Draft: draft-ietf-tls-md5-sha1-deprecate-02

Commentary: Addressing Roman 's AD comments . 
 has 2 conflicts , not sure how to resolve , the updates look fine . Please merge . 
 There was a conflict with the 8174 reference being in the other branch . I it in because it 's now part of the terminology paragraph . 
 Please address the following IDNits : -- The document seems to lack an IANA Considerations section . ( See Section 2.2 of for how to handle the case when there are no actions for IANA . ) -- The draft header indicates that this document updates  , but the abstract does n't seem to mention this , which it should . -- The draft header indicates that this document updates RFC7525 , but the abstract does n't seem to mention this , which it should . Section 1 . Editorial . -- s / RFC 5246 [  -- s / RFC 6151 [ RFC6151]/[RFC6151]/ -- s / RFC7525 [ RFC7525]/[RFC7525]/ Section 1 . Editorial . For symmetry with the rest of the text : OLD RFC 6151 [ RFC6151 ] details the security considerations , including collision attacks for MD5 , published in 2011 . NEW In 2011 , [ RFC6151 ] detailed the security considerations , including collision attacks for MD5 . Section 1 . Please provide a reference for "  , et   . Is there a reference to provide for the " the potential for brute - force attack " Section 6 .   . s / RFC5246 [ RFC5246]/[RFC5246]/ Section 6 . Move the text " In Section 7.4.1.4.1 : the text should be revised from " out of the " OLD " block of text to be its own intro paragraph so that the OLD vs. NEW is a clear cut - and - paste . Section 7 . Editorial . s/ RFC7525 [ RFC7525]/[RFC7525]/ Section 7 . SHA-1 is also not mentioned in RFC7525 . Recommend : OLD The prior text did not explicitly include MD5 and this text adds it to ensure it is understood as having been deprecated . NEW The prior text did not explicitly include MD5 or SHA-1 ; and this text adds guidance to ensure that these algorithms have been deprecated . Section 7 . Editorial .  . OLD In addition , the use of the SHA-256 hash algorithm is RECOMMENDED , SHA-1 or MD5 MUST NOT be used NEW In addition , the use of the SHA-256 hash algorithm is RECOMMENDED ; and SHA-1 or MD5 MUST NOT be used Section 10.2 Please make  a normative reference .
The MD5 and SHA-1 hashing algorithms are steadily weakening in
strength and their deprecation process should begin for their use in
TLS 1.2 digital signatures.  However, this document does not
deprecate SHA-1 in HMAC for record protection.
The usage of MD5 and SHA-1 for signature hashing in TLS 1.2 is
specified in RFC5246.  MD5 and SHA-1 have been proven to be insecure,
subject to collision attacks.  RFC6151 details the security
considerations, including collision attacks for MD5, published in
2011.  NIST formally deprecated use of SHA-1 in 2011
NISTSP800-131A-R2 and disallowed its use for digital signatures at
the end of 2013, based on both the Wang, et. al, attack and the
potential for brute-force attack.  In 2016, researchers from INRIA
identified a new class of transcript collision attacks on TLS (and
other protocols) that rely on efficient collision-finding algorithms
on the underlying hash constructions Transcript-Collision.  Further,
in 2017, researchers from Google and CWI Amsterdam SHA-1-Collision
proved SHA-1 collision attacks were practical.  This document updates
RFC5246 and RFC7525 in such a way that MD5 and SHA-1 MUST NOT be used
for digital signatures.  However, this document does not deprecate
SHA-1 in HMAC for record protection.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119.
The MD5 and SHA-1 hashing algorithms are steadily weakening in
strength and their deprecation process should begin for their use in
TLS 1.2 digital signatures.  However, this document does not
deprecate SHA-1 in HMAC for record protection.  This document updates
RFC 5246 and RFC 7525.
The usage of MD5 and SHA-1 for signature hashing in TLS 1.2 is
specified in RFC5246.  MD5 and SHA-1 have been proven to be insecure,
subject to collision attacks Wang.  In 2011, RFC6151 detailed the
security considerations, including collision attacks for MD5.  NIST
formally deprecated use of SHA-1 in 2011 NISTSP800-131A-R2 and
disallowed its use for digital signatures at the end of 2013, based
on both the Wang, et. al, attack and the potential for brute-force
attack.  In 2016, researchers from INRIA identified a new class of
transcript collision attacks on TLS (and other protocols) that rely
on efficient collision-finding algorithms on the underlying hash
constructions Transcript-Collision.  Further, in 2017, researchers
from Google and CWI Amsterdam SHA-1-Collision proved SHA-1 collision
attacks were practical.  This document updates RFC5246 and RFC7525 in
such a way that MD5 and SHA-1 MUST NOT be used for digital
signatures.  However, this document does not deprecate SHA-1 in HMAC
for record protection.
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.
RFC7525, Recommendations for Secure Use of Transport Layer Security
(TLS) and Datagram Transport Layer Security (DTLS) recommends use of
SHA-256 as a minimum requirement.  This update moves the minimum
recommendation to use stronger language deprecating use of both SHA-1
and MD5.  The prior text did not explicitly include MD5 and this text
adds it to ensure it is understood as having been deprecated.
RFC7525, Recommendations for Secure Use of Transport Layer Security
(TLS) and Datagram Transport Layer Security (DTLS) recommends use of
SHA-256 as a minimum requirement.  This update moves the minimum
recommendation to use stronger language deprecating use of both SHA-1
and MD5.  The prior text did not explicitly include MD5 or SHA-1; and
this text adds guidance to ensure that these algorithms have been
deprecated..
In addition, the use of the SHA-256 hash algorithm is RECOMMENDED,
SHA-1 or MD5 MUST NOT be used (see CAB-Baseline for more details).
Clients MUST indicate to servers that they request SHA-256, by using
the "Signature Algorithms" extension defined in TLS 1.2.