The Correct answer is A cryptographic software which provides for key-based asymmetric cryptography for encryption and authentication.Gnu Privacy Guard (GPG):The GNU Privacy Guard is an encryption tool that allows easy access to certain symmetric and asymmetric functions.It can be used primarily for encryption of documents and email.GPG implements the Pretty Good Privacy (PGP) protocol.For asymmetric encryption, each individual has a publicly known encryption key and a private key known only to them. One encrypts a message to send to someone else using their public key, who then decrypts it using their private key.Additional InformationPGP Protocol:It stands for Pretty Good Privacy Protocol.It was invented by Phil Zimmermann.It is the encryption method used for secure and meaningful communication.PGP was designed to provide all four aspects of security, i.e., privacy, integrity, authentication, and non-repudiation in the sending of email.PGP uses a digital signature (a combination of hashing and public key encryption) to provide integrity, authentication, and non-repudiation.PGP is an open source and freely available software package for email security.