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Can I decode a message that was encrypted with a one-time pad if I have the key used to encrypt it? If so, how?

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    Normally it would just be a matter of XORing the key and the message. The specific details would depend on the form of the key - if it's binary, it's probably a bitwise XOR. If it's text, it might be bitwise, or at letter level (so message "A" with key "X" gives "Y") – Matthew Jan 24 '17 at 11:04
  • yes, and that key you have is the only way to decrypt it. – dandavis Jan 24 '17 at 15:01
  • If you tell us the format, we could write a code implementation to actually perform the decryption – J.A.K. Jan 24 '17 at 19:31
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Yes, you can.

The one-time pad is usually employed as a symmetric encryption, i.e., encryption key and decryption key are the same. It is often as simple as applying XOR of key and message.

Note that the one-time pad suffers from some problems:

  • You can use a key exactly one time, otherwise the encryption is broken
  • There is no protection against altering the encrypted message
  • You need a way to exchange the one time pad keys in a secure way.

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