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Re: [TLS] Moving SHA-1 signature schemes to not recommended in draft-ietf-tls-md5-sha1-deprecate

David Benjamin <davidben@chromium.org> Fri, 18 September 2020 14:49 UTC

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From: David Benjamin <davidben@chromium.org>
Date: Fri, 18 Sep 2020 10:49:07 -0400
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To: Sean Turner <sean@sn3rd.com>
Cc: "Salz, Rich" <rsalz=40akamai.com@dmarc.ietf.org>, "draft-ietf-tls-md5-sha1-deprecate@ietf.org" <draft-ietf-tls-md5-sha1-deprecate@ietf.org>, TLS List <tls@ietf.org>, Benjamin Kaduk <kaduk@mit.edu>
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Subject: Re: [TLS] Moving SHA-1 signature schemes to not recommended in draft-ietf-tls-md5-sha1-deprecate
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On Fri, Sep 18, 2020 at 10:28 AM Sean Turner <sean@sn3rd.com> wrote:

> Also, should we be adding “_legacy” to the names of the code points as was
> done for rsa_pkcs1_sha256_legacy by:
> https://www.ietf.org/archive/id/draft-davidben-tls13-pkcs1-00.txt?
>

My inclination is no. We didn't go about renaming the huge mess of TLS
cipher suites or anything else that I remember.

The "_legacy" suffix in that draft has a slightly different meaning
(perhaps I should have picked a different name). The existing
rsa_pkcs1_sha256 code points from TLS 1.2 were carried over into TLS 1.3
but with a subsetted meaning. In TLS 1.2, rsa_pkcs1_sha256 advertises both
TLS and X.509 capabilities, but in TLS 1.3 it advertises only X.509
capabilities. rsa_pkcs1_sha256 is undefined for a TLS CertificateVerify
because we took PKCS#1 v1.5 out. So, in order for TLS 1.3 servers to opt
into accepting PKCS#1 v1.5 signatures in CertificateVerify, the draft
needed to define new code points with a CertificateVerify capability.

rsa_pkcs1_sha256_tls1_3_certificate_verify_for_legacy_clients was a
mouthful, so I just added a "legacy" suffix. :-)

David

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