72 lines
1.8 KiB
Python
Executable File
72 lines
1.8 KiB
Python
Executable File
#!python3
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from pwn import *
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from Crypto.Cipher import DES
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#conn = process(["python3", "./ddes.py"])
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conn = remote("mercury.picoctf.net", 5958)
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conn.recvline()
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flag_encrypted = unhex(conn.recvline())
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log.info("encrypted flag: {}".format(enhex(flag_encrypted)))
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conn.recvuntil(b"? ")
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def encrypt_remote(data):
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conn.sendline(enhex(data).encode())
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enc = unhex(conn.recvline())
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conn.recvuntil(b"? ")
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return enc
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def pad(msg):
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block_len = 8
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over = len(msg) % block_len
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pad = block_len - over
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return (msg + b" " * pad)
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def des(data1, data2, k):
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cipher = DES.new(k, DES.MODE_ECB)
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return (cipher.encrypt(data1), cipher.decrypt(data2))
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def ddes(data, k1, k2):
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cipher1 = DES.new(k1, DES.MODE_ECB)
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cipher2 = DES.new(k2, DES.MODE_ECB)
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return cipher1.decrypt(cipher2.decrypt(data))
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msg = b"abcdef"
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log.info("encrypting message remotely: {}".format(msg.decode()))
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denc = encrypt_remote(msg)
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log.info("encrypted message: {}".format(enhex(denc)))
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conn.close()
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a, b = des(pad(msg), pad(msg), b"123456 ")
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c, d = des(b, a, b"123456 ")
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assert c == d
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to_enc = pad(msg)
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to_dec = denc
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P = log.progress("calculating encryptions...")
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keyspace = 10**6
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encs = set()
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encs_dict = {}
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decs = set()
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decs_dict = {}
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for i in range(keyspace):
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k = pad(str(i).encode())
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a, b = des(to_enc, to_dec, k)
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a = enhex(a)
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b = enhex(b)
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encs.add(a)
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encs_dict[a] = i
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decs.add(b)
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decs_dict[b] = i
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collisions = encs & decs
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P.success("{} collision(s) found".format(len(collisions)))
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collision = collisions.pop()
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k1 = pad(str(encs_dict[collision]).encode())
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k2 = pad(str(decs_dict[collision]).encode())
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log.info("k1: {}".format(k1.decode()))
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log.indented("k2: {}".format(k2.decode()))
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flag = ddes(flag_encrypted, k1, k2)
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log.success("flag: {}".format(flag.decode()))
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