This program is also excellent for decoding binary files for emailing and just compressing and securing your own personal files. It protects, encrypts, authenticates and compresses E-mail and other data files, but still has good ergonomic design and sophisticated key management. PGP lets you communicate securely with people you have never met, with no secure channels needed for prior exchange of keys.
Source code is free.
Yahoo's - Security and Encryption Page and PGP Page .