312-50 Question 471
Single answer▪ Cryptography Attack CountermeasuresA security consultant is reviewing a legacy customer portal that still accepts TLS 1.0 connections for compatibility with older clients. During testing, the consultant notes that the server supports CBC-mode cipher suites and that some application cookies are sent over encrypted sessions. The organization is concerned about practical cryptographic attacks against these sessions and wants the most effective countermeasure without relying on users to change behavior. Which action should the consultant recommend first?
- A
Disable TLS 1.0 and 1.1, and allow only modern TLS versions with AEAD cipher suites such as AES-GCM or ChaCha20-Poly1305
- B
Keep TLS 1.0 enabled but rotate the web server certificate every 30 days to reduce exposure to session hijacking
- C
Increase the RSA key size on the server certificate to 4096 bits while continuing to use CBC cipher suites
- D
Replace the public CA-signed certificate with a self-signed certificate and distribute it to internal users manually
Show answer and explanation
Correct answer: A
Explanation
The best first recommendation is to remove support for legacy TLS versions and prefer modern cipher suites that use authenticated encryption. Older TLS deployments that rely on CBC-mode cipher suites have historically been exposed to practical attacks such as BEAST, especially when combined with predictable secrets like cookies. While some historical browser-side mitigations reduced exploitation, the correct server-side countermeasure is to disable obsolete protocols and use current TLS configurations. Industry best practices from organizations such as NIST and OWASP support using modern TLS versions and strong cipher suite selection, with TLS 1.2+ and preferably TLS 1.3, while avoiding deprecated protocols and weak/legacy ciphers. In short, protocol and cipher modernization is the effective cryptographic attack countermeasure; certificate rotation, larger RSA keys alone, or self-signed certificates do not address the root cause.
- A. Correct.
Correct. Disabling outdated protocol versions such as TLS 1.0 and 1.1 and moving to modern TLS with AEAD cipher suites is the strongest practical countermeasure against known attacks that target weaknesses in older protocol/cipher combinations, including CBC-related issues such as BEAST and similar downgrade-era risks. AEAD suites like AES-GCM and ChaCha20-Poly1305 provide integrated confidentiality and integrity and are the standard recommendation in modern TLS deployments.
- B. Incorrect.
Incorrect. Certificate rotation does not address the underlying protocol weakness. Attacks against CBC-mode handling in older TLS versions exploit how the protocol and cipher mode operate, not the age of the certificate. Someone might choose this because certificate hygiene is a good practice, but it is not the primary countermeasure for this class of cryptographic attack.
- C. Incorrect.
Incorrect. Increasing RSA key size affects the strength of the certificate's asymmetric key exchange or authentication component, but it does not mitigate protocol-level weaknesses related to TLS 1.0 and CBC-mode cipher suites. This distractor reflects the common misconception that 'stronger key size' solves all cryptographic problems, even when the issue is the protocol design.
- D. Incorrect.
Incorrect. A self-signed certificate does not protect against CBC or legacy TLS attacks. In many cases, it creates trust-management and usability problems and can even encourage insecure exception handling by users. The issue here is not who signed the certificate, but the continued use of outdated TLS versions and vulnerable cipher suite constructions.