pretty good privacy (PGP)

Widely used data encryption software that ensures integrity, security, and privacy of data and messages sent over the internet. It uses two digital equivalents of physical keys: a public key used for 'locking' (encrypting) data that can be given by its owner to anyone who wants to send a secure transmission; and a private key used for 'unlocking' (decrypting) the data and known only to its owner. Invented by Phil Zimmerman in 1991 and based on RSA encryption algorithm, PGP is very secure and available free on the internet. It is also used to digitally 'sign' an electronic document, thus authenticating its origin.