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Security Fundamentals & Crypto · Foundational

Private Key

The secret half of an asymmetric key pair, used to decrypt data or create digital signatures.

Definition

The private key must remain under the exclusive control of its owner, ideally in an HSM, TPM, smart card, or secure enclave. Compromise of a private key requires revoking the associated certificate. Private keys should never be escrowed for signing purposes, since that would undermine non-repudiation.

Example

A web server's private key is stored in an HSM so it cannot be exported even by administrators.

Exam tip

If a private key is compromised, revoke the certificate immediately and reissue with a new key pair.

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