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jdege Jul 29 2008, 04:20 AM
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 How fast does cryptographic knowledge spread throughout society?

Not very fast, given how tightly so many people hold information to their chests.

Consider, for example, the Vig. I will continue to maintain, with no evidence whatsoever, that the professionals knew how to break it in Vigenere's time. I ground that belief in two observations:

1: That Vigenere wrote about improvements to it that were intended to break the periodicity. Why, if he didn't know that the periodicity was a weakness?

2: That nobody actually used it. Or none of the professionals, anyway. They persisted with nomenclatures and codes. Why, if they believed the Vig to be indecipherable?

But leave that aside. We know that Charles Babbage knew a method for breaking Vigs in 1854, because he did so, though he didn't publish how. We know that Kasiski knew a method for breaking Vigs in 1862, because he published it. We know that Charles Dodgson (Lewis Carroll) still considered the Vig to be worthy of use in 1868, because he published a description of it.

When did the Vig's weakness become common knowledge?

What I just came across was an 1878 Brittanica (9th edition). The article on Cryptography includes:

Quote:
 
The greatest security against the decipherer has been found in the use of elaborate tables of letters, arranged in the form of the multiplication table, the message being constructed by the aid of preconcerted key-words. Details of the working of these ciphers may be found in the treatises named in this article. The deciphering of them is one of the most difficult of tasks.


Britannica doesn't often get things flat wrong, but there's not a hint that this cipher has known weaknesses. There's a comment congratulating the late Admiral Beaufort for his improvements, but no mention of Kasiski at all.

(All-in-all, it's an astoundingly uninformative article - little discussion of mechanics, and no discussion of cryptanalytic techniques. Very different from an earlier encyclopedia article I've been looking at - of which more later.)
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.
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