What Is a TLS Handshake? Process and Importance
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Key Takeaways
- The TLS handshake is essential for establishing secure communication between a client and server.
- Each TLS handshake involves a series of steps where the client and server exchange messages to verify identities and agree on encryption methods.
- TLS certificates are crucial for confirming the identity of the server during the handshake process.
- Improved versions like TLS 1.3 streamline the handshake process, enhancing security and performance.
- Using TLS protects sensitive information from cyberattacks, making it vital for any business or web application that handles personal data.
The TLS handshake is the first and most crucial step in establishing a secure online connection. Every time you visit a website that uses HTTPS, a handshake takes place behind the scenes to ensure your communication is private and trustworthy. It utilizes asymmetric cryptography to establish encryption keys, authenticate the server’s identity, and lay the groundwork for protecting data as it traverses the internet.
Without this process, sensitive information such as login credentials, payment details, and personal data could be easily exposed to attackers. In this blog, we’ll walk through the TLS handshake in detail, explain its steps, and highlight why it’s essential for encryption, authentication, and secure communication.
What is a TLS Handshake?
Like the handshake we do in real life, the TLS handshake is an introduction. It indicates safe communication between two servers where messages are exchanged to acknowledge each other, verify each other, set up cryptographic codes, and agree on session keys.
The TLS handshake process starts with the initial ‘Hello’ and continues to the stage where a client and server can talk over a secured connection.
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How Does TLS Handshake Work?
Now that you know what is a TLS handshake, let’s see how it works.
So, the TLS handshake process works only when a TLS certificate is set up on the server for a website or application. This certificate includes important details about the domain owner and server’s public key to confirm the server’s identity. This sequential process established a TLS connection. So, whenever a user requests to access a TLS-enabled website, the TLS handshake between their device and the web browser begins and exchanges the following set of details:
- TLS version used (TLS 1.0, 1.2, 1.3, etc.).
- Evaluate the encryption suites to be used.
- Verification of the server’s identity using the TLS certificate.
- Once the initial handshake process is complete, a session key is generated to encrypt messages between the client and server.
The TLS handshake establishes a cipher suite for all communications. The cipher suite is described as a set of algorithms used in establishing a secure communications connection. An important role of TLS handshake is determining which cipher suite will be used. TLS sets matching session keys across an unencrypted channel using public-key cryptography.
Handshake also verifies the genuineness of the sender by checking the server using public keys. Public keys are one-way encryption keys which means that no one except the original sender can decrypt the encrypted data. The original sender uses their private key to decrypt data.
TLS handshake failed means the connection is terminated, and the client sees a ‘503 Service Unavailable’ error message.
TLS vs SSL Handshakes
SSL stands for Secure Sockets Layer, the original security protocol produced for HTTP. SSL was replaced by TLS and SSL handshakes are now termed as TSL handshakes.
When Does a TLS Handshake Occur?
The browser queries the website’s origin server whenever a user requests to navigate a website over a secured connection. It also occurs when any other communication channel uses HTTPS. This includes API calls and DNS over a secured network.
Steps of a TLS Handshake
TLS handshake steps consist of a series of datagrams, or messages, transferred between the client and server. The precise steps will differ depending on the type of key exchange algorithm used and the cipher suites supported by both sides. Here’s what you can expect.
Step 1 – The ‘Client Hello’ Message
The client’s server starts the TLS handshake process by sending a ‘hello’ message to the website’s main server. The message consists of important details like the TLS version and cipher suites supported, and some random bytes called the “client random”.
Step 2 – The ‘Server Hello’ Message
The server replies to the client’s hello message by sending a response having an SSL certificate, the server’s chosen cipher suite, and the ‘server random’ string generated by the server.
Step 3 – Authentication and Key Exchange
At this stage, the client verifies the server’s certificate by checking whether it is signed by a trusted Certificate Authority (CA) and ensuring the domain name matches. If the certificate is valid, the process continues.
Next, the client and server perform a key exchange, which can happen in different ways depending on the chosen cipher suite (e.g., RSA or Diffie–Hellman). This exchange allows both sides to securely generate a shared secret that will later be used for encryption.
Step 4 – Session Keys Established
Using the shared secret, both client and server independently generate identical session keys. These symmetric keys are used to encrypt and decrypt data during the session. Finally, both parties send a confirmation message to signal that future communication will be encrypted, officially establishing a secure channel.
Why the TLS Handshake Matters
The TLS handshake is the foundation of secure online communication. By setting up encryption and authentication at the very start of a connection, it ensures that sensitive data is protected from unauthorized access. This prevents attackers from eavesdropping on traffic or tampering with information in transit.
Equally important, the handshake verifies the server’s identity, which helps build trust between users and websites. For businesses, especially in sectors like e-commerce, online banking, and healthcare, this trust is critical. Customers need assurance that their payment details, login credentials, and personal information are handled safely. Without the TLS handshake, secure browsing, online shopping, and digital banking as we know them would not be possible.
Common Issues with TLS Handshake
While the TLS handshake is designed to run seamlessly, errors can occur that prevent a secure connection from being established.
Some of the most common issues include:
- Expired certificates – If a server’s TLS certificate is outdated, browsers will flag the connection as insecure.
- Mismatched cipher suites – If the client and server cannot agree on a shared encryption algorithm, the handshake will fail.
- Unsupported protocol versions – Older TLS versions may be disabled for security reasons, causing compatibility problems with outdated systems.
These issues highlight the importance of proper configuration and certificate management. Regularly updating certificates, using strong and widely supported cipher suites, and keeping servers aligned with modern TLS standards ensures smooth, secure communication.
Conclusion
The TLS handshake is a crucial process that enables secure communication on the internet. Though invisible to everyday users, it establishes the encryption, authentication, and trust that protect sensitive data from eavesdropping or tampering. Every secure login, online purchase, or banking transaction relies on this foundational step to keep information private and reliable.
To ensure your organization stays ahead of potential risks, proper TLS configuration and certificate management are key. With solutions like PowerDMARC, you can strengthen your TLS setup, improve security, and build lasting trust with your users.
Frequently Asked Questions
When does a TLS handshake occur?
A TLS handshake takes place at the start of a secure session, whenever a client (like a browser) connects to a server over HTTPS. It happens before any actual data is exchanged, ensuring that encryption and authentication are in place first.
What is the difference between a TLS and SSL handshake?
SSL (Secure Sockets Layer) is the predecessor of TLS (Transport Layer Security). While the handshake process is conceptually similar, TLS is more secure and efficient. Today, the term “SSL handshake” is often used interchangeably, but modern secure connections always use TLS.
Domain & Email Security Expert at PowerDMARC
Yunes is an Operations Team Lead at PowerDMARC with expert knowledge in email authentication and security. Yunes is a Microsoft-certified Azure Administrator Associate with certifications in CompTIA A+ and many more.
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