Contrarily to Kerckhoffs’ principle, many applications of today’s cryptography still adopt the security by obscurity paradigm. Furthermore, in order to rely on its proven or empirical security, some realizations are based on a given well known and widely used cryptographic algorithm. In particular, a possible design would obfuscate a standard block cipher E by surrounding it with two secret external encodings P1 and P2 (one-to-one mappings), leading to the proprietary