SSL/TLS Handshake: Behind the Scenes of a Secure Connection

Written by Holly Landis | Sep 11, 2024 5:07:18 AM

Every time you browse the web, shop online, or even send an email, your data moves from your device to servers on the internet. But how often do we stop to think about how secure this transfer actually is.

The good news is that encryption tools ease that worry. They make sure data stays protected between devices and websites to make everything we do online safer and easier. 

The Secure Socket Layer (SSL) was a standard security protocol used worldwide but has since been replaced by Transport Layer Security (TLS). However, both terms are used interchangeably to refer to this process. 

You might be familiar with SSL certificates which provide users with a safe browsing experience and proof that the site is abiding by current security standards. You’ll know a site is secure if it’s URL starts with “https”. Sites without this certification may face penalties from search engines, as they can’t guarantee a safe browsing experience.

What's the difference between SSL and TLS protocols?

Although both SSL and TLS work to protect your information online, there are some important differences to know about SSL and TLS. 

In SSL, a message authentication code (MAC) is used to create a master secret that encrypts data from possible hackers. TLS, on the other hand, employs a more efficient system where a pseudo-random function creates the master secret, and a hashed message authentication code (HMAC) protocol creates the encryption.

TLS is generally considered to be more secure, reliable, and often faster than SSL. Think of TLS as the upgraded version of the SSL handshake system, providing higher security with upgraded features and less latency than SSL.

How an SSL/TLS handshake works

For SSL/TLS handshakes to work, there must be a connection made between two parties—the client and the server. A negotiation happens to decide how these two points will communicate and transfer data to each other safely through encryption. 

During the handshake, both ends verify security protocols and create encrypted session keys. Once this connection has been made, data can be safely exchanged, protecting user information and ensuring that any transactions on the website are secure from third-party attacks or cybercrime.

A step-by-step guide to what happens in an SSL handshake

While the process may seem complicated, all of this takes place in only a few milliseconds. To establish this connection, the handshake must go through a variety of steps:

  • Introduction/client hello: The client initiates the process by attempting to connect to a website. This introductory message, known as the “Client Hello,” sends the client’s SSL version number and ciphers, along with randomly generated IDs, to the web server.
  • Response/server hello: The web server response, or the “Server Hello,” contains the version number for their SSL certificate with their own cipher information.
  • Server credential verification: The server sends its certificate, which includes its public key and identity information, to the client. This authenticates that they’re up to date with current security protocols.
  • Client credential verification: The client has verified the server’s information against a list of trusted certificates. At this point, the SSL or TLS generates a premaster secret, encrypts it with the server public key from the certificate, and then sends this back to the server for confirmation.
  • Server decryption: The server decrypts the premaster secret from the client using their private key and confirms that the client’s information matches their own.
  • Session keys created: With both sides confirming that information is correct and secure, they each create a session key to encrypt any future transmitted data between each side during this web browsing session.
  • Secure connection established: Finally, both sides exchange a "finished" message encrypted with the session key, signaling that the SSL/TLS handshake is now complete and secure browsing can begin.

What happens if the process fails?

At any time during the connection, the process could fail due to a terminated connection or incorrect data being transferred. This is when a “503 Service Unavailable” error message will be triggered. 

Such errors occur when websites are experiencing downtime. If SSL and TLS certificates are unable to load, this error message makes the site unavailable instead of sending a user to a possibly unsecured site until the server is back online and operational.

Is it still possible for hackers to gain access to user information?

Although The information exchanged during an SSL/TLS handshake is encrypted to prevent any tampering, there’s still a risk of cybercriminals gaining access through advanced attacks like “man-in-the-middle” hacking. This is where an attacker intercepts data by inserting themselves between the client and server, making both the parties believe they’re still communicating directly with each other while the attacker accesses sensitive information. 

The most common way these attacks happen is through website spoofing, where a fake website is created to mimic a legitimate one and tempt users into sharing login or payment details. Never click on links that appear in suspicious emails, as this is often a phishing attempt to take users to spoofed websites to gain access to their private information.

Since these attacks are possible as no system is 100% foolproof, any SSL and TLS protocols you’re using must be the newest versions to include bug patches and the latest security features.

Features of an SSL/TLS handshake

During the handshake process, several important elements determine the type of encryption being used. 

Asymmetric encryption

Asymmetric encryption generates the public key on the server, which is hosted in its security certificate and accessible to anyone. A matching private key is then used by the server to decrypt the client data in the handshake process. Secure connections are established only when this pair of private and public keys is correctly generated.

Symmetric encryption

After the asymmetric encryption phase, a shared key is created between the two parties to establish a secure connection. This session key is used once and is unique to that browsing session.

Another key feature: the cipher suites

Cipher suites are a group of algorithms that define the parameters for the SSL/TLS session. These algorithms enable key exchange methods and encrypt this information with hashes for added security. Without these, encryption and data exchange cannot happen. 

Why SSL/TLS handshakes are important

SSL/TLS handshakes are vital in ensuring the safe transmission of data between users and websites. Without them, private information like financial details or addresses would be vulnerable to possible access by cybercriminals for exploitation and extortion. 

Using these handshakes is the only way to be sure that information passed between each party is securely encrypted and decrypted in the right way, without giving criminals access to this data.

Authentication

Confirming the identity of both the client and the server is one of the biggest advantages of using an SSL/TLS handshake. By passing cookies and other data back and forth during the handshake process, both sides are able to confirm that they’re communicating with the intended recipient and not an imposter.

Encryption

Encrypting data at various stages of the handshake process better protects it from malicious users trying to infiltrate the website server to steal client data. Only the client and server can decode the relevant information through the carefully planned system of encryption and decryption using public and private keys.

Privacy

By using encryption, data stays private throughout the entire process, with information only viewable by the sender and receiver. 

Compliance

A number of national and global regulations govern the use of personal data, such as the general data protection regulation (GDPR) in Europe and the payment card industry data security standard (PCI DSS), which protects the financial details of users during online payments. 

In order to remain compliant with these regulations, businesses must use an SSL/TLS handshake to protect user information through encryption.

Trust and brand reputation

Data breaches can significantly impact businesses, not only in loss of revenue but also in trust between themselves and their customers. Implementing SSL/TLS handshake protocols can reassure website users that your brand is trustworthy and takes the protection of their data seriously.

Handshakes that mean business!

Using SSL/TLS handshakes is essential for establishing secure connections between your business website and your customers and for keeping your own web browsing activities safe. Keep your private data away from the prying eyes of cybercriminals and build trust between you and your audience with the latest security protocols.

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