Cryptography
Python includes several modules for [http://www.python.org/doc/lib/module-hashlib.html hashing] and even basic [http://www.python.org/doc/lib/module-socket.html ssl support] which is integrated into the socket module.
For more serious cryptography work, have a look at the following extension modules.
Interfaces to OpenSSL
[http://www.openssl.org/ 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
[http://pyopenssl.sf.net/ pyOpenSSL] - Python interface to OpenSSL, with focus on SSL networking
[http://www.egenix.com/products/python/pyOpenSSL/ eGenix pyOpenSSL Distribution] - An easy-to-install distribution of pyOpenSSL
Stand-alone Cryptographic Libraries
[http://www.amk.ca/python/code/crypto.html Python Cryptography Toolkit] - A collection of crypto-related algorithms and protocols implemented as Python extension
Resources
[http://listserv.surfnet.nl/archives/python-crypto.html python-crypto Mailing List] - A mailing list for discussing Python and cryptography