Transport Layer Security (TLS) and application performance

5 min read
Feb 6, 2024 9:58:00 AM

Every day, we enter website passwords or use credit cards and bank cards to purchase items and services on the web. How can we make these transactions without worrying that our data will be intercepted and stolen? One of the keys to securing data between users and applications is Transport Layer Security (TLS). The ubiquitous “S” at the end of HTTPS indicates the use of TLS.

Everyone wants their sensitive data protected from prying eyes. However, businesses must also consider how security features affect the user experience, especially application performance.

In this article, we will discover:

  • What is TLS?
  • How TLS affects application performance
  • How TLS affects performance testing
  • Tips on TLS optimization

What is TLS?

Transport Layer Security (TLS) is a cryptographic protocol that ensures privacy between communicating applications and users on the Internet. TLS provides a secure and reliable communication channel over an insecure network (like the Internet). It is commonly used to secure transactions on the web, including login credentials, personal data, and financial information.

Released in 2018, TLS 1.3 is the latest protocol version. TLS 1.3 offers several advantages over the earlier version, including shortening the TLS handshake time and securing cryptographic vulnerabilities.

Key features of TLS include:

Encryption: TLS uses encryption algorithms to protect the data's confidentiality. Encryption scrambles the data so that if someone intercepts the communication, they cannot read it without the correct key.

Authentication: TLS provides a mechanism for both the server and, optionally, the client to authenticate each other. Ensuring that the parties involved in the communication are who they claim to be.

Integrity: TLS includes mechanisms to ensure the data's integrity, preventing unauthorized tampering or modification of the data during transit.

Forward Secrecy: TLS can provide forward secrecy, also called perfect forward secrecy (PFS). With PFS, there are two types of keys: a long-term key and a single session key. You need both keys to unlock the data. Past communications are protected even if the long-term secret keys are compromised.


TLS and web application performance

TLS (Transport Layer Security) can impact web application performance, especially under high traffic conditions. Here are several ways in which TLS can affect performance in the context of high web traffic:

Encryption Overhead: TLS adds encryption and decryption overhead to the data transmitted between clients and servers. The cryptographic operations require additional computational resources, impacting the CPU usage on both the client and server sides. Under high traffic conditions, the cumulative effect of encryption overhead can contribute to increased response times and reduced throughput.

TLS Handshake Latency: The TLS handshake establishes a secure connection by exchanging keys and negotiating cryptographic parameters. The TLS handshake can introduce latency, especially for new connections. Under high traffic, the time spent on handshakes can become a bottleneck, leading to increased connection setup times.

Cipher Suite Selection: The choice of cipher suites used in TLS can impact performance. Some cipher suites are more computationally intensive than others. High-traffic web applications should carefully select cipher suites that balance security requirements with performance considerations.

Connection Reuse: TLS supports connection reuse through mechanisms like session resumption and TLS ticket extension. Reusing established TLS sessions can reduce the overhead associated with repeated handshakes, improving performance for subsequent requests. However, managing and maintaining a session state can also introduce complexities under high traffic.

Server Resource Utilization: TLS-related operations can cause increased CPU and memory usage for Web servers. Adequate server resources and optimizations, such as hardware acceleration or offloading, may be necessary to handle encryption demands efficiently.

CDN and TLS Termination: Content Delivery Networks (CDNs) often handle TLS termination. They decrypt traffic at edge locations before forwarding it to the origin servers. Moving TLS operations to the CDN can help distribute the load, but it requires careful consideration of the TLS termination point. For example, will you encrypt the communication between the CDN and the application server? CDN TLS configuration decisions will affect overall performance.

Network Latency: TLS introduces additional round-trip times during the handshake process. Network latency can become more pronounced in high-traffic scenarios, especially if multiple hops exist between clients and servers. CDNs and proper geographical distribution of servers can help mitigate this effect.

Load Balancing Considerations: Load balancers may play a role in distributing traffic among multiple servers. TLS termination at load balancers can impact their ability to make optimal routing decisions. It's crucial to configure load balancers appropriately and consider the impact on overall performance.


TLS and performance testing

Transport Layer Security (TLS) plays a significant role in performance testing. This is specifically true for applications with secure network communication. Here are some key aspects of TLS in the context of performance testing:
Secure Communication: TLS ensures secure communication by encrypting the data transmitted between your application and the users or between different system components. This encryption adds an overhead to the data transmission, impacting the overall performance.

Overhead Impact: The encryption and decryption processes involved in TLS introduce computational overhead. During performance testing, you may observe increased CPU usage and potentially longer response times due to this overhead.

Handshake Time: The TLS handshake increases the time for the initial connection setup. Performance testers should consider the impact of this handshake time, especially when dealing with short-lived connections.

Cipher Suite Selection: TLS supports various cipher suites, each with its own level of security and performance characteristics. Changing the cipher suite might improve performance if TLS handshake times are too long. Cipher suites balance performance and security, so the best choice depends on your business needs.

Load Balancing and TLS Termination: Load balancers may handle TLS termination, including decrypting the traffic before forwarding it to the application servers. Load balancers simplify the workload of application servers by handling TLS termination. However, this also adds complexity to load balancing and routing decisions. Performance testers need to account for this architecture in their testing scenarios.

Simulating Real-World Conditions: Performance testing with TLS enabled reflects real-world conditions where secure communication is essential. It helps assess the application's performance with the encryption-related overhead. Measuring whether the system can handle the expected load while maintaining the security standards.

Scalability and Resource Usage: TLS can limit the scalability of your application. The resources required for encryption and decryption may limit the number of simultaneous connections your system can handle. Performance testing helps identify the point at which resource limitations become a bottleneck.

Monitoring and Analysis: Performance testing tools and monitoring solutions should measure TLS-related metrics like handshake times, error rates, and resource consumption. Analyzing these metrics helps in optimizing TLS configurations for better performance.

TLS is critical during performance testing to ensure your application can handle the additional computational and time overhead associated with secure communication. Quantifying how TLS affects response times, resource usage, and overall system scalability under various load conditions is essential.

TLS optimization tips

To mitigate the performance impact of TLS under high traffic conditions, it's essential to:

Regular performance testing and tuning can help identify and address TLS-related bottlenecks in web applications. Performance testing software such as Gatling Enterprise provides detailed TLS performance data. Correlating performance issues with TLS handshake durations can help you optimize your application for peak performance.