Bob Lord’s Crypto Museum and Charles S. Larrabee, 1871
Charles S. Larrabee set himself the goal of developing a better cryptographic method. In 1874, he proposed his method to the US Congress.
Basically, his code is a Vigenére cipher that also works with numbers. Two letters are inserted before each number:
- the first letter as an introduction/switch
- the second letter to encode the number of digits
Encrypting with Larrabee
First, the keyword is defined, which must be written in the same way by everyone. Then the keyword is written above the message and repeated in order to assign a letter of the keyword to each letter of the message.
In the table on the right, the letters of the keyword are written one after the other in the left-hand column, and next to them, under the corresponding letter of the message, is the cipher letter. Continue like this until the end of the message.
For example, if “anchor” were the keyword and “open fire” the message, “OCGUTZRR” would be the cipher.
a n c h o r a n
o p e n f i r e
O C G U T Z R R
Decrypting with Larrabee
Write down the ciphers received, then the keyword above them and repeat this as often as necessary until there is a letter of the keyword above each cipher. In Table II, write the letters of the keyword in the left-hand column one after the other, and opposite, under the corresponding letter of the cipher, write the letter of the message. Continue in this way until the end of the cipher.
Encrypting and decrypting numbers
The letters a, b, c, d, e, f, g, h, i, j stand for the digits 1, 2, 3, 4, 5, 6, 7, 8, 9, 0.
When writing down the message, if digits occur, these letters are replaced by the letter Q and other letters from A to I, which indicate the number of letters following as digits. The whole message is then converted into a cipher as usual.
When you receive a message, you translate the cipher and replace the letters indicated by Q and the letter following it with the numbers mentioned above.
Example: QDAHGD would stand for 1874.