A public key may be placed in an open access directory for decryption of the digital signature of the sender, the public key of the message recipient encrypts the sender’s message. Public key infrastructure (PKI) produces public and private keys.

The open access public key may also be e-mailed to trusted contacts and users. Pretty Good Privacy (PGP) is a popular form of public key cryptography. Public PGP keys are housed in a public key server directory to allow public key sharing. PGP server directory keys may be updated but not removed.