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arXiv 0804.0409cs.CRcs.DM
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两种基于准循环码的McEliece密码体制的分析

Cryptanalysis of Two McEliece Cryptosystems Based on Quasi-Cyclic Codes

Ayoub Otmani, Jean-Pierre Tillich, Leonard Dallot

摘要:

我们在这里密码分析两个变种的McEliece密码系统的基础上准循环码。这两种算法都是通过将公钥和秘密生成矩阵限制为准循环形式来减小密钥大小。第一种变体考虑原始BCH码的子码。我们证明了这种变体是不安全的,通过寻找和解决一个线性系统所满足的秘密置换矩阵的条目。另一种变体使用准循环低密度奇偶校验码。该方案通过在McEliece方案中选择比置换矩阵更一般的一对一映射来免疫基于低密度奇偶校验码的McEliece型密码系统的一般攻击。我们建议在这里利用准循环结构的代码和一定的弱点,在选择的线性变换隐藏的代码的生成矩阵的结构攻击。我们的分析表明,具有高概率的密码的打孔版本的奇偶校验矩阵可以恢复在其长度的三次时间复杂度。准循环低密度奇偶校验码的秘密校验矩阵的完全重构需要搜索低权重的码字,这可以通过针对所提出的特定参数的大约$2^{37}$操作来完成。

英文摘要:

We cryptanalyse here two variants of the McEliece cryptosystem based on quasi-cyclic codes. Both aim at reducing the key size by restricting the public and secret generator matrices to be in quasi-cyclic form. The first variant considers subcodes of a primitive BCH code. We prove that this variant is not secure by finding and solving a linear system satisfied by the entries of the secret permutation matrix. The other variant uses quasi-cyclic low density parity-check codes. This scheme was devised to be immune against general attacks working for McEliece type cryptosystems based on low density parity-check codes by choosing in the McEliece scheme more general one-to-one mappings than permutation matrices. We suggest here a structural attack exploiting the quasi-cyclic structure of the code and a certain weakness in the choice of the linear transformations that hide the generator matrix of the code. Our analysis shows that with high probability a parity-check matrix of a punctured version of the secret code can be recovered in cubic time complexity in its length. The complete reconstruction of the secret parity-check matrix of the quasi-cyclic low density parity-check codes requires the search of codewords of low weight which can be done with about $2^{37}$ operations for the specific parameters proposed.

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