SECURING IMPLEMENTATION OF CRYPTOGRAPHIC ALGORITHMS USING ADDITIONAL ROUNDS

摘要

In the field of computer enabled cryptography, such as a keyed block cipher having a plurality of sequenced rounds, the cipher is hardened against an attack by a protection process which adds rounds to the cipher process. This is especially advantageous in a “White Box” environment where an attacker has full access to the cipher algorithm (process), including the algorithm's internal state during its execution. In one version, a specific number of rounds are added over those of a standard version of the cipher to both encryption and the complementary decryption. The added rounds are inserted immediately after the last of the standard rounds in the sequence. In another version, the added rounds are one or more opposing paired rounds of encryption/decryption or decryption/encryption which effectively cancel each other out, and may be inserted anywhere in the sequence of standard rounds.