Public Key Infrastructure (PKI)
Public Key Infrastructure (PKI) is the set of policies, roles, and technology used to create, manage, distribute, and revoke digital certificates that bind public cryptographic keys to verified identities, enabling secure authentication…
Definition
Public Key Infrastructure (PKI) is the set of policies, roles, and technology used to create, manage, distribute, and revoke digital certificates that bind public cryptographic keys to verified identities, enabling secure authentication and encrypted communication.
Overview
PKI is the trust framework underlying much of the secure internet. At its core is Asymmetric Encryption, where every party holds a mathematically linked key pair: a private key kept secret, and a public key that can be shared openly. PKI solves a critical problem with asymmetric cryptography on its own — how do you know a given public key genuinely belongs to the entity claiming it? — by introducing a trusted third party called a Certificate Authority (CA) that issues digital certificates cryptographically binding a public key to a verified identity. When a browser connects to a website over HTTPS, the site presents a certificate issued by a trusted Certificate Authority, and the browser validates that certificate's chain of trust back to a small set of root CAs it inherently trusts. This is the mechanism that powers TLS/SSL encrypted web traffic, and it's why a padlock icon in a browser signals that the connection is both encrypted and verified as belonging to the claimed domain. Free, automated certificate issuance from providers like Let's Encrypt has made this once-costly process accessible to virtually every website. Beyond web traffic, PKI underpins Digital Signatures (proving a document or piece of code hasn't been tampered with and originates from a specific signer), client certificate authentication (used in some corporate VPN and Wi-Fi deployments as an alternative to passwords), and code-signing for verifying software hasn't been altered since it was published by its developer. Certificates are issued with an expiration date and can be revoked before that date if a private key is compromised, using mechanisms like Certificate Revocation Lists (CRLs) or the Online Certificate Status Protocol (OCSP), so that relying parties can check whether a certificate they're presented with is still trustworthy at the moment it's used.
Key Concepts
- Binds public cryptographic keys to verified identities via digital certificates
- Relies on trusted Certificate Authorities to issue and vouch for certificates
- Powers the chain of trust behind HTTPS/TLS encrypted web connections
- Enables digital signatures for documents, code, and messages
- Supports certificate-based authentication as an alternative to passwords
- Includes revocation mechanisms (CRL, OCSP) for compromised certificates
- Free, automated issuance (e.g., Let's Encrypt) has made PKI widely accessible
Use Cases
Frequently Asked Questions
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