Transport Layer Security (TLS), also called Secure Sockets Layer (SSL), is a security protocol that encrypts data exchanged between two points on the internet (e.g., a web server and a browser). It also authenticates a website’s identity.

TLS is essential for protecting sensitive customer data and business-critical information. It provides encryption capabilities required by most data privacy regulations. Meanwhile, HTTPS, which indicates that a website uses the TLS/SSL protocol, is an SEO ranking factor.

However, purchasing and installing a TLS certificate is just the first step. You must also ensure users can establish a secure connection by preventing and addressing TLS errors, such as TLS handshake failure or timeouts.  

A TLS handshake error prevents a browser from establishing a secure connection with a website or online service. It can be detrimental to business because hackers may intercept or manipulate sensitive data such as personal information, login credentials, and credit card numbers. The ensuing security breach could tarnish your reputation, diminish customer trust, lead to loss of business, and cause compliance issues.

So why do TLS/SSL handshake failures or timeouts occur, and how can you fix them? Let’s look at the most common causes, how to address them, and how to prevent these errors proactively.

What is a TLS handshake failure?

An “SSL handshake failed” message indicates that an error has occurred when the server and the client try to establish a secure connection. 

What causes a TLS handshake failed error and how to fix it?

TLS errors have various causes, which require different fixes. The most common ones include:

Client-side causes of a TLS handshake error

• Incorrect system time: A TLS error happens when the system clock is different from the actual time. Since an SSL/TLS certificate specifies a validity time frame, a mismatch in date/time can lead to a handshake failure. The user can fix this error by correcting the system time and date.
• Browser error: A browser misconfiguration or plugin may cause an SSL/TLS handshake error. The user can switch to a different browser to find out if a TLS handshake failure is caused by the browser’s configuration. If the site still fails to connect, then disable all plugins and try again.
• Man-in-the-middle (MITM) attack: Besides malicious activities, this error can occur when a connection is interrupted by a network component like a firewall. If the disruption occurs on the client side, the user may adjust their VPN or antivirus settings to address the issue.

Server-side causes of a TLS handshake error

• Protocol mismatch: A TLS handshake failure occurs when the client and the server don’t mutually support a TLS version, e.g., the browser supports TLS 1.0 or TLS 1.1 while the server supports TLS 1.3. In this case, the user should upgrade their browser to work with the latest TLS version.
• Cipher suite incompatibility: An error occurs when the client and the server don’t have a compatible cipher suite, i.e., they can’t agree on how to encrypt and decrypt data. Since TLS 1.3 has deprecated outdated ciphers, it’s best to have the client upgrade to the latest TLS version.
• SNI-enabled servers: Server name indication (SNI) can lead to TLS errors when an older client/device doesn’t support SNI, or the server has incorrect SNI configurations. You can fix this error by ensuring accurate server SNI configurations and that the SSL/TLS certificate corresponds to the hostnames.
• Certificate issues: Revoked, inactive, or expired certificates can cause TLS errors. A handshake failure may also occur when the hostname doesn’t match the common name (CN) in the certificate. You can prevent these issues by purchasing your TLS certificates from a reputable certificate authority (CA) and establishing a robust digital certificate management process.

What is a TLS handshake timeout?

This TLS error occurs when the handshake process takes longer than the predetermined duration. The connection attempt is considered unsuccessful and the handshake is aborted.

What causes a TLS handshake timeout and how to fix it?

These issues may cause a timeout error:

• Network latency and slow network connections delaying the transmission of handshake messages
• A heavy server load or resource constraint increasing the time required to complete the handshake
• Intermediate network devices like firewalls or proxies that may introduce interferences or delays
• A server that is unreachable, unavailable, or experiencing downtime 
• Client-side issues, such as slow or poor-performing devices

There are various ways to address TLS handshake timeout errors, depending on the root cause. You may optimize server performance by provisioning sufficient resources to handle incoming requests. You may also implement load balancing to prevent overloading a single server.

Also, verify your TLS settings, cipher suites, and other server configurations. Monitor network conditions and address issues or latency that may cause potential delays. Keep your server software and SSL/TLS libraries current to stay on top of performance improvements and bug fixes.

How to prevent TLS/SSL handshake errors

Proactively preventing TLS/SSL handshake errors helps ensure users and customers can access your website or online services without disruptions. It also helps deliver a seamless experience to promote operational efficiency, minimize costly downtime, and build trust with visitors. 

Since TLS handshake failures can be caused by different reasons, proactive prevention must cover various aspects, including proper configuration, monitoring, and maintenance best practices.

Configure your server to support the latest TLS protocols (e.g., TLS 1.2 and 1.3) and strong encryption algorithms. Verify that the certificate chain is complete and your server’s SNI configuration matches the certificate’s CN and hostnames. Also, balance server resources (e.g., CPU, memory, bandwidth) to ensure prompt handling of handshake requests. Update your server and operating systems regularly to minimize performance issues.

Monitor network conditions to prevent latency, and avoid overloading servers. Implement an error-handling process to communicate issues to users and a logging workflow to help diagnose and troubleshoot issues. Also, test your website or service on various browsers and client devices to verify compatibility and identify potential problems that may cause TLS errors.

Most importantly, maintain active and accurate TLS/SSL certificates from a trusted CA. For example, Sectigo offers various types of TLS/SSL certificates (e.g., extended validation, organization validation, domain validation, wildcard, and multi-domain). These certificates meet the highest standards with 256-bit encryption, the strongest encryption available for web connections.

But purchasing TLS certificates is just the first step. You must also implement an airtight certificate management process to prevent expired, inactive, or revoked certificates from causing TLS errors. The best way to ensure nothing falls through the cracks is to automate your workflows with a robust certificate management platform.

Sectigo’s Certificate Manager (SCM) is a CA-agnostic, universal platform that helps enterprises discover, consolidate, and manage all digital certificates in one place. Start your free trial to see how you can get a bird’s-eye view of your certificate inventory, streamline workflows, and minimize TLS errors.

*** This is a Security Bloggers Network syndicated blog from Sectigo authored by Nick France. Read the original post at: https://www.sectigo.com/resource-library/tls-ssl-handshake-errors-how-to-fix-them