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

Loganaden Velvindron <loganaden@gmail.com> Tue, 14 May 2019 06:34 UTC

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From: Loganaden Velvindron <loganaden@gmail.com>
Date: Tue, 14 May 2019 10:34:38 +0400
Message-ID: <CAOp4FwTNiTg+g2utyst330bc14-Q-_A2z1QEHi_FEMv14wa=iA@mail.gmail.com>
To: Martin Thomson <mt@lowentropy.net>
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Subject: Re: [TLS] Proposal to deprecate sha1 and md5 for digital signatures in TLS 1.2
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[comments in-line]

On Fri, May 10, 2019 at 5:47 AM Martin Thomson <mt@lowentropy.net> wrote:

> It might pay to spend more time on explaining what you are trying to do.
>
> The goal appears to be to remove a dependency on signature schemes that
> include these weaker hash functions.  But the introduction just says that
> the functions are bad.
>
> We've updated the draft.


> You should be very clear about what effect this has on the use of SHA-1 in
> HMAC for record protection.  It looks like you don't intend to deprecate
> that.  Say that.
>
> Added.

> The change to the enum is silly.  Overall, I think that the updates to
> 5246 are unnecessary.  Concentrate on 7525.
>
> Removed change to enum.

> The 7525 text starts with "When using RSA", so it could be read to not
> apply to ECDSA.  That would be a mistake.  I recommend splitting the
> paragraph into talking about the group size (the first sentence) and a
> separate paragraph on hash functions used as part of the signing process.
>
> This change was also incorporated.

> As part of that, this probably needs to be a MUST: "Clients SHOULD
> indicate to servers that they request SHA-256, by using the "Signature
> Algorithms" extension defined in TLS 1.2."
>
> And then I think we should publish something.  Like David, I'm acutely
> aware of the compatibility hazard that this presents, but it's no less
> worth doing.
>
> We also agree with you.
Latest draft is here:
https://www.ietf.org/id/draft-lvelvindron-tls-md5-sha1-deprecate-04.txt

>
> On Fri, May 10, 2019, at 00:12, Loganaden Velvindron wrote:
> > Hi all,
> >
> > Following the recent thread on TLS 1.0 and TLS 1.1 deprecation, we
> > came up with a proposal to deprecate md5 and sha1 for digital
> > signatures in the TLS 1.2 spec.
> >
> > Please find the draft at this url:
> > https://tools.ietf.org/html/draft-lvelvindron-tls-md5-sha1-deprecate-03
> >
> > We look forward to your feedback.
> >
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> >
>
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