The Ultimate Guide to SSL/TLS Client Authentication: Know How it Works
Are You Aware That SSL/TLS Is Not Only Meant for Servers, but It Can Be Used for Client Authentication?
If you come into the debate that SSL/TLS Certificates are used on servers, yes, you’re right, it’s used for installing on the servers. But, that’s also true that SSL/TLS certificates are helpful in client authentication. And, today, we’ll explore this in detail.
As the name implies, SSL/TLS client authentication is intended towards clients instead of a server. Usually, when it comes to server certificates, the client (browser) is the one who does the verification of the server’s identity. In return, if the server and its certificate are legit entities, then it establishes a connection. Also, this entire process is known as SSL/TLS handshake.
Now, let’s look at it from the opposite direction.
What if a server verifies the client? Quite unheard. Well, it happens. SSL/TLS client authentication is quite like SSL server authentication, but it does contrarily.
What is SSL/TLS Client Authentication?
In other words, both client and server certificates are digital certificates that involve client and server applications. But they’re entirely different things. For instance, a server certificate is sent to the client at the beginning of a session, and the client uses it to authenticate the server. Whereas a client certificate is sent to the server from the client at the beginning of a session, and the server uses it for the client authentication.
Put simply, SSL/TLS client authentication is one of the mechanisms, which allows applications to identify certificates. SSL/TLS client authentication lets your application make sure that the client is an authorized certificate, though it doesn’t make any claim whether it’s trustworthy. Also, it’s often combined with strong password-based authentication, which helps to attain better security.
Here’s Where SSL/TLS Client Authentication Can Be Used
Also, among these two, Server certificates are often used, making them well known, as it’s an integral part of every SSL/TLS session. On the other hand, Client certificates are used on rare occasions because,
- The client certificate has to be installed on client applications/machines, which is quite a tedious job for system admins.
- Mostly, clients or end-users are not technical, and they are not interested in getting into it that stuff.
Typical Client Handshake:
And, this process takes place after the completion of certain certificate verification like:
- Digital signature is trustworthy.
- Timestamps are valid – Not before and after dates.
- Certificate is not revoked (OCSP or CRL.)
- Certificate Transparency (CT) are correctly logged.
Benefits of SSL/TLS Client Certificate Authentication
- 2-FA (Two-Factor Authentication) can be performed without an email being sent or an SMS code.
- It’s one of the inexpensive methods to accomplish 2FA.
- Encrypts network transactions.
- Offers more than authentication, like integrity and confidentiality.
- Based upon Active Directory, access is restricted by users, groups, roles, or devices.