What is Mutual TLS?
Mutual TLS (mTLS) is a security protocol where both parties in a connection authenticate each other using digital certificates. Unlike standard TLS where only the server is authenticated, mTLS requires the client to also present a certificate.
Standard TLS vs mTLS
| Standard TLS | Mutual TLS |
|---|---|
| Server cert only | Both have certs |
| Server verified | Both verified |
| One-way auth | Two-way auth |
| Web browsers | Service-to-service |
How mTLS Works
-
Client Hello
- Request connection
- Supported protocols
-
Server Certificate
- Server sends certificate
- Client validates
-
Client Certificate Request
- Server requests client cert
-
Client Certificate
- Client sends certificate
- Server validates
-
Secure Connection
- Both authenticated
- Encrypted channel
Use Cases
Service Mesh
- Istio, Linkerd
- Zero trust networking
API Security
- Machine-to-machine auth
- High-security APIs
Microservices
- Service authentication
- Internal communications
Implementation
Certificate Management
- PKI infrastructure
- Certificate rotation
- Revocation handling
Configuration
- Server setup
- Client configuration
- CA trust stores
Challenges
- Certificate management
- Complexity
- Performance overhead
- Debugging difficulty