A secure logging mechanism named haplog is proposed. In essence, haplog uses only one-way hash functions to achieve the security and functional requirements of logging. This makes haplog more concise and efficient than schemes previously proposed. In addition, haplog considers that all events logged as log entries should be private and only the system can decide what event information the verifier can obtain. Even the trusted center, who helps to initialize the log mechanism and possesses shared secret with the system, should not be able to learn event information when verifying the integrity of the log.