TCTF/0CTF 2020 Quals - emmm (crypto)
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#!/usr/bin/python2 | |
import random | |
from struct import pack,unpack | |
from flag import flag | |
P = 247359019496198933 | |
C = 223805275076627807 | |
M = 2**60 | |
K0 = random.randint(1, P-1) | |
K1 = random.randint(1, P-1) | |
# not a bijection? can be adjusted but I'm lazy | |
def encrypt_block(x): | |
tmp = x * K0 % P | |
tmp = tmp * C % M | |
tmp = tmp * K1 % P | |
return tmp | |
for i in range(2**24): | |
pt = random.randint(1, P-1) | |
ct = encrypt_block(pt) | |
print pt, ct | |
pt = flag[5:-1] | |
assert flag.startswith('flag{') and flag.endswith('}') and len(pt)%8==0 | |
fmt = '%dQ' % (len(pt)/8) | |
ct = pack(fmt, *map(encrypt_block, unpack(fmt, pt))) | |
print ct.encode('hex') |
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https://nbviewer.jupyter.org/urls/gist.github.com/hellman/c3894350f5c917b31011192162484384/raw/918e8dfd7d5e96d570704e1dd36982d541f6fb9f/2_writeup.ipynb