Cryptography Stack Exchange is a question and answer site for software developers, mathematicians and others interested in cryptography. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I need to crack a stream cipher. I have a set of plain text and encrypted text pairs.

The hint to the question asks me to use entropy analysis and look at the hex dump of the encrypted text. However, I couldn't find anything useful in either of them.

What should be the approach to solve this cipher?

share|improve this question
Try xoring two ciphertexts and look at the entropy. Also, to recover the encryption stream, xor the pt and ct. Then you could compare multiple encryption streams. – mikeazo Feb 1 '14 at 20:48

If the key is always the same and there is no IV (or fixed IV), then

$$plaintext1 \oplus ciphertext1 \oplus ciphertext2 = plaintext2$$

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.