A new mode of operation for block ciphers and length preserving MACs Conference Paper


Author(s): Dodis, Yevgeniy; Pietrzak, Krzysztof; Puniya, Prashant
Title: A new mode of operation for block ciphers and length preserving MACs
Title Series: LNCS
Affiliation
Abstract: We propose a new mode of operation, enciphered CBC, for domain extension of length-preserving functions (like block ciphers), which is a variation on the popular CBC mode of operation. Our new mode is twice slower than CBC, but has many (property-preserving) properties not enjoyed by CBC and other known modes. Most notably, it yields the first constant-rate Variable Input Length (VIL) MAC from any length preserving Fixed Input Length (FIL) MAC. This answers the question of Dodis and Puniya from Eurocrypt 2007. Further, our mode is a secure domain extender for PRFs (with basically the same security as encrypted CBC). This provides a hedge against the security of the block cipher: if the block cipher is pseudorandom, one gets a VIL-PRF, while if it is "only" unpredictable, one "at least" gets a VIL-MAC. Additionally, our mode yields a VIL random oracle (and, hence, a collision-resistant hash function) when instantiated with length-preserving random functions, or even random permutations (which can be queried from both sides). This means that one does not have to re-key the block cipher during the computation, which was critically used in most previous constructions (analyzed in the ideal cipher model).
Conference Title: EUROCRYPT: Theory and Applications of Cryptographic Techniques
Volume: 4965
Conference Dates: April 13-17, 2008
Conference Location: Istanbul, Turkey
Publisher: Springer  
Date Published: 2008-04-28
Start Page: 198
End Page: 219
Copyright Statement: © International Association for Cryptologic Research 2008
DOI: 10.1007/978-3-540-78967-3_12
Open access: no
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