PROBLEM TO BE SOLVED: To make it difficult to deduce processing operations of a data processing apparatus.SOLUTION: The data processing apparatus is configured to perform a data processing operation on at least one data value in response to a data processing instruction. The data processing apparatus comprises a delay unit on its own path, which is configured to apply a delay to propagation of a signal on the path. Propagation of the signal forms part of the data processing operation. The data processing apparatus is configured to determine a result of the data processing operation at a predetermined time point, which follows initiation of the data processing operation at a predetermined time interval, and the delay unit is configured such that the time for the data processing operation to be performed plus the delay is less than the predetermined time interval. The delay unit is further configured such that the delay applied is changed for a subsequent performance of the data processing operation on at least one data value in response to the data processing instruction.
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