Modular exponentiation with transparent side channel attack countermeasures

A machine-readable storage medium having one or more instructions for implementing security in a modular exponentiation function which when executed by at least one processing circuit causes the at least one processing circuit to:

• obtain a key as a parameter when the modular exponentiation function is invoked;
• ascertain, within the modular exponentiation function, whether the key is greater than L bits long, where L is a positive integer;
• implement a countermeasure against an attack if the key is greater than L bits long;
• and
• perform one or more exponentiation operations using the key.

A device comprising:

• means for obtaining a key as a parameter when a modular exponentiation function is invoked;
• means for ascertaining, within the modular exponentiation function, whether the key is greater than L bits long, where L is a positive integer;
• means for implementing a countermeasure against an attack if the key is greater than L bits long;
• and
• means for performing one or more exponentiation operations using the key.

A modular exponentiation circuit, comprising:

• a register to obtain a key as a parameter when a modular exponentiation operation is invoked;
• and
• a processing circuit coupled to the register, the processing circuit configured to
• ascertain whether the key is greater than L bits long, where L is a positive integer,
• implement a countermeasure against an attack if the key is greater than L bits long, and
• perform one or more exponentiation operations using the key.