Mutual TLS

What is Mutual TLS?

Mutual TLS (Transport Layer Security) is a security protocol that ensures both the client and server authenticate each other during a secure connection. This is achieved through the exchange and validation of digital certificates, which include public keys. Each party also uses its private key to prove ownership of the certificate and establish trust.

In the traditional TLS model, only the server's identity is verified/authenticated by the client. In contrast, mutual TLS requires both parties to present and validate their digital certificates, establishing a two-way authentication process. The private keys remain securely stored and are used to sign data, while the public keys in the certificates are used for verification.

1. Client Initiates Connection: The client begins by sending a request to the server to establish a secure connection (e.g., using the TLS protocol).
2. Server's Certificate: The server sends its digital certificate, which includes its public key, to the client. The client will validate this certificate against its trusted CA store.
3. Client Validates Server's Certificate: The client verifies the server's certificate by checking the signature against the trusted Certificate Authority (CA) it has in its trusted store. This process confirms that the server's certificate is valid and trusted.
4. Certificate Presentation: If the server's certificate is valid, the client proceeds with the mTLS handshake process.
5. Client Sends Its Certificate: The client then sends its own digital certificate, which also contains its public key, to the server for validation.
6. Server Validates Client's Certificate: The server checks the client’s certificate against its trusted CA store to ensure it is valid and trusted.
7. Mutual Authentication: Once both the client and server validate each other's certificates, they can confirm mutual authentication.
8. Key Exchange: During the handshake, both the client and server use their private keys and a key exchange algorithm (e.g., Diffie-Hellman) to establish a shared session key for encrypting subsequent traffic.
9. Secure Connection Established: A secure, encrypted connection is established between the client and server, ensuring mutual trust and privacy.