1. Popular encryption program. It was created by a fellow named Phil Zimmerman as a subversive act. Phil later exploited it as a social-engineering attack against the business community. Key point: All true hackers use open-source versions of PGP to encrypt their data. Resources: RFC 1991: PGP Message Exchange Formats RFC 2015: MIME Security with Pretty Good Privacy (PGP) RFC 2440: OpenPGP Message Format Point: Users of PGP have choices of the following algorithms. Note that older v2.6 users can only use RSA/MD5/IDEA to read messages. encryption 3DES (aka. Triple-DES) The best choice for conservative people. The NSA claims that further proliferation of triple-DES is counter to national security interests, presumably because they cannot break it. It is the most analyzed cipher (and therefore believed to be the most secure) and is extensively used in the finance industry to protect transactions. IDEA A bad choice from the standpoint that it is protected by patents and many people are unable to use it. CAST5 AES The new United States standard, a good second choice, especially if speed is a concern. Twofish Blowfish public key RSA DSS (aka. DSA) DH/ELG-E Diffie-Hellman used for encryption, but not signing. ELG ElGamal signing, not recommended as it is considered weak. hash SHA1 The best choice for security paranoid people. MD5 The worst choice for paranoids, however, it is often the most popular. RIPEMD160 From Hacking-Lexicon