--- 1/draft-ietf-cose-hash-algs-08.txt 2020-09-14 10:13:11.320828717 -0700 +++ 2/draft-ietf-cose-hash-algs-09.txt 2020-09-14 10:13:11.344829322 -0700 @@ -1,18 +1,18 @@ Network Working Group J. Schaad Internet-Draft August Cellars -Intended status: Informational 29 July 2020 -Expires: 30 January 2021 +Intended status: Informational September 14, 2020 +Expires: March 18, 2021 CBOR Object Signing and Encryption (COSE): Hash Algorithms - draft-ietf-cose-hash-algs-08 + draft-ietf-cose-hash-algs-09 Abstract 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, such as indirect signatures where the hash of one or more contents are signed, and X.509 certificate or other object identification by the use of a fingerprint. This document defines a set of hash algorithms that are identified by COSE @@ -35,21 +35,21 @@ 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 30 January 2021. + This Internet-Draft will expire on March 18, 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 @@ -145,38 +145,39 @@ A hash function is a map from one, normally large, bit string to a second, usually smaller, bit string. As the number of possible input values is far greater than the number of possible output values, it is inevitable that there are going to be collisions. The trick is to make sure that it is difficult to find two values that are going to map to the same output value. A "Collision Attack" is one where an attacker can find two different messages that have the same hash value. A hash function that is susceptible to practical collision attacks, SHOULD NOT be used for a cryptographic purpose. The discovery of theoretical collision attacks against a given hash - function SHOULD trigger a review of the continued suitability of the - algorithm if alternatives are available and migration is viable. The - only reason why such a hash function is used is when there is - absolutely no other choice (e.g. a Hardware Security Module (HSM) - that cannot be replaced), and only after looking at the possible - security issues. Cryptographic purposes would include the creation - of signatures or the use of hashes for indirect signatures. These - functions may still be usable for non-cryptographic purposes. + function SHOULD trigger protocol maintainers and users to do a review + of the continued suitability of the algorithm if alternatives are + available and migration is viable. The only reason why such a hash + function is used is when there is absolutely no other choice (e.g. a + Hardware Security Module (HSM) that cannot be replaced), and only + after looking at the possible security issues. Cryptographic + purposes would include the creation of signatures or the use of + hashes for indirect signatures. These functions may still be usable + for non-cryptographic purposes. An example of a non-cryptographic use of a hash is for filtering from - a collection of values to find a set of possible candidates, the - candidates can then be check to see if they can successfully be used. - A simple example of this is the classic fingerprint of a certificate. - If the fingerprint is used to verify that it is the correct - certificate, then that usage is a cryptographic one and is subject to - the warning above about collision attack. If, however, the - fingerprint is used to sort through a collection of certificates to - find those that might be used for the purpose of verifying a + a collection of values to find a set of possible candidates; the + candidates can then be checked to see if they can successfully be + used. A simple example of this is the classic fingerprint of a + certificate. If the fingerprint is used to verify that it is the + correct certificate, then that usage is a cryptographic one and is + subject to the warning above about collision attack. If, however, + the fingerprint is used to sort through a collection of certificates + to find those that might be used for the purpose of verifying a signature, a simple filter capability is sufficient. In this case, one still needs to confirm that the public key validates the signature (and the certificate is trusted), and all certificates that don't contain a key that validates the signature can be discarded as false positives. To distinguish between these two cases, a new value in the recommended column of the COSE Algorithms registry is to be added. "Filter Only" indicates that the only purpose of a hash function should be to filter results and it is not intended for applications @@ -237,36 +238,36 @@ The SHA-1 hash algorithm [RFC3174] was designed by the United States National Security Agency and published in 1995. Since that time a large amount of cryptographic analysis has been applied to this algorithm and a successful collision attack has been created ([SHA-1-collision]). The IETF formally started discouraging the use of SHA-1 with the publishing of [RFC6194]. Despite the above, there are still times where SHA-1 needs to be used and therefore it makes sense to assign a codepoint for the use of this hash algorithm. Some of these situations are with historic HSMs - where only SHA-1 is implemented, other situations are where the SHA-1 + where only SHA-1 is implemented; other situations are where the SHA-1 value is used for the purpose of filtering and thus the collision resistance property is not needed. Because of the known issues for SHA-1 and the fact that it should no longer be used, the algorithm will be registered with the recommendation of "Filter Only". This provides guidance about when the algorithm is safe for use, while discouraging usage where it is not safe. - The COSE capabilities for these algorithms is an empty array. + The COSE capabilities for this algorithm is an empty array. +=====+======+=============+==============+===========+=============+ |Name |Value | Description | Capabilities | Reference | Recommended | +=====+======+=============+==============+===========+=============+ - |SHA-1| TBD6 | SHA-1 Hash | [] | [This | Filter Only | + |SHA-1| -14 | SHA-1 Hash | [] | [This | Filter Only | | | | | | Document] | | +-----+------+-------------+--------------+-----------+-------------+ Table 1: SHA-1 Hash Algorithm 3.2. SHA-2 Hash Algorithms The family of SHA-2 hash algorithms [FIPS-180-4] was designed by the United States National Security Agency and published in 2001. Since that time some additional algorithms have been added to the original @@ -275,21 +276,21 @@ that time, the SHA-2 algorithms are still broadly used. There are a number of different parameters for the SHA-2 hash functions. The set of hash functions which have been chosen for inclusion in this document are based on those different parameters and some of the trade-offs involved. * *SHA-256/64* provides a truncated hash. The length of the truncation is designed to allow for smaller transmission size. The trade-off is that the odds that a collision will occur - increase proportionally. Use of this hash function needs analyze + increase proportionally. Use of this hash function needs analysis of the potential problems with having a collision occur, or must be limited to where the function of the hash is non-cryptographic. The latter is the case for [I-D.ietf-cose-x509]. The hash value is used to select possible certificates and, if there are multiple choices remaining then, each choice can be tested by using the public key. * *SHA-256* is probably the most common hash function used currently. SHA-256 is an efficient hash algorithm for 32-bit @@ -300,74 +301,72 @@ * *SHA-512/256* provides a hash function that runs more efficiently on 64-bit hardware, but offers the same security levels as SHA- 256. The COSE capabilities array for these algorithms is empty. +===========+=====+===========+==============+=========+============+ | Name |Value|Description| Capabilities |Reference|Recommended | +===========+=====+===========+==============+=========+============+ - |SHA-256/64 |TBD1 | SHA-2 | [] | [This |Filter Only | + |SHA-256/64 | -15 | SHA-2 | [] | [This |Filter Only | | | | 256-bit | |Document]| | | | | Hash | | | | | | | truncated | | | | | | |to 64-bits | | | | +-----------+-----+-----------+--------------+---------+------------+ - | SHA-256 |TBD2 | SHA-2 | [] | [This | Yes | + | SHA-256 | -16 | SHA-2 | [] | [This | Yes | | | | 256-bit | |Document]| | | | | Hash | | | | +-----------+-----+-----------+--------------+---------+------------+ - | SHA-384 |TBD3 | SHA-2 | [] | [This | Yes | + | SHA-384 | -43 | SHA-2 | [] | [This | Yes | | | | 384-bit | |Document]| | | | | Hash | | | | +-----------+-----+-----------+--------------+---------+------------+ - | SHA-512 |TBD4 | SHA-2 | [] | [This | Yes | + | SHA-512 | -44 | SHA-2 | [] | [This | Yes | | | | 512-bit | |Document]| | | | | Hash | | | | +-----------+-----+-----------+--------------+---------+------------+ - |SHA-512/256|TBD5 | SHA-2 | [] | [This | Yes | + |SHA-512/256| -17 | SHA-2 | [] | [This | Yes | | | | 512-bit | |Document]| | | | | Hash | | | | | | | truncated | | | | | | |to 256-bits| | | | +-----------+-----+-----------+--------------+---------+------------+ Table 2: SHA-2 Hash Algorithms 3.3. SHAKE Algorithms The family of SHA-3 hash algorithms [FIPS-202] was the result of a competition run by NIST. The pair of algorithms known as SHAKE-128 and SHAKE-256 are the instances of SHA-3 that are currently being standardized in the IETF. This is the reason for including these algorithms in this document. The SHA-3 hash algorithms have a significantly different structure - than the SHA-2 hash algorithms. One of the benefits of this - difference is that when computing a shorter SHAKE hash value, the - value is not a prefix of the result of computing the longer hash. + than the SHA-2 hash algorithms. Unlike the SHA-2 hash functions, no algorithm identifier is created for shorter lengths. The length of the hash value stored is 256-bits for SHAKE-128 and 512-bits for SHAKE-256. The COSE capabilities array for these algorithms is empty. +========+=====+=============+==============+=========+=============+ | Name |Value| Description | Capabilities |Reference| Recommended | +========+=====+=============+==============+=========+=============+ - |SHAKE128|TBD10| SHAKE-128 | [] | [This | Yes | + |SHAKE128| -18 | SHAKE-128 | [] | [This | Yes | | | |256-bit Hash | |Document]| | | | | Value | | | | +--------+-----+-------------+--------------+---------+-------------+ - |SHAKE256|TBD11| SHAKE-256 | [] | [This | Yes | + |SHAKE256| -45 | SHAKE-256 | [] | [This | Yes | | | |512-bit Hash | |Document]| | | | | Value | | | | +--------+-----+-------------+--------------+---------+-------------+ Table 3: SHAKE Hash Functions 4. IANA Considerations The IANA actions in [I-D.ietf-cose-rfc8152bis-struct] and [I-D.ietf-cose-rfc8152bis-algs] need to be executed before the @@ -380,24 +379,24 @@ Algorithms" registry. * The SHA-1 hash function found in Table 1. * The set of SHA-2 hash functions found in Table 2. * The set of SHAKE hash functions found in Table 3. Many of the hash values produced are relatively long and as such the use of a two byte algorithm identifier seems reasonable. SHA-1 is - tagged as deprecated and thus a longer algorithm identifier is + tagged as 'Filter Only' and thus a longer algorithm identifier is appropriate even though it is a shorter hash value. - In addition, IANA is to add the value of 'Filter Only' to the set of + IANA is requested to add the value of 'Filter Only' to the set of legal values for the 'Recommended' column. This value is only to be used for hash functions and indicates that it is not to be used for purposes which require collision resistance. IANA is requested to add this document to the reference section for this table due to this addition. 5. Security Considerations Protocols need to perform a careful analysis of the properties of a hash function that are needed and how they map onto the possible @@ -425,23 +424,23 @@ 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, . [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-11, 1 July 2020, + draft-ietf-cose-rfc8152bis-struct-12, August 24, 2020, . + struct-12>. [FIPS-180-4] National Institute of Standards and Technology, "Secure Hash Standard", FIPS PUB 180-4, August 2015. [FIPS-202] National Institute of Standards and Technology, "SHA-3 Standard: Permutation-Based Hash and Extendable-Output Functions", FIPS PUB 202, August 2015. [RFC3174] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1 @@ -455,41 +454,41 @@ . [ESS] Hoffman, P., Ed., "Enhanced Security Services for S/MIME", RFC 2634, DOI 10.17487/RFC2634, June 1999, . [I-D.ietf-cose-x509] Schaad, J., "CBOR Object Signing and Encryption (COSE): Header parameters for carrying and referencing X.509 certificates", Work in Progress, Internet-Draft, draft- - ietf-cose-x509-06, 9 March 2020, + ietf-cose-x509-06, March 9, 2020, . [RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security Considerations for the SHA-0 and SHA-1 Message-Digest Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011, . [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-11, 1 July 2020, + draft-ietf-cose-rfc8152bis-algs-11, July 1, 2020, . [I-D.ietf-suit-manifest] Moran, B., Tschofenig, H., Birkholz, H., and K. Zandberg, "A Concise Binary Object Representation (CBOR)-based Serialization Format for the Software Updates for Internet of Things (SUIT) Manifest", Work in Progress, Internet- - Draft, draft-ietf-suit-manifest-09, 13 July 2020, + Draft, draft-ietf-suit-manifest-09, July 13, 2020, . [BCP201] Housley, R., "Guidelines for Cryptographic Algorithm Agility and Selecting Mandatory-to-Implement Algorithms", BCP 201, RFC 7696, November 2015. [SHA-1-collision] Stevens, M., Bursztein, E., Karpman, P., Albertini, A.,