Viewing Single Post From: Double cipher challenge

Viewing Single Post From: Double cipher challenge
jdege	Aug 13 2007, 04:38 PM
Elite member Posts: 263 Group: Admin Member #246 Joined: December 7, 2006	Revelation Aug 12 2007, 02:09 PM Quote: Now think about what happens, if you encrypt with a simple substitution, then again with Vigenere - the result is the same as if you'd encrypted with Vigenere alone. The keyword for this equivalent Vigenere is different than what you used in the original, but that doesn't matter to the cryptanalyst, who doesn't know the keyword anyway. I don't think this is right, since a substitution is not a shift. By Vig, I meant to include Vigs that use mixed alphabets, rather than just simple shifts. Shifts are a small subset of substitutions. And a shift plus a shift yields a shift. But a substitution plus a substitution yields a substitution, and therefore a shift plus a substitution yields a substitution. If it is a simple sub plus a shifted normal alphabet vig, the result is a shifted mixed alphabet vig. If it is a simple sub plus a shifted mixed alphabet vig, the result is still a shifted mixed alphabet vig.
	When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

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