To ensure that the same fingerprint can be recreated later, the encoding must be deterministic, and any additional data must be exchanged and stored alongside the public key. The additional data is typically information which anyone using the public key should be aware of. Examples of additional data include: which protocol versions the key should be used with (in the case of PGP fingerprints); and the name of the key holder (in the case of X.509 trust anchor fingerprints, where the additional data consists of an X.509 self-signed certificate).