Shared secret

A shared secret ( english shared secret ) referred to in the cryptography a secret that only in a communication to know the parties involved. The shared secret can be, for example, a password , a passphrase , a large number or a series of randomly generated bytes .

If the shared secret was exchanged between the two parties before the communication, it is also called a pre-shared key . However, it can also be exchanged at the beginning of a communication session using a key exchange protocol . One of the first (publicly known) key exchange protocols is the Diffie-Hellman key exchange .

The shared secret can be used for authentication , encryption or to calculate a message authentication code . Before using it as a key, a key derivation function, such as B. PBKDF2 applied.

The shared secret is not to be confused with secret sharing . There both parties have only partial knowledge of a shared secret.