public key cryptography. A mathematical technology enabling private communication of data over public channels (even when the parties involved are not previously known to each other) and unforgeable digital signatures that can be used to conclusively prove the origin of a message. In public-key cryptography, instead of a single secret key, one uses a pair of complementary keys, each of which can unscramble messages scrambled with the other. However, because of the mathematics underlying PKC, knowing one key of the pair does not make it practical to guess or calculate the other. A PKC user can make one key of the pair his public key, known to the world, and keep the other as his private key.