Determining whether a given cryptographic function is a permutation of another given cryptographic function-A problem in intellectual property

摘要

Imagine that, in order to avoid patent fees, licensing agreements, or export restrictions, someone permutes the plaintext bits, ciphertext bits, or key bits of a block cipher. All security properties of the block cipher would be preserved. There are many possible such permutations (e.g. 2(311632) for the Advanced Encryption Standard, AES-256). It might seem infeasible to detect this fraud, and even harder to determine the permutation matrices used. Instead of a block cipher, it could be the compression function of a cryptographic hash, or any other cryptographic function.