USN-179-1: openssl weak default configuration

The current default algorithm for creating “message digests”
(electronic signatures) for certificates created by openssl is MD5.
However, this algorithm is not deemed secure any more, and some
practical attacks have been demonstrated which could allow an attacker
to forge certificates with a valid certification authority signature
even if he does not know the secret CA signing key.

Therefore all Ubuntu versions of openssl have now been changed to use
SHA-1 by default. This is a more appropriate default algorithm for
the majority of use cases; however, if you still want to use MD5 as
default, you can revert this change by changing the two instances of
“default_md = sha1” to “default_md = md5″ in /etc/ssl/openssl.cnf.

A detailed explanation and further links can be found at

http://www.cits.rub.de/MD5Collisions/