Improved Meet-in-the-Middle Attacks on Reduced-Round Deoxys-BC-256. (22nd June 2020)

• Record Type: Journal Article
• Authors: Liu, Ya; Shi, Bing; Gu, Dawu; Zhao, Fengyu; Li, Wei; Liu, Zhiqiang
• Is Part Of: Computer journal. Volume 63:Number 12(2020)
• Page Start: 1859
• Page End: 1870
• Publication Date: 2020-06-22
• Subjects: authentication encryption schemes -- tweakable block ciphers -- Deoxys-BC -- the meet-in-the-middle attack -- the meet-in-the-middle distinguisher; Computers -- Periodicals; 005.1
• DOI: 10.1093/comjnl/bxaa028
• Languages: English
• ISSNs: 0010-4620

Abstract

Abstract: In ASIACRYPT 2014, Jean et al. proposed the authentication encryption scheme Deoxys, which is one of the third-round candidates in CAESAR competition. Its internal block cipher is called Deoxys-BC that adopts the tweakey frame. Deoxys-BC has two versions of the tweakey size that are 256 bits and 384 bits, denoted by Deoxys-BC-256 and Deoxys-BC-384, respectively. In this paper, we revaluate the security of Deoxys-BC-256 against the meet-in-the-middle attack to obtain some new results. First, we append one round at the top and two rounds at the bottom of a 6-round distinguisher to form a 9-round truncated differential path with the probability of $2^{-144}$ . Based on it, the adversary can attack 9-round Deoxys-BC-256 with $2^{108}$ chosen plaintext-tweaks, $2^{113.6}$ encryptions and $2^{102}$ blocks. Second, we construct a new 6.5-round distinguisher to form 10-round attacking path with the probability of $2^{-152}$ . On the basis of it, the adversary could attack 10-round Deoxys-BC-256 with $2^{115}$ chosen plaintext-tweaks, $2^{171}$ encryptions and $2^{152}$ blocks. These two attacks improve the previous cryptanalytic results on reduced-round Deoxys-BC-256 against the meet-in-the-middle attack.