US Patent 7778419 Key masking for cryptographic processes

Countermeasures for differential power or electromagnetic analysis attacks are provided with the definition and use of key encryption masks and masked substitution tables in a cryptographic process. Different key encryption masks and masked substitution tables are applied to different portions of masked keys used in the cryptographic process and are rotated as the cryptographic operations are carried out. The rotation of the key encryption masks and the masked substitution tables is non-uniform. Input and output masking for the substitution tables is provided.