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Re: [TLS] TLSv1.2 with DSA client cert and key size >1024 bits

Wan-Teh Chang <wtc@google.com> Mon, 14 February 2011 20:50 UTC

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Date: Mon, 14 Feb 2011 12:50:31 -0800
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From: Wan-Teh Chang <wtc@google.com>
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Cc: tls@ietf.org
Subject: Re: [TLS] TLSv1.2 with DSA client cert and key size >1024 bits
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The problem isn't limited to DSA client certs.  DSA server certs have
the same problem with DHE_DSS cipher suites.

I believe TLS 1.2 assumes DSA keys are 1024 bits and needs to be
updated for the larger DSA keys specified in FIPS 186-3.

The avoid the need to buffer the handshake messages for the
CertificateVerify message, the hash algorithm should ideally be chosen
so that it can be reused for the verify_data in the Finished message.
But clients with 1024-bit DSA client certs
already need to either buffer the handshake messages or compute their
SHA-1 hash, in addition to their SHA-256 hash for verify_data.

Wan-Teh Chang

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