98 lines
2.4 KiB
Python
98 lines
2.4 KiB
Python
#!/usr/bin/env python3
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import os, sys, signal, binascii, random
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from Crypto.Cipher import AES
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from Crypto.Util.Padding import pad, unpad
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from Crypto.Util.number import bytes_to_long, long_to_bytes
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random.seed(os.urandom(16))
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K0 = os.urandom(16)
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K1 = os.urandom(16)
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S0 = os.urandom(16)
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S1 = os.urandom(16)
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M0 = os.urandom(16)
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M1 = os.urandom(16)
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with open("/flag.txt","rb") as f:
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flag = f.read()
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def hex_input(q):
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s = input(q).strip()
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try: return binascii.unhexlify(s)
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except: print("err"); return None
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def enc1(b16: bytes) -> bytes:
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x = AES.new(K1, AES.MODE_ECB).encrypt(b16)
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return bytes(a ^ b for a, b in zip(x, b16))
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def enc2(iv: bytes, m: bytes) -> bytes:
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return AES.new(K0, AES.MODE_CBC, iv=iv).encrypt(pad(m, 16))
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def enc3(m: bytes) -> bytes:
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return AES.new(K1, AES.MODE_CBC, iv=b"\x00"*16).encrypt(pad(m, 16))[-16:]
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def T(iv: bytes, ct: bytes):
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n = len(ct)
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if n < 96 or (n & 15):
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return None
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v = memoryview(ct)
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W = [bytes(v[i:i+16]) for i in range(0, n, 16)]
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m = len(W)
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r = ((iv[0] & 7) + 2) % m
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if r:
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W = W[r:] + W[:r]
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j = 1 + (W[0][0] & 1)
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if len(W) <= j:
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return None
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del W[j]
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if len(W) < 2:
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return None
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a0 = long_to_bytes(bytes_to_long(W[0]) ^ bytes_to_long(M0))
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a1 = long_to_bytes(bytes_to_long(W[1]) ^ bytes_to_long(M1))
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return b"".join((S0, a0, S1, a1, *W[2:]))
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def C(iv: bytes, ct: bytes) -> bool:
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z = T(iv, ct)
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if z is None:
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ok = False
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else:
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try:
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x = AES.new(K0, AES.MODE_CBC, iv=iv).decrypt(z)
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unpad(x, 16)
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ok = True
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except:
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ok = False
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if random.random() < 0.08:
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ok = not ok
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return ok
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iv = os.urandom(16)
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MK = enc3(iv + iv)
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H0 = (flag + b"\x00"*16)[:16]
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H1 = bytes(a ^ b for a, b in zip(H0, MK))
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pt = H1 + flag[16:]
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ct = enc2(iv, pt)
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print("iv:", iv.hex())
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print("ct:", ct.hex())
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print()
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while True:
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try:
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blob = hex_input("blob: ")
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if blob is None:
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print("err\n"); continue
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L = len(blob)
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if L == 16:
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y = enc1(blob)
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print("blk:", y.hex()); print()
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elif L >= 32 and (L % 16) == 0:
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iv, ct = blob[:16], blob[16:]
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print("ok\n" if C(iv, ct) else "no\n")
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else:
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print("err\n")
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except EOFError:
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break |