The Security of Elastic Block Ciphers Against Key-Recovery Attacks

The authors analyze the security of elastic block ciphers against key-recovery attacks. An elastic version of a fixed-length block cipher is a variable-length block cipher that supports any block size in the range of one to two times the length of the original block. The method for creating an elastic block cipher involves inserting the round function of the original cipher into a substitution-permutation network. In this paper, they form a polynomial-time reduction between the elastic and original versions of the cipher by exploiting the underlying network structure.