In the not so unlikely scenario of total compromise of computers accessible to a group of users, they might be tempted to resort to human-computable paper-and-pencil cryptographic methods aided by a classic Tabula Recta, which helps to perform addition and subtraction directly with letters. But do these classic algorithms, or some new ones using the same simple tools, have any chance against computer-aided cryptanalysis? In this paper I discuss how some human-computable algorithms can indeed afford sufficient security in this situation, drawing conclusions from computer-based statistical analysis. Three kinds of algorithms are discussed: those that concentrate entropy from shared text sources, stream ciphers based on arithmetic of non-binary spaces, and hash-like algorithms that may be used to generate a password from a challenge text.

翻译：在用户可访问的计算机完全被攻陷这一并非不可能的场景中，他们可能被迫求助基于塔布拉·莱克塔（Tabula Recta）辅助的人类可计算纸笔加密方法——该经典工具有助于直接对字母进行加减运算。但面对计算机辅助密码分析，这些经典算法或使用相同简单工具的新算法是否仍有一线生机？本文通过计算机统计分析得出结论：某些人类可计算算法确实能在这种极端情况下提供充分安全保障。文中讨论三类算法：从共享文本源集中熵值的算法、基于非二进制空间算术的流密码，以及可用于从挑战文本生成密码的类哈希算法。