Failing badly
Failing badly and failing well are concepts in systems security and network security describing how a system reacts to failure. The terms have been popularized by Bruce Schneier, a cryptographer and security consultant.[1]
A system that fails badly is one that fails catastrophically once failure occurs. A single point of failure can thus bring down the whole system. Examples include:
- Databases (such as credit card databases) protected only by a password. Once this security is breached, all data can be accessed.
- Buildings depending on a single column or truss, whose removal would cause a chain reaction collapse under normal loads.
- Security checks which concentrate on establishing identity, not intent (thus allowing, for example, suicide attackers to pass).
- Internet access provided by a single service provider. If the provider's network fails, all Internet connectivity is lost.
- Ring networks in which the failure of a single node or connection between nodes brings down the entire network.
A system that fails well is one that compartmentalizes or contains failure. Examples include:
- Compartmentalized hulls in watercraft, ensuring that a hull breach in one compartment will not flood the entire vessel.
- Databases that do not allow downloads of all data in one attempt, limiting the amount of compromised data.
- Structurally redundant buildings conceived to resist loads beyond those expected under normal circumstances, or resist loads when the structure is damaged.
- Concrete structures, which show fractures long before breaking under load, thus giving early warning.
- Armoured cockpit doors on airplanes, which confine a potential hijacker within the cabin even if they are able to bypass airport security checks.[1]
- Internet connectivity provided by more than one vendor or discrete path, known as multihoming.
- Star or mesh networks, which can continue to operate when a node or connection has failed (though for a star network, failure of the central hub will still cause the network to fail).
Designing a system to 'fail well' has also been alleged to be a better use of limited security funds than the typical quest to eliminate all potential sources of errors and failure.[2]
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References