Improved Integral Cryptanalysis on Block Cipher uBlock
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摘要: 积分攻击是由Daemen等人(doi: 10.1007/BFb0052343)于1997年提出的一种密码分析方法,是继差分分析和线性分析之后最有效的密码分析方法之一。作为2018年全国密码算法设计竞赛分组算法的获胜算法,uBlock抵抗积分攻击的能力受到较多的关注。为了重新评估uBlock家族密码算法抵抗积分攻击的安全性,该文利用单项式传播技术,结合混合整数线性规划(MILP)工具搜索积分区分器,并利用部分和技术进行密钥恢复攻击。对于uBlock-128/128和uBlock-128/256,基于搜索到的9轮积分区分器分别进行了首个11轮和12轮攻击,数据复杂度为$ {2}^{127} $选择明文,时间复杂度分别为$ {2}^{127.06} $和$ {2}^{224} $次加密,存储复杂度分别为$ {2}^{44.58} $和 $ {2}^{138} $字节;对于uBlock-256/256,基于搜索到的10轮积分区分器进行了首个12轮攻击,数据复杂度为$ {2}^{253} $选择明文,时间复杂度为$ {2}^{253.06} $次加密,存储复杂度为$ {2}^{44.46} $字节。与之前uBlock的最优积分攻击结果相比,uBlock-128/128和uBlock-256/256的攻击轮数分别提高2轮,uBlock-128/256的攻击轮数提高3轮。本文的攻击说明,uBlock针对积分攻击依然有足够的安全冗余。Abstract: Integral attack is one of the most powerful cryptanalytic methods after differential and linear cryptanalysis, which was presented by Daemen et al. in 1997 (doi: 10.1007/BFb0052343). As the winning block cipher of China’s National Cipher Designing Competition in 2018, the security strength of uBlock against integral attack has received much attention. To better understand the integral property, this paper constructs the Mixed Integer Linear Programming (MILP) models for monomial prediction to search for the integral distinguishers and uses the partial sum techniques to perform key-recovery attacks. For uBlock-128/128 and uBlock-128/256, this paper gives the first 11 and 12-round attacks based on a 9-round integral distinguisher, respectively. The data complexity is $ {2}^{127} $ chosen plaintexts. The time complexities are $ {2}^{127.06} $ and $ {2}^{224} $ times encryptions, respectively. The memory complexities are $ {2}^{44.58} $ and $ {2}^{138} $ Byte, respectively. For uBlock-256/256, this paper gives the first 12-round attack based on a 10-round integral distinguisher. The data complexity is $ {2}^{253} $ chosen plaintexts. The time and memory complexities are $ {2}^{253.06} $ times encryptions and $ {2}^{44.46} $ Byte, respectively. The number of attacked rounds for uBlock-128/128 and uBlock-256/256 are improved by two rounds compared with the previous best ones. Besides, the number of attacked rounds for uBlock-128/256 is improved by three rounds. The results show that uBlock has enough security margin against integral attack.
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Key words:
- Cryptanalysis /
- Block cipher /
- uBlock /
- Integral attack
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表 1 uBlock积分分析结果比较
算法版本 攻击轮数 积分区分器 数据复杂度 时间复杂度 存储复杂度 参考文献 uBlock-128/128 9 $ \left({\mathcal{C}}^{4},{\mathcal{A}}^{124}\right)\stackrel{8\mathrm{R}}{\to }{\left({\mathcal{B}}^{1},{\mathcal{U}}^{2},{\mathcal{B}}^{1}\right)}^{32} $ $ {2}^{124} $ $ {2}^{125.47} $ $ {2}^{6.25} $ [24] 10 $ \left({\mathcal{C}}^{4},{\mathcal{A}}^{124}\right)\stackrel{8\mathrm{R}}{\to }{\left({\mathcal{B}}^{1},{\mathcal{U}}^{1},{\mathcal{B}}^{2}\right)}^{32} $ $ {2}^{124} $ $ {2}^{124.07} $ $ {2}^{44.32} $ 本文 11 $ \left({\mathcal{A}}^{1},{\mathcal{C}}^{1},{\mathcal{A}}^{126}\right)\stackrel{9\mathrm{R}}{\to }{\left({\mathcal{U}}^{3},{\mathcal{B}}^{1}\right)}^{32} $ $ {2}^{127} $ $ {2}^{127.06} $ $ {2}^{44.58} $ 本文 uBlock-128/256 9 $ \left({\mathcal{C}}^{4},{\mathcal{A}}^{124}\right)\stackrel{8\mathrm{R}}{\to }{\left({\mathcal{B}}^{1},{\mathcal{U}}^{2},{\mathcal{B}}^{1}\right)}^{32} $ $ {2}^{124} $ $ {2}^{125.47} $ $ {2}^{6.25} $ [24] 11 $ \left({\mathcal{C}}^{4},{\mathcal{A}}^{124}\right)\stackrel{8\mathrm{R}}{\to }{\left({\mathcal{B}}^{1},{\mathcal{U}}^{1},{\mathcal{B}}^{2}\right)}^{32} $ $ {2}^{124} $ $ {2}^{179.19} $ $ {2}^{137.81} $ 本文 11 $ \left({\mathcal{A}}^{1},{\mathcal{C}}^{1},{\mathcal{A}}^{126}\right)\stackrel{9\mathrm{R}}{\to }{\left({\mathcal{U}}^{3},{\mathcal{B}}^{1}\right)}^{32} $ $ {2}^{127} $ $ {2}^{224} $ $ {2}^{46} $ 本文 12 $ \left({\mathcal{A}}^{1},{\mathcal{C}}^{1},{\mathcal{A}}^{126}\right)\stackrel{9\mathrm{R}}{\to }{\left({\mathcal{U}}^{3},{\mathcal{B}}^{1}\right)}^{32} $ $ {2}^{127} $ $ {2}^{224} $ $ {2}^{138} $ 本文 uBlock-256/256 10 $ \left({\mathrm{C}}^{8},{\mathcal{A}}^{248}\right)\stackrel{9\mathrm{R}}{\to }{\left({\mathcal{B}}^{1},{\mathcal{U}}^{2},{\mathcal{B}}^{1}\right)}^{64} $ $ {2}^{248} $ $ {2}^{249.38} $ $ {2}^{7.25} $ [24] 11 $ \left({\mathcal{C}}^{8},{\mathcal{A}}^{248}\right)\stackrel{9\mathrm{R}}{\to }{\left({\mathcal{B}}^{1},{\mathcal{U}}^{2},{\mathcal{B}}^{1}\right)}^{64} $ $ {2}^{248} $ $ {2}^{248.06} $ $ {2}^{44.32} $ 本文 12 $ \left({\mathcal{C}}^{3},{\mathcal{A}}^{253}\right)\stackrel{10\mathrm{R}}{\to }{\left({\mathcal{U}}^{3},{\mathcal{B}}^{1}\right)}^{64} $ $ {2}^{253} $ $ {2}^{253.06} $ $ {2}^{44.46} $ 本文 表 2 4-bit S盒(S)
x 0x0 0x1 0x2 0x3 0x4 0x5 0x6 0x7 0x8 0x9 0xa 0xb 0xc 0xd 0xe 0xf S(x) 0x7 0x4 0x9 0xc 0xb 0xa 0xd 0x8 0xf 0xe 0x1 0x6 0x0 0x3 0x2 0x5 表 3 $ \mathrm{P}{\mathrm{L}}_{{n}} $和$ \mathrm{P}{\mathrm{R}}_{{n}} $
类型 置换后 $ \mathrm{P}{\mathrm{L}}_{128} $ {1, 3, 4, 6, 0, 2, 7, 5} $ \mathrm{P}{\mathrm{R}}_{128} $ {2, 7, 5, 0, 1, 6, 4, 3} $ \mathrm{P}{\mathrm{L}}_{256} $ {2, 7, 8, 13, 3, 6, 9, 12, 1, 4, 15, 10, 14, 11, 5, 0} $ \mathrm{P}{\mathrm{R}}_{256} $ {6, 11, 1, 12, 9, 4, 2, 15, 7, 0, 13, 10, 14, 3, 8, 5} -
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