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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.




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   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.



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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.




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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,
              <https://tools.ietf.org/html/draft-ietf-cose-rfc8152bis-
              struct-06>.

   [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,
              <https://tools.ietf.org/html/draft-ietf-cbor-7049bis-07>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC5649]  Housley, R. and M. Dworkin, "Advanced Encryption Standard
              (AES) Key Wrap with Padding Algorithm", RFC 5649,
              DOI 10.17487/RFC5649, September 2009,
              <https://www.rfc-editor.org/info/rfc5649>.

   [RFC3394]  Schaad, J. and R. Housley, "Advanced Encryption Standard
              (AES) Key Wrap Algorithm", RFC 3394, DOI 10.17487/RFC3394,
              September 2002, <https://www.rfc-editor.org/info/rfc3394>.

Author's Address

   Jim Schaad
   August Cellars

   Email: ietf@augustcellars.com










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