1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
|
#!/usr/bin/env python3
from pwn import *
from hashlib import md5
from ctypes import CDLL
import subprocess
import sys
# context.log_level = "DEBUG"
args = sys.argv[1:]
if args == []:
args = ["nc", "localhost", "1024"]
libc = CDLL("libc.so.6")
def connect():
io = process(args)
io.readuntil(b"After ")
leak = int(io.readline().split()[0])
flips = ""
for _ in range(5):
io.sendline(b"H")
io.readuntil(b"The coin lands on ")
flips += io.readline().decode()[0]
return io, leak, flips
def gen_key(seed, flips):
libc.srand(seed)
libc.rand()
for _ in flips:
libc.rand()
key = flips
value = libc.rand() & 0x7fff
for _ in range(32):
concat = (key + str(value) + "\n").encode()
key = md5(concat).hexdigest() + " -"
return key
def test_seed(seed, leak, flips):
libc.srand(seed)
value = libc.rand() & 0x7fff
if value != leak:
return False
nflips = ""
for _ in flips:
value = libc.rand() & 0x7fff
nflips += 'H' if value % 2 == 1 else 'T'
return flips == nflips
def main():
while True:
io, _, _ = connect()
io.sendline(b"P")
io.sendline(b"H")
io.readuntil(b"The coin lands on")
io.readline()
if b"Fortune smiles upon you" in io.readline():
io.readuntil(b"light is the flag part:")
flag_suffix = io.readline().split(b"'")[1].decode()
io.close()
break
io.close()
while True:
timestamp = int(time.time())
io, leak, flips = connect()
io.sendline(b"O")
io.sendline(b"H")
io.readuntil(b"The coin lands on ")
flips += io.readline().decode()[0]
if b"Fortune smiles upon you" in io.readline():
io.readuntil(b"cipher:\n")
flag_prefix_enc = b""
while True:
line = io.readline()
if b" " not in line:
break
print(line)
parts = line.decode().split(" ")
hexline = (parts[1] + parts[2]).replace(" ", "")
flag_prefix_enc += bytes.fromhex(hexline)
print(flag_prefix_enc)
io.close()
break
io.close()
flag_prefix = None
for offset in range(-2000000, 2000001):
seed = timestamp + offset
if test_seed(seed, leak, flips):
key = gen_key(seed, flips)
cmd = ["openssl", "enc", "-aes-256-cbc",
"-d", "-pass", f"pass:{key}"]
out = subprocess.run(cmd, stdout=subprocess.PIPE,
input=flag_prefix_enc).stdout
print(out)
if b"CSCG" in out:
flag_prefix = out.decode().strip()
break
assert(flag_prefix)
print(flag_prefix + flag_suffix)
if __name__ == "__main__":
main()
|
