Passwords can be stolen, phished, or brute-forced. Client authentication certificates replace shared secrets with cryptographic proof of identity, enabling stronger, passwordless authentication for users, devices, and services across enterprise environments.
For decades, the username-and-password combination has been the default way to prove identity online. But passwords are fundamentally flawed: they can be guessed, intercepted, reused across services, or harvested through phishing. Even with strong password policies, credential theft remains the leading cause of data breaches year after year.
Client authentication certificates offer a fundamentally different approach. Instead of proving who you are by something you know (a password), you prove it with something you have: a digital certificate bound to a private key stored securely on your device. The server doesn't just check a shared secret; it verifies a cryptographic signature that only your private key could have produced.
This model is at the heart of mutual TLS (mTLS), where both the client and the server present certificates and verify each other's identity. While standard TLS ensures you're talking to the right server, mTLS adds the other half: the server also confirms that you are who you claim to be. It's the foundation of modern zero-trust architectures, where no connection is trusted by default, regardless of whether it originates inside or outside the corporate network.
The client initiates a connection to the server. The server responds with its own TLS certificate, which the client validates against trusted Certificate Authorities. So far, this is identical to a normal HTTPS connection.
The server sends a CertificateRequest message, specifying which Certificate Authorities it trusts for client certificates. This tells the client: "I need you to prove your identity too."
The client selects a matching certificate from its local store and sends it, along with a CertificateVerify message, a digital signature over the handshake data, created with the client's private key.
The server verifies the client certificate's chain of trust, checks that it hasn't been revoked, and validates the signature. If everything checks out, the connection is established, and the server knows exactly who (or what) is on the other end.
Passwords are a shared secret: if either side is compromised, the credential is useless. Client certificates use asymmetric cryptography: the private key never leaves the device, so there's nothing to steal from the server side. They're immune to phishing, credential stuffing, and password reuse attacks.
MFA adds a second factor (SMS code, TOTP, push notification) on top of a password. Client certificates can serve as a single, strong factor that combines possession (the device with the key) and often a local authentication step (PIN or biometric to unlock the keystore). In many regulatory frameworks, a hardware-bound certificate qualifies as multi-factor on its own.
FIDO2 passkeys also use asymmetric cryptography and resist phishing. However, FIDO2 is designed for web-based, user-facing authentication, while client certificates operate at the TLS layer, making them suitable for machine-to-machine, VPN, WiFi, and scenarios where browser-based flows aren't available.
API keys and bearer tokens are simple to implement but are static secrets that can be leaked. Client certificates offer built-in expiration, revocation, and identity binding. They also authenticate at the transport layer, before any application logic runs, reducing the attack surface significantly.
Issue client certificates at scale — Evertrust PKI acts as your internal Certificate Authority, issuing client certificates via SCEP, EST, CMP, and ACME. Whether you're enrolling 100 users or 100,000 devices, the platform handles provisioning automatically.
Full lifecycle visibility — Evertrust CLM gives you a real-time inventory of every client certificate in your environment: who holds it, when it expires, and whether it complies with your certificate policies.
Seamless MDM integration — Native connectors for major MDM platforms allow you to push client certificates to managed devices without custom development. Certificates are enrolled, renewed, and revoked through your existing device management workflows.
Instant revocation — When a device is lost or an employee departs, revoke their client certificate immediately through the Evertrust dashboard or API. OCSP and CRL distribution ensure relying parties are notified in real time.
