Re: [TLS] Proposal to deprecate sha1 and md5 for digital signatures in TLS 1.2

Hubert Kario <hkario@redhat.com> Tue, 14 May 2019 18:57 UTC

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From: Hubert Kario <hkario@redhat.com>
To: Loganaden Velvindron <loganaden@gmail.com>
Cc: "<tls@ietf.org>" <tls@ietf.org>, Martin Thomson <mt@lowentropy.net>
Date: Tue, 14 May 2019 20:57:18 +0200
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Subject: Re: [TLS] Proposal to deprecate sha1 and md5 for digital signatures in TLS 1.2
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On Tuesday, 14 May 2019 20:16:17 CEST Loganaden Velvindron wrote:
> On Tue, May 14, 2019 at 3:24 PM Hubert Kario <hkario@redhat.com> wrote:
> > On Tuesday, 14 May 2019 08:34:38 CEST Loganaden Velvindron wrote:
> > > Latest draft is here:
> > > https://www.ietf.org/id/draft-lvelvindron-tls-md5-sha1-deprecate-04.txt
> > 
> > why did you drop SHA-1 from Section 4 and 5?
> 
> It was done following this comment from David Cooper.
> 
> "
> [..] While they may be subject to collision attacks, SHA-1 is still
> considered secure in cases in which collision resistance is not required,
> and I do not believe that collision resistance is required when SHA-1 is
> used to create the "signatures" in the ServerKeyExchange and
> CertificateVerify messages.
> "

SLOTH paper disagrees on that as far as CertificateVerify message is concerned

SP 800-52 rev-2 does not provide much in terms of justification why SLOTH 
paper would be wrong and allows for SHA-1 signatures only in TLS 1.0 and TLS 
1.1, it does not explicitly state that SHA-1 signatures in TLS 1.2 are 
allowed...
-- 
Regards,
Hubert Kario
Senior Quality Engineer, QE BaseOS Security team
Web: www.cz.redhat.com
Red Hat Czech s.r.o., Purkyňova 115, 612 00  Brno, Czech Republic