Re: [TLS] TLS 1.2 hash agility

Eric Rescorla <ekr@networkresonance.com> Fri, 07 September 2007 16:55 UTC

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Date: Fri, 07 Sep 2007 09:52:13 -0700
From: Eric Rescorla <ekr@networkresonance.com>
To: Pasi.Eronen@nokia.com
Subject: Re: [TLS] TLS 1.2 hash agility
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At Thu, 9 Aug 2007 12:34:07 +0300,
<Pasi.Eronen@nokia.com> wrote:
> 
> Mike (mike-list@pobox.com) wrote:
> 
> > I think the solution we need is to specifically list each supported
> > signature algorithm, e.g.
> > 
> >      enum {
> >        rsa_with_md5(0),    rsa_with_sha1(1),
> >        rsa_with_sha256(2), rsa_with_sha384(3),
> >        rsa_with_sha512(4), dsa_with_sha1(5),
> >        (65535)
> >      };
> > 
> > These may not be specific enough, as I've seen suggestions for,
> > e.g. rsa_pkcs1v1_5_with_sha1, and I've heard that some algorithms
> > need parameters, but I think I've made my point.
> 
> I think your suggestion looks good; it seems to handle the DSA and
> ECDSA cases better than just a list of hashes, and it's more
> in TLS style than sending DER-encoded AlgorithmIdentifiers. 
> And then we could change Signature structure to
> 
>    struct {
>       SignatureAlgorithm signature_algorithm;
>       opaque signature_value<0..2^16-1>;
>    } Signature;  
> 
> Eric, what's your opinion?

This seems superficially reasonable. I'll try to cram it into
the new version and see if it causes trouble.

-Ekr

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