Cryptology ePrint Archive: Report 2020/1492

Automated ciphertext-only attack on the Wheatstone Cryptograph and related devices

Thomas Kaeding

Abstract: We examine some historical proto-mechanical cryptographic devices, such as the Wheatstone Cryptograph, that employ revolving clock hands or rotating concentric disks. The action of these “cipher clocks” can be factored into a stream cipher followed by a monoalphabetic substitution. This allows us to perform a stochastic hill-climbing attack to break the substitution. The attack maximizes a fitness that measures how well a decryption of the substitution cipher resembles an encryption of the stream cipher alone.

Category / Keywords: Wheatstone Cryptograph, Wadsworth cipher disk, Urkryptografen, cipher clock, hill-climbing attack

Date: received 28 Nov 2020

Contact author: hippykitty at protonmail com

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Version: 20201129:191711 (All versions of this report)

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