Hardware Security Modules sit at the very bottom of your key management stack — and yet most developers encounter them only when something has already gone wrong. This post explains what an HSM actually does, how to reason about buying a used one, and what to check before you power it up. What an HSM actually does An HSM is a tamper-resistant piece of hardware whose sole job is to generate, store, and use cryptographic keys without ever exposing those keys to the host system . O...