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"Deduce" = "guess, and test your guess" You know where the letters t,h, and e are, so you might find a sequence "the-e". You can guess this will be "there" in the message, and then you have the substitution for r which you can also try, filling in more gaps and giving you essential clues for other words. If anything starts to look wrong, backtrack and ...


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In general, the key length and number of rounds are the dominant factors in deciding cipher strength. But you need to consider how the rounds are constructed and how the key is used. Substitution and permutation are the bread and butter of DES. That's literally all it is - substitution, permutation, and XOR. Here is a diagram of the DES fiestel function ...


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Your subtracting two known solutions would be one way to eliminate $b$ from the equations and allow you to work only with $A$. However, you've already been told that $b = (0,0)$, and so we don't need to eliminate it. Instead, we know that the cipher satisfies the relations (omitting $b$ because that's known to be 0): $$\begin{gathered} A \times \left[ ...


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There are different approaches to crack a substitution cipher. A human would use a different strategy than a computer. But as the word boundaries are not preserved it will be rather challenging for a human solving this cipher. The quipqiuq tool mentioned by John is using word lists, but there are other methods as well. Resources: ...


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You can solve it at http://www.quipqiup.com/index.php in about 5 seconds. contrariwise continued tweedle dee if it was so it might be and if it were so it would be but as it isnt it aint thats logic It's an excerpt from Through the Looking-Glass by Lewis Carroll Information on how quipqiup works is available at http://www.quipqiup.com/howwork.php



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