Hi. Visit https://www.ssllabs.com/ssltest/viewMyClient.html and check out "Protocol Details -> Signature algorithms". I expect you'll find that your browser doesn't offer SHA512/RSA.

Judging from a recent discussion on the IETF TLS list [1], there seems to be some confusion over whether the TLS signature_algorithms extension should 1) restrict the permitted certificate signature algorithms and the non-certificate uses of digital signatures in the TLS protocol or 2) only restrict the non-certificate uses of digital signatures in the TLS protocol.

Those taking view 2 don't offer SHA512/RSA because no cipher suites require it. I've concluded that, sadly, certs signed with SHA512/RSA basically don't work for TLS.

[1] http://www.ietf.org/mail-archive/web/tls/current/msg13606.html

On 02/10/14 07:00, mayak wrote:
hi all,

indeed -- i generated a new set of certs and tested:

a signature of sha256 results in TLSv* begin offered
a signature of sha512 results in TLSv* _not_ being offered
certs with 4096 bit keys work fine

i suspect that there is a variable that is not long enough to support
the signature ...

thanks!

m

--
Rob Stradling
Senior Research & Development Scientist
COMODO - Creating Trust Online

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