If you AES the last line,
With a key made of something divine,
And then you XOR
The SHA-1 of "4",

Can you figure out what the "divine thing" is and then follow the instructions to determine what the keyword hidden in the last line of this limerick is?

Important hint:

The AES key is a word padded with null characters at the end to make it 16 bytes total.

  • $\begingroup$ purely aes or also an operation mode like cbc? $\endgroup$ – Vincent Apr 17 '15 at 21:58
  • $\begingroup$ Oh, yes, I forgot to mention, it's AES ECB, like you're probably thinking. Nothing fancy. $\endgroup$ – Joe Z. Apr 17 '15 at 21:59
  • $\begingroup$ 128 bit aes? :p $\endgroup$ – Vincent Apr 17 '15 at 22:04
  • $\begingroup$ AES is always 128-bit unless specified otherwise. (At least, I think that's the convention...) $\endgroup$ – Joe Z. Apr 17 '15 at 22:04
  • 2
    $\begingroup$ @IanMacDonald Neither does the last line :p $\endgroup$ – Tryth Apr 17 '15 at 22:50

The key (before null padding) is


After properly decoded, AESed and XORed the last line is

`You'll find that the answer is 'brine'.\x00You'll find that the answer is 'brine'.\x00


Not an answer, i just wanted to create some activity

Well.. after a long talk with the OP i figured out the following:

With a key made of something divine,

GOD, god is something divine (obviously)

Sha-1 of 4


The last line

now if you AES this line with god (encrypt or decrypt) rubbish comes out, XOR this with the hash of 4 and it still makes no sense.

I'm just too stupid to follow simple instructions, it's a miracle my house isn't on fire yet :P

  • $\begingroup$ I can tell you, the divine thing is not a soul. $\endgroup$ – Joe Z. Apr 24 '15 at 17:37
  • $\begingroup$ Also, the base 64 encoding is just to transcribe encrypted binary data. You need to apply all the ciphers to the bytes of the last line. $\endgroup$ – Joe Z. Apr 24 '15 at 17:38
  • $\begingroup$ Thirdly, notice that the SHA-1 of 4 is only a fifth of the length of the line. You may need to repeat the key multiple times. $\endgroup$ – Joe Z. Apr 24 '15 at 17:39
  • $\begingroup$ @JoeZ. use all the ciphers on the last line? do you know how many ciphers there are in the world? :P I'll never get them all ;) $\endgroup$ – Vincent Apr 24 '15 at 17:45
  • $\begingroup$ All the ciphers mentioned in the question, i.e. the AES and the XOR. $\endgroup$ – Joe Z. Apr 24 '15 at 17:45

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