From the course: Symmetric Cryptography Essential Training

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Permutation and transposition ciphers

Permutation and transposition ciphers

From the course: Symmetric Cryptography Essential Training

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Permutation and transposition ciphers

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- [Instructor] Now we're talking about a different kind of cipher, something that's called a permutation or a transposition cipher. And really, all that happens is input text just gets rearranged. And like shift ciphers, this is mostly of historical importance and also to introduce the concept of diffusion, which is important in modern crypto systems. We can use frequency analysis on permutation ciphers too. Permutation is really easy to detect, and that's because the letters don't change. So when I run a frequency analysis on it, it will show the same patterns as the language used. If I have permuted version of an English language document, it will have exactly the same letter frequency as the original did. One of the kinds of permutation ciphers is something called a matrix or a table transposition. If we have a message, super secrecy, we will write it into a table row by row like this: S-U-P-E go into the top row and so on. But when we read the letters out, we read it out column by…

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