[Python-apps-team] Bug#918475:

[Doug Freed]

I spent some time debugging this in a fresh sid debootstrap, using
tcpdump to capture the handshakes and analyzing them with Wireshark.
I also tested with my local browser (Chrome on Windows 7) for
comparison, which worked.  I narrowed it down to Atlassian's
webservers requiring the presence of the rsa_pkcs1_sha1 signature
algorithm in the signature algorithm list of the handshake, even
though this algorithm is never used.  The openssl cipherlist
preference of "DEFAULT at SECLEVEL=2" prevents this algorithm from being
added to the list, even if explicitly given via openssl s_client's
sigalgs parameter.  Changing the cipherlist to "DEFAULT at SECLEVEL=1"
doesn't change the ciphers offered, but does allow rsa_pkcs1_sha1 to
be sent in the signature algorithm list, and the handshake succeeds.
The only difference between the values of SECLEVEL is that 1 includes
the 3 SHA1 signature algorithms (1 each for DSA, RSA, and ECDSA) in
the signature algorithm list, whereas 2 does not.

-dwfreed