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Dec 5: Only One Hint
Challenge
Here is your flag:
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0x69355f71
0xc2c8c11c
0xdf45873c
0x9d26aaff
0xb1b827f4
0x97d1acf4
and the one and only hint:
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0xFE8F9017 XOR 0x13371337
Solution
0xFE8F9017 XOR 0x13371337 is 0xedb88320 which is a polynomial involved in CRC32, and indeed
crc32('HV17') is 0x69355f71
Let’s try to bruteforce the other parts:
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import binascii
import itertools
import string
alphabet=string.printable
ct = [0x69355f71, 0xc2c8c11c, 0xdf45873c, 0x9d26aaff, 0xb1b827f4, 0x97d1acf4]
perms = list(itertools.product(alphabet, repeat=4))
for p in perms:
out = binascii.crc32( ''.join(p) ) & 0xffffffff # & 0xffffffff only needed in python2
if out in ct:
print("bingo! "+ tst +" ("+hex(out)+")")
which gives the following output:
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bingo! 7pKs (0xc2c8c11c)
bingo! h4rp (0xb1b827f4)
bingo! o6wF (0x9d26aaff)
bingo! whyz (0xdf45873c)
bingo! HV17 (0x69355f71)
bingo! Qlt6 (0x97d1acf4)
whoo!
Flag
HV17-7pKs-whyz-o6wF-h4rp-Qlt6