Briefly describe how PGP (or GPG) works.

What will be an ideal response?

Both PGP and GPG use both public and private key cryptography. PGP/GPG generates a random private (symmetric) key and uses it to encrypt the message. The private key is then encrypted using the receiver's public key and sent along with the message. When the recipient gets the message, the PGP/GPG software first decrypts the private key with the private key that belongs to the recipient.The decrypted private key is then used to decrypt the rest of the message.