PKId

PKId, short for Public Key Identifier, is a label or value used to uniquely identify a specific public key in a cryptographic system, a public-key infrastructure, or a key-management environment. A PKId enables applications and security services to refer to a key without transmitting the full key material, simplify key lookup, and support association with identities, certificates, or credentials.

PKId values are not standardized to a single format; they are typically derived in one of two ways. In many systems, a PKId is the key’s fingerprint—a hash of the public key material, often rendered as a hex string or base64. In PKI contexts, a certificate or directory may expose a known key identifier such as a Subject Key Identifier (SKI) derived from the public key’s information. Alternatively, an organization may assign an application-level ID (for example a UUID or numeric identifier) to each public key stored in a key vault or directory service.

PKId is used for key lookup, revocation checks, and policy enforcement. It can facilitate cross-system key matching, certificate pinning, and rotation workflows by providing a stable reference to a key across changes in the key material.

Security considerations include ensuring that PKId bindings remain authentic and tamper-evident, as incorrect or leaked bindings could lead to misattribution of keys. When using fingerprints, care should be taken to use sufficiently long hash algorithms to prevent collisions.

See also: fingerprint, Subject Key Identifier, X.509, PKI, key management, SSH fingerprint.