## Solution to A Puzzle with the Answer CRONIN

Author: Quinn Mahoney

The puzzle shows the Cheshire Nyan Cat, speeding through a field of stars. The filenames for the puzzle, cronin.html, and the music, cronin.mp3, clue the false answer CRONIN. After you've stared at the Cat for a while, and incorrectly guessed NYAN as the title, you'll notice that the stars seem to come in groups. An inspection of the source code shows that the stars arrive in groups of 32 and the vertical position of each is dictated by the contents of the file, data.txt.

data.txt contains about 3.3 megabytes of hexadecimal data. It seems random, but once the data is broken up into 32-character pieces, you should notice a particular string repeated a dozen times:

```d41d8cd98f00b204e9800998ecf8427e
57cec4137b614c87cb4e24a3d003a3e0
3700f097e741a7702f7e4ac61ed88c1a
cae8d14edd025e72c59dbab6f378c95a
b4bd7238111424a17180fc52c88fed96
d41d8cd98f00b204e9800998ecf8427e
03c7c0ace395d80182db07ae2c30f034
0b180078d994cb2b5ed89d7ce8e7eea2
a587b16e0a2c4a9c61feee6486c3a6c5
d5e1f5a7f2fe3dab21da19f1c04fbd2b
d41d8cd98f00b204e9800998ecf8427e
e358efa489f58062f10dd7316b65649e
01b6e20344b68835c5ed1ddedf20d531
…
```

The repeated string is: d41d8cd98f00b204e9800998ecf8427e. You might recognize it anyway, but copy it into Google and you'll find that it is the MD5 hash of the empty string, represented in hexadecimal. It seems the contents of data.txt is a series of MD5 hashes. Also notice that the 'empty' hashes are spaced anywhere from two to ten hashes apart; this is a hint that the hashes are divided up by words. You wouldn't ordinarily try to brute-force cryptographic hashes, but it's Mystery Hunt, so it's worth a shot. You'll find that each hash builds on the hash before it, adding one character each time, and resetting every time there's an empty hash. That looks like the following:

```d41d8cd98f00b204e9800998ecf8427e
57cec4137b614c87cb4e24a3d003a3e0  Y
3700f097e741a7702f7e4ac61ed88c1a  Yo
cae8d14edd025e72c59dbab6f378c95a  You
b4bd7238111424a17180fc52c88fed96  You're
d41d8cd98f00b204e9800998ecf8427e
03c7c0ace395d80182db07ae2c30f034  s
0b180078d994cb2b5ed89d7ce8e7eea2  su
a587b16e0a2c4a9c61feee6486c3a6c5  sur
d5e1f5a7f2fe3dab21da19f1c04fbd2b  sure
d41d8cd98f00b204e9800998ecf8427e
e358efa489f58062f10dd7316b65649e  t
01b6e20344b68835c5ed1ddedf20d531  to
…
```

Once you've decoded the entire data.txt, you get a quotation from the Cheshire Cat, followed by a second stream of data:

```You're sure to get somewhere, if you only walk long enough.
da39a3ee5e6b4b0d3255bfef95601890afd80709
08a914cde05039694ef0194d9ee79ff9a79dde33
0d94103eaba0e8fcbb475d8c9ebcf4752ef898ed
da39a3ee5e6b4b0d325…
```

The repeated string in this stream of data is the SHA-1 hash of the empty string, da39a3ee5e6b4b0d3255bfef95601890afd80709. Follow the steps above to decode again. You'll get another quotation from the Cheshire Cat, followed by a third stream of data:

```Oh you can't help that. We're all mad here. I'm mad. You're mad.