Developed by Phil Zimmermann in 1991 as free email security program, Pretty Good Privacy is an encryption program used for signing, encrypting and decrypting texts, e-mails, files, directories and whole disk partitions.

PGP uses International Data Encryption Algorithm (IDEA) invented by Xuejia Lai and James Massey in 1991, which is the private key protocol and uses RSA as public key encryption system. It uses both Public and Private cryptosystem to increase the security and privacy of data and e-mail communications.

PGP survived law suits from NSA and US Government in its early days as it helped people and enterprises to secure their communications and insulate them from trapdoors that would have existed in secure communications equipment so that messages could be decrypted and read by the Government.