Format Preserving Encryption in the Bounded Retrieval Model

Abstract: In the bounded retrieval model, the adversary can leak a certain amount of information from the message sender's computer (e.g., 10 percent of the hard drive). Bellare, Kane and Rogaway give an efficient symmetric encryption scheme in the bounded retrieval model. Their scheme uses a giant key (a key so large only a fraction of it can be leaked.) One property of their scheme is that the encrypted message is larger than the original message. Rogaway asked if an efficient scheme exists that does not increase the size of the message. In this paper we present such a scheme.