An important function of the log is to time-stamp the arrival of 4. The time-stamps used should include clock time information, since transaction authorization expiration will be in terms of real time. In order to reduce the trust that the parties must place in the log's honesty, cryptographic time-stamping [13] may also be employed. Cryptographic time-stamping will give the additional property that if the log is compromised, the log entries made prior to the time of compromise may still be trusted.