An application server was recently upgraded to prefer TLS 1.3, and now users are unable to connect their clients to the server. Attempts to reproduce the error are confirmed, and clients are reporting the following:
ERR_SSL_VERSION_OR_CIPHER_MISMATCH
Which of the following is MOST likely the root cause?
C
Reference:
https://kinsta.com/knowledgebase/err_ssl_version_or_cipher_mismatch/
Option C is the correct one. The client application is configured to use RC4, is the most likely root cause of the issue. TLS 1.3 is a newer version of the SSL/TLS protocol that was designed to improve security and performance. It introduces several new cipher suites and removes support for older cipher suites, such as RC4. If the client application is configured to use RC4, which is not supported in TLS 1.3, it will not be able to establish a secure connection to the server. Option A, the client application is testing PFS (Perfect Forward Secrecy), is not related to the issue. Option B, the client application is configured to use ECDHE (Elliptic Curve Diffie-Hellman), is not necessarily a problem as ECDHE is supported in TLS 1.3. Option D, the client application is configured to use AES-256 in GCM (Galois/Counter Mode), is not necessarily a problem as AES-256 in GCM is a cipher suite supported in TLS 1.3.
Probably C, as RC4 is deprecated.
"issues that may trigger ERR_SSL_VERSION_OR_CIPHER_MISMATCH error: SSL certificate name mismatch, old TLS version, and enabled RC4 cipher suite."
server was recently upgraded to TLS 1.3. My best guess is that it had TLS 1.2 that uses ECDHE and now TLS 1.3 prefers AES and CHACHA20.
You're half right. TLS 1.3 prefers AES and CHACHA20, but it also uses ECDHE or PSK with ECDHE, which provides perfect Forward Secrecy.
RC4 Cipher: RC4 is a deprecated cipher and is not supported in TLS 1.3. If the client application is configured to use RC4, it will not be able to establish a connection with a server that prefers TLS 1.3.
Error Message Interpretation: Insecure Cipher Suite Error: When the client attempts to negotiate using RC4 and the server does not support RC4 (especially with modern TLS versions like TLS 1.3), the server will typically respond with an error indicating that the cipher suite offered by the client (RC4) is insecure or not supported.
Correction, I'll change to C, as AES256 in GCM is also supported in TLS 1.3, so it's the same as ECDHE, hence, it might not be the correct answer.
B. The client application is configured to use ECDHE (Elliptic Curve Diffie-Hellman Ephemeral): ECDHE is a key exchange mechanism commonly used in TLS 1.3 for forward secrecy. If the client application is configured to use ECDHE, but the server does not support it or has issues with its configuration, it can lead to a cipher mismatch error. Given that the server was recently upgraded to prefer TLS 1.3, which often uses ECDHE, and clients are experiencing SSL version or cipher mismatch errors, misconfiguration or lack of support for ECDHE could indeed be the root cause.
The error message "ERR_SSL_VERSION_OR_CIPHER_MISMATCH" is typically related to a mismatch between the supported SSL/TLS versions or cipher suites between the client and server. Option C suggests that the client application is configured to use RC4. While RC4 is an outdated and insecure cipher, it's not directly related to the TLS version mismatch indicated by the error message. Option B (The client application is configured to use ECDHE) would be more relevant to the issue. ECDHE (Elliptic Curve Diffie-Hellman Ephemeral) is a key exchange mechanism commonly used with TLS 1.3. If the client is configured to use an incompatible key exchange mechanism, it could result in the mentioned error.
RC4 is too weak for TLS.13 Source: Verifying each answer against Chat GPT, my experience, other test banks, a written book, and weighing in the discussion from all users to create a 100% accurate guide for myself before I take the exam. (It isn't easy because of the time needed, but it is doing my diligence)