What is the difference between a public CA and a private CA?

The core difference between a public and a private CA lies in who is expected to trust the certificates each one issues, which in turn shapes how each is operated, audited, and used.

Key distinctions:

• Public CA: Trusted by default across operating systems and browsers because it meets independent industry and audit requirements, making it suitable for certificates that external users or systems need to trust automatically, such as public website TLS certificates.
• Private CA: Operated internally by an organization and trusted only within its own environment, since it has not undergone the same public trust program requirements.
• Flexibility trade-off: A private CA offers more flexibility for internal use cases such as device or employee authentication, where broad external trust is unnecessary.
• Cost and control trade-off: Public CAs typically involve per-certificate costs and less configuration control, while private CAs give an organization full control at the cost of managing the CA itself.

Most enterprise environments use both in combination: public CAs for externally facing services, and a private CA, often run on a platform like primeID Certify, for internal authentication needs.