Paper 2018/594 Original: eprint.iacr.org/2018/594 ↗

Cryptanalysis of SFN Block Cipher

Abstract

SFN is a lightweight block cipher designed to be compact in hardware environment and also efficient in software platforms. Compared to the conventional block ciphers that are either Feistel or Substitution-Permutation (SP) network based, SFN has a different encryption method which uses both SP network structure and Feistel network structure to encrypt. SFN supports key lengths of 96 bits and its block length is 64 bits. In this paper, we propose an attack on full SFN by using the related key distinguisher. With this attack, we are able to recover the keys with a time complexity of $2^{60.58}$ encryptions. The data and memory complexity of the attacks are negligible. In addition, in the single key mode, we present a meet in the middle attack against the full rounds block cipher for which the time complexity is $2^{80}$ SFN calculations and the memory complexity is $2^{87}$ bytes. The date complexity of this attack is only a single known plaintext and its corresponding ciphertext.