failsecure

Failsecure, or fail-secure, is a design principle in security engineering stating that in the event of a failure the system remains in a secure or restricted state. This approach contrasts with fail-safe (or fail-open), where a failure allows access or an open condition. Fail-secure designs prioritize containment and protection of assets over uninterrupted accessibility.

Common applications include physical access control, where a door lock may be designed to stay locked if power or hardware fails; for example, a fail-secure electric strike keeps the door locked when power is lost. In data security, a fail-secure authentication service may deny access if the authentication backend becomes unavailable, preventing unauthorized access at the risk of a service disruption. In electrical systems and industrial control, fail-secure configurations may isolate circuits or keep safety-critical equipment in a safe state during faults even if this reduces availability.

Designers must balance security with usability; fail-secure can impede emergency egress or essential operations during outages. Redundancy watchdog timers and secure fallbacks can mitigate risks, but must be carefully implemented to prevent bypass.

Examples include door hardware with fail-secure locks that stay engaged on power loss, and networked systems that shut down access when central services are offline to avoid partial authorization states.

See also: fail-safe, fail-open, security design principles.