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This seems like a really simple problem. I just can't seem to figure it out. A message was encrypted using a Block Cipher that seems to follow an Electronic Codebook method. I know that they took it in blocks of 3 characters at a time. I know what the message says and I know what the cipher text says; but I want to know the keys. The problem says that it was encrypted using the same method twice but with different keys. Is it possible to find the keys without brute forcing it?

If not, then how would I minimize the time needed to brute force the key?

BTW: The key is in hex and it can only be 6 characters long maximum. So the biggest key possible in decimal would be 16777215

Pranav Jain
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  • And your intention is? I hope it is not something related to hacking. – Cem Özer Nov 07 '14 at 07:05
  • it is a cryptographic problem that someone posted... it is related to hacking, but the problem was supposed to be hacked. Nobody actually used ECB to encrypt their data. Plus, you almost never have both the plaintext and the cipher text. – Pranav Jain Nov 07 '14 at 07:11
  • @PranavJain That last statement is wrong, having both plaintext and cipher text is extremely common as a message almost never consists of random characters in real life. – Maarten Bodewes Nov 07 '14 at 13:19
  • You need to implement a meet in the middle attack here. Try it and come back if your implementation keeps failing after debugging. – Maarten Bodewes Nov 07 '14 at 13:22
  • But doesn't it require a lot of resources to store and run all 16777215 options twice – Pranav Jain Nov 07 '14 at 18:01
  • Ok... I tried it, and outputted the results of the encryption and decryption into two separate text files... how do I find the similar lines with minimal compute time. – Pranav Jain Nov 08 '14 at 00:33

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