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I'm currently studying for a cryptography exam. I've been given ciphertext that has been encrypted by a columnar transposition cipher. I've been given no shift key length or key word, the only thing I know is that only 2 columns have been shifted.

How can I determine the key? Or better yet, is there another way to decipher the ciphertext?

otus
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EMJ
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  • I am not looking for someone to decipher, simply to assist in how I would go about this. I find myself going around in circles. – EMJ Oct 06 '15 at 07:39
  • Are you allowed to just perform plain brute-force? BTW: The #1 technique for this would be *sliding window*. – SEJPM Oct 06 '15 at 12:38
  • *" the only thing I know is that only 2 columns have been shifted."* - So you don't have just a [simple columnar transposition cipher](https://en.wikipedia.org/wiki/Columnar_transposition_cipher#Columnar_transposition) but rather some combination of a columnar transposition and a shift cipher? – SEJPM Oct 06 '15 at 15:47

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(Although your question is for a long time ago) Transposition ciphers don't change the frequency of letters in their ciphertexts. So, you can implement a frequency attack. For decryption by this you only need the table of frequency of English letters and your ciphertext. (Your encryption scheme here is a Columnar transposition with a key that all its letters are in order except 2 of them.)

ssss1
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