Automatic Key Structure Extraction

Abstract

Studying original cipher keys constructed throughout history gives important insights into encryption methods and cipher systems. We can study the type of encryption used, the code structure and their corresponding plaintext entities, be it letters, morphemes, words, or named entities. The insights can lead us to better decryption methods, and the understanding of the development of historical ciphers. In this paper, we present a tool for automatic key structure extraction that describes the symbol system and the code structure along with the encoded plaintext features and the mapping between the two. The tool is aimed at the empirical study of historical keys given transcribed keys.

Key Design in the Early Modern Era in Europe

“…We provide automatic description of keys based on their transcription and extract statistical information from the transcription file b y u tilising a Python script that analyses the text file and returns a detailed analysis of its content, as described in Tudor (2019) and Tudor et al (2020).…”

Transcription of Historical Ciphers and Keys

“…symbols without any corresponding plaintext characters to confuse the cryptanalyst to make decryption even harder, explained in cleartext, or given as cipher symbol (Megyesi et al, 2019). Codes might also be present without any plaintext, serving as placeholders (Tudor et al, 2020).…”

“…We list the key items as <CODE-PLAINTEXT> pairs where each unique pair is written in a line, first the code followed by the separator '-', then the plaintext unit, being it a character in the alphabet, syllable, word, null, or punctuation mark. Nulls are transcribed as <NULL> and missing plaintext of a code is transcribed as <EMPTY> (Tudor et al, 2020).…”