The SSL (Secure Sockets Layer) handshake is an important process that enables secure communication between a client and a server over the internet. It allows the client and server to establish an encrypted connection before exchanging data.
However, sometimes the SSL handshake fails with an “SSL handshake error” due to various reasons. In this comprehensive guide, we will cover the details of the SSL handshake process, common causes of SSL handshake failures, and solutions to fix the “error during SSL handshake with remote server” issue.
What is an SSL Handshake?
An SSL handshake is a process that enables two parties, a client and a server, to establish an encrypted and secure connection. It involves the following steps:
- Client Hello: The client sends a “ClientHello” message to the server indicating its SSL version, ciphers, and other settings it supports.
- Server Hello: The server responds with a “ServerHello” message selecting the SSL options to use.
- Server Certificate: The server sends its SSL certificate to the client.
- Certificate Verification: The client verifies whether the server’s certificate is valid and trusted.
- Key Exchange: The client and server exchange keys to create a shared secret key used to encrypt data.
- Change Cipher Spec: The client and server inform that future messages will be encrypted.
- Finished: The client and server send finished messages to confirm the handshake was completed successfully.
This handshake allows the client and server to authenticate each other, agree on encryption algorithms, and establish encrypted communication.
Common Causes of SSL Handshake Errors
There are various reasons why the SSL handshake process may fail with errors like “SSL handshake failed”, “SSL error handshake failure”, etc. Here are some of the common causes:
1. Expired or Invalid Certificate
If the SSL certificate on the server has expired or is invalid, the client cannot establish trust. The certificate verification step will fail.
2. Certificate Name Mismatch
The domain name on the certificate must match the server address. If the certificate is for www.example.com but the client is accessing server.example.com, there will be a hostname mismatch.
3. Incompatible SSL/TLS Versions
If the client and server support different versions of SSL/TLS protocols, they may be unable to negotiate compatible options. Older protocols may be insecure.
4. Weak Ciphers
The server must support strong ciphers for encryption. Weak ciphers will cause the client to abort the handshake.
5. Certificate Authority Untrusted
The CA (Certificate Authority) that issued the server’s certificate must be trusted by the client. If the client doesn’t trust the CA, it will reject the certificate.
6. Revoked Certificate
If the server certificate has been revoked by the issuing CA due to security concerns, the client will reject it during verification.
7. Web Server Misconfiguration
Incorrect SSL configuration on the web server can cause handshake failures. Common mistakes include incorrect protocol versions, cipher suites, and certificate paths.
8. Client Software Issues
Problems with SSL libraries or outdated software on the client side can also lead to handshake failures if they do not support the required encryption standards.
9. Network Interruptions
Unstable networks or interruptions during the handshake can cause timeouts and failed connections. Packet loss leads to incomplete handshakes.
Solutions to Fix SSL Handshake Errors
Here are some troubleshooting tips to solve SSL handshake failures and establish secure connections:
1. Check Server Certificate Validity
Use a tool like OpenSSL or check with the issuing CA to verify that the server certificate is valid, active, and not revoked. Renew expired or revoked certificates.
2. Verify Certificate Names Match
The common name (CN) on the certificate must match the server name requested by the client. Use subject alternative names (SAN) to add multiple domains.
3. Enable TLS 1.2 or Higher
TLS 1.2+ is the current recommended version with secure cipher suites. Disable old protocols like SSLv2, SSLv3, or TLS 1.0.
4. Use Strong Ciphers
The server should support AES encryption with 128 bits or higher, and SHA-2 for message authentication. Weak ciphers like DES, 3DES, RC4, and MD5 must be avoided.
5. Install Trusted CA Certificates
For CAs that are not trusted by default on the client, their root certificates must be manually installed to avoid rejections.
6. Check Certificate Revocation
Use OCSP or CRL to check the certificate revocation status. For privacy, staple OCSP responses to certs.
7. Correct Web Server Config
Review the web server’s SSL configuration and ensure correct protocols, cipher suites, and certificate paths are specified.
8. Update Client Software
Upgrade clients to software versions that support modern, secure encryption standards required for SSL handshakes.
9. Improve Network Reliability
For timeout errors, improve network reliability between the client and server by addressing issues like packet loss, latency, or intermittent connections.
Conclusion
The SSL/TLS handshake is a critical process to establish secure and encrypted channels for communication over the internet. Handshake failures can prevent clients from accessing websites and applications.
By understanding the potential causes and implementing the suggested solutions, you can diagnose and fix the “SSL error during handshake” problems in the client-server connection. Using up-to-date software, valid certificates, secure ciphers, and reliable networks is key to successful SSL handshakes.
