In a cryptographic system, the unlocking of secret keys on a user system is audited and correlated with other events that typically occur after the secret key is used to perform a cryptographic operation. Audit evidence of secret key cryptographic operations is recorded for later review and/or analysis,...http://www.google.de/patents/US7418728?utm_source=gb-gplus-sharePatent US7418728 - Auditing secret key cryptographic operations
