Network Working Group J. Schaad Internet-Draft August Cellars Intended status: Informational 17 November 2019 Expires: 20 May 2020 CBOR Object Signing and Encryption (COSE): Additional Algorithms draft-schaad-cose-more-algs-00 Abstract The CBOR Object Signing and Encryption (COSE) syntax [I-D.ietf-cose-rfc8152bis-struct] allows for adding additional algorithms to the registries. This document adds one additional key wrap algorithm to the registry using the AES Wrap with Padding Algorithm [RFC5649]. Contributing to this document This note is to be removed before publishing as an RFC. The source for this draft is being maintained in GitHub. Suggested changes should be submitted as pull requests at https://github.com/ cose-wg/X509 Editorial changes can be managed in GitHub, but any substantial issues need to be discussed on the COSE mailing list. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. 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 20 May 2020. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. Schaad Expires 20 May 2020 [Page 1] Internet-Draft COSE Algorithms November 2019 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 and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Terminology . . . . . . . . . . . . . . . . 2 1.2. Open Issues . . . . . . . . . . . . . . . . . . . . . . . 2 2. AES Key Wrap with Padding . . . . . . . . . . . . . . . . . . 3 2.1. Security Considerations for AES-KW with Padding . . . . . 3 3. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Normative References . . . . . . . . . . . . . . . . . . 4 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction The CBOR Object Signing and Encryption (COSE) syntax [I-D.ietf-cose-rfc8152bis-struct] is defined to have an object based set of security primatives using CBOR [I-D.ietf-cbor-7049bis] for use in constrained environments. COSE has algorithm agility so that documents like this one can register algorithms which are needed. In this document we add the AES Wrap with Padding algorithm to the registry and describe how to use it. 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. 1.2. Open Issues This section is to be removed before publishing as an RFC. * A desire has been expressed to all for the use of AES Key Wrap with Padding as a content encryption algorithm. This is not compatible with the requirement that all content encryption algorithms "support authentication of both the content and additional data." AES Key Wrap is an AE not an AEAD algorithm. Schaad Expires 20 May 2020 [Page 2] Internet-Draft COSE Algorithms November 2019 2. AES Key Wrap with Padding The AES Key Wrap with Padding is defined in [RFC5649]. This algorithm uses an AES key to wrap a value that is a multiple of 8 bits. As such, it can be used to wrap not only the key sizes for the content encryption algorithms, but additionally it can be used to encrypt off size keys that can be used with the keyed hash functions or key derivation functions. The algorithm uses a single fixed parameter, the initial value. This value is fixed in section 3 of [RFC5649], this is a different value from that used for the AES Key Wrap algorithm of [RFC3394]. There are no public parameters that very on a per-invocation bases. This algorithm does not support additional data and thus the protected header field MUST be empty. When using a COSE key for this algorithm, the following checks are made: * The 'kty' field MUST be present, and it MUST be 'Symmetric'. * If the 'alg' field is present, it MUST match the AES Key Wrap algorithm being used. * If the 'key_ops' field is present, it MUST include 'encrypt' or 'wrap key' when encrypting. * If the 'key_ops' field is present, it MUST include 'decrypt' or 'unwrap key' when decrypting. +------------+-------+----------+------------------------+ | Name | Value | Key Size | Description | +============+=======+==========+========================+ | A128KW-Pad | TBD1 | 128 | AES Key Wrap w/padding | | | | | and a 128-bit key | +------------+-------+----------+------------------------+ | A192KW-Pad | TBD2 | 192 | AES Key Wrap w/padding | | | | | and a 192-bit key | +------------+-------+----------+------------------------+ | A256KW-Pad | TBD3 | 256 | AES Key Wrap w/padding | | | | | and a 256-bit key | +------------+-------+----------+------------------------+ Table 1: AES Key Wrap Algorithm Values 2.1. Security Considerations for AES-KW with Padding The shared secret needs to have some method to be regularly updated over time. The shared secret is the basis of trust. Schaad Expires 20 May 2020 [Page 3] Internet-Draft COSE Algorithms November 2019 3. References 3.1. Normative References [I-D.ietf-cose-rfc8152bis-struct] Schaad, J., "CBOR Object Signing and Encryption (COSE): Structures and Process", Work in Progress, Internet-Draft, draft-ietf-cose-rfc8152bis-struct-06, 11 September 2019, . [I-D.ietf-cbor-7049bis] Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", Work in Progress, Internet-Draft, draft-ietf-cbor-7049bis-07, 25 August 2019, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC5649] Housley, R. and M. Dworkin, "Advanced Encryption Standard (AES) Key Wrap with Padding Algorithm", RFC 5649, DOI 10.17487/RFC5649, September 2009, . [RFC3394] Schaad, J. and R. Housley, "Advanced Encryption Standard (AES) Key Wrap Algorithm", RFC 3394, DOI 10.17487/RFC3394, September 2002, . Author's Address Jim Schaad August Cellars Email: ietf@augustcellars.com Schaad Expires 20 May 2020 [Page 4]