A Traceable Block Cipher

In this paper1 we propose a new symmetric block cipher with the following paradoxical traceability properties: it is computationally easy to derive many equivalent secret keys providing distinct descriptions of the same instance of the block cipher. But it is computationally difficult, given one or even up to k equivalent keys, to recover the so called meta-key from which they were derived, or to find any additional equivalent key, or more generally to forge any new untraceable description of the same instance of the block cipher. Therefore, if each legitimate user of a digital content distribution system based on encrypted information broadcast (e.g. scrambled pay TV, distribution over the Internet of multimedia content, etc.) is provided with one of the equivalent keys, he can use this personal key to decrypt the content. But it is conjectured infeasible for coalitions of up to k traitors to mix their legitimate personal keys into untraceable keys they might redistribute anonymously...

• Type: Conference
• Year: 2003
• Where: ASIACRYPT
• Authors: Olivier Billet, Henri Gilbert
• Keywords: ASIACRYPT 2003, Block Cipher, Cryptology, Equivalent Keys, Symmetric Block Cipher