(PGP) A high security RSA public-key encryption application for MS-DOS, Unix, VAX/VMS, and other computers. It was written by Philip R. Zimmermann of Phil's Pretty Good(tm) Software and later augmented by a cast of thousands, especially including Hal Finney, Branko Lankester, and Peter Gutmann. PGP was distributed as "guerrilla freeware". PGP uses a public-key encryption algorithm claimed by US patent #4,405,829. PGP allows people to exchange files or messages with privacy and authentication. Privacy and authentication are provided without managing the keys associated with conventional cryptographic software. No secure channels are needed to exchange keys between users, which makes PGP much easier to use. This is because PGP is based on public-key cryptography.