What is mTLS?

The internet is not as secure as we assume, and the communications and data transfers we do online are prone to attacks. Attackers tamper with and misuse your sensitive information, causing you great harm.

To secure these communications over a network, the widely used protocol is Transport Layer Security (TLS). When web browsers want to connect to a secure web server, they use the TLS protocol, which not only secures the private information but also checks whether the server that you are connecting to is genuine and trusted.

But what is TLS exactly, and does it secure communications from more sophisticated attacks? Let us explore answers to such questions in this post.

Table of Contents

1. What is TLS?
2. What is mTLS?
3. Why use mTLS?
4. Use cases of mTLS
5. Wrapping Up

What is TLS?

TLS, formerly called SSL, is a widely used encryption protocol that authenticates the server in a client-server architecture. It ensures that attackers cannot manipulate the data in transit and pick up valuable information.

Before we proceed further, it is essential that you understand the following three important concepts.

• Private and public keys: TLS uses key pairs, namely private and public keys. It relies on public-key encryption to encrypt data. Data encrypted with a public key can only be decrypted by a private key and vice versa.
• TLS certificate: TLS certificates are data files that contain data for verifying the server’s authenticity and identity, the public key, and the certificate’s expiration date.
• TLS handshake: This is the process where the TLS certificate and the private key procured by the server are verified.

TLS is secure but not unbreachable. This is because only the server is in possession of the private key and the TLS certificate. The server’s authenticity is done by the client, which is a loophole as the client is not authenticated by the server during the handshake.

This is where mTLS comes into the picture. mTLS performs a two-way handshake which is much more secure compared to TLS. Let us understand a little more about mTLS.

What is mTLS?

Mutual TLS, abbreviated as mTLS, is an extension of TLS that ensures that both the endpoints are who they claim to be. This is done by verifying the TLS certificates at both ends and checking if the private key is possessed by both the client and server.

mTLS is used in a zero-trust security framework, primarily to verify devices, users, and networks within an IT enterprise. To the uninitiated, a zero-trust security framework is a network in which no user or device is trusted by default. This helps to avoid many types of security discrepancies.

The steps involved in mTLS to verify both endpoints are as follows:

1. The client sends the request to the server
2. The server presents its TLS certificate to the client and requests the TLS certificate from the client
3. The client shows its TLS certificate
4. The server verifies the TLS certificate presented by the client and grants permission
5. Having established an encrypted TLS connection, the client and server can now exchange information without any security issues.

Usually, the organization implementing mTLS is its own certificate authority. However, in TLS, an external authority comes into the picture who verifies that a legitimate organization owns the associated domain. On the other hand, a root TLS certificate is required for mTLS which enables the enterprise to be its own certificate authority. Any certificate used by servers and networks should adhere to the root certificate. The root certificate is root-aligned, which means it is created by the organization itself.

Why use mTLS?

mTLS provides secure and reliable connections in both directions of the parties involved. This provides an additional layer of security for users who log into their enterprise’s network and applications. mTLS allows only verified connections on client devices that do not require a login, such as IoT devices.

mTLS provides robust security and protects from various sophisticated attacks such as -

• On-path attacks
• Spoofing attacks
• Brute force attacks
• Phishing attacks
• Malicious API requests

Use cases of mTLS

Mutual certificate authentication can be used whenever the server needs to authenticate and verify a specific user or device in any network. For instance, a client certificate can be issued to a company-owned laptop to authorize and validate the device and the user inside a corporate network.

Also, a client certificate can be used to authorize an employee. It can be stored in smart cards to access applications based on privileges and also provide access to restricted areas of the building (using the smart cards).

In organizations, mTLS can identify and authorize endpoints in the following scenarios:

• Devices on a corporate network
• Authorizing content delivery networks and cloud security services to backend servers
• Business to Business(B2B) data transactions that use APIs
• In a microservices architecture, to ensure that each microservice communicates with a component that is validated without the data being tampered with

Wrapping up

The mTLS protocol is great for authenticating both the client and server endpoints as it provides a reliable security passage for communication. However, it is not suitable for public websites, as management of digital certificates is a lot complex and requires many trained network architects. To summarize -

• mTLS is ideal for a fixed number of clients, including laptops, end-users, mobile phones, or IoT devices within enterprises.
• Adopting mTLS in microservices-based architecture is helpful as it offers top-notch security to microservices interacting with different components.