Towards a Characterization of the Related-Key Attack Security of the Iterated Even-Mansour Cipher

We prove the related-key security of the Iterated Even-Mansour cipher under broad classes of related key derivation (RKD) functions. Our result extends the classes of RKD functions considered by Farshim and Procter (FSE, 15). Moreover, we present a far simpler proof which uses techniques similar to those used by Cogliati and Seurin (EUROCRYPT, 15) in their proof that the four-round Even-Mansour cipher is secure against XOR related-key attacks—a special case of our result and the result of Farshim and Proctor. Finally, we give a concrete example of a class of RKD functions covered by our result which does not satisfy the requirements given by Farshim and Procter and prove that the three-round Even-Mansour cipher is secure against this class of RKD functions. ∗Dept. of Electrical and Computer Engineering, University of Maryland. Email: [email protected]. Work supported in part by NSF CAREER award #1453045. This work was performed under financial assistance award 70NANB15H328 from the U.S. Department of Commerce, National Institute of Standards and Technology. †Cornell University. Email: [email protected]. This work was done when the author was visiting the University of Maryland. ‡Dept. of Computer Science, University of Maryland. Email: [email protected].