Subject: [TLS] regd. signature algorithm 0x0804 (rsa_pss_rsae_sha256) use in TLSv1.2 CertificateVerify

From: M K Saravanan <[email-masked]>
Date: Wed, 21 Nov 2018 00:27:34 +0800

Hi,

If a TLSv1.2 Certificate Request message contains 0x0804
(rsa_pss_rsae_sha256) as one of the supported signature algorithms,
can a client sign the CertificateVerify message using that algorithm?
(client cert is RSA).  Is it allowed in TLSv1.2?

with regards,
Saravanan

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From: M K Saravanan <[email-masked]>
Date: Wed, 21 Nov 2018 00:35:24 +0800

Hi,

RFC8446:
=================================================
4.2.3.  Signature Algorithms

[...]
-  Implementations that advertise support for RSASSA-PSS (which is
      mandatory in TLS 1.3) MUST be prepared to accept a signature using
      that scheme even when TLS 1.2 is negotiated.  In TLS 1.2,
      RSASSA-PSS is used with RSA cipher suites.

=================================================

The above paragraph gives me an impression that, in TLSv1.2, if
CertificateRequest message advertise 0x0804, then the client can sign
the CertificateVerify message with 0x0804 if client cert is RSA.

0x0804 = rsa_pss_rsae_sha256

Can some one please confirm whether my understanding is correct?

with regards,
Saravanan

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From: David Benjamin <[email-masked]>
Date: Tue, 20 Nov 2018 12:07:39 -0600

Yes, this is correct.

On Tue, Nov 20, 2018 at 10:35 AM M K Saravanan <[email-masked]> wrote:

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From: M K Saravanan <[email-masked]>
Date: Wed, 21 Nov 2018 02:45:48 +0800

Thanks David.

with regards,
Saravanan.