What is an SSL Handshake? Everything You Need to Know

By Tibor Moes / Updated: June 2023

What is an SSL Handshake? Everything You Need to Know (2023)

What is an SSL Handshake?

The world of cybersecurity is an ever-evolving landscape where the good guys and the bad guys are in a constant, high-stakes game of cat and mouse. As technology advances, so do the techniques to keep our data safe and secure. One such essential tool in the battle for cybersecurity is the SSL/TLS handshake, a fascinating and intricate process that enables secure communication between clients and servers.

But what is this mysterious handshake, and why is it so important? Strap in, as we’re about to embark on a thrilling journey to uncover the secrets behind SSL/TLS handshakes, their evolution, and how to keep them running smoothly, while answering the question: What is an SSL handshake?

Summary

  • SSL handshakes establish secure communication between a client and server, where the data can only be accessed with the right encryption keys.

  • TCP handshakes establish the connection between two devices, while SSL handshakes enable them to securely communicate over that connection.

  • TLS 1.3 is the latest version of SSL, providing faster and more secure encryption than its predecessor.

Don’t become a victim of cybercrime. Protect your devices with the best antivirus software and your privacy with the best VPN service.

Understanding SSL Handshakes

Imagine a secret agent meeting a fellow agent in a dark alley, exchanging a secret handshake to confirm the other’s identity before divulging top-secret information. This is similar to what happens during an SSL handshake, albeit in the digital realm. The SSL handshake ensures a secure connection between clients and servers, where sensitive data can only be accessed with the right encryption keys for encoding and decoding. In simpler terms, it’s like a digital secret handshake that keeps our online communications safe from prying eyes.

The SSL/TLS handshake process involves several steps, including initiating the connection, cipher suite negotiation, server authentication, and key exchange. As technology advances, so does the handshake process, with the latest TLS 1.3 version offering faster and more secure handshakes than its predecessors.

To keep our online communications safe, it’s crucial to understand the common causes of SSL handshake failures and how to troubleshoot them.

What is an SSL handshake?

An SSL handshake is the digital equivalent of our secret agent scenario, where a secure communication session is established between a client and a server. This process is initiated using the Handshake Protocol, a subprotocol that allows both parties to communicate over an SSL-enabled connection. When the client or server cannot establish a secure connection, we encounter the dreaded “SSL Handshake Failed” error message, prompting us to investigate and resolve the issue.

During the SSL/TLS handshake process, authentication plays a vital role in confirming the server’s legitimacy. The server’s public key is compared to the digital signature from the SSL certificate authority, ensuring the server is who it claims to be. This level of authentication is crucial in maintaining the trust and security of online communications.

Why are SSL handshakes important?

SSL handshakes play a critical role in securing our sensitive information online. They protect data from being intercepted by unauthorized parties, ensuring that only the intended recipient can access the information. This level of security is not just a “nice-to-have” feature; it’s an absolute necessity in today’s world of cyber threats and data breaches.

To ensure the trustworthiness of SSL certificates, Certificate Authorities (CAs) follow strict protocols when issuing and managing them. This diligence helps maintain a secure and reliable online environment, where sensitive information can be exchanged with confidence.

In essence, SSL handshakes are the gatekeepers of the digital world, ensuring that our online interactions remain confidential and secure.

Evolution from SSL to TLS

As the digital landscape evolved, so did the need for more secure communication protocols. Enter TLS (Transport Layer Security), the successor to SSL (Secure Socket Layer). Created as an upgrade to SSL 3.0 in 1999, TLS is now considered more secure than its predecessor, with both terms often being used interchangeably. While they both encrypt information in a similar fashion, TLS outshines SSL in terms of security and standardization.

Tracing back to SSL’s origins, Netscape Communications developed the protocol in 1994 in response to growing concerns about internet security. As the years went by, TLS emerged as the new standard, offering better security and an improved handshake process, along with other enhancements. This evolution from SSL to TLS laid the foundation for the secure communication protocols we use today.

The history of SSL

SSL’s inception can be traced back to Netscape Communications, with chief scientist Taher Elgamal often referred to as the “father of SSL”. Developed as a response to increasing concerns about internet security, SSL went through several iterations, with SSL 3.0 being released in 1996.

However, it was eventually replaced by TLS 1.0 in 1999, marking the beginning of a new era in secure communication protocols. The transition to TLS in the early 2000s was spurred by the need for increased security. As the digital landscape evolved, so did the threats and vulnerabilities that plagued it.

TLS offered a more secure alternative to SSL, incorporating various enhancements and improvements, such as the lightning-fast and secure TLS 1.3 handshake process.

Differences between SSL and TLS

While SSL and TLS may appear similar on the surface, there are key differences between the two protocols. TLS stands out due to its improved standardization process. This simplifies the creation of new and more secure cipher suites such as RC4, Triple DES, and AES. Additionally, TLS and SSL differ in their handshake processes, with TLS calculating hashes over the handshake message, as opposed to SSL’s reliance on the master secret and pad for hash calculations.

These differences highlight the advancements in security that TLS brings to the table. TLS 1.3, for example, boasts features such as perfect forward secrecy, enhanced encryption algorithms, and advanced authentication methods. As technology continues to advance, TLS remains at the forefront of secure communication protocols, outshining SSL in both security and performance.

The SSL/TLS Handshake Process

Having established the importance and evolution of SSL/TLS handshakes, it’s time to delve into the nitty-gritty of the handshake process itself. The SSL/TLS handshake process consists of several steps, including initiating the connection, cipher suite negotiation, server authentication, and key exchange. Each step plays a crucial role in ensuring a secure connection between the client and server, ultimately allowing for the safe exchange of sensitive information.

The exact steps of the handshake process are determined by the key exchange algorithm and cipher suites supported by both the client and server. In the event of a problem during the handshake, the Alert Protocol comes into play, notifying the other party of the issue and either terminating the connection or resolving the problem and continuing the handshake process.

Initiating the connection

The SSL/TLS handshake process is triggered when a user navigates to a website using HTTPS. The client initiates a TCP connection with the server, and the SSL/TLS handshake takes place, establishing a secure communication channel between the two parties. This initial step is critical to ensuring the subsequent exchange of information is protected from potential eavesdroppers or malicious actors.

In addition to website navigation, TLS handshakes also occur during other HTTPS-based communications, such as API calls and DNS over HTTPS queries. By monitoring the handshake process and ensuring its successful completion, we can maintain a secure and reliable online environment for our sensitive information.

Cipher suite negotiation

Once the connection is initiated, the client and server must agree on the cryptographic algorithms and session keys to be used during the handshake process. Computer suite negotiation is a process known in computer security. It is used to negotiate a secure connection between two hosts or applications. A cipher suite is a collection of digital signature algorithms, hash functions, asymmetric encryption algorithms, and symmetric encryption algorithms that work together to create a secure connection between the client and server.

The importance of cipher suite negotiation cannot be overstated, as it sets the stage for the security and performance of the SSL/TLS handshake. By agreeing on the most secure and compatible set of cryptographic algorithms and session keys, the client and server can establish a solid foundation for secure communication throughout the duration of their interaction.

Server authentication

With the cipher suite negotiation complete, the next step in the SSL/TLS handshake process is server authentication. This involves the client verifying the server’s identity using digital certificates. The server sends its certificate to the client, who then compares the server’s public key with the digital signature from the SSL certificate authority. By confirming the authenticity of the server, the client can trust that they are communicating with the intended party.

This level of authentication is essential in maintaining the security of online communications, ensuring that sensitive information is only exchanged with legitimate and trusted parties. Failure to properly authenticate the server could lead to unauthorized access or interception of data, emphasizing the importance of this step in the SSL/TLS handshake process.

Key exchange

The final step in the SSL/TLS handshake process is key exchange, the secure exchange of encryption keys between the client and server. These keys, known as session keys, are used to encrypt and decrypt data during the secure communication session. The methods used to exchange these keys vary depending on the specific key exchange algorithm being employed, with RSA and Diffie-Hellman being two of the most common methods.

Key exchange is a critical component of the SSL/TLS handshake process, as it establishes the session key used for secure communication between the client and server. By securely exchanging encryption keys, the client and server can ensure that their communication remains confidential and protected from potential eavesdroppers or malicious actors.

Improvements in TLS 1.3 Handshakes

With the release of TLS 1.3, the handshake process has undergone significant improvements, offering faster and more secure encryption compared to previous versions. These enhancements include a reduced number of round trips required for the handshake process, as well as the enforcement of forward secrecy and the encryption of all handshake messages after the initial “Hello” from the server to the client.

These improvements in TLS 1.3 handshakes have far-reaching implications for the security and efficiency of online communications. By offering faster and more secure encryption, as well as a streamlined handshake process, TLS 1.3 sets a new standard in secure communication protocols, ensuring that our digital interactions remain private and protected.

Faster and more secure

One of the most significant improvements in TLS 1.3 handshakes is the reduced number of round trips needed for the handshake process. This is achieved by combining the client and server authentication steps into one, resulting in fewer messages being exchanged between the two parties.

In addition to faster handshakes, TLS 1.3 also enforces forward secrecy by using ephemeral key exchange algorithms like Diffie-Hellman. This ensures that session keys used to encrypt data are not stored and can only be decrypted by the client and server involved in the communication.

Furthermore, all handshake messages are encrypted after the initial “Hello” from the server to the client, providing an additional layer of security and protection for our online communications.

Unsupported features in TLS 1.3

While the improvements in TLS 1.3 handshakes are undoubtedly impressive, some features from previous versions have been deprecated due to their potential vulnerabilities. Unsupported features in TLS 1.3 include the RC4 Stream Cipher, RSA Key Exchange, SHA-1 Hash Function, CBC (Block) Mode Ciphers, and MD5. By removing these features, TLS 1.3 provides a more secure and reliable handshake process.

The decision to remove these features from TLS 1.3 reflects the ongoing commitment to enhancing the security and performance of secure communication protocols. As technology continues to advance and new threats emerge, the SSL/TLS handshake process must adapt and evolve to stay ahead of potential vulnerabilities and maintain the highest levels of protection for our online interactions.

Troubleshooting SSL Handshake Failures

As with any complex process, SSL/TLS handshakes can occasionally encounter issues that result in handshake failures. These failures may stem from a variety of causes, including different cipher suites, invalid SSL certificates, protocol mismatch, or incorrect date and time settings on the local device. The SSL handshake failed, resulting in the connection to be terminated. The client received a 503 Service Unavailable error as a consequence.

To maintain optimal website performance and security standards, it’s essential to identify and resolve common SSL handshake issues. By understanding the potential causes of handshake failures and implementing appropriate troubleshooting measures, we can ensure that our online communications remain secure and reliable.

Common causes of SSL handshake failures

Various factors can contribute to SSL handshake failures, such as incorrect system time, an expired or invalid SSL certificate, a mismatch in SSL certificates, an unsupported SSL protocol version, or firewall and network issues. Server-side issues, including an invalid SSL certificate, a free SSL certificate obtained from a fraudulent source, or incorrect certificates, can also lead to handshake failures.

Understanding the common causes of SSL handshake failures is crucial for maintaining optimal website performance and security. By proactively addressing these issues, we can minimize the occurrence of handshake failures and ensure a seamless and secure online experience for our users.

Steps to fix SSL handshake failures

To resolve SSL handshake failures, several practical solutions can be implemented. These include updating browsers to support the latest TLS version, checking SSL certificates for validity and proper configuration, ensuring protocol compatibility between the client and server, and adjusting firewall settings as needed.

Addressing server-side issues, such as an invalid SSL certificate or incorrect certificates, is also essential in resolving handshake failures. By taking these steps to troubleshoot and resolve common SSL handshake issues, we can maintain a secure and reliable online environment for our sensitive information and digital interactions.

Monitoring SSL/TLS Handshakes

In addition to troubleshooting SSL handshake failures, it’s also essential to monitor the performance and security of SSL/TLS handshakes. By keeping an eye on these handshakes and ensuring their successful completion, we can optimize website performance and uphold security standards.

Monitoring SSL/TLS handshakes is an invaluable tool in maintaining a secure and reliable online environment. By analysing handshake performance and identifying potential issues, we can proactively address vulnerabilities and ensure the continued protection of our online communications.

Why monitor SSL/TLS handshakes?

Monitoring SSL/TLS handshakes is crucial for optimizing website performance and maintaining security standards. By keeping a close eye on these handshakes, we can ensure that the connection between the client and server remains secure and private, as well as confirm the identities of those participating in the communication.

By monitoring SSL/TLS handshakes, we can also identify potential issues that may lead to handshake failures or security vulnerabilities. In doing so, we can proactively address these problems and maintain a secure and reliable online environment for our users.

Tools for monitoring SSL/TLS handshakes

There are several popular tools and services available for tracking and analyzing SSL/TLS handshake performance, such as Wireshark, SSLMonitor, and ssl-handshake.

By leveraging these tools, we can gain valuable insights into the performance and security of our SSL/TLS handshakes, enabling us to maintain a secure and reliable online environment for our sensitive information.

Summary

In conclusion, the SSL/TLS handshake process is a vital component of secure online communication, enabling private and protected exchanges of sensitive information. As technology continues to advance, the handshake process must adapt and evolve to stay ahead of potential threats and vulnerabilities. By understanding the intricacies of the handshake process, troubleshooting common issues, and monitoring the performance and security of SSL/TLS handshakes, we can ensure a safer and more reliable online environment for all. So let’s keep the digital world secure, one handshake at a time.

How to stay safe online:

  • Practice Strong Password Hygiene: Use a unique and complex password for each account. A password manager can help generate and store them. In addition, enable two-factor authentication (2FA) whenever available.
  • Invest in Your Safety: Buying the best antivirus for Windows 11 is key for your online security. A high-quality antivirus like Norton, McAfee, or Bitdefender will safeguard your PC from various online threats, including malware, ransomware, and spyware.
  • Be Wary of Phishing Attempts: Be cautious when receiving suspicious communications that ask for personal information. Legitimate businesses will never ask for sensitive details via email or text. Before clicking on any links, ensure the sender's authenticity.
  • Stay Informed. We cover a wide range of cybersecurity topics on our blog. And there are several credible sources offering threat reports and recommendations, such as NIST, CISA, FBI, ENISA, Symantec, Verizon, Cisco, Crowdstrike, and many more.

Happy surfing!

Frequently Asked Questions

Below are the most frequently asked questions.

How do you fix an SSL handshake error?

Fixing the “SSL Handshake Failed” error is easy. You can start by making sure that your local device’s date and time are up to date. Then, check your SSL Certificate to make sure it is valid.

Additionally, ensure that you have the latest TLS protocol supported by your browser and verify your server’s SNI configuration. Lastly, confirm that your cipher suites match for a successful connection.

What is the difference between TCP and SSL handshake?

In a nutshell, the TCP handshake establishes the connection between two computers while the SSL Handshake enables them to securely communicate over that connection. The SSL Handshake creates a secure session by exchanging encryption keys so that all transmitted data remains secure and private.

In summary, TCP is used to establish a connection between two computers while the SSL Handshake uses that connection to create an encrypted, secure session for transmitting data. Through an exchange of encryption keys, the SSL Handshake ensures privacy and security for both parties involved in the communication.

What causes SSL handshake failure?

SSL Handshake failure is typically caused by misconfigured SSL certificates, an inability to access the necessary ports, or blocked communication between the web server and your computer.

These issues can all result in a failed SSL handshake, leading to the error message being displayed.

Author: Tibor Moes

Author: Tibor Moes

Founder & Chief Editor at SoftwareLab

Tibor has tested 39 antivirus programs and 30 VPN services, and holds a Cybersecurity Graduate Certificate from Stanford University.

He uses Norton to protect his devices, CyberGhost for his privacy, and Dashlane for his passwords.

You can find him on LinkedIn or contact him here.