Network Sales and Services Handbook (Cisco Press Networking Technology)

Pretty Good Privacy (PGP) is a hybrid cryptosystem, enabling the best of both worlds public, and private key algorithms. To the user, PGP acts like any other public-key cryptosystem, using the RSA Laboratories public-key algorithm and the IDEA encryption engine for encryption. A single IDEA key is used to encrypt the message, and the same key is used to decrypt the message (symmetric encryption). RSA is used to encrypt the IDEA key used for encryption with the recipient public key (asymmetric). The receiver uses a private key to decrypt the RSA-encrypted IDEA key. Then the decrypted IDEA key is used to decrypt the rest of the message.

PGP is freely distributed in versions that run on a variety of platforms, including DOS/Windows, UNIX, and Macintosh. PGP was not developed, nor controlled by, any government or standards organization. PGP supports the use of digital signatures, message encryption, compression, e-mail compatibility and segmentation (to accommodate protocol message size limitations).