Optimized χ 2-Attack against RC6

Digital Image Encryption using Logistic Chaotic Key-based RC6

“…[12] applied the same attack as [11] expect that it considered RC6 without post whitening (RC6P) and showed that with 2 117.84 texts, the RC6 with 128bit key can be broken after 16 rounds. The ability of Linear cryptanalysis to break RC6 was investigated in [13] and showed that after 16 rounds with 2 119 text the RC6 can be broken. Multiple linear attack was also conducted in [14] and shows that with 2119,68 text and 192-bit key, RC6 can be broken at 14 rounds.…”

“…Nonetheless, some recent studies reported that RC6 can be broken under some attacks such as statistical attack, linear cryptanalysis, correlation attack and brute force attack [8][9][10][11][12][13][14]. One of the main reason behind the vulnerability of RC6 to attack is the ability to predict it cryptographic keys.…”

The Security of RC6 against Asymmetric Chi-square Test Attack

“…(D r+2 ) by using such plaintexts that make the final-round rotation 27 for each key candidate of S 2r+2 . For a correct key, z c is exactly equal to C [5,7] r = D [5,7] r−1 and, thus, Attack 2 computes the χ 2 -value on D [5,7] r−1 lsb 3 (D r+2 ) = D [5,7] r−1 lsb 3 (D r+1 ) for a correct key. For a wrong key, z c is not equal to D [5,7] r−1 , thus, wrong keys output lower χ 2 -value on z c lsb 3 (D r+2 ) compared to a correct key.…”

“…However, our attack cannot assume that each distribution of χ 2 -value with each wrong key is Table 5 The relation between lsb 2 (S 2r+1 ) lsb 2 (S 2r+3 ) and C [5,6] r in the case of a correct S 2r+2 .…”

“…The χ 2 -attacks to a simplified variant of RC6 such as RC6 without pre-or post-whitening 11) or RC6 without only post-whitening 5) have been further improved. The variance as well as the average of χ 2 -value is taken into account when recovering a key in their attacks 5),11) .…”