100 lines
2.5 KiB
Python
100 lines
2.5 KiB
Python
#!/usr/bin/env python3
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import os, sys, 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); S1 = os.urandom(16)
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m0 = os.urandom(16); 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 xex(b16):
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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 enc1(iv, msg):
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return AES.new(k0, AES.MODE_CBC, iv=iv).encrypt(pad(msg,16))
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def dec1(iv, c):
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return unpad(AES.new(k0, AES.MODE_CBC, iv=iv).decrypt(c), 16)
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def enc2(msg):
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return AES.new(k1, AES.MODE_CBC, iv=b"\x00"*16).encrypt(pad(msg,16))[-16:]
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def F(iv, ct):
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n = len(ct)
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if n < 96 or (n & 15): return None
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W = [ct[i:i+16] for i in range(0, n, 16)]
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m = len(W)
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digest = enc2(iv)
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r = ((iv[0]^iv[-1]) & 7) + 2
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r %= m
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if r: W = W[r:] + W[:r]
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if len(W) < 3: 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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j = 1 + (digest[0] & 1)
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del W[j]
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if len(W) < 2: return None
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return b"".join((s0, A0, S1, A1, *W[2:]))
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def O(iv, ct):
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z = F(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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dec1(iv, z)
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ok = True
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except:
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ok = False
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if random.random() < 0.10:
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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 = enc2(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 = enc1(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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inp = hex_input("inp: ")
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if inp is None:
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print("hmmm\n"); continue
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L = len(inp)
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if L == 16:
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y = xex(inp)
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print("blk:", y.hex()); print()
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elif L >= 32 and (L % 16) == 0:
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ivq, ctq = inp[:16], inp[16:]
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print("ok\n" if O(ivq, ctq) else "zzz\n")
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else:
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print("hmmm\n")
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except EOFError:
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break
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