PGP

PGP: Pretty Good Privacy
Application and protocol (RFC 1991) for secure e-mail and file encryption developed by Phil R. Zimmermann. The source code was freely distributed from the start and has always remained available for inspection. PGP uses various algorithms such as IDEA, RSA, DSA, MD5, SHA- 1 for encryption, authentication, message integrity and key management. PGP is based on the "web of trust" model and is used the world over.