Let’s take a closer look at client and server certificates, and the difference between the two.
In recent times if you’ve tried to access a website and not been greeted by a “Not Secure” warning, you’ve used a digital certificate. Every website that doesn’t have an SSL/TLS certificate installed on the web server is flagged by Google and throws up a security warning. SSL certificates are a type of X.509 certificate that’s used for encrypted browsing. Both client and server certificates help us to communicate securely using an encrypted channel. Let’s get a better understanding of the specific purpose that they solve before getting started with a discussion on their differences.
What’s a Client SSL Certificate?
Client certificates are used to authenticate the client and validate their identity before granting access to the server. Client certificates prove their identity to a remote server and are based on the X.509 format. X.509 is a standard that defines the format for public-key certificates, verifies the identity of the certificate holder, and maps a public key with the user, computer, or service. Consider a scenario in an organization’s corporate network where a central server holds some confidential files. Even if accessing those files require a password, what’s the assurance that an attacker won’t be able to brute force and gain access? Using a client certificate solves this problem as the identity of the client or user is not assessed on the basis of whether they know a password, but it relies on the systems they use. But if a user requests access from a client machine that has permission and whose identity has been validated, the server knows it’s talking to a legitimate entity. Adding another layer of security, such as applying multi-factor authentication, strengthens the defenses against any potential attacks.
What’s a Server SSL Certificate?
Server certificates serve a twofold purpose of authenticating the server's identity and providing a secure, encrypted communication channel between the server and the connecting client. Server certificates are referred to more commonly as SSL/TLS certificates and are responsible for upgrading an HTTP to an HTTPS connection. Whenever you type in a website in the address bar or connect to a system by using its hostname, you’re making use of a server certificate.
Difference Between Client Certificate vs Server Certificate
Now that we have an idea about what these certificates do, it’s time to draw a comparison to better understand them relative to each other. Aside from the evident difference in terms of which party they authenticate, client or server, they differ greatly in terms of their operation. Server certificates are used to encrypt the information exchanged between the client browser and the web server. However, client certificates do not encrypt any data and are solely responsible for authenticating the client’s identity to the server. The table below summarizes the similarities and the differences between the client certificate and the server certificate:
|Client Certificate||Server Certificate|
|A client certificate is used to identify a client or a user and authenticate them to the server.||A server certificate authenticates the server’s identity to the client.|
|Client certificates do not encrypt any data. They only serve as a more efficient authentication mechanism than passwords.||Server certificates encrypt the data-in-transit to ensure its confidentiality.|
|Client certificates are based on the public key infrastructure (PKI).||Server certificates are also based on PKI.|
|Object identifier (OID) for client authentication is 220.127.116.11.18.104.22.168.2.||OID for server authentication is 22.214.171.124.126.96.36.199.1.|
|Client certificates have an “Issued To” and an “Issued By” section.||Server certificates also have the same two fields.|
|Example: E-mail client certificates||Example: SSL certificates|