| Viewing Single Post From: Double cipher challenge | |
|---|---|
| jdege | Aug 11 2007, 06:43 PM |
Elite member
  ![]](http://209.85.122.85/static/1/pip_r.png)
|
Think about it a bit more. Consider what happens when you apply a substitution to the output of a substitution. The result is just another substitution. That is, if in the first substitution, A=>X, and in the second X=>G, then you've really done nothing more that A=>G. The same holds true no matter how many different substitutions you apply - there is always a single substitution that produces the same result. Multiple passes of Vigenere using different keys, but of the same length, is the same. Encrypt once with keyword FRED and then again with the keyword ADAM, and the result is the same as if you'd encrypted with the keyword FUEP. 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. |
| When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl. | |
 |
|
| Double cipher challenge · Challenges | |
2:56 PM Nov 26
