Could someone please give a walkthrough of how this works: Decrypting a vigenere cipher with a reused one-time pad.

It was never fully answered with the example given in the comment.


Plaintext 1 - apples

Plaintext 2 - orange

Key : fruits

They are all 6 letters. If 'fruits' was used to encrypt both 'apples' and 'oranges' using vigenere, how could an attacker obtain the plaintexts and key with only knowing the ciphertexts?

  • $\begingroup$ Thanks, can you explain why, and is it the same case for two plaintexts and key all of 10 characters? $\endgroup$ Commented Nov 1, 2019 at 13:07
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    $\begingroup$ Note that there was a mistake with that answer. I've corrected it now. After you subtract you will get a relation of plaintext. Then you can use crib-draging. After you found some part of the plaintexts you get the key. you are done. $\endgroup$
    – kelalaka
    Commented Nov 1, 2019 at 13:17
  • $\begingroup$ Can you explain how please. Say I have two 10 letter plaintexts and one 10 letter key which is OTP. I use that OTP on both plaintexts two obtain 2 10 letter ciphertexts. I do c1 - c2 to obtain p1-p2. From p1-p2 how do i get the key and/or the actual plaintext values. Appreciate the help, thank you $\endgroup$ Commented Nov 1, 2019 at 13:20
  • $\begingroup$ Did you look into crib dragging already? It's in the comment, but not in your response. $\endgroup$
    – Maarten Bodewes
    Commented Nov 1, 2019 at 14:56
  • $\begingroup$ Yeah I dont understand it and wanted an exmaple $\endgroup$ Commented Nov 1, 2019 at 15:51


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