Skip to content

Instantly share code, notes, and snippets.

@hellman
Last active June 29, 2020 13:51
Show Gist options
  • Save hellman/c3894350f5c917b31011192162484384 to your computer and use it in GitHub Desktop.
Save hellman/c3894350f5c917b31011192162484384 to your computer and use it in GitHub Desktop.
TCTF/0CTF 2020 Quals - emmm (crypto)
#!/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')
Display the source blob
Display the rendered blob
Raw
Loading
Sorry, something went wrong. Reload?
Sorry, we cannot display this file.
Sorry, this file is invalid so it cannot be displayed.