Hardware Security Module (HSM)

Applies to. Requirement 3.6.1.2 names a hardware security module as an example of a secure cryptographic device in which secret and private keys protecting stored account data may be kept; keys held inside an HSM satisfy that requirement's storage-form test without needing a separate key-encrypting key. For service providers, 3.6.1.1 requires the cryptographic architecture document to inventory every HSM, key management system and other secure cryptographic device used for key management, with type and location. The standard does not require an HSM; it is one of three acceptable key storage forms.

Example. A payment gateway generates its PAN encryption keys inside a pair of HSMs in two data centres. Application servers call the HSM to encrypt and decrypt but never receive the key itself; the HSM administrator cards are split between named custodians, and the architecture document lists both devices by type and location.

Limits. An HSM protects keys, not the data flowing through it: an application that can call the HSM to decrypt PAN on demand still handles cleartext PAN wherever that application runs. Using an HSM does not remove the key-management obligations in 3.7; generation, cryptoperiods, custodians and substitution controls still have to be documented and shown. Software-only key stores are not HSMs; the term means dedicated hardware that resists physical and logical attack.