CBOR Object Signing and Encryption (COSE): Hash Algorithms

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Document Type Active Internet-Draft (cose WG)
Author Jim Schaad 
Last updated 2019-03-11
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Network Working Group                                          J. Schaad
Internet-Draft                                            August Cellars
Intended status: Informational                             11 March 2019
Expires: 12 September 2019

       CBOR Object Signing and Encryption (COSE): Hash Algorithms


   The CBOR Object Signing and Encryption (COSE) syntax
   [I-D.ietf-cose-rfc8152bis-struct] does not define any direct methods
   for using hash algorithms.  There are however circumstances where
   hash algorithms are used: Indirect signatures where the hash of one
   or more contents are signed.  X.509 certificate or other object
   identification by the use of a thumbprint.  This document defines a
   set of hash algorithms that are identified by COSE Algorithm

Contributing to this document

   The source for this draft is being maintained in GitHub.  Suggested
   changes should be submitted as pull requests at TBD.  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
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   This Internet-Draft will expire on 12 September 2019.

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   Copyright (c) 2019 IETF Trust and the persons identified as the
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Table of Contents

   1.  Introduction
       1.1.  Requirements Terminology
       1.2.  Open Issues
   2.  Hash Algorithm Identifiers
       2.1.  SHA-1 Hash Algorithm
       2.2.  SHA-2 Hash Algorithms
       2.3.  SHAKE Algorithms
   3.  IANA Considerations
       3.1.  COSE Algorithm Registry
   4.  Security Considerations
   5.  Normative References
   6.  Informative References
   Author's Address

1.  Introduction

   The CBOR Object Signing and Encryption (COSE) syntax does not define
   any direct methods for the use of hash algorithms.  It also does not
   define a structure syntax that is used to encode a digested object
   structure along the lines of the DigestedData ASN.1 structure in
   [CMS].  This omission was intentional as a structure consisting of
   jut a digest identifier, the content, and a digest value does not by
   itself provide any strong security service.  Additional, an
   application is going to be better off defining this type of structure
   so that it can add any additional data that needs to be hashed as
   well as methods of obtaining the data.

   While the above is true, there are some cases where having some
   standard hash algorithms defined for COSE with a common identifier
   makes a great deal of sense.  Two of the cases where these are going
   to be used are:

   *  Indirect signing of content, and

   *  Object identification.

   Indirect signing of content is a paradigm where the content is not
   directly signed, but instead a hash of the content is computed and
   that hash value, along with the hash algorithm, is included in the
   content that will be signed.  Doing indirect signing allows for the a
   signature to be validated without first downloading all of the
   content associated with the signature.  This capability can be of
   even grater importance in a constrained environment as not all of the
   content signed may be needed by the device.

   The use of hashes to identify objects is something that has been very
   common.  One of the primary things that has been identified by a hash
   function for secure message is a certificate.  Two examples of this
   can be found in [ESS] and the newly defined COSE equivalents in

1.1.  Requirements Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
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