Security in Computing 5th Edition by Shari Lawrence Pfleeger, Charles P Pfleeger, Jonathan Margulies

Exercise 39

A synchronous password token has to operate at the same pace as the receiver. That is, the token has to advance to the next random number at the same time the receiver advances. Because of clock imprecision, the two units will not always be perfectly together; for example, the token’s clock might run 1 second per day slower than the receiver’s. Over time, the accumulated difference can be significant. Suggest a means by which the receiver can detect and compensate for clock drift on the part of the token.

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Time-Synchronous Password Token Time Drift

Time drift or clock drift is a phenomenon associated with time synchronous passwords (such as One Time Passwords). In this phenomenon, the difference in the clock counters in the password token clock and the recipient clock may accumulate to a significant value leading to imprecision and finally, invalidation of the token.