A pipelined processor comprising a cache memory system, fetching instructions for execution from a portion of said cache memory system, an instruction commencing processing before a digital signature of the cache line that contained the instruction is verified against a reference signature of the cache line, the verification being done at the point of decoding, dispatching, or committing execution of the instruction, the reference signature being stored in an encrypted form in the processor's memory, and the key for decrypting the said reference signature being stored in a secure storage location. The instruction processing proceeds when the two signatures exactly match and, where further instruction processing is suspended or processing modified on a mismatch of the two said signatures.