Flag: affe
The challenge flavortext says "Found some old pseudocode, but I never implemented it."
import crypt
label START
$rand = random.range(21..29)
if $rand mod 22 == 1
continue
else
goto START
$hash = crypt.md5($rand)
print("flag{"+$hash[29]+$hash[6]+$hash[6]+$hash[14]+"}")
quit
Examining the code, we see that it seeds an md5 hash implementation with a
number between 21 and 29 that is 1 mod 22, and constructs a flag from bits in
the hash.
The hash function is deterministic for a given seed, and 23 is the only number in the allowed range that is 1 mod 22, so we can implement the pseudocode using 23 as the seed to construct the flag:
>>> import hashlib
>>> m = hashlib.md5("23")
>>> digest = m.hexdigest()
>>> print digest[29] + digest[6] + digest[6] + digest[14]
affe
The flag is thus affe.