Attacking Decipherment Problems Optimally with Low-Order N-gram Models

We introduce a method for solving substitution ciphers using low-order letter n-gram models. This method enforces global constraints using integer programming, and it guarantees that no decipherment key is overlooked. We carry out extensive empirical experiments showing how decipherment accuracy varies as a function of cipher length and n-gram order. We also make an empirical investigation of Shannon's (1949) theory of uncertainty in decipherment.

• Type: Conference
• Year: 2008
• Where: EMNLP
• Authors: Sujith Ravi, Kevin Knight
• Keywords: Decipherment Accuracy, Decipherment Key, EMNLP 2008, Letter N-gram Models, Natural Language Processing