# pki

Source: https://startwithidentity.com/glossary/pki/
Last updated: 2026-08-29
License: content by Start with Identity. Cite the source URL.

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Public Key Infrastructure. The system of certificate authorities, certificates, and keys that binds public keys to identities. Underpins TLS, code signing, and machine identity.

Enterprise PKI is where machine identity actually lives, and it is usually the least inventoried part of the estate: certificates issued by a forgotten internal CA, private keys copied between hosts, and no owner for the one that expires on a Sunday. Shrinking certificate lifetimes turn that from an annual annoyance into a continuous automation requirement.

See also: [X.509](https://startwithidentity.com/glossary/x509/), [certificate lifecycle](https://startwithidentity.com/glossary/certificate-lifecycle/), [what is machine identity](https://startwithidentity.com/guides/fundamentals/what-is-machine-identity/), [PKI vendors](https://startwithidentity.com/vendors/pki/)