PREVENTION OF DETERMINATION OF TIME OF EXECUTION OF PREDETERMINED DATA PROCESSING ROUTINE IN RELATION TO OCCURRENCE OF PRIOR OBSERVABLE EXTERNAL EVENT

摘要

Compromise of a predetermined secure data processing routine by a procedu re known as a "clock attack" is prevented by a method that inhibits synchronization with externally generated instructions by preventing determination of the time of execution of the predetermined data processing routine in relation to occurrence of an externally observable event that precedes the execution of the predetermined routine. T he method includes the step of (a) randomly varying the duration between the occurrenc e of the externally observable event and the execution of the predetermined routine. Step (a) includes the steps of (b) executing one or more interim data processing routines between the occurrence of the externally observable event and the execution of the predetermined routine; and (c) randomly varying the duration of said interim routines. Ste ps (b) and (c) may include the step of (d) randomly assembling m said interim routines for said execution from a group of n stored routines having different durations, wherein m and n are integers, with n being greater than m. Step (d) may include either the step of (e) randomly accessing said m interim routines from a secure memory; or the step s of (f) randomly accessing pointers for said m interim routines from a secure memory ; and (g) accessing said m interim routines from a memory in response to said pointers . Step (c) includes the step of (h) randomly varying the duration of the interim routin es in response to dynamically processed data that does not repetitively recur each time sai d interim routines are accessed. The method further includes the steps of (i) monitori ng said interim routines to detect whether said interim routines are being tampered with; an d (j) preventing the execution of said predetermined routine in response to detecting that said interim routines are being tampered with.