Eventually, a public key will need to be removed from service. This may be because that the corresponding private key has been compromised or irretrievably lost. ``Role'' keys, such as those for Postmaster, provide good examples of innocently compromised keys. When a member of staff leaves an institution, it is undesirable that they should still be able to read mail addressed to Postmaster, or to be able to sign documents as if they still had that role. Key revocation is the manner in which PGP public keys are permanently retired.
It is suggested that a key revocation certificate should be generated as soon as the key pair is created. This certificate should be held by a trusted third party, exactly as the key-escrow facility described above. Once more, adequate proof of identity will be required before the certificate is released and issued, to guard against malicious denial of service attacks. If the keys are generated by the institution, there will be no difficulty in also generating the revocation certificate and storing it securely. If the user generates the key pair, they must be able to obtain advice on how safely to create, store, recover and use a revocation certificate. The present PGP documentation is rather lacking in this respect.