How is PKI Used in Authentication? Securing Digital Identities in the Modern World

In today’s technologically driven landscape, verifying identities online has become crucial for businesses and individuals alike. Public Key Infrastructure (PKI) stands as one of the most robust frameworks for authentication, providing the foundation for secure communications across the internet. But how exactly does PKI work in authentication processes, and why is it considered the gold standard for digital identity verification?

What is PKI Authentication?

PKI authentication uses a sophisticated system of digital certificates and cryptographic keys to verify identities. Unlike password-based systems that rely on shared secrets, PKI employs asymmetric cryptography—utilising mathematically related key pairs that provide significantly stronger security guarantees and removing the need for a ‘shared secret’ that can be compromised.

The Critical Components of PKI Authentication

Digital Certificates: Your Electronic Passport

Digital certificates function as electronic credentials that bind a public key to an identity. These certificates, often following the X.509 standard, contain critical information including:

• The subject’s identity (person or organisation)
• The public key associated with that identity
• The certificate’s validity period
• The issuing Certificate Authority’s digital signature
• A location where the validity (revocation status) of the certificate can be checked

When you connect to your banking website securely, your browser automatically verifies the bank’s certificate, confirming you are communicating with the legitimate organisation rather than an impostor.

Certificate Authorities: The Trust Anchors

Certificate Authorities (CAs) serve as trusted third parties that validate identities before issuing certificates. This hierarchical trust model includes:

• Root CAs: The highest level of trust, whose certificates come pre-installed in browsers and operating systems
• Intermediate CAs: Organisations that receive their authority from root CAs
• Registration Authorities: Entities that verify identifying information before certificate issuance

This chain of trust ensures that when you authenticate to a system, both parties can verify each other’s identities with confidence.

The Public-Private Key Mechanism

At the heart of PKI authentication lies the concept of key pairs:

The private key remains securely stored with the owner and never shared. The public key can be distributed freely via a certificate. This arrangement enables two fundamental security functions:

1. Authentication: When a certificate is presented during authentication, it can prove possession of a corresponding private key through a cryptographic signature process, verifying identity.
2. Encryption: Data encrypted with the public key can only be decrypted with the matching private key, ensuring confidentiality.

Hardware Security Modules: Protecting the Keys to the Kingdom

For high-security environments, Hardware Security Modules (HSMs) provide specialised physical protection for cryptographic keys used as part of the PKI process, but that are not generated on end user devices such as smart cards or smartphones. These tamper-resistant devices:

• Generate and store private keys in hardened environments
• Perform cryptographic operations without exposing keys
• Provide physical security controls against theft or tampering
• Can maintain detailed audit logs of all key usage
• Enable private keys used in encryption to be securely recovered.

Organisations managing critical infrastructure or sensitive financial data typically deploy HSMs to protect their PKI implementation against sophisticated attacks.

The Server Authentication Process in Action

When you connect to a secure website, PKI authentication of the website happens seamlessly:

1. The server presents its digital certificate
2. Your browser verifies the certificate against trusted root certificates
3. The server proves possession of the private key through a cryptographic challenge
4. A secure encrypted session is established once mutual authentication completes, ensuring transmitted data is kept private.

This process happens in milliseconds but provides a high level of security.

The User Authentication Process in Action

When a user authenticates using PKI it is the private key of the user that is critical in providing strong authentication:

1. A user starts an authentication process to a system (relying party) protected by PKI
2. The relying party sends a random challenge to the user
3. The end user digitally signs the challenge with their private key, typically protected on a secure device such as a smart card or USB token and requiring a second authentication factor such as a PIN or fingerprint to enable access to the private key
4. The challenge is digitally signed on the secure device and returned to the relying party requiring authentication
5. The relying party verifies the digital signature using the public key contained within the certificate
6. The relying party verifies that the certificate was issued by a trusted authority and that it is still valid
7. The user is authenticated.

Conclusion

PKI authentication has become the cornerstone of secure digital interactions, from website connections to email encryption and secure remote access. By understanding how certificates, key pairs, and the trust infrastructure work together, organisations can implement robust authentication systems that provide strong identity verification while maintaining usability for end users.

Get in touch today to find out more information about how Intercede can help you with stronger authentication from passwords to PKI.