Hardware security module (HSM)

An HSM is a dedicated appliance or plug-in card built to protect keys. Keys are created inside it and, by design, never leave in plain form: applications send data to the module, which signs or decrypts internally and returns the result. Physical tampering triggers erasure, and access is controlled by roles, quorum cards and detailed logs. Many models are certified under FIPS 140-2 or 140-3 at Level 3 or higher.

Banks have used HSMs for decades to protect card PINs and payment keys, and crypto custodians, exchanges and staking providers adopted them for signing keys. Cloud providers rent HSMs as a service, and some custody platforms combine HSMs with MPC or multisig so that no single device or employee can move funds alone.

Not every HSM supports the elliptic curves blockchains use, such as secp256k1 or ed25519, so firmware or custom code may be needed. An HSM also signs whatever an authorized application asks for: if the server that talks to it is compromised, it will faithfully sign malicious transactions. Policy engines and transaction checks around the module matter as much as the hardware.