Treyfer

Abstract: TREYFER is a lightweight cipher designed for resource constrained environments. In this paper, we present a related-key attack that directly recovers the secret key of TREYFER using about 211 chosen plaintext encryptions. Our attack is based on a set of deterministic algebraic relationships between TREYFER ciphertexts corresponding to related plaintexts encrypted under circularly byte shifted versions of the same key. The attack complexity is independent of the number of rounds of the cipher.

Abstract: Boolean functions are critical building blocks of symmetric-key ciphers. In most cases, the security of a cipher against a particular kind of attacks can be explained by the existence of certain properties of its underpinning Boolean functions. Therefore, the design of appropriate functions has received significant attention from researchers for several decades. Heuristic methods have become very powerful tools for designing such functions. In this thesis, we apply simulated annealing methods to construct Boolean functions with particular properties. Our results meet or exceed the best results of available theoretical constructions and/or heuristic searches in the literature, including a 10-variable balanced Boolean function with resiliency degree 2, algebraic degree 7, and nonlinearity 488 for the first time. This construction affirmatively answers the open problem about the existence of such functions. This thesis also includes results of cryptanalysis for symmetric ciphers, such as Geffe cipher and TREYFER cipher.