I'm trying to learn how to go about cracking RC4 ciphers (nothing illegal, its an old, i.e., not active challenge for a job application, so no cheating).

I have nine md5 hashes with their own ciphers. One cipher is significantly shorter than the rest. Two "ciphers" are blanks with only MD5 hashes. Six ciphers are of the same length.

They hint that the key is very long, and my assumption is that brute forcing the key is out of the question. In the python code that they provided, I can see that the same key has been used for each cipher.

Any guidance on how to do this? I've been at it for the past week, learning quite a bit, but not enough.


There is one class in their code that says it's a test and will be removed later. That could be a possible hint and potentially be plaintext I suppose.

  • $\begingroup$ Try Crib-Dragging... search this site for this. $\endgroup$
    – kelalaka
    Feb 21 at 0:34
  • $\begingroup$ Thing is, the ciphers are mostly encoded python code, to make the main script run. I find crib dragging python code a bit awkward, because I suppose the main idea of crib dragging is guessing words until you got a plaintext? $\endgroup$
    – rizzlan
    Feb 21 at 0:50
  • 1
    $\begingroup$ One thing that I did once is to try all possible characters for a location. When you XOR the ciphertext streams you get the XOR of the plaintexts. So if the result of the tried character XOR'ed with one of those streams results in an invalid character it is obviously not part of either of the two plaintexts..Actually, if you do this for a plaintext that has been XOR'ed with many other plaintext you can quickly rule out a lot of options. Only works if you have more than a few ciphertexts of course. $\endgroup$
    – Maarten Bodewes
    Feb 21 at 1:02
  • 1
    $\begingroup$ i could not get this line please -Two "ciphers" are blanks with only MD5 hashes. what does blank cipher mean $\endgroup$
    – Uraguan
    Feb 21 at 4:01

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