# Hardware Security Module (HSM) One-sentence definition: Tamper-resistant appliance/card that **generates, stores, and uses cryptographic keys** without exposing plaintext keys. ## Key Facts - Supports key ceremonies, dual control/split knowledge. - Performs crypto operations inside boundary (signing, decryption). - Certified assurance levels (FIPS 140, etc.). - Used for CA keys, payment HSMs, code signing, database master keys. - Cloud HSM/KMS variants with isolation models. - **Verify:** check official (ISC)² CBK and current exam outline. ## Exam Relevance - Select HSM when key custody and assurance are critical. **Mnemonic:** “Keys stay **inside**.” ## Mini Scenario Q: CA root key protection—control? A: Offline HSM with dual control and ceremony procedures. ## Revision Checklist - Define dual control vs split knowledge. - List three HSM use-cases. - Note why plaintext keys shouldn’t leave. ## Related [[Trusted Platform Module (TPM)]] · [[Public Key Infrastructure (PKI) Components]] · [[Certificates, Revocation, and Pinning]] · [[Symmetric Encryption Overview]] · [[Key Management Basics (Asset Security)]] · [[Domain 3 - Index]]