Programming Lewis Carroll's *Memoria Technica*

Charles Dodgson (pen name Lewis Carroll) had difficulty remembering numbers, such as dates. He developed a cipher to help him remember numbers by embedding them in couplets or phrases. For example, the couplet “Brass trumpet and brazen bassoon, will speedily mark you a tune” encodes the specific gravity of brass (8.39) in the last four consonants: r k t n (y is treated as a vowel). In this article, we describe the cipher, present online tools for encoding and decoding, discuss how we implemented the algorithms in TypeScript, and the cipher’s relevancy to steganography.

The cipher encodes plaintext’s of sequences of digits. Using the cipher, consonants (except ‘y’) are mapped to digits. Vowels, punctuation, and ‘y’ are ignored and thus can be freely added to the ciphertext The mapping follows the figure:

Decoding ciphertext involves extracting the consonants from a message and finding the mapped integer. Vowels, y, and punctuation are ignored.

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