FatSeal: An Efficient Lattice-based Signature Algorithm
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摘要: 当前基于格设计的能够抵抗量子计算机攻击的签名方案是基于数论难题的传统签名方案的热门候选替代。通过Fiat-Shamir变换以及拒绝采样技术构造格签名是一种重要方法,共有5个格签名方案提交到美国国家标准与技术局的后量子算法项目中,基于Fiat-Shamir变换进行设计的有两个方案。其中Dilithium是基于模错误学习(MLWE)问题构造的Fiat Shamir签名,它的一个特性是在签名算法中使用了高效简洁的均匀采样。Dilithium签名方案构造在一般格上,为了获得更紧凑的公钥尺寸,Dilithium对公钥进行了压缩。另一方面,NTRU格上的密码方案比一般格上的密码方案在效率和参数尺寸上有更大的优势,该文给出了Dilithium签名在NTRU格上的一个高效变种方案,在继承Dilithium简洁设计的基础上,综合了NTRU和拒绝采样的技术优势而无需额外的压缩处理,进一步提升了基于格的Fiat-Shamir签名的效率。
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关键词:
- 数字签名 /
- 格 /
- Fiat-Shamir签名 /
- 后量子 /
- 拒绝采样
Abstract: The lattice-based signature schemes are promising quantum-resistant replacements for classical signature schemes based on number theoretical hard problems. An important approach to construct lattice-based signature is utilizing the Fiat-Shamir transform and rejection sampling techniques. There are two Fiat-Shamir signatures among five lattice signature schemes submitted to the post-quantum project initiated by National Institute of Standards and Technology. One of them is called Dilithium, which is based on Module-Learning-With-Errors (MLWE) problem, it features on its simple design in the signing algorithm by using uniform sampling. The Dilithium is built on the generic lattices, to make the size of public key more compact, Dilithium adopts compression technique. On the other hand, schemes using NTRU lattices outperform schemes using generic lattices in efficiency and parameter sizes. This paper devotes to designing an efficient NTRU variant of Dilithium, by combining the advantage of NTRU and uniform rejection sampling, this scheme enjoys a concise structure and gains performance improvement over other lattice-based Fiat-Shamir signature without using extra compression techniques.-
Key words:
- Digital signature /
- Lattice /
- Fiat-Shamir transform /
- Post-quantum /
- Rejection sampling
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表 1 FatSeal密钥生成算法
算法1 FatSeal.KeyGen() 输入:$n,q$ 输出:公钥$h$,私钥$(f,g)$ (1) $f,g \leftarrow T(d{\rm{ + 1}},d)$ (2) 如果$f$在${R_q}$中不可逆,跳转(1) (3) 计算$h = (g + \alpha ){f^{ - 1}}$ (4) 输出$pk = h$, $sk = (f,g)$ 表 2 FatSeal签名算法
算法2 FatSeal.Sign() 输入:消息$M$,公钥$h$,私钥$(f,g)$ 输出:消息$M$的签名$(z,c)$ (1) $r \leftarrow {{\mathbb Z}_\alpha }[x]/({x^n} + 1)$ (2) 计算$w = hr{od ^\alpha }q$ (3) 若$w$的某分量等于$q - 1 - \alpha /2$,跳转(1) (4) 计算$c = H(M,{\rm{quo}}(w))$ (5) 计算$z = r + cf$ (6) 若${\left\| {cg} \right\|_\infty } \le \gamma ,\;{\left\| {cf} \right\|_\infty } \le \gamma ,\;{\left\| {cg + {\rm{rem}}(w)} \right\|_\infty } \le \alpha /2 - \gamma , $ ${\left\| z \right\|_\infty } < \alpha /2 - \gamma $,输出$(z,c)$ (7) 否则,跳转步骤(1) 表 3 FatSeal验签算法
算法3 FatSeal.Verify() 输入:消息$M$,公钥$h$,签名$(z,c)$ 输出:验证成功输出1,否则输出0 (1) 如果${\left\| z \right\|_\infty } \ge \alpha /2 - \gamma $或${w{'} } = hz - \alpha c{od ^\alpha }q$的某个分
量等于$q - 1 - \alpha /2$,输出0(2) 否则 (3) 计算${c{'} } = H(M,{\rm{quo} }({w{'} }))$ (4) 如果${c{'} } = c$,输出1 (5) 否则,输出0 表 4 FatSeal签名方案的参数选取及迭代概率估计
$n$ $T(d + 1,d)$ $q$ $\omega $ $t$ $\alpha $ $\gamma $ 迭代概率(%) 1024 T(257, 256) 286712 106 44 35840 20 10.2 2048 T(413, 412) 724993 287 87 90624 24 11.4 表 5 FatSeal签名128 bit和256 bit安全强度下的参数大小(Byte)
体制 公钥长度 私钥长度 签名长度 FatSeal-1024 2321 385 2048 FatSeal-2048 4984 719 4352 表 6 qTESLA签名128 bit和256 bit安全强度下的参数大小(Byte)
体制 公钥长度 私钥长度 签名长度 qTESLA-Ⅱ 2336 1600 2144 qTESLA-Ⅴ 5024 3520 4640 表 7 混合攻击下的FatSeal比特安全性
模型 体制 $b$ $N$ ${r_1}$ 比特安全性 classical FatSeal-1024 510 1770 91 150 quantum FatSeal-1024 522 1799 75 139 plausible FatSeal-1024 549 1865 40 115 classical FatSeal-2048 1130 3440 240 331 quantum FatSeal-2048 1157 3503 207 307 plausible FatSeal-2048 1219 3646 132 253 表 8 NewHope攻击模型下的比特安全性
体制 攻击模型 m b classical quantum plausible FatSeal-1024 primal 874 503 147 133 104 FatSeal-1024 dual 862 502 146 133 104 FatSeal-2048 primal 1671 1076 314 285 223 FatSeal-2048 dual 1697 1072 313 284 222 表 9 SIS攻击下的比特安全性
模型 体制 $b$ $w$ 比特安全性 classical FatSeal-1024 577 2048 181 quantum FatSeal-1024 577 2048 166 plausible FatSeal-1024 577 2048 132 classical FatSeal-2048 1276 4039 379 quantum FatSeal-2048 1278 4041 344 plausible FatSeal-2048 1284 4049 270 -
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