For more serious cryptography work, have a look at the following extension modules.
Interfaces to OpenSSL
OpenSSL is an open-source library that implements SSL and comes with a large number of very fast crypto and hash algorithm implementations.
M2Crypto - Python interface to OpenSSL
pyOpenSSL - Python interface to OpenSSL, with focus on SSL networking
eGenix pyOpenSSL Distribution - An easy-to-install distribution of pyOpenSSL
Stand-alone Cryptographic Libraries
Python Cryptography Toolkit - A collection of crypto-related algorithms and protocols implemented as Python extension
python-crypto Mailing List - A mailing list for discussing Python and cryptography