Signal Corps Association Reenactors Division (SCARD)

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Posted By: Dave Gaddy on: 05/15/2010 23:07:15 EDT
Subject: RE: Cipher disk

Message Detail:
The CS disk is a "reader" to facilitate use of the Court (aka Diplomatic aka Signal Corps aka Government aka Richmond) cipher, now commonly called the Vigenere, which is polyalphabetic substitution with keyword. The disk was one of a half dozen or so ways of using the cipher, most of which were intended to guide the eye and avoid errors in the process. At least one user griped that the "alphabet within an alphabet" was all that he had (i.e., a disk) and he asked for a reel or "box reader," referring to a couple of the forms attributed to Capt. Barker. I agree with him -- the disk does not "guide the eye" and I don't use it, preferring paper and pencil (with eraser) on grid paper. Porter Alexander said that, over time, the signalmen learned the mathematical basis behind the cipher and could "work it in their heads," which I suppose is the fastest method, but again provides no "garble check," a problem with the disk.
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