Int 3: ️ Padding Oracle Attack - Membongkar Enkripsi CBC tanpa Key

cd ~ && mkdir crypto-int3 && cd crypto-int3

python3 << 'PYEOF'
import os

# === SETUP: Simulasi server dengan padding oracle ===
KEY = os.urandom(16)
IV = os.urandom(16)

def encrypt(plaintext):
    """AES-CBC encrypt (simplified for demo)"""
    from Crypto.Cipher import AES
    cipher = AES.new(KEY, AES.MODE_CBC, IV)
    return IV + cipher.encrypt(plaintext + b'\x10' * 16)  # padding dummy

def padding_oracle(ciphertext):
    """Server: return True jika padding valid, False jika tidak"""
    from Crypto.Cipher import AES
    iv = ciphertext[:16]
    ct = ciphertext[16:]
    cipher = AES.new(KEY, AES.MODE_CBC, iv)
    try:
        pt = cipher.decrypt(ct)
        # Cek padding (PKCS#7)
        pad_len = pt[-1]
        if pad_len < 1 or pad_len > 16:
            return False
        if pt[-pad_len:] != bytes([pad_len] * pad_len):
            return False
        return True
    except:
        return False

# === ATTACK: Padding Oracle ===
print("=== Padding Oracle Attack Demonstration ==*")
print()

# Encrypt a message
plaintext = b"Transaksi: Rp 500.000 ke Rek 1234"
iv, ct = encrypt(plaintext)[:16], encrypt(plaintext)[16:]
print(f"Plaintext: {plaintext}")
print(f"IV: {iv.hex()}")
print(f"Ciphertext: {ct.hex()}")
print()

# Attack simulation
print("Server akan mengembalikan:")
print("  ✅ True - jika padding VALID (byte trial benar)")
print("  ❌ False - jika padding INVALID (byte trial salah)")
print()
print("Attacker memodifikasi CIPHERTEXT byte-by-byte")
print("sampai server mengembalikan True → berarti byte benar!")
print()
print("Dengan 256 percobaan per byte, attacker bisa")
print("mendekripsi seluruh pesan tanpa tahu KEY! 🔓")
print()

# Demo: trial satu byte
print("=== Demo: Trial Byte Pertama ==*")
for trial in range(256):
    modified_ct = bytearray(ct)
    modified_ct[15] = trial  # modifikasi byte terakhir blok pertama
    if padding_oracle(iv + bytes(modified_ct)):
        print(f"  Oracle True pada byte 0x{trial:02x} ({chr(trial) if 32<=trial<127 else '?'})")
        break
PYEOF