Which approach mitigates padding oracle vulnerabilities most effectively?

• A. Use authenticated encryption such as AES-GCM
• B. Disable encryption
• C. Increase padding
• D. Rely on TLS 1.0

Answer: (A)

Padding oracle vulnerabilities come from decryption revealing whether the padding is valid, typically through different error messages or timings. An attacker can exploit that distinction to learn information about the plaintext by tampering with ciphertext and observing the responses.

Using authenticated encryption such as AES-GCM is the strongest defense because it combines encryption with a built-in integrity check. Decryption first verifies the authentication tag, and if it fails, the system returns a uniform failure without revealing anything about padding or plaintext. This means there’s no separate padding-validity signal to exploit, effectively removing the padding oracle risk.

Disabling encryption isn’t a viable security solution because it leaves data unprotected. Simply increasing padding doesn’t fix the underlying issue, since the vulnerability lies in how decryption verifies and reveals padding validity. Relying on TLS 1.0 is not a reliable safeguard either; older TLS versions can be susceptible to padding oracle vulnerabilities in CBC modes and are generally considered outdated and less secure.