Cryptology ePrint Archive: Report 2017/339

ElsieFour: A Low-Tech Authenticated Encryption Algorithm For Human-to-Human Communication

Alan Kaminsky

Abstract: ElsieFour (LC4) is a low-tech cipher that can be computed by hand; but unlike many historical ciphers, LC4 is designed to be hard to break. LC4 is intended for encrypted communication between humans only, and therefore it encrypts and decrypts plaintexts and ciphertexts consisting only of the English letters A through Z plus a few other characters. LC4 uses a nonce in addition to the secret key, and requires that different messages use unique nonces. LC4 performs authenticated encryption, and optional header data can be included in the authentication. This paper defines the LC4 encryption and decryption algorithms, analyzes LC4's security, and describes a simple appliance for computing LC4 by hand.

Category / Keywords: secret-key cryptography / low-tech ciphers, authenticated encryption

Date: received 12 Apr 2017

Contact author: ark at cs rit edu

Available format(s): PDF | BibTeX Citation

Version: 20170421:213331 (All versions of this report)

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