How does TLS handshake affect TCP slow start performance?

1 What is TLS handshake?

TLS handshake is the first step of any TLS connection. It involves the exchange of messages between the client and the server to negotiate the parameters of the secure session, such as the protocol version, the cipher suite, and the key material. TLS handshake also verifies the identity of the server using certificates, and optionally, the identity of the client using mutual authentication. TLS handshake can take several round trips of network communication, depending on the protocol version and the configuration of the client and the server.

2 What is TCP slow start?

TCP slow start is a congestion control algorithm that aims to avoid sending more data than the network or the receiver can handle. TCP slow start works by starting with a small amount of data, called the congestion window, and increasing it exponentially with every successful acknowledgment from the receiver. TCP slow start continues until it reaches a threshold, called the slow start threshold, or until it detects a packet loss, which indicates congestion. TCP slow start is designed to adapt to the varying conditions of the network and to avoid wasting bandwidth and resources.

3 How does TLS handshake affect TCP slow start performance?

The performance of TCP slow start depends on how fast it can increase the congestion window and how soon it can reach the optimal data rate. However, TLS handshake can delay or interrupt the TCP slow start process, depending on how it is implemented and how long it takes. There are two main factors that can affect the interaction between TLS handshake and TCP slow start: the number of round trips and the amount of data.

4 How does the number of round trips affect TCP slow start performance?

The number of round trips refers to how many times the client and the server have to exchange messages to complete the TLS handshake. The more round trips, the longer it takes to establish the secure session, and the more time TCP slow start has to wait before sending data. For example, TLS 1.2 typically requires two round trips for the TLS handshake, while TLS 1.3 can reduce it to one round trip or even zero round trip with certain optimizations. Reducing the number of round trips can improve the TCP slow start performance by minimizing the latency and maximizing the throughput.

5 How does the amount of data affect TCP slow start performance?

The amount of data refers to how much data the client and the server have to send and receive during the TLS handshake. The more data, the more bandwidth and resources are consumed by the TLS handshake, and the less are available for the TCP slow start. For example, TLS 1.2 uses larger certificates and longer cipher suites than TLS 1.3, which can increase the amount of data transferred during the TLS handshake. Reducing the amount of data can improve the TCP slow start performance by freeing up the bandwidth and resources for the data transmission.

6 How can you optimize TLS handshake and TCP slow start performance?

If you are looking to optimize the TLS handshake and TCP slow start performance, then there are several solutions available. Upgrading to TLS 1.3 is one of the most common methods, as it offers faster and more secure TLS handshake than TLS 1.2. Session resumption is also useful, as it allows the client and the server to reuse the previous session parameters and skip some steps of the TLS handshake. Additionally, certificate compression reduces the size of the certificates sent during the TLS handshake. TCP fast open allows the client to send data in the first packet of the TCP connection, without waiting for the TCP handshake, while HTTP/2 or HTTP/3 are newer versions of the web protocol that support multiplexing, stream prioritization, and header compression. By utilizing these methods, you can reduce latency and increase throughput of your TLS connections while improving user experience and security.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?