PGP (Pretty Good Privacy) is an encryption standard that uses asymmetric cryptography to encrypt and digitally sign emails and files. Each user has a key pair: a public key for encryption and a private key for decryption. The open standard is called OpenPGP (RFC 4880), and the best-known free implementation is GnuPG (GPG). PGP provides end-to-end encryption where even the email provider cannot read the content. The biggest practical challenge is key management, particularly the secure exchange and verification of public keys.