Protecting Cryptographic Operations Using Conjugacy Class Functions

摘要

Some embodiments provide for an improved method for performing AES cryptographic operations. The method applies a look up table operation that includes several operations embedded within look up tables. The embedded operations include a permutation operation to permute several bytes of AES state, a multiplication operation to apply a next round's protection to the AES state, an affine function and an inverse affine function to conceal the multiplication operation, and an inverse permutation operation to remove a previous round's protection. Some embodiments provide for an optimized method for efficiently performing such protected AES operations. The method alternates rounds of AES processing between software processing (e.g. processing by a CPU, performed according to software instructions) and hardware processing (e.g. processing by cryptographic ASIC).

主权项

1. A method for performing a block cryptographic process, the method comprising: receiving an input portion of cryptographic state that has been multiplied by a particular value;
applying a cryptographic operation to the input portion over a series of rounds, each round of the cryptographic operation comprising a table look up operation that preserves protection of the input portion between rounds, the table look up operation comprising a composition of:
a permutation operation to permute several bytes of the input portion;a multiplication operation;an affine function; andan inverse permutation operation.