Photo of a CSP-488.
Photo of a CSP-488 partialy disassembled.
DESCRIPTION OF CSP-488 a.k.a. M-94:CSP-488 (M-94) is composed of a central shaft on which is mounted a number of revolving disks containing alphabets on their peripheries. The disks can be removed from the central shaft and replaced in any given prearranged order. After the disks are mounted on the shaft in the order agreed upon, the plain text of the message to be enciphered is aligned across the device in a horizontal line by revolving the disks one by one. The cipher text is chose at random from the horizontal lines of letters resulting from this plain-text alignment. Succeeding lines of plain text are enciphered in the same manner until the entire message has been converted into cipher text. Decipherment is performed by a reversal of the procedure, that is, the cipher text is aligned across the device and the resulting plain text can be found by examining the other horizontal line of the letters thus formed, only one of which will "read".
The revolving wheel cryptographic principle that underlies CSP-488 was invented by Leo Battista Alberti during the fifteenth century. Centuries later, Thomas Jefferson re-invented a "Wheel Cipher" that was practically identical in principle, then followed by Major Bazeries around 1901 and Colonel Parker Hitt in 1914. All independently conceived of a device employing the same principle.
Cipher Device M-94 was adopted for Army use after WW I, its instructions were published in Feb 1922. In Oct 1926, a naval version of the same device CSP-488 was adopted.
The underlying cryptographic principle for these devices is not secure. At the beginning of WW II the M-209 (CSP-1500) device was created to replace CSP-488 as a low level, tactical cipher device. Although declared insecure in early 1942 and obsolete in Aug of 1943 by the Signal Corps Technical Committee the device remained available until fully replaced by M-209 and saw use where other systems were not available.
The operating manual from 1926 is available online at: Instructions for the Cylindrical Cipher Device, CSP 493.
DETAILS:The end plate is 1/16" thick, 1 7/16" diameter with a 1/4" hole in the center. It reads "U.S.NAVY" on the top, "CSP488" on the bottom. The letters all bottom on the same side so both texts are legible at the same time. Both are in 10 pt. fonts. The letters of U.S.NAVY are a little thicker.
The wheels are each the same 1 7/16" diameter with a 1/4" hole in the center. Each is 3/16" thick. They appear to be die stamped. The 26 notches on the left side are 3/13" deep. On the right (inside) side is stamped the letter on top and number of the disk on the bottom in 12 pt. font. With the disk rotated so the disk identifying letter and number are aligned vertically, the letter A on the outside rim is just below the index notch on the right (inside) at the 9 o'clock position. The lettering around the rim is in 10 pt. font. Below are the actual disk letter stampings. Take a look at R17 and you will note that this was first used by the Army.
REFERENCES:The information enclosed here is excerpted from:
Historical Survey Of Strip Cipher Systems. This is available from NARA; NSA Historical Collections 190/37/7/1, NR 3525 CBRK24 12957A 19450000.
SRH-366 History of Army Strip Cipher. This is available from NARA; RG 0457: NSA/CSS Finding Aid A1, 9020 US Navy Records Relating to Cryptology 1918-1950 Stack 190 Begin Loc 36/12/04 Location 1-19
Photographs by Russell Booth, San Francisco, CA.
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