Method and apparatus for improving the speed of advanced encryption standard (aes) decryption algorithm

Abstract

A method is provided for decrypting data encrypted according to a cipher key according the advanced encryption standard (AES). The method includes precomputing a product of each element value of an InvMixColumn matrix and each possible value of an input state array and deriving a set of round keys from the cipher key and the set of round keys. The deriving includes providing an initial round key and a plurality of further round keys, performing an initial decryption round, and performing N full decryption rounds at least in part using the precomputed product of each element value of an InvMixColumn matrix and each possible value of the input state array.

1 - 12 . (canceled) 
     
     
         13 . A method of decrypting data encrypted according to a cipher key according the advanced encryption standard (AES), comprising:
 precomputing a product of each element value of an InvMixColumn matrix and each possible value of an input state array;   deriving a set of round keys from the cipher key, the set of round keys; comprising an initial round key and a plurality of further round keys;   performing an initial decryption round on a state array comprising at least a portion of the data; and   performing N full decryption rounds on a result of the initial decryption round at least in part using the precomputed product of each element value of an InvMixColumn matrix and each possible value of the input state array.   
     
     
         14 . The method of  claim 13 , wherein:
 performing N full decryption rounds at least in part using the precomputed product of each element value of an InvMixColumn matrix and each possible value of an input state array comprises:
 performing an inverse mix columns operation (InvMixColumn) on the input state array to generate an output state array using the precomputed product of each element of the InvMixColumn matrix and each possible value of the input state array.