Differential power analysis—resistant cryptographic processing

A cryptographic processing device for securely performing a cryptographic processing operation in a manner resistant to discovery of a secret by external monitoring of variations in the amount of power consumed, comprising:

• (a) an input interface for receiving a quantity to be processed;
• (b) a source of unpredictable information;
• (c) a processor for performing said cryptographic processing operation in a manner decorrelated from externally-monitorable signals produced by said device, by using outputs from said source to select between operating on an instruction and inserting a delay before operating on said instruction, wherein inserting said delay includes performing a no-operation processor instruction prior to said cryptographic processing operation, said selection being based on a determination of whether the received quantity is to be processed cryptographically;
• and
• (d) an output interface for providing said processed quantity to a recipient thereof.