Importance

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Abstract

A client/server-based secure timekeeping computer system is provided. A secure-time server which is located in a physically trusted environment, includes a highly accurate time-of-day (TOD) clock, along with a key storage area containing a table of public/private key pairs corresponding to clients in the client/server network. The server encrypts a current time value from its TOD clock using a private key corresponding to a selected client. The encrypted time value is then sent to the client over an open communications channel. Each client in the network is equipped with its own secure timekeeping facility housed within the secure boundaries of a single, tamper-proof VLSI chip. Upon receipt of a secure-time transmission, a client uses its own copy of its private key to decrypt the time value, then loads the decrypted time value into its TOD clock. The tamper-proof VLSI chip in each client also includes an authenticated-time indicator, which is set to TRUE to indicate that the TOD clock contains a trusted time. Programs that require secure time may clock the authenticated time indicator before executing and may cancel execution if a secure time is not available. Programs that do not require secure time are able to execute regardless. To maintain the ongoing accuracy of the client TOD clock once it is set with a trusted time value, the secure timekeeping facility in a client may further include calibration and clock stability adjustment mechanisms which receive client clock calibration adjustment values and accuracy duration values, and which apply these values at intervals to maintain the accuracy of the client TOD clock within acceptable limits and mark the clock as untrusted when it can no longer be maintained within acceptable limits.

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First Claim