The Pseudorandomness of Elastic Block Ciphers
Debra L. Cook, Moti M. Yung, Angelos D. Keromytis · 2005
We investigate elastic block ciphers, a method for constructing variable length block ciphers, from a theorectical perspective. We view the underlying structure of an elastic block cipher as a network, which we refer to as an elastic network, and analyze the network in a manner similar to the analysis performed by Luby and Rackoff on Fesitel networks. We prove that a three round elastic network is a pseudorandom permutation and a four round network is a strong pseudorandom permutation when the round functions are pseudorandom permutations.