Abstract A Vigenère cipher applies a single short key repeatedly to encrypt a plaintext. If a cryptanalyst correctly finds out the key length, the ciphertext can be divided into multiple instances of shift cipher and be broken by frequency analysis. To determine the key length, the twist algorithm, an alternate method to the standard Kasiski and Friedman tests, was recently proposed. In this article, we propose the twist+ algorithm, an improved twist algorithm, which can estimate the key length more accurately than the original twist algorithm.

中文翻译：

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寻找维吉尼亚密码的密钥长度：如何改进扭曲算法

摘要 Vigenère 密码重复应用单个短密钥来加密明文。如果密码分析者正确地找出密钥长度，则密文可以被分成多个移位密码实例并通过频率分析被破解。为了确定密钥长度，最近提出了扭曲算法，这是标准 Kasiski 和 Friedman 测试的替代方法。在本文中，我们提出了twist+算法，一种改进的twist算法，可以比原始twist算法更准确地估计密钥长度。