Go straight to the demonstrators: Alphabet CipherTelegraph Cipher

Introduction

Dodgson’s interest in ciphers and the processes he developed are referred to in his diaries and letters and in two cases (the Alphabet Cipher and the Telegraph Cipher), were privately published. These are the primary sources of information relating to his work and interest in this subject and the foundation for these pages and facilities.

The Key-Vowel and Matrix Ciphers

Several of Dodgson’s diaries are now missing, including the first two volumes. The first reference to ciphers in the surviving diaries is dated 15 February 1856, in which Dodgson states: “I am thinking of writing on ‘Cipher’ for the Train, but must first consult Mr. Yates as to whether the subject will be admissible.” The Train was a newly published journal edited by Edmund Yates. Dodgson received his copy of the first issue on 8 January 1856. On 16 March 1856, Dodgson met with Yates to discuss possible contributions to The Train; “Cipher” was one of the proposed topics.

The level of Dodgson’s interest in ciphers around this time is unknown. His proposed article for The Train might have been a simple explanation of known coding systems of the time or he might have already developed some processes of his own. It is probably safe to assume, at least, that he was exploring the concept and understanding what had been developed so far.

Dodgson’s diary entry for 24 February 1858 reveals some progress with developing his own systems: “Invented a system of cipher, which I think looks promising, as it may be carried entirely in the head.”

This system, later referred to as the Key-Vowel Cipher is described in full on the subsequent pages of the diary. It is based on simple substitution of one letter for another, using a shared key word and a process for deriving the encoded letter.

Two days later, Dodgson records in diary that he has invented “another cipher, far better than the last”. He goes on to describe the advantages of this new system. The system, the Matrix-Cipher, uses a table of letters and a numerical system to encode the message, based on the location of the letters in the table. The system is rather more complex than Carroll’s other ciphers and requires a number of additional actions to ensure the system is safe and usable.

Full details of these two systems can be found in The Mathematical Pamphlets of Charles Lutwidge Dodgson and Related Pieces by Francine Abeles, published by the Lewis Carroll Society of North America, 1994. The terms Key-Vowel and Matrix Cipher were coined by Abeles in this publication.

The Alphabet and Telegraph Ciphers

The subject of ciphers re-appears in correspondence and diary entries around 1868, first in a letter to Agnes Argles (17? April 1868) in which he suggests that he will send Edith [her sister] a key-word, “if she wants to try her hand at writing in cipher”.

The reference to sending a “keyword” suggests that Carroll might have been teaching Edith the Alphabet-Cipher, which was published on a single sheet of white card, but is difficult to date precisely. Click Here for a large image of the published Alphabet Table and Click Here for the Instructions printed on the other side of the card.

In a subsequent letter (dated 22 April 1868) he writes again to Agnes Argles stating “Don’t let Edith torture you with that funny way of writing, but tell her I’m going to send her a better way that’ll make her hair stand on end with delight. Babies of six months old easily learn how to write it in a minute, and a whole regiment with fixed bayonets couldn’t find it out in a fortnight, without knowing the key-word. Also I’ll send the new rules, when I’ve had time to invent them”.

Dodgson’s diary for this same date refers to a “new” cipher: “Sitting up at night I invented a new cipher, which I think of calling the ‘telegraph-cipher’”. His diary entry for 24 April 1868 also refers to the Telegraph-Cipher and his showing it to George Hunt, the Chancellor of the Exchequer. The Telegraph Cipher was published in the form of a single white card, undated, with instructions on one side and diagrams on the other which were to be cut-out for use. Dodgson’s letter, dated 29 April 1868, to Edith Argles describes this new cipher and gives an example, which uses the same technique as described in the published single-sheet undated version.

For full bibliographical details of the Alphabet-Cipher and the Telegraph-Cipher see Charles Lutwidge Dodgson, A Bibliogrpaphy... by Charlie Lovett, published by The Lewis Carroll Society of North America, 2024, page 51.

The only two subsequent references to ciphers in Dodgson’s diaries (29 March 1885 and 24 February 1893) are brief and do not reveal the aspects of the subject to which he is referring.

Alan Garner’s Red Shift

The two characters, Tom and Jan, in Garner’s novel, use Carroll’s Alphabet Cipher when writing to each other in order to stop Tom’s mother from reading their letters. In the end papers of the published book, the final encoded letter from Tom to Jan is printed. If you can work out the keyword that Tom uses, then, in theory, you should be able to decode his final letter using this facility. However, there are two complications. Firstly, Garner uses Carroll’s code incorrectly, by transposing the rows and columns when using the grid. This means that in order to decode Tom’s letter you will actually need to treat it as a message you are encoding it rather than decoding. Secondly, our facility only handles messages of up to 145 characters - it is, after all, a demonstrator, not a tool for practical use. Tom’s letter can be broken down into short sections, but care much be taken to ensure that the number of letters in each section is divisible by the number of letters in the keyword.