The
CSP-488 is a cipher wheel used by the United States Navy since 1930 until
declared insecure over a decade later. It's predecessor, the
M94 was adapted for Army use after World War I. It's instructions
were published in February of 1922, coinciding with archaeologist Howard
Carter's discovery of King Tut's tomb in the Egyptian Valley of Kings.The underlying cryptographic wheel concept was invented by Leo Battista Alberti in the fifteenth century, only to be reinvented centuries later by Thomas Jefferson. Major Bazeries and Colonel Parker Hitt also independently invented devices in the early 1900's that operated under the identical principle.
The CSP-488 is composed of a shaft on which 25 rotating discs can be placed in any order. The discs each contain a complete alphabet in a seemingly random order around their peripheries. After the discs are mounted in a predetermined order based on a key, they are individually rotated so that the given cipher text is shown across a single horizontal line in chunks of 25 characters. The unit as a whole is then rotated until a legible plaintext appears on any of the other non-ciphertext lines. You can try an interactive CSP-488 here.
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The table above is a representation of the wheels on the CSP-488. Notice the clever order of the alphabet etched onto wheel R 17.
The predetermined order of the wheels used to decipher or encipher a message are based on a key. This key is repeated in a table until 25 characters are satisfied. This is how the table would look for the key phrase IN GOD WE TRUST:
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 |
| I | N | G | O | D | W | E | T | R | U | S | T | I | N | G | O | D | W | E | T | R | U | S | T | I |
To determine the wheel order, move through this table from left to right, numbering the letters in alphabetical order. The first letter of the alphabet used in our key is D, because not A, B, nor C appears in the phrase IN GOD WE TRUST:
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 |
| I | N | G | O | D | W | E | T | R | U | S | T | I | N | G | O | D | W | E | T | R | U | S | T | I |
| 1 | 2 |
The next letter of the alphabet in our key is E:
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 |
| I | N | G | O | D | W | E | T | R | U | S | T | I | N | G | O | D | W | E | T | R | U | S | T | I |
| 1 | 3 | 2 | 4 |
Continue this process until all 25 characters are assigned a number:
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 |
| I | N | G | O | D | W | E | T | R | U | S | T | I | N | G | O | D | W | E | T | R | U | S | T | I |
| 7 | 10 | 5 | 12 | 1 | 24 | 3 | 18 | 14 | 22 | 16 | 19 | 8 | 11 | 6 | 13 | 2 | 25 | 4 | 20 | 15 | 23 | 17 | 21 | 9 |
This sequence is the wheel order used to decipher or encipher a message with the key IN GOD WE TRUST. Each wheel is assigned a letter/number combination for identification. Using the number from each ID, the wheels are placed on the shaft in order beginning with 7, 10, 5, 12, and continuing to the last wheel, 9, according to the sequence we determined above.
Decrypting a message is as easy as rotating the wheels so a single line shows the cipher text, and then finally rotating the entire device to find the only line that can be read. Encryption is the reverse process. The message can be encoded by choosing any of the 25 non-plaintext lines as cipher text. That's all there is to it!
For fun, using the key IN GOD WE TRUST, decipher the following cipher text with the CSP-488: HSCSBPBBEONTJMSIJJJJIFZN
I challenged myself to write a CSP-488 simulator for VB.NET. I wanted an easy way to change the key on the fly while viewing all 26 lines of the cipher wheel simultaneously. I also wanted a way to modify both the plaintext and cipher text at any given time without changing any other variables. The result is the neat little application that allows real-time key, plaintext, and cipher text editing with all 26 lines visible in an organized table. The mathematical processes by which all of the variables are calculated are quite complicated, but this virtual CSP-488 yields flawless results. If you are uncomfortable downloading executables, don't hesitate to contact me for the source code. NOTE: THE SOURCE CODE IS NO LONGER AVAILABLE. (AUG. 2007)
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Download 64KB: CSP-488.exe
Maritime: USS Pampanito - CSP-488
http://www.maritime.org/csp488.htm
Virtual U. S. Army Cipher Device, Model M-94
http://members.aon.at/cipherclerk/VirtualM94.html
M-94 (CSP-488)
http://webhome.idirect.com/~jproc/crypto/m94.html