decipherment

Decipherment is the process of interpreting encoded information in order to recover its original meaning. The term is used in two primary contexts: cryptanalysis, the study of breaking ciphers and recovering plaintext without the intended key, and the decipherment of unknown writing systems, where researchers seek to reconstruct a language from inscriptions.

In cryptography, decipherment involves testing hypotheses about the encryption method, exploiting linguistic patterns, and applying computational methods. Classical methods include frequency analysis and crib techniques for substitution ciphers; more recently, algorithmic and probabilistic approaches, various forms of known-plaintext or chosen-plaintext attacks, and extensive use of computers. Historic milestones include the break of the German Enigma in World War II, accomplished by Allied cryptanalysts at Bletchley Park, and the understanding of simple substitution ciphers such as the Caesar cipher. In modern cryptography, decipherment is governed by mathematical principles and is a legitimate security concern; decryption with the correct key is distinct from unauthorized cryptanalysis.

In unknown-script decipherment, scholars use bilingual texts, linguistic comparison, and cross-disciplinary evidence to infer the language and its writing. Notable successes include the decipherment of Egyptian hieroglyphs by Jean-François Champollion with the Rosetta Stone, and the complete decipherment of Linear B by Michael Ventris (with John Chadwick). Earlier breakthroughs contributed to deciphering cuneiform. Some scripts, such as the Voynich manuscript and several proposed proto-writing systems, remain undeciphered or controversial.