the padded Partial IV with the context IV. counter signature: This header parameter holds one or more counter signature values. Counter signatures provide a method of having a second party sign some data. The counter signature header parameter can occur as an unprotected attribute in any of the following structures: COSE_Sign1, COSE_Signature, COSE_Encrypt, COSE_recipient, COSE_Encrypt0, COSE_Mac, and COSE_Mac0. These structures all have the same beginning elements, so that a consistent calculation of the counter signature can be computed. Details on counter signatures are found in Section 5. - +---------+-----+----------------+-----------------+----------------+ + +=========+=====+================+=================+================+ | Name |Label| Value Type | Value Registry | Description | +=========+=====+================+=================+================+ | alg | 1 | int / tstr | COSE Algorithms | Cryptographic | | | | | registry |algorithm to use| +---------+-----+----------------+-----------------+----------------+ | crit | 2 | [+ label] | COSE Header |Critical header | | | | | Parameters |parameters to be| | | | | registry | understood | +---------+-----+----------------+-----------------+----------------+ | content | 3 | tstr / uint | CoAP Content- |Content type of | @@ -811,22 +818,22 @@ be converted between each other; as the signature computation includes a parameter identifying which structure is being used, the converted structure will fail signature validation. 4.1. Signing with One or More Signers The COSE_Sign structure allows for one or more signatures to be applied to a message payload. Header parameters relating to the content and header parameters relating to the signature are carried along with the signature itself. These header parameters may be - authenticated by the signature, or just present. An example of - header a parameter about the content is the content type header + authenticated by the signature, or just present. An example of a + header parameter about the content is the content type header parameter. Examples of header parameters about the signature would be the algorithm and key used to create the signature and counter signatures. RFC 5652 indicates that: | When more than one signature is present, the successful validation | of one signature associated with a given signer is usually treated | as a successful signature by that signer. However, there are some | application environments where other rules are needed. An @@ -872,24 +879,25 @@ If the payload is not present in the message, the application is required to supply the payload separately. The payload is wrapped in a bstr to ensure that it is transported without changes. If the payload is transported separately ("detached content"), then a nil CBOR object is placed in this location, and it is the responsibility of the application to ensure that it will be transported without changes. Note: When a signature with a message recovery algorithm is used (Section 9.1), the maximum number of bytes that can be recovered - is 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 of the payload are consumed, then the payload is encoded as - a zero-length byte string rather than as being absent. + is the length of the original payload. The size of the encoded + payload is reduced by the number of bytes that will be recovered. + If all of the bytes of the original payload are consumed, then the + transmitted payload is encoded as a zero-length byte string rather + than as being absent. signatures: This field is an array of signatures. Each signature is represented as a COSE_Signature structure. The CDDL fragment that represents the above text for COSE_Sign follows. COSE_Sign = [ Headers, payload : bstr / nil, @@ -961,37 +970,37 @@ is not carried as part of the COSE object. The primary reason for supporting this can be seen by looking at the CoAP message structure [RFC7252], where the facility exists for options to be carried before the payload. Examples of data that can be placed in this location would be the CoAP code or CoAP options. If the data is in the headers of the CoAP message, then it is available for proxies to help in performing its operations. For example, the Accept Option can be used by a proxy to determine if an appropriate value is in the proxy's cache. But the sender can cause a failure at the server if a proxy, or an attacker, changes the set of accept values by including - the field in the application-supplied data. + the field in the externally supplied data. This document describes the process for using a byte array of externally supplied authenticated data; the method of constructing the byte array is a function of the application. Applications that use this feature need to define how the externally supplied authenticated data is to be constructed. Such a construction needs to take into account the following issues: * If multiple items are included, applications need to ensure that the same byte string cannot be produced if there are different - inputs. This would occur by appending the text strings 'AB' and - 'CDE' or by appending the text strings 'ABC' and 'DE'. This is - usually addressed by making fields a fixed width and/or encoding - the length of the field as part of the output. Using options from - CoAP [RFC7252] as an example, these fields use a TLV structure so - they can be concatenated without any problems. + inputs. This would occur by concatenating the text strings 'AB' + and 'CDE' or by concatenating the text strings 'ABC' and 'DE'. + This is usually addressed by making fields a fixed width and/or + encoding the length of the field as part of the output. Using + options from CoAP [RFC7252] as an example, these fields use a TLV + structure so they can be concatenated without any problems. * If multiple items are included, an order for the items needs to be defined. Using options from CoAP as an example, an application could state that the fields are to be ordered by the option number. * Applications need to ensure that the byte string is going to be the same on both sides. Using options from CoAP might give a problem if the same relative numbering is kept. An intermediate node could insert or remove an option, changing how the relative @@ -1008,54 +1017,85 @@ application data (external source). A Sig_structure is a CBOR array. The fields of the Sig_structure in order are: 1. A context text string identifying the context of the signature. The context text string is: "Signature" for signatures using the COSE_Signature structure. "Signature1" for signatures using the COSE_Sign1 structure. - "CounterSignature" for signatures used as counter signature - attributes. + "CounterSignature" for signatures using the + COSE_Countersignature structure. - "CounterSignature0" for signatures used as CounterSignature0 - attributes. + "CounterSignature0" for signatures used as + COSE_Countersignature0 structure. 2. The protected attributes from the body structure encoded in a bstr type. If there are no protected attributes, a zero-length byte string is used. 3. The protected attributes from the signer structure encoded in a bstr type. If there are no protected attributes, a zero-length byte string is used. This field is omitted for the COSE_Sign1 signature structure and CounterSignature0 attributes. - 4. The protected attributes from the application encoded in a bstr - type. If this field is not supplied, it defaults to a zero- + 4. The externally supplied data from the application encoded in a + bstr type. If this field is not supplied, it defaults to a zero- length byte string. (See Section 4.3 for application guidance on constructing this field.) 5. The payload to be signed encoded in a bstr type. The payload is placed here independent of how it is transported. The CDDL fragment that describes the above text is: Sig_structure = [ context : "Signature" / "Signature1" / "CounterSignature" / "CounterSignature0", body_protected : empty_or_serialized_map, ? sign_protected : empty_or_serialized_map, external_aad : bstr, payload : bstr ] + A countersignature, like a signature needs a well-defined byte + string. The process uses the same Sig_structure but fills it in + slightly differently. The signing and verification process takes in + the target information (COSE_Sign, COSE_Sign1, COSE_Mac, COSE_Mac0, + COSE_Encrypt, COSE_Encrypt0, COSE_Recipient, and + COSE_Countersignature), the signer information (COSE_Signature) and + the application data (external source). The target structure of the + countersignature needs to have all of it's cryptographic functions + finalized before the computing the signature. The fields of the + Sig_stucture in order are: + + 1. A context string identifing the context of the signature as + above. + + 2. The protected attributes from the target structure encoded in a + bstr type. If there are no protected attributes, a zero-length + byte string is used. + + 3. The protected attributes from the countersignture structure + encoded in a bstr type. If there are no protected attributes, a + zero-length byte string is used. This field is omitted when + computing the CounterSignature0 attributes. + + 4. The externally supplied data from the application encoded in a + bstr type. If this field is not supplied, it defaults to a zero- + length byte string. (See Section 4.3 for application guidance on + constructing this field.) + + 5. The payload from the target structure encoded in a bstr type. + The payload is placed here independent of how it is transported. + How to compute a signature: 1. Create a Sig_structure and populate it with the appropriate fields. 2. Create the value ToBeSigned by encoding the Sig_structure to a byte string, using the encoding described in Section 10. 3. Call the signature creation algorithm passing in K (the key to sign with), alg (the algorithm to sign with), and ToBeSigned (the @@ -1091,27 +1131,27 @@ as witnessing that you have signed the document. Thus applying a counter signature to either the COSE_Signature or COSE_Sign1 objects match this traditional definition. This document extends the context of a counter signature to allow it to be applied to all of the security structures defined. It needs to be noted that the counter signature needs to be treated as a separate operation from the initial operation even if it is applied by the same user as is done in [I-D.ietf-core-groupcomm-bis]. COSE supports two different forms for counter signatures. Full - counter signatures use the structure COSE_Countersign. This is same - structure as COSE_Signature and thus it can have protected - attributes, chained counter signatures and information about - identifying the key. Abbreviated counter signatures use the - structure COSE_Countersign1. This structure only contains the - signature value and nothing else. The structures cannot be converted - between each other; as the signature computation includes a parameter + counter signatures use the structure COSE_Countersignature. This is + same structure as COSE_Signature and thus it can have protected and + unprotected attributes, including chained counter signatures. + Abbreviated counter signatures use the structure + COSE_Countersignature0. This structure only contains the signature + value and nothing else. The structures cannot be converted between + each other; as the signature computation includes a parameter identifying which structure is being used, the converted structure will fail signature validation. COSE was designed for uniformity in how the data structures are specified. One result of this is that for COSE one can expand the concept of counter signatures 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 counter signature, one needs to be clear about the security properties that result. When done on a COSE_Signature, the normal counter signature semantics @@ -1126,37 +1166,39 @@ 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 use of two different keys will appear to result in a successful decryption (the tag check success), but which produce two completely different plaintexts. This situation is not detectable by a counter signature on the encrypted data. 5.1. Full Counter Signatures The COSE_Countersignature structure allows for the same set of - capabilities of a COSE_Signature. This means that all of the + capabilities as a COSE_Signature. This means that all of the capabilities of a signature are duplicated with this structure. Specifically, the counter signer 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 counter signature attributes. This also means that the counter signature can itself be counter signed. 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]. + archiving services. More information on how counter signatures is + used can be found in the evidence record syntax described in + [RFC4998]. The full counter signature structure can be encoded as either tagged or untagged depending on the context it is used in. A tagged - COSE_Countersign structure is identified by the CBOR tag TBD0. The - CDDL fragment for full counter signatures is: + COSE_Countersignature structure is identified by the CBOR tag TBD0. + The CDDL fragment for full counter signatures is: - COSE_CounterSignature_Tagged = #6.98(COSE_CounterSignature) - COSE_CounterSignature = COSE_Signature + COSE_Countersignature_Tagged = #6.9999(COSE_Countersignature) + COSE_Countersignature = COSE_Signature + COSE_CounterSignature = COSE_Countersignature The details of the fields of a counter signature can be found in Section 4.1. The process of creating and validating abbreviated counter signatures is defined in Section 4.4. 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 object can be found in Appendix C.3.3. It should be noted that only a signature algorithm with appendix (see @@ -1170,34 +1212,38 @@ Abbreviated counter signatures were designed primarily to deal with the problem of having encrypted group messaging, but still needing to know who originated the message. The objective was to keep the counter signature as small as possible while still providing the needed security. For abbreviated counter signatures, there is no provision for any protected attributes related to the signing operation. Instead, the parameters for computing or verifying the abbreviated counter signature are inferred from the same context used to describe the encryption, signature, or MAC processing. + The CDDL fragment for the abbreviated counter signatures is: + + COSE_Countersignature0 = bstr + The byte string representing the signature value is placed in the CounterSignature0 attribute. This attribute is then encoded as an unprotected header parameter. The attribute is defined below. The process of creating and validating abbreviated counter signatures is defined in Section 4.4. - +-------------------+-------+-------+-------+-------------------+ - | Name | Label | Value | Value | Description | - | | | Type | | | - +===================+=======+=======+=======+===================+ - | CounterSignature0 | 9 | bstr | | Abbreviated | - | | | | | Counter Signature | - +-------------------+-------+-------+-------+-------------------+ + +==================+=====+========================+=====+===========+ + | Name |Label| Value Type |Value|Description| + +==================+=====+========================+=====+===========+ + |CounterSignature0 | 9 | COSE_Countersignature0 | |Abbreviated| + | | | | | Counter | + | | | | | Signature | + +------------------+-----+------------------------+-----+-----------+ Table 4: Header Parameter for CounterSignature0 6. Encryption Objects COSE supports two different encryption structures. COSE_Encrypt0 is 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. This includes cases where there are multiple recipients or a recipient algorithm other than direct (i.e. pre-shared secret) is @@ -1371,22 +1417,22 @@ "Mac_Recipient" for a recipient encoding to be placed in a MACed message structure. "Rec_Recipient" for a recipient encoding to be placed in a recipient structure. 2. The protected attributes from the body structure encoded in a bstr type. If there are no protected attributes, a zero-length byte string is used. - 3. The protected attributes from the application encoded in a bstr - type. If this field is not supplied, it defaults to a zero- + 3. The externally supplied data from the application encoded in a + bstr type. If this field is not supplied, it defaults to a zero- length byte string. (See Section 4.3 for application guidance on constructing this field.) The CDDL fragment that describes the above text is: Enc_structure = [ context : "Encrypt" / "Encrypt0" / "Enc_Recipient" / "Mac_Recipient" / "Rec_Recipient", protected : empty_or_serialized_map, external_aad : bstr @@ -1635,22 +1681,22 @@ in order are: 1. A context text string that identifies the structure that is being encoded. This context text string is "MAC" for the COSE_Mac structure. This context text string is "MAC0" for the COSE_Mac0 structure. 2. The protected attributes from the COSE_MAC structure. If there are no protected attributes, a zero-length bstr is used. - 3. The protected attributes from the application encoded as a bstr - type. If this field is not supplied, it defaults to a zero- + 3. The externally supplied data from the application encoded as a + bstr type. If this field is not supplied, it defaults to a zero- length byte string. (See Section 4.3 for application guidance on constructing this field.) 4. The payload to be MACed encoded in a bstr type. The payload is placed here independent of how it is transported. The CDDL fragment that corresponds to the above text is: MAC_structure = [ context : "MAC" / "MAC0", @@ -1692,21 +1738,21 @@ alg (the algorithm to MAC with), and ToBeMaced (the value to compute the MAC on). 5. Compare the MAC value to the 'tag' field of the COSE_Mac or COSE_Mac0 structure. 8. Key Objects A COSE Key structure is built on a CBOR map. The set of common parameters that can appear in a COSE Key can be found in the IANA - "COSE Key Common Parameters" registry (Section 12.4). Additional + "COSE Key Common Parameters" registry (Section 12.3). Additional parameters defined for specific key types can be found in the IANA "COSE Key Type Parameters" registry ([COSE.KeyParameters]). 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 at least one element in the array. Examples of COSE Key Sets can be found in Appendix C.7. 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 @@ -1729,21 +1775,21 @@ COSE_KeySet = [+COSE_Key] 8.1. COSE Key Common Parameters This document defines a set of common parameters for a COSE Key object. Table 5 provides a summary of the parameters defined in this section. There are also parameters that are defined for specific key types. Key-type-specific parameters can be found in [I-D.ietf-cose-rfc8152bis-algs]. - +---------+-------+--------+------------+--------------------+ + +=========+=======+========+============+====================+ | Name | Label | CBOR | Value | Description | | | | Type | Registry | | +=========+=======+========+============+====================+ | kty | 1 | tstr / | COSE Key | Identification of | | | | int | Types | the key type | +---------+-------+--------+------------+--------------------+ | kid | 2 | bstr | | Key identification | | | | | | value -- match to | | | | | | kid in message | +---------+-------+--------+------------+--------------------+ @@ -1778,51 +1824,50 @@ cryptographic operation. Note that the same key can be in a different key structure with a different or no algorithm specified; however, this is considered to be a poor security practice. kid: This parameter is used to give an identifier for a key. The identifier is not structured and can be anything from a user- provided byte string to a value computed on the public portion of the key. This field is intended for matching against a 'kid' parameter in a message in order to filter down the set of keys - that need to be checked. + that need to be checked. The value of the identifier is not a + unique value and can occur in other key objects, even for + different keys. 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 of values from Table 6. Algorithms define the values of key ops that are permitted to appear and are required for specific operations. The set of values matches that in [RFC7517] and [W3C.WebCrypto]. 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 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 - per message basis with the Partial IV. + to associate a Base IV with a key that is then modified on a per + message basis with the Partial IV. Extreme care needs to be taken when using a Base IV in an application. Many encryption algorithms lose security if the same IV is used twice. - If different keys are derived for each sender, using the same Base - IV with Partial IVs starting at zero is likely to ensure that the - IV would not be used twice for a single key. If different keys - are derived for each sender, starting at the same Base IV is - likely to satisfy this condition. If the same key is used for - multiple senders, then the application needs to provide for a - method of dividing the IV space up between the senders. This - could be done by providing a different base point to start from or - a different Partial IV to start with and restricting the number of - messages to be sent before rekeying. + If different keys are derived for each sender, starting at the + same Base IV is likely to satisfy this condition. If the same key + is used for multiple senders, then the application needs to + provide for a method of dividing the IV space up between the + senders. This could be done by providing a different base point + to start from or a different Partial IV to start with and + restricting the number of messages to be sent before rekeying. - +---------+-------+----------------------------------------------+ + +=========+=======+==============================================+ | Name | Value | Description | +=========+=======+==============================================+ | sign | 1 | The key is used to create signatures. | | | | Requires private key fields. | +---------+-------+----------------------------------------------+ | verify | 2 | The key is used for verification of | | | | signatures. | +---------+-------+----------------------------------------------+ | encrypt | 3 | The key is used for key transport | | | | encryption. | @@ -1849,22 +1894,21 @@ | verify | | | +---------+-------+----------------------------------------------+ Table 6: Key Operation Values 9. Taxonomy of Algorithms used by COSE In this section, a taxonomy of the different algorithm types that can be used in COSE is laid out. This taxonomy should not be considered to be exhaustive. New algorithms will be created which will not fit - into this taxonomy. If this occurs, then new documents addressing - this new algorithms are going to be needed. + into this taxonomy. 9.1. Signature Algorithms Signature algorithms provide data origination and data integrity services. Data origination provides the ability to infer who originated the data based on who signed the data. Data integrity provides the ability to verify that the data has not been modified since it was signed. There are two signature algorithm schemes. The first is signature @@ -1976,22 +2020,22 @@ is created by a good random number generator. * Secrets that are not uniformly random: This is type of secret that is created by operations like key agreement. * Secrets that are not random: This is the type of secret that people generate for things like passwords. General KDFs work well with the first type of secret, can do reasonably well with the second type of secret, and generally do - poorly with the last type of secret. Functions like PBES2 [RFC8018] - need to be used for non-random secrets. + poorly with the last type of secret. Functions like Argon2 + [I-D.irtf-cfrg-argon2] need to be used for non-random secrets. The same KDF can be set up to deal with the first two types of secrets in a different way. The KDF defined in section 5.1 of [I-D.ietf-cose-rfc8152bis-algs] is such a function. This is reflected in the set of algorithms defined around the HMAC-based Extract-and-Expand Key Derivation Function (HKDF). When using KDFs, one component that is included is context information. Context information is used to allow for different keying information to be derived from the same secret. The use of @@ -2036,48 +2080,49 @@ encrypted by a shared secret between the sender and the recipient. All of the currently defined key wrap algorithms for COSE are AE algorithms. Key wrap mode is considered to be superior to direct encryption if the system has any capability for doing random key 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 fact be repeating the same content. The use of key wrap loses the weak data origination that is provided by the direct encryption algorithms. - The COSE_Encrypt structure for the recipient is organized as follows: + The COSE_Recipient structure for the recipient is organized as + follows: * The 'protected' field MUST be absent if the key wrap algorithm is an AE algorithm. * The 'recipients' field is normally absent, but can be used. Applications MUST deal with a recipient field being present that - has an unsupported algorithm, not being able to decrypt that + has an unsupported algorithm. Failing to decrypt that specific recipient is an acceptable way of dealing with it. Failing to process the message is not an acceptable way of dealing with it. * The plaintext to be encrypted is the key from next layer down (usually the content layer). * At a minimum, the 'unprotected' field MUST contain the 'alg' header parameter and SHOULD contain a header parameter identifying the shared secret. 9.5.3. Key Transport Key transport mode is also called key encryption mode in some standards. Key transport mode differs from key wrap mode in that it uses an asymmetric encryption algorithm rather than a symmetric encryption algorithm to protect the key. A set of key transport algorithms are defined in [RFC8230]. - When using a key transport algorithm, the COSE_Encrypt structure for - the recipient is organized as follows: + When using a key transport algorithm, the COSE_Recipient structure + for the recipient is organized as follows: * The 'protected' field MUST be absent. * The plaintext to be encrypted is the key from the next layer down (usually the content layer). * At a minimum, the 'unprotected' field MUST contain the 'alg' header parameter and SHOULD contain a parameter identifying the asymmetric key. @@ -2086,23 +2131,23 @@ The 'direct key agreement' class of recipient algorithms uses a key agreement method to create a shared secret. A KDF is then applied to the shared secret to derive a key to be used in protecting the data. This key is normally used as a CEK or MAC key, but could be used for other purposes if more than two layers are in use (see Appendix B). The most commonly used key agreement algorithm is Diffie-Hellman, but other variants exist. Since COSE is designed for a store and forward environment rather than an online environment, many of the DH variants cannot be used as the receiver of the message cannot provide - any dynamic key material. One side effect of this is that perfect - forward secrecy (see [RFC4949]) is not achievable. A static key will - always be used for the receiver of the COSE object. + any dynamic key material. One side effect of this is that forward + secrecy (see [RFC4949]) is not achievable. A static key will always + be used for the receiver of the COSE object. Two variants of DH that are supported are: Ephemeral-Static (ES) DH: where the sender of the message creates a one-time DH key and uses a static key for the recipient. The use of the ephemeral sender key means that no additional random input is needed as this is randomly generated for each message. Static-Static (SS) DH: where a static key is used for both the sender and the recipient. The use of static keys allows for the @@ -2110,56 +2155,59 @@ message. When static-static key agreement is used, then some piece of unique data for the KDF is required to ensure that a different key is created for each message. When direct key agreement mode is used, there MUST be only one recipient in the message. This method creates the key directly, and that makes it difficult to mix with additional recipients. If multiple recipients are needed, then the version with key wrap needs to be used. - The COSE_Encrypt structure for the recipient is organized as follows: + The COSE_Recipient structure for the recipient is organized as + follows: * At a minimum, headers MUST contain the 'alg' header parameter and SHOULD contain a header parameter identifying the recipient's asymmetric key. * The headers SHOULD identify the sender's key for the static-static versions and MUST contain the sender's ephemeral key for the ephemeral-static versions. 9.5.5. Key Agreement with Key Wrap 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 the shared secret computed by the key agreement algorithm. The function for this would be: encryptedKey = KeyWrap(KDF(DH-Shared, context), CEK) - The COSE_Encrypt structure for the recipient is organized as follows: + The COSE_Recipient structure for the recipient is organized as + follows: * The 'protected' field is fed into the KDF context structure. * The plaintext to be encrypted is the key from the next layer down (usually the content layer). * The 'alg' header parameter MUST be present in the layer. * A header parameter identifying the recipient's key SHOULD be present. A header parameter identifying the sender's key SHOULD be present. 10. CBOR Encoding Restrictions - The document limits the restrictions it imposes on the CBOR Encoder - needs to work. + This document limits the restrictions it imposes on how the CBOR + Encoder needs to work. It has been narrowed down to the following + restrictions: * The restriction applies to the encoding of the Sig_structure, the Enc_structure, and the MAC_structure. * Encoding MUST be done using definite lengths and values MUST be the minimum possible length. This means that the integer 1 is encoded as "0x01" and not "0x1801". * Applications MUST NOT generate messages with the same label used twice as a key in a single map. Applications MUST NOT parse and @@ -2207,21 +2255,22 @@ * Applications need to determine the set of security algorithms that are to be used. When selecting the algorithms to be used as the mandatory-to-implement set, consideration should be given to choosing different types of algorithms when two are chosen for a specific purpose. An example of this would be choosing HMAC- SHA512 and AES-CMAC as different MAC algorithms; the construction is vastly different between these two algorithms. This means that a weakening of one algorithm would be unlikely to lead to a weakening of the other algorithms. Of course, these algorithms do not provide the same level of security and thus may not be - comparable for the desired security functionality. + comparable for the desired security functionality. Additional + guidence can be found in [BCP201]. * Applications may need to provide some type of negotiation or discovery method if multiple algorithms or message structures are permitted. The method can be as simple as requiring pre- configuration of the set of algorithms to providing a discovery method built into the protocol. S/MIME provided a number of different ways to approach the problem that applications could follow: - Advertising in the message (S/MIME capabilities) [RFC5751]. @@ -2243,59 +2292,49 @@ IANA assigned tags in the "CBOR Tags" registry as part of processing [RFC8152]. IANA is requested to update the references from [RFC8152] to this document. IANA is requested to register a new tag for the CounterSignature type. * Tag: TBD0 - * Data Item: COSE_Signature + * Data Item: COSE_Countersignature * Semantics: COSE standalone counter signature * Reference: [[this document]] 12.2. COSE Header Parameters Registry IANA created a registry titled "COSE Header Parameters" as part of - processing [RFC8152]. The registry has been created to use the - "Expert Review Required" registration procedure [RFC8126]. - - IANA is requested to update the reference for entries in the table - from [RFC8152] to this document. This document does not update the - expert review guidelines provided in [RFC8152]. - -12.3. COSE Header Algorithm Parameters Registry + processing [RFC8152]. IANA is requested to update the reference for + entries in the table from [RFC8152] to this document. - IANA created a registry titled "COSE Header Algorithm Parameters" as - part of processing [RFC8152]. The registry has been created to use - the "Expert Review Required" registration procedure [RFC8126]. + Additionally, the type for the attribute CounterSignature0 is to be + updated from 'bstr' to 'COSE_Countersignature0'. - IANA is requested to update the references from [RFC8152] to this - document. This document does not update the expert review guidelines - provided in [RFC8152]. + IANA is requested to update the pointer for expert rview to [[this + document]]. -12.4. COSE Key Common Parameters Registry +12.3. COSE Key Common Parameters Registry IANA created a registry titled "COSE Key Common Parameters" as part - of the processing of [RFC8152]. The registry has been created to use - the "Expert Review Required" registration procedure [RFC8126]. - - IANA is requested to update the reference for entries in the table - from [RFC8152] to this document. This document does not update the - expert review guidelines provided in [RFC8152]. + of the processing of [RFC8152]. IANA is requested to update the + reference for entries in the table from [RFC8152] to this document. -12.5. Media Type Registrations + IANA is requested to update the pointer for expert rview to [[this + document]]. -12.5.1. COSE Security Message +12.4. Media Type Registrations +12.4.1. COSE Security Message This section registers the 'application/cose' media type in the "Media Types" registry. These media types are used to indicate that the content is a COSE message. Type name: application Subtype name: cose Required parameters: N/A @@ -2323,29 +2362,29 @@ - Magic number(s): N/A - File extension(s): cbor - Macintosh file type code(s): N/A Person & email address to contact for further information: iesg@ietf.org Intended usage: COMMON + Restrictions on usage: N/A Author: Jim Schaad, ietf@augustcellars.com Change Controller: IESG - Provisional registration? No -12.5.2. COSE Key Media Type +12.4.2. COSE Key Media Type This section registers the 'application/cose-key' and 'application/ cose-key-set' media types in the "Media Types" registry. These media types are used to indicate, respectively, that content is a COSE_Key or COSE_KeySet object. The template for registering 'application/cose-key' is: Type name: application @@ -2417,45 +2456,89 @@ Additional information: - Deprecated alias names for this type: N/A - Magic number(s): N/A - File extension(s): cbor - Macintosh file type code(s): N/A + Person & email address to contact for further information: iesg@ietf.org Intended usage: COMMON Restrictions on usage: N/A - Author: Jim Schaad, ietf@augustcellars.com Change Controller: IESG Provisional registration? No -12.6. CoAP Content-Formats Registry +12.5. CoAP Content-Formats Registry - IANA added the following entries to the "CoAP Content-Formats" - registry while processing [RFC8152]. IANA is requested to update the - reference value from [RFC8152] to [[This Document]]. + IANA added entries to the "CoAP Content-Formats" registry while + processing [RFC8152]. IANA is requested to update the reference + value from [RFC8152] to [[This Document]]. + +12.6. Expert Review Instructions + + All of the IANA registries established by [RFC8152] are, at least in + part, 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: + + * 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. + + * 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. + + * 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. + + * 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. 13. Security Considerations There are a number of security considerations that need to be taken - into account by implementers of this specification. The security - considerations that are specific to an individual algorithm are - placed next to the description of the algorithm. While some + into account by implementers of this specification. While some considerations have been highlighted here, additional considerations may be found in the documents listed in the references. Implementations need to protect the private key material for any individuals. There are some cases that need to be highlighted on this issue. * Using the same key for two different algorithms can leak information about the key. It is therefore recommended that keys be restricted to a single algorithm. @@ -2508,34 +2591,23 @@ * Have the restrictions associated with the key, such as algorithm or freshness, been checked and are they correct? * Is the request something that is reasonable, given the current state of the application? * Have any security considerations that are part of the message been enforced (as specified by the application or 'crit' header parameter)? - There are a large number of algorithms presented in - [I-D.ietf-cose-rfc8152bis-algs] that use nonce values. Nonces - generally have some type of restriction on their values. Generally a - nonce needs to be a unique value either for a key or for some other - conditions. In all of these cases, there is no known requirement on - the nonce being both unique and unpredictable; under these - circumstances, it's reasonable to use a counter for creation of the - nonce. In cases where one wants the pattern of the nonce to be - unpredictable as well as unique, one can use a key created for that - purpose and encrypt the counter to produce the nonce value. - - One area that has been starting to get exposure is doing traffic - analysis of encrypted messages based on the length of the message. - This specification does not provide for a uniform method of providing + One area that has been getting exposure is traffic analysis of + encrypted messages based on the length of the message. This + specification does not provide for a uniform method of providing padding as part of the message structure. An observer can distinguish between two different messages (for example, 'YES' and 'NO') based on the length for all of the content encryption algorithms that are defined in [I-D.ietf-cose-rfc8152bis-algs] document. This means that it is up to the applications to document how content padding is to be done in order to prevent or discourage such analysis. (For example, the text strings could be defined as 'YES' and 'NO '.) 14. Implementation Status @@ -2571,21 +2643,21 @@ * Implementation Location: https://github.com/cose-wg * Primary Maintainer: Jim Schaad * Languages: There are three different languages that are currently supported: Java, C# and C. * Cryptography: The Java and C# libraries use Bouncy Castle to provide the required cryptography. The C version uses OPENSSL - Version 1.0 for the cryptography. + Version 1.1 for the cryptography. * Coverage: The C version currently does not have full counter sign support. The other two versions do. They do have support to allow for implicit algorithm support as they allow for the application to set attributes that are not to be sent in the message. * Testing: All of the examples in the example library are generated by the C# library and then validated using the Java and C libraries. All three libraries have tests to allow for the @@ -2629,87 +2702,55 @@ * Testing: Basic testing plus running against the common example library. * Licensing: BSD 3-Clause License 14.4. COSE Testing Library * Implementation Location: https://github.com/cose-wg/Examples * Primary Maintainer: Jim Schaad - * Description: A set of tests for the COSE library is provided as part of the implementation effort. Both success and fail tests have been provided. All of the examples in this document are part of this example set. * Coverage: An attempt has been made to have test cases for every 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 Curve25519 and Goldilocks are missing. * Licensing: Public Domain 15. References 15.1. Normative References - [COAP.Formats] - IANA, "CoAP Content-Formats", - . - - [COSE.Algorithms] - IANA, "COSE Algorithms", - . - - [COSE.KeyParameters] - IANA, "COSE Key Parameters", - . - - [COSE.KeyTypes] - IANA, "COSE Key Types", - . - [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, October 2013, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . - [DSS] National Institute of Standards and Technology, "Digital - Signature Standard (DSS)", DOI 10.6028/NIST.FIPS.186-4, - FIPS PUB 186-4, July 2013, - . - - [RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital - Signature Algorithm (EdDSA)", RFC 8032, - DOI 10.17487/RFC8032, January 2017, - . - [I-D.ietf-cose-rfc8152bis-algs] Schaad, J., "CBOR Object Signing and Encryption (COSE): Initial Algorithms", Work in Progress, Internet-Draft, - draft-ietf-cose-rfc8152bis-algs-08, 14 May 2020, + draft-ietf-cose-rfc8152bis-algs-10, 26 June 2020, . + algs-10>. 15.2. Informative References [RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)", RFC 8152, DOI 10.17487/RFC8152, July 2017, . [RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data Definition Language (CDDL): A Notational Convention to Express Concise Binary Object Representation (CBOR) and @@ -2756,24 +2797,30 @@ "Use of the RSA-KEM Key Transport Algorithm in the Cryptographic Message Syntax (CMS)", RFC 5990, DOI 10.17487/RFC5990, September 2010, . [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, January 2013, . - [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data - Interchange Format", STD 90, RFC 8259, - DOI 10.17487/RFC8259, December 2017, - . + [STD90] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data + Interchange Format", STD 90, RFC 8259, December 2017. + + + + [BCP201] Housley, R., "Guidelines for Cryptographic Algorithm + Agility and Selecting Mandatory-to-Implement Algorithms", + BCP 201, RFC 7696, November 2015. + + [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, . [RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 2015, . @@ -2782,24 +2829,30 @@ . [RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517, DOI 10.17487/RFC7517, May 2015, . [RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518, DOI 10.17487/RFC7518, May 2015, . - [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for - Writing an IANA Considerations Section in RFCs", BCP 26, - RFC 8126, DOI 10.17487/RFC8126, June 2017, - . + [RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital + Signature Algorithm (EdDSA)", RFC 8032, + DOI 10.17487/RFC8032, January 2017, + . + + [DSS] National Institute of Standards and Technology, "Digital + Signature Standard (DSS)", DOI 10.6028/NIST.FIPS.186-4, + FIPS PUB 186-4, July 2013, + . [PVSig] Brown, D. and D. Johnson, "Formal Security Proofs for a Signature Scheme with Partial Message Recovery", DOI 10.1007/3-540-45353-9_11, LNCS Volume 2020, June 2000, . [W3C.WebCrypto] Watson, M., "Web Cryptography API", W3C Recommendation, January 2017, . @@ -2810,39 +2863,70 @@ [RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", BCP 205, RFC 7942, DOI 10.17487/RFC7942, July 2016, . [RFC4998] Gondrom, T., Brandner, R., and U. Pordesch, "Evidence Record Syntax (ERS)", RFC 4998, DOI 10.17487/RFC4998, August 2007, . + [RFC3394] Schaad, J. and R. Housley, "Advanced Encryption Standard + (AES) Key Wrap Algorithm", RFC 3394, DOI 10.17487/RFC3394, + September 2002, . + [I-D.ietf-cose-hash-algs] Schaad, J., "CBOR Object Signing and Encryption (COSE): Hash Algorithms", Work in Progress, Internet-Draft, draft- ietf-cose-hash-algs-04, 29 May 2020, . [I-D.ietf-core-groupcomm-bis] Dijk, E., Wang, C., and M. Tiloca, "Group Communication for the Constrained Application Protocol (CoAP)", Work in Progress, Internet-Draft, draft-ietf-core-groupcomm-bis- 00, 30 March 2020, . [RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz, "Object Security for Constrained RESTful Environments (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019, . + [I-D.irtf-cfrg-argon2] + Biryukov, A., Dinu, D., Khovratovich, D., and S. + Josefsson, "The memory-hard Argon2 password hash and + proof-of-work function", Work in Progress, Internet-Draft, + draft-irtf-cfrg-argon2-10, 25 March 2020, + . + + [COAP.Formats] + IANA, "CoAP Content-Formats", + . + + [COSE.Algorithms] + IANA, "COSE Algorithms", + . + + [COSE.KeyParameters] + IANA, "COSE Key Parameters", + . + + [COSE.KeyTypes] + IANA, "COSE Key Types", + . + Appendix A. Guidelines for External Data Authentication of Algorithms During development of COSE, the requirement that the algorithm identifier be located in the protected attributes was relaxed from a must to a should. There were two basic reasons that have been advanced to support this position. First, the resulting message will be smaller if the algorithm identifier is omitted from the most common messages in a CoAP environment. Second, there is a potential bug that will arise if full checking is not done correctly between the different places that an algorithm identifier could be placed @@ -2988,26 +3072,26 @@ For these cases, the following additional items need to be considered: * Applications need to ensure that the multiple contexts stay associated. If one of the contexts is invalidated for any reason, all of the contexts associated with it should also be invalidated. Appendix B. Two Layers of Recipient Information All of the currently defined recipient algorithm classes only use two - layers of the COSE_Encrypt structure. The first layer is the message - content, and the second layer is the content key encryption. - However, if one uses a recipient algorithm such as the RSA Key - Encapsulation Mechanism (RSA-KEM) (see Appendix A of RSA-KEM - [RFC5990]), then it makes sense to have three layers of the - COSE_Encrypt structure. + layers of the COSE structure. The first layer (COSE_Encrypt) is the + message content, and the second layer (COSE_Recipint) is the content + key encryption. However, if one uses a recipient algorithm such as + the RSA Key Encapsulation Mechanism (RSA-KEM) (see Appendix A of RSA- + KEM [RFC5990]), then it makes sense to have two layers of the + COSE_Recipient structure. These layers would be: * Layer 0: The content encryption layer. This layer contains the payload of the message. * Layer 1: The encryption of the CEK by a KEK. * Layer 2: The encryption of a long random secret using an RSA key and a key derivation function to convert that secret into the KEK. @@ -3020,42 +3104,42 @@ * Layer 1: Uses the AES Key Wrap algorithm with a 128-bit key. * Layer 2: Uses ECDH Ephemeral-Static direct to generate the layer 1 key. In effect, this example is a decomposed version of using the ECDH-ES+A128KW algorithm. Size of binary file is 183 bytes 96( - [ - / protected / h'a10101' / { - \ alg \ 1:1 \ AES-GCM 128 \ - } / , + [ / COSE_Encrypt / + / protected h'a10101' / << { + / alg / 1:1 / AES-GCM 128 / + } >>, / unprotected / { / iv / 5:h'02d1f7e6f26c43d4868d87ce' }, / ciphertext / h'64f84d913ba60a76070a9a48f26e97e863e2852948658f0 811139868826e89218a75715b', / recipients / [ - [ + [ / COSE_Recipient / / protected / h'', / unprotected / { / alg / 1:-3 / A128KW / }, / ciphertext / h'dbd43c4e9d719c27c6275c67d628d493f090593db82 18f11', / recipients / [ - [ - / protected / h'a1013818' / { - \ alg \ 1:-25 \ ECDH-ES + HKDF-256 \ - } / , + [ / COSE_Recipient / + / protected h'a1013818' / << { + / alg / 1:-25 / ECDH-ES + HKDF-256 / + } >> , / unprotected / { / ephemeral / -1:{ / kty / 1:2, / crv / -1:1, / x / -2:h'b2add44368ea6d641f9ca9af308b4079aeb519f11 e9b8a55a600b21233e86e68', / y / -3:false }, / kid / 4:'meriadoc.brandybuck@buckland.example' }, @@ -3115,23 +3199,23 @@ * Signature Algorithm: ECDSA w/ SHA-256, Curve P-256 Size of binary file is 103 bytes 98( [ / protected / h'', / unprotected / {}, / payload / 'This is the content.', / signatures / [ [ - / protected / h'a10126' / { - \ alg \ 1:-7 \ ECDSA 256 \ - } / , + / protected h'a10126' / << { + / alg / 1:-7 / ECDSA 256 / + } >>, / unprotected / { / kid / 4:'11' }, / signature / h'e2aeafd40d69d19dfe6e52077c5d7ff4e408282cbefb 5d06cbf414af2e19d982ac45ac98b8544c908b4507de1e90b717c3d34816fe926a2b 98f53afd2fa0f30a' ] ] ] ) @@ -3145,34 +3229,34 @@ * Signature Algorithm: ECDSA w/ SHA-512, Curve P-521 Size of binary file is 277 bytes 98( [ / protected / h'', / unprotected / {}, / payload / 'This is the content.', / signatures / [ [ - / protected / h'a10126' / { - \ alg \ 1:-7 \ ECDSA 256 \ - } / , + / protected h'a10126' / << { + / alg / 1:-7 / ECDSA 256 / + } >>, / unprotected / { / kid / 4:'11' }, / signature / h'e2aeafd40d69d19dfe6e52077c5d7ff4e408282cbefb 5d06cbf414af2e19d982ac45ac98b8544c908b4507de1e90b717c3d34816fe926a2b 98f53afd2fa0f30a' ], [ - / protected / h'a1013823' / { - \ alg \ 1:-36 - } / , + / protected h'a1013823' / << { + / alg / 1:-36 / ECDSA 521 / + } >> , / unprotected / { / kid / 4:'bilbo.baggins@hobbiton.example' }, / signature / h'00a2d28a7c2bdb1587877420f65adf7d0b9a06635dd1 de64bb62974c863f0b160dd2163734034e6ac003b01e8705524c5c4ca479a952f024 7ee8cb0b4fb7397ba08d009e0c8bf482270cc5771aa143966e5a469a09f613488030 c5b07ec6d722e3835adb5b2d8c44e95ffb13877dd2582866883535de3bb03d01753f 83ab87bb4f7a0297' ] ] @@ -3187,37 +3271,37 @@ * The same header parameters are used for both the signature and the counter signature. Size of binary file is 180 bytes 98( [ / protected / h'', / unprotected / { / countersign / 7:[ - / protected / h'a10126' / { - \ alg \ 1:-7 \ ECDSA 256 \ - } / , + / protected h'a10126' / << { + / alg / 1:-7 / ECDSA 256 / + } >>, / unprotected / { / kid / 4:'11' }, / signature / h'5ac05e289d5d0e1b0a7f048a5d2b643813ded50bc9e4 9220f4f7278f85f19d4a77d655c9d3b51e805a74b099e1e085aacd97fc29d72f887e 8802bb6650cceb2c' ] }, / payload / 'This is the content.', / signatures / [ [ - / protected / h'a10126' / { - \ alg \ 1:-7 \ ECDSA 256 \ - } / , + / protected h'a10126' / << { + / alg / 1:-7 / ECDSA 256 / + } >>, / unprotected / { / kid / 4:'11' }, / signature / h'e2aeafd40d69d19dfe6e52077c5d7ff4e408282cbefb 5d06cbf414af2e19d982ac45ac98b8544c908b4507de1e90b717c3d34816fe926a2b 98f53afd2fa0f30a' ] ] ] ) @@ -3226,34 +3310,34 @@ This example uses the following: * Signature Algorithm: ECDSA w/ SHA-256, Curve P-256 * There is a criticality marker on the "reserved" header parameter Size of binary file is 125 bytes 98( [ - / protected / h'a2687265736572766564f40281687265736572766564' / - { + / protected h'a2687265736572766564f40281687265736572766564' / + << { "reserved":false, - \ crit \ 2:[ + / crit / 2:[ "reserved" ] - } / , + } >>, / unprotected / {}, / payload / 'This is the content.', / signatures / [ [ - / protected / h'a10126' / { - \ alg \ 1:-7 \ ECDSA 256 \ - } / , + / protected h'a10126' / << { + / alg / 1:-7 / ECDSA 256 / + } >>, / unprotected / { / kid / 4:'11' }, / signature / h'3fc54702aa56e1b2cb20284294c9106a63f91bac658d 69351210a031d8fc7c5ff3e4be39445b1a3e83e1510d1aca2f2e8a7c081c7645042b 18aba9d1fad1bd9c' ] ] ] ) @@ -3262,23 +3346,23 @@ C.2.1. Single ECDSA Signature This example uses the following: * Signature Algorithm: ECDSA w/ SHA-256, Curve P-256 Size of binary file is 98 bytes 18( [ - / protected / h'a10126' / { - \ alg \ 1:-7 \ ECDSA 256 \ - } / , + / protected h'a10126' / << { + / alg / 1:-7 / ECDSA 256 / + } >>, / unprotected / { / kid / 4:'11' }, / payload / 'This is the content.', / signature / h'8eb33e4ca31d1c465ab05aac34cc6b23d58fef5c083106c4 d25a91aef0b0117e2af9a291aa32e14ab834dc56ed2a223444547e01f11d3b0916e5 a4c345cacb36' ] ) @@ -3288,33 +3372,33 @@ This example uses the following: * CEK: AES-GCM w/ 128-bit key * Recipient class: ECDH Ephemeral-Static, Curve P-256 Size of binary file is 151 bytes 96( [ - / protected / h'a10101' / { - \ alg \ 1:1 \ AES-GCM 128 \ - } / , + / protected h'a10101' / << { + / alg / 1:1 / AES-GCM 128 / + } >>, / unprotected / { / iv / 5:h'c9cf4df2fe6c632bf7886413' }, / ciphertext / h'7adbe2709ca818fb415f1e5df66f4e1a51053ba6d65a1a0 c52a357da7a644b8070a151b0', / recipients / [ [ - / protected / h'a1013818' / { - \ alg \ 1:-25 \ ECDH-ES + HKDF-256 \ - } / , + / protected h'a1013818' / << { + / alg / 1:-25 / ECDH-ES + HKDF-256 / + } >>, / unprotected / { / ephemeral / -1:{ / kty / 1:2, / crv / -1:1, / x / -2:h'98f50a4ff6c05861c8860d13a638ea56c3f5ad7590bbf bf054e1c7b4d91d6280', / y / -3:true }, / kid / 4:'meriadoc.brandybuck@buckland.example' }, @@ -3338,33 +3422,33 @@ - PartyU identity: "lighting-client" - PartyV identity: "lighting-server" - Supplementary Public Other: "Encryption Example 02" Size of binary file is 91 bytes 96( [ - / protected / h'a1010a' / { - \ alg \ 1:10 \ AES-CCM-16-64-128 \ - } / , + / protected h'a1010a' / << { + / alg / 1:10 / AES-CCM-16-64-128 / + } >>, / unprotected / { / iv / 5:h'89f52f65a1c580933b5261a76c' }, / ciphertext / h'753548a19b1307084ca7b2056924ed95f2e3b17006dfe93 1b687b847', / recipients / [ [ - / protected / h'a10129' / { - \ alg \ 1:-10 - } / , + / protected h'a10129' / << { + / alg / 1:-10 + } >>, / unprotected / { / salt / -20:'aabbccddeeffgghh', / kid / 4:'our-secret' }, / ciphertext / h'' ] ] ] ) @@ -3372,46 +3456,46 @@ This example uses the following: * CEK: AES-GCM w/ 128-bit key * Recipient class: ECDH Ephemeral-Static, Curve P-256 Size of binary file is 326 bytes 96( [ - / protected / h'a10101' / { - \ alg \ 1:1 \ AES-GCM 128 \ - } / , + / protected h'a10101' / << { + / alg / 1:1 / AES-GCM 128 / + } >>, / unprotected / { / iv / 5:h'c9cf4df2fe6c632bf7886413', / countersign / 7:[ / protected / h'a1013823' / { \ alg \ 1:-36 } / , / unprotected / { / kid / 4:'bilbo.baggins@hobbiton.example' }, / signature / h'00929663c8789bb28177ae28467e66377da12302d7f9 594d2999afa5dfa531294f8896f2b6cdf1740014f4c7f1a358e3a6cf57f4ed6fb02f cf8f7aa989f5dfd07f0700a3a7d8f3c604ba70fa9411bd10c2591b483e1d2c31de00 3183e434d8fba18f17a4c7e3dfa003ac1cf3d30d44d2533c4989d3ac38c38b71481c c3430c9d65e7ddff' ] }, / ciphertext / h'7adbe2709ca818fb415f1e5df66f4e1a51053ba6d65a1a0 c52a357da7a644b8070a151b0', / recipients / [ [ - / protected / h'a1013818' / { - \ alg \ 1:-25 \ ECDH-ES + HKDF-256 \ - } / , + / protected h'a1013818' / << { + / alg / 1:-25 / ECDH-ES + HKDF-256 / + } >> , / unprotected / { / ephemeral / -1:{ / kty / 1:2, / crv / -1:1, / x / -2:h'98f50a4ff6c05861c8860d13a638ea56c3f5ad7590bbf bf054e1c7b4d91d6280', / y / -3:true }, / kid / 4:'meriadoc.brandybuck@buckland.example' }, @@ -3428,23 +3512,23 @@ * CEK: AES-GCM w/ 128-bit key * Recipient class: ECDH static-Static, Curve P-256 with AES Key Wrap * Externally Supplied AAD: h'0011bbcc22dd44ee55ff660077' Size of binary file is 173 bytes 96( [ - / protected / h'a10101' / { - \ alg \ 1:1 \ AES-GCM 128 \ - } / , + / protected h'a10101' / << { + / alg / 1:1 / AES-GCM 128 / + } >> , / unprotected / { / iv / 5:h'02d1f7e6f26c43d4868d87ce' }, / ciphertext / h'64f84d913ba60a76070a9a48f26e97e863e28529d8f5335 e5f0165eee976b4a5f6c6f09d', / recipients / [ [ / protected / h'a101381f' / { \ alg \ 1:-32 \ ECHD-SS+A128KW \ } / , @@ -3464,46 +3548,46 @@ C.4.1. Simple Encrypted Message This example uses the following: * CEK: AES-CCM w/ 128-bit key and a 64-bit tag Size of binary file is 52 bytes 16( [ - / protected / h'a1010a' / { - \ alg \ 1:10 \ AES-CCM-16-64-128 \ - } / , + / protected h'a1010a' / << { + / alg / 1:10 / AES-CCM-16-64-128 / + } >> , / unprotected / { / iv / 5:h'89f52f65a1c580933b5261a78c' }, / ciphertext / h'5974e1b99a3a4cc09a659aa2e9e7fff161d38ce71cb45ce 460ffb569' ] ) C.4.2. Encrypted Message with a Partial IV This example uses the following: * CEK: AES-CCM w/ 128-bit key and a 64-bit tag * Prefix for IV is 89F52F65A1C580933B52 Size of binary file is 41 bytes 16( [ - / protected / h'a1010a' / { - \ alg \ 1:10 \ AES-CCM-16-64-128 \ - } / , + / protected h'a1010a' / << { + / alg / 1:10 / AES-CCM-16-64-128 / + } >> , / unprotected / { / partial iv / 6:h'61a7' }, / ciphertext / h'252a8911d465c125b6764739700f0141ed09192de139e05 3bd09abca' ] ) C.5. Examples of MACed Messages @@ -3511,23 +3595,23 @@ This example uses the following: * MAC: AES-CMAC, 256-bit key, truncated to 64 bits * Recipient class: direct shared secret Size of binary file is 57 bytes 97( [ - / protected / h'a1010f' / { - \ alg \ 1:15 \ AES-CBC-MAC-256//64 \ - } / , + / protected h'a1010f' / << { + / alg / 1:15 / AES-CBC-MAC-256//64 / + } >> , / unprotected / {}, / payload / 'This is the content.', / tag / h'9e1226ba1f81b848', / recipients / [ [ / protected / h'', / unprotected / { / alg / 1:-6 / direct /, / kid / 4:'our-secret' }, @@ -3542,32 +3626,32 @@ This example uses the following: * MAC: HMAC w/SHA-256, 256-bit key * Recipient class: ECDH key agreement, two static keys, HKDF w/ context structure Size of binary file is 214 bytes 97( [ - / protected / h'a10105' / { - \ alg \ 1:5 \ HMAC 256//256 \ - } / , + / protected h'a10105' / << { + / alg / 1:5 / HMAC 256//256 / + } >> , / unprotected / {}, / payload / 'This is the content.', / tag / h'81a03448acd3d305376eaa11fb3fe416a955be2cbe7ec96f012c99 4bc3f16a41', / recipients / [ [ - / protected / h'a101381a' / { - \ alg \ 1:-27 \ ECDH-SS + HKDF-256 \ - } / , + / protected h'a101381a' / << { + / alg / 1:-27 / ECDH-SS + HKDF-256 / + } >> , / unprotected / { / static kid / -3:'peregrin.took@tuckborough.example', / kid / 4:'meriadoc.brandybuck@buckland.example', / U nonce / -22:h'4d8553e7e74f3c6a3a9dd3ef286a8195cbf8a23d 19558ccfec7d34b824f42d92bd06bd2c7f0271f0214e141fb779ae2856abf585a583 68b017e7f2a9e5ce4db5' }, / ciphertext / h'' ] ] @@ -3578,23 +3662,23 @@ This example uses the following: * MAC: AES-MAC, 128-bit key, truncated to 64 bits * Recipient class: AES Key Wrap w/ a pre-shared 256-bit key Size of binary file is 109 bytes 97( [ - / protected / h'a1010e' / { - \ alg \ 1:14 \ AES-CBC-MAC-128//64 \ - } / , + / protected h'a1010e' / << { + / alg / 1:14 / AES-CBC-MAC-128//64 / + } >> , / unprotected / {}, / payload / 'This is the content.', / tag / h'36f5afaf0bab5d43', / recipients / [ [ / protected / h'', / unprotected / { / alg / 1:-5 / A256KW /, / kid / 4:'018c0ae5-4d9b-471b-bfd6-eef314bc7037' }, @@ -3614,32 +3698,32 @@ * Recipient class: Uses three different methods 1. ECDH Ephemeral-Static, Curve P-521, AES Key Wrap w/ 128-bit key 2. AES Key Wrap w/ 256-bit key Size of binary file is 309 bytes 97( [ - / protected / h'a10105' / { - \ alg \ 1:5 \ HMAC 256//256 \ - } / , + / protected h'a10105' / << { + / alg / 1:5 / HMAC 256//256 / + } >> , / unprotected / {}, / payload / 'This is the content.', / tag / h'bf48235e809b5c42e995f2b7d5fa13620e7ed834e337f6aa43df16 1e49e9323e', / recipients / [ [ - / protected / h'a101381c' / { - \ alg \ 1:-29 \ ECHD-ES+A128KW \ - } / , + / protected h'a101381c' / << { + / alg / 1:-29 / ECHD-ES+A128KW / + } >> , / unprotected / { / ephemeral / -1:{ / kty / 1:2, / crv / -1:3, / x / -2:h'0043b12669acac3fd27898ffba0bcd2e6c366d53bc4db 71f909a759304acfb5e18cdc7ba0b13ff8c7636271a6924b1ac63c02688075b55ef2 d613574e7dc242f79c3', / y / -3:true }, / kid / 4:'bilbo.baggins@hobbiton.example' @@ -3666,23 +3750,23 @@ This example uses the following: * MAC: AES-CMAC, 256-bit key, truncated to 64 bits * Recipient class: direct shared secret Size of binary file is 37 bytes 17( [ - / protected / h'a1010f' / { - \ alg \ 1:15 \ AES-CBC-MAC-256//64 \ - } / , + / protected h'a1010f' / << { + / alg / 1:15 / AES-CBC-MAC-256//64 / + } >> , / unprotected / {}, / payload / 'This is the content.', / tag / h'726043745027214f' ] ) Note that this example uses the same inputs as Appendix C.5.1. C.7. COSE Keys @@ -3839,19 +3923,19 @@ The following individuals are to blame for getting me started on this project in the first place: Richard Barnes, Matt Miller, and Martin Thomson. The initial version of the specification was based to some degree on the outputs of the JOSE and S/MIME working groups. The following individuals provided input into the final form of the document: Carsten Bormann, John Bradley, Brain Campbell, Michael B. - Jones, Ilari Liusvaara, Francesca Palombini, Ludwig Seitz, and Goran - Selander. + Jones, Ilari Liusvaara, Francesca Palombini, Ludwig Seitz, and + Göran Selander. Author's Address Jim Schaad August Cellars Email: ietf@augustcellars.com