A certificate authority (CA) is an organization responsible for storing, signing, and issuing digital certificates. These certificates contain a cryptographic key—which essentially says "I am who (or what) I say I am." 

While one can be their own client authentication CA for their organization (sidestepping the need to self-verify), third-party CAs are also quite popular. Your choice of a potential CA provider will depend on your infrastructure setup and unique security needs.

How does a certificate authority (CA) operate?

Certificate authorities are critical to security across the web. Certificates allow two parties to securely communicate via authentication, encryption, non-repudiation (evidence that a message was sent), and message integrity verification (to prevent tampering). The exchange of public keys enables this by establishing a chain of trust from CA to client. 

Each successful certificate applicant receives a public key, and the CA processes a client-generated certificate signing request upon verification. Next, the client takes their self-created private key and signs their request with it. Finally, the CA will return a public certificate to the client. Certificates are therefore a key component of an organization's public key infrastructure (PKI). 

Each key recipient is responsible for controlling and owning their respective keys. However, the certificate authority will sometimes securely store these private keys using hardware secure modules. This backup location provides additional protection in case a private key is lost. 

Browser vendors can pre-install trusted root certificates, intermediate certificates, or end-entity certificates into the browser. These are stored within operating systems, browsers, devices, and applications. 

CAs allow entities to apply for new certificates by submitting requests through online forms. However, certain authorities (and scripts) can enable automated certificate renewal in the event of expiry or loss. While this process might seem centralized, there are actually over 100 certificate authorities in the world today! While big names like Let's Encrypt and GlobalSign dominate the CA market, many others are integral to supporting internet security.

What makes a certificate authority (CA) useful?

While it's true that a certificate authority supports internet encryption and therefore security, this is an oversimplification of how they work. CAs and certificates can enable the following depending on the type(s) of certificates involved (such as X.509 certificates):

  • HTTPS enablement and encrypted communication

  • Code signing for executables and scripts

  • Email security using S/MIME certificates

  • Document signing

  • Client authentication (installed on-device)

In some of these cases, just a private key and digital signature are needed. While certificates are important, they're not infallible. Certificates can be compromised and require replacement, and regular certificate updates (which mirror password policies) are necessary to keep systems secure. Certificate expiration dates enforce this turnover.

How does HAProxy handle certificate authorities (CAs)?

HAProxy can dynamically store SSL/TLS certificates, bolstered by SNI functionality, ALPN support, and OCSP stapling. Teams can update their certificates in-memory without needing to restart or reload the service. Plus, support and integration with ACME-based issuers such as Let's Encrypt provide automated certificate management. 

To learn more about certificate authorities and certificates in HAProxy, check out our Dynamic SSL Storage in HAProxy blog post or our HAProxy and Let's Encrypt guide.