The security of triple encryption and a framework for code-based game-playing proofs

Abstract

We show that, in the ideal-cipher model, triple encryption (the cascade of three independently-keyed blockciphers) is more secure than single or double encryption, thereby resolving a long-standing open problem. Our result demonstrates that for DES parameters (56-bit keys and 64-bit plaintexts) an adversary's maximal advantage against triple encryption is small until it asks about 2 78 queries. Our proof uses code-based game-playing in an integral way, and is facilitated by a framework for such proofs that we provide. © International Association for Cryptologic Research 2006.