GNUPG is a free software alternative to the PGP software. It is a publicly available encryption scheme that uses the “public key” approach. With GnuPG, messages are encrypted using a “public key” however, they can only be decrypted by a “private key”, which is retained by the intended recipient of the message.
GNUPG program has a command line interface with various front ends which provides it with Graphical User Interface. This encrypts messages using asymmetric keypairs individually generated by GnuPG users.