draft-ietf-cose-hash-algs-02.txt   draft-ietf-cose-hash-algs-03.txt 
Network Working Group J. Schaad Network Working Group J. Schaad
Internet-Draft August Cellars Internet-Draft August Cellars
Intended status: Informational 4 November 2019 Intended status: Informational 9 March 2020
Expires: 7 May 2020 Expires: 10 September 2020
CBOR Object Signing and Encryption (COSE): Hash Algorithms CBOR Object Signing and Encryption (COSE): Hash Algorithms
draft-ietf-cose-hash-algs-02 draft-ietf-cose-hash-algs-03
Abstract Abstract
The CBOR Object Signing and Encryption (COSE) syntax The CBOR Object Signing and Encryption (COSE) syntax
[I-D.ietf-cose-rfc8152bis-struct] does not define any direct methods [I-D.ietf-cose-rfc8152bis-struct] does not define any direct methods
for using hash algorithms. There are however circumstances where for using hash algorithms. There are however circumstances where
hash algorithms are used: Indirect signatures where the hash of one hash algorithms are used: Indirect signatures where the hash of one
or more contents are signed. X.509 certificate or other object or more contents are signed. X.509 certificate or other object
identification by the use of a thumbprint. This document defines a identification by the use of a fingerprint. This document defines a
set of hash algorithms that are identified by COSE Algorithm set of hash algorithms that are identified by COSE Algorithm
Identifiers. Identifiers.
Contributing to this document Contributing to this document
This note is to be removed before publishing as an RFC. This note is to be removed before publishing as an RFC.
The source for this draft is being maintained in GitHub. Suggested The source for this draft is being maintained in GitHub. Suggested
changes should be submitted as pull requests at https://github.com/ changes should be submitted as pull requests at https://github.com/
cose-wg/X509 Editorial changes can be managed in GitHub, but any cose-wg/X509 Editorial changes can be managed in GitHub, but any
skipping to change at page 1, line 46 skipping to change at page 1, line 46
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on 7 May 2020. This Internet-Draft will expire on 10 September 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/ Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text extracted from this document must include Simplified BSD License text
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provided without warranty as described in the Simplified BSD License. provided without warranty as described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Terminology . . . . . . . . . . . . . . . . 3 1.1. Requirements Terminology . . . . . . . . . . . . . . . . 3
1.2. Open Issues . . . . . . . . . . . . . . . . . . . . . . . 3
2. Hash Algorithm Usage . . . . . . . . . . . . . . . . . . . . 3 2. Hash Algorithm Usage . . . . . . . . . . . . . . . . . . . . 3
2.1. Example CBOR hash structure . . . . . . . . . . . . . . . 4 2.1. Example CBOR hash structure . . . . . . . . . . . . . . . 4
3. Hash Algorithm Identifiers . . . . . . . . . . . . . . . . . 5 3. Hash Algorithm Identifiers . . . . . . . . . . . . . . . . . 5
3.1. SHA-1 Hash Algorithm . . . . . . . . . . . . . . . . . . 5 3.1. SHA-1 Hash Algorithm . . . . . . . . . . . . . . . . . . 5
3.2. SHA-2 Hash Algorithms . . . . . . . . . . . . . . . . . . 6 3.2. SHA-2 Hash Algorithms . . . . . . . . . . . . . . . . . . 6
3.3. SHAKE Algorithms . . . . . . . . . . . . . . . . . . . . 7 3.3. SHAKE Algorithms . . . . . . . . . . . . . . . . . . . . 7
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
4.1. COSE Algorithm Registry . . . . . . . . . . . . . . . . . 8 4.1. COSE Algorithm Registry . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. Normative References . . . . . . . . . . . . . . . . . . . . 9 6. Normative References . . . . . . . . . . . . . . . . . . . . 9
7. Informative References . . . . . . . . . . . . . . . . . . . 9 7. Informative References . . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
The CBOR Object Signing and Encryption (COSE) syntax does not define The CBOR Object Signing and Encryption (COSE) syntax does not define
any direct methods for the use of hash algorithms. It also does not 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 define a structure syntax that is used to encode a digested object
structure along the lines of the DigestedData ASN.1 structure in structure along the lines of the DigestedData ASN.1 structure in
[CMS]. This omission was intentional as a structure consisting of [CMS]. This omission was intentional as a structure consisting of
just a digest identifier, the content, and a digest value does not by just a digest identifier, the content, and a digest value does not by
skipping to change at page 3, line 34 skipping to change at page 3, line 32
[I-D.ietf-cose-x509]. [I-D.ietf-cose-x509].
1.1. Requirements Terminology 1.1. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
1.2. Open Issues
This section is to be removed before publishing as an RFC.
* No Open Issues
2. Hash Algorithm Usage 2. Hash Algorithm Usage
As noted in the previous section, hash functions can be used for a As noted in the previous section, hash functions can be used for a
variety of purposes. Some of these purposes require that a hash variety of purposes. Some of these purposes require that a hash
function be cryptographically strong, these include direct and function be cryptographically strong, these include direct and
indirect signatures. That is, using the hash as part of the indirect signatures. That is, using the hash as part of the
signature or using the hash as part of the body to be signed. Other signature or using the hash as part of the body to be signed. Other
uses of hash functions do not require the same level of strength. uses of hash functions do not require the same level of strength.
This document contains some hash functions that are not designed to This document contains some hash functions that are not designed to
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used is when there is absolutely no other choice (e.g. a Hardware used is when there is absolutely no other choice (e.g. a Hardware
Security Module (HSM) that cannot be replaced), and only after Security Module (HSM) that cannot be replaced), and only after
looking at the possible security issues. Cryptographic purposes looking at the possible security issues. Cryptographic purposes
would include the creation of signatures or the use of hashes for would include the creation of signatures or the use of hashes for
indirect signatures. These functions may still be usable for non- indirect signatures. These functions may still be usable for non-
cryptographic purposes. cryptographic purposes.
An example of a non-cryptographic use of a hash is for filtering from An example of a non-cryptographic use of a hash is for filtering from
a collection of values to find possible candidates that can later be a collection of values to find possible candidates that can later be
checked to see if they are the correct one. A simple example of this checked to see if they are the correct one. A simple example of this
is the classic thumbprint of a certificate. If the thumbprint is is the classic fingerprint of a certificate. If the fingerprint is
used to verify that it is the correct certificate, then that usage is used to verify that it is the correct certificate, then that usage is
subject to a collision attack as above. If however, the thumbprint subject to a collision attack as above. If however, the fingerprint
is used to sort through a collection of certificates to find those 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 that might be used for the purpose of verifying a signature, a simple
filter capability is sufficient. In this case, one still needs to filter capability is sufficient. In this case, one still needs to
validate that the public key validates the signature (and the validate that the public key validates the signature (and the
certificate is trusted), and all certificates that don't contain a certificate is trusted), and all certificates that don't contain a
key that validates the signature can be discarded as false positives. key that validates the signature can be discarded as false positives.
To distinguish between these two cases, a new value in the To distinguish between these two cases, a new value in the
recommended column of the COSE Algorithms registry is to be added. recommended column of the COSE Algorithms registry is to be added.
"Filter Only" indicates that the only purpose of a hash function "Filter Only" indicates that the only purpose of a hash function
skipping to change at page 5, line 13 skipping to change at page 5, line 6
* The hash algorithm identifier. * The hash algorithm identifier.
* The hash value. * The hash value.
* A pointer to the value that was hashed, this could be a pointer to * A pointer to the value that was hashed, this could be a pointer to
a file, an object that can be obtained from the network, or a a file, an object that can be obtained from the network, or a
pointer to someplace in the message, or something very application pointer to someplace in the message, or something very application
specific. specific.
* Additional data, this can be something as simple as a random value * Additional data, this can be something as simple as a random value
to make finding hash collisions slightly harder as the value to make finding hash collisions slightly harder (as the value
handed to the application cannot have been selected to have a handed to the application cannot have been selected to have a
collision, or as complicated as a set of processing instructions collision), or as complicated as a set of processing instructions
that are used with the object that is pointed to. The additional that are used with the object that is pointed to. The additional
data can be dealt with in a number of ways, prepending or data can be dealt with in a number of ways, prepending or
appending to the content, but it is strongly suggested to it appending to the content, but it is strongly suggested to it
either be a fixed known size, or the lengths of the pieces being either be a fixed known size, or the lengths of the pieces being
hashed be included. (Encoding as a CBOR array accomplished this hashed be included. (Encoding as a CBOR array accomplished this
requirement.) requirement.)
An example of a structure which permits all of the above fields to An example of a structure which permits all of the above fields to
exist would look like the following. exist would look like the following.
COSE_Hash_V = ( 1 : int / tstr, # Algorithm identifier 2 : bstr, # Hash value 3 : tstr ?, # Location of object hashed 4 : any ? # object containing other details and things ) COSE_Hash_V = (
1 : int / tstr, # Algorithm identifier
2 : bstr, # Hash value
3 : tstr ?, # Location of object hashed
4 : any ? # object containing other details and things
)
An alternate structure that could be used for situations where one is An alternate structure that could be used for situations where one is
searching a group of objects for a match. In this case, the location searching a group of objects for a match. In this case, the location
would not be needed and adding extra data to the hash would be would not be needed and adding extra data to the hash would be
counterproductive. This results in a structure that looks like this: counterproductive. This results in a structure that looks like this:
COSE_Hash_Find = [ hashAlg : int / tstr, hashValue : bstr ] COSE_Hash_Find = [
hashAlg : int / tstr,
hashValue : bstr
]
3. Hash Algorithm Identifiers 3. Hash Algorithm Identifiers
3.1. SHA-1 Hash Algorithm 3.1. SHA-1 Hash Algorithm
The SHA-1 hash algorithm [RFC3174] was designed by the United States The SHA-1 hash algorithm [RFC3174] was designed by the United States
National Security Agency and published in 1995. Since that time a National Security Agency and published in 1995. Since that time a
large amount of cryptographic analysis has been applied to this large amount of cryptographic analysis has been applied to this
algorithm and a successful collision attack has been created algorithm and a successful collision attack has been created
([SHA-1-collision]). The IETF formally started discouraging the use ([SHA-1-collision]). The IETF formally started discouraging the use
skipping to change at page 6, line 9 skipping to change at page 6, line 9
and therefore it makes sense to assign a point for the use of this and therefore it makes sense to assign a point for the use of this
hash algorithm. Some of these situations are with historic HSMs hash algorithm. Some of these situations are with historic HSMs
where only SHA-1 is implemented or where the SHA-1 value is used for where only SHA-1 is implemented or where the SHA-1 value is used for
the purpose of filtering and thus the collision resistance property the purpose of filtering and thus the collision resistance property
is not needed. is not needed.
Because of the known issues for SHA-1 and the fact that is should no Because of the known issues for SHA-1 and the fact that is should no
longer be used, the algorithm will be registered with the longer be used, the algorithm will be registered with the
recommendation of "Filter Only". recommendation of "Filter Only".
+-------+-------+-------------+-----------------+-------------+ The COSE capabilities for this algorithm is an empty array.
| Name | Value | Description | Reference | Recommended |
+=======+=======+=============+=================+=============+ +-----+------+-------------+--------------+-----------+-------------+
| SHA-1 | TBD6 | SHA-1 Hash | [This Document] | Filter Only | |Name |Value | Description | Capabilities | Reference | Recommended |
+-------+-------+-------------+-----------------+-------------+ +=====+======+=============+==============+===========+=============+
|SHA-1| TBD6 | SHA-1 Hash | [] | [This | Filter Only |
| | | | | Document] | |
+-----+------+-------------+--------------+-----------+-------------+
Table 1: SHA-1 Hash Algorithm Table 1: SHA-1 Hash Algorithm
3.2. SHA-2 Hash Algorithms 3.2. SHA-2 Hash Algorithms
The family of SHA-2 hash algorithms [FIPS-180-4] was designed by the The family of SHA-2 hash algorithms [FIPS-180-4] was designed by the
United States National Security Agency and published in 2001. Since United States National Security Agency and published in 2001. Since
that time some additional algorithms have been added to the original that time some additional algorithms have been added to the original
set to deal with length extension attacks and some performance set to deal with length extension attacks and some performance
issues. While the SHA-3 hash algorithms have been published since issues. While the SHA-3 hash algorithms have been published since
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currently. SHA-256 is an efficient hash algorithm for 32-bit currently. SHA-256 is an efficient hash algorithm for 32-bit
hardware. hardware.
* *SHA-384* and *SHA-512* hash functions are efficient for 64-bit * *SHA-384* and *SHA-512* hash functions are efficient for 64-bit
hardware. hardware.
* *SHA-512/256* provides a hash function that runs more efficiently * *SHA-512/256* provides a hash function that runs more efficiently
on 64-bit hardware, but offers the same security levels as SHA- on 64-bit hardware, but offers the same security levels as SHA-
256. 256.
+-------------+-------+----------------+-----------+-------------+ The COSE capabilities for these algorithms is an empty array.
| Name | Value | Description | Reference | Recommended |
+=============+=======+================+===========+=============+
| SHA-256/64 | TBD1 | SHA-2 256-bit | [This | Filter Only |
| | | Hash truncated | Document] | |
| | | to 64-bits | | |
+-------------+-------+----------------+-----------+-------------+
| SHA-256 | TBD2 | SHA-2 256-bit | [This | Yes |
| | | Hash | Document] | |
+-------------+-------+----------------+-----------+-------------+
| SHA-384 | TBD3 | SHA-2 384-bit | [This | Yes |
| | | Hash | Document] | |
+-------------+-------+----------------+-----------+-------------+
| SHA-512 | TBD4 | SHA-2 512-bit | [This | Yes |
| | | Hash | Document] | |
+-------------+-------+----------------+-----------+-------------+
| SHA-512/256 | TBD5 | SHA-2 512-bit | [This | Yes |
| | | Hash truncated | Document] | |
| | | to 256-bits | | |
+-------------+-------+----------------+-----------+-------------+
Table 2: SHA-2 Hash Algorithms +-----------+-----+-----------+--------------+---------+------------+
| Name |Value|Description| Capabilities |Reference|Recommended |
+===========+=====+===========+==============+=========+============+
|SHA-256/64 |TBD1 | SHA-2 | [] | [This |Filter Only |
| | | 256-bit | |Document]| |
| | | Hash | | | |
| | | truncated | | | |
| | |to 64-bits | | | |
+-----------+-----+-----------+--------------+---------+------------+
| SHA-256 |TBD2 | SHA-2 | [] | [This | Yes |
| | | 256-bit | |Document]| |
| | | Hash | | | |
+-----------+-----+-----------+--------------+---------+------------+
| SHA-384 |TBD3 | SHA-2 | [] | [This | Yes |
| | | 384-bit | |Document]| |
| | | Hash | | | |
+-----------+-----+-----------+--------------+---------+------------+
| SHA-512 |TBD4 | SHA-2 | [] | [This | Yes |
| | | 512-bit | |Document]| |
| | | Hash | | | |
+-----------+-----+-----------+--------------+---------+------------+
|SHA-512/256|TBD5 | SHA-2 | [] | [This | Yes |
| | | 512-bit | |Document]| |
| | | Hash | | | |
| | | truncated | | | |
| | |to 256-bits| | | |
+-----------+-----+-----------+--------------+---------+------------+
Table 2: SHA-2 Hash Algorithms
3.3. SHAKE Algorithms 3.3. SHAKE Algorithms
The family SHA-3 hash algorithms [FIPS-202] was the result of a The family SHA-3 hash algorithms [FIPS-202] was the result of a
competition run by NIST. The pair of algorithms known as SHAKE-128 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 and SHAKE-256 are the instances of SHA-3 that are currently being
standardized in the IETF. standardized in the IETF.
The SHA-3 hash algorithms have a significantly different structure The SHA-3 hash algorithms have a significantly different structure
than the SHA-2 hash algorithms. One of the benefits of this than the SHA-2 hash algorithms. One of the benefits of this
differences is that when computing a shorter SHAKE hash value, the differences is that when computing a shorter SHAKE hash value, the
value is not a prefix of the result of computing the longer hash. value is not a prefix of the result of computing the longer hash.
Unlike the SHA-2 hash functions, no algorithm identifier is created Unlike the SHA-2 hash functions, no algorithm identifier is created
for shorter lengths. Applications can specify a minimum length for for shorter lengths. Applications can specify a minimum length for
any hash function. A validator can infer the actual length from the any hash function. A validator can infer the actual length from the
hash value in these cases. hash value in these cases.
+----------+-------+---------------+-----------------+-------------+ The COSE capabilities for these algorithms is an empty array.
| Name | Value | Description | Reference | Recommended |
+==========+=======+===============+=================+=============+
| SHAKE128 | TBD10 | 128-bit SHAKE | [This Document] | Yes |
+----------+-------+---------------+-----------------+-------------+
| SHAKE256 | TBD11 | 256-bit SHAKE | [This Document] | Yes |
+----------+-------+---------------+-----------------+-------------+
Table 3: SHAKE Hash Functions +--------+-----+-------------+--------------+---------+-------------+
| Name |Value| Description | Capabilities |Reference| Recommended |
+========+=====+=============+==============+=========+=============+
|SHAKE128|TBD10|128-bit SHAKE| [] | [This | Yes |
| | | | |Document]| |
+--------+-----+-------------+--------------+---------+-------------+
|SHAKE256|TBD11|256-bit SHAKE| [] | [This | Yes |
| | | | |Document]| |
+--------+-----+-------------+--------------+---------+-------------+
Table 3: SHAKE Hash Functions
4. IANA Considerations 4. IANA Considerations
4.1. COSE Algorithm Registry 4.1. COSE Algorithm Registry
IANA is requested to register the following algorithms in the "COSE IANA is requested to register the following algorithms in the "COSE
Algorithms" registry. Algorithms" registry.
* The SHA-1 hash function found in Table 1. * The SHA-1 hash function found in Table 1.
skipping to change at page 9, line 28 skipping to change at page 9, line 39
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[I-D.ietf-cose-rfc8152bis-struct] [I-D.ietf-cose-rfc8152bis-struct]
Schaad, J., "CBOR Object Signing and Encryption (COSE): Schaad, J., "CBOR Object Signing and Encryption (COSE):
Structures and Process", Work in Progress, Internet-Draft, Structures and Process", Work in Progress, Internet-Draft,
draft-ietf-cose-rfc8152bis-struct-06, 11 September 2019, draft-ietf-cose-rfc8152bis-struct-07, 17 November 2019,
<https://tools.ietf.org/html/draft-ietf-cose-rfc8152bis- <https://tools.ietf.org/html/draft-ietf-cose-rfc8152bis-
struct-06>. struct-07>.
[FIPS-180-4] [FIPS-180-4]
National Institute of Standards and Technology, "Secure National Institute of Standards and Technology, "Secure
Hash Standard", FIPS PUB 180-4, August 2015. Hash Standard", FIPS PUB 180-4, August 2015.
[FIPS-202] National Institute of Standards and Technology, "SHA-3 [FIPS-202] National Institute of Standards and Technology, "SHA-3
Standard: Permutation-Based Hash and Extendable-Output Standard: Permutation-Based Hash and Extendable-Output
Functions", FIPS PUB 202, August 2015. Functions", FIPS PUB 202, August 2015.
[COSE] Schaad, J., "CBOR Object Signing and Encryption (COSE)", [COSE] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
skipping to change at page 10, line 10 skipping to change at page 10, line 20
RFC 5652, DOI 10.17487/RFC5652, September 2009, RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>. <https://www.rfc-editor.org/info/rfc5652>.
[ESS] Hoffman, P., Ed., "Enhanced Security Services for S/MIME", [ESS] Hoffman, P., Ed., "Enhanced Security Services for S/MIME",
RFC 2634, DOI 10.17487/RFC2634, June 1999, RFC 2634, DOI 10.17487/RFC2634, June 1999,
<https://www.rfc-editor.org/info/rfc2634>. <https://www.rfc-editor.org/info/rfc2634>.
[I-D.ietf-cose-x509] [I-D.ietf-cose-x509]
Schaad, J., "CBOR Object Signing and Encryption (COSE): Schaad, J., "CBOR Object Signing and Encryption (COSE):
Headers for carrying and referencing X.509 certificates", Headers for carrying and referencing X.509 certificates",
Work in Progress, Internet-Draft, draft-ietf-cose-x509-04, Work in Progress, Internet-Draft, draft-ietf-cose-x509-05,
12 September 2019, 4 November 2019,
<https://tools.ietf.org/html/draft-ietf-cose-x509-04>. <https://tools.ietf.org/html/draft-ietf-cose-x509-05>.
[RFC3174] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1 [RFC3174] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1
(SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001, (SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001,
<https://www.rfc-editor.org/info/rfc3174>. <https://www.rfc-editor.org/info/rfc3174>.
[RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security [RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security
Considerations for the SHA-0 and SHA-1 Message-Digest Considerations for the SHA-0 and SHA-1 Message-Digest
Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011, Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011,
<https://www.rfc-editor.org/info/rfc6194>. <https://www.rfc-editor.org/info/rfc6194>.
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