A survivable-system design must include explicit requirements for recognition of attack. These requirements ensure the use of one or more of the preceding strategies through the specification of architectural features, automated tools, and manual processes. Since intruder techniques are constantly advancing, recognition requirements should be frequently reviewed and continuously improved. Recovery Service Requirements. Recovery is a system s ability to restore services after an intrusion has occurred.
Recovery also contributes to a system s ability to maintain essential services during intrusion.
Requirements for recoverability are what most clearly distinguish survivable systems from systems that are merely secure. Once security is breached, damage may follow with little to stand in the way. The ability of a system to react during an active intrusion is central to its capacity to survive an attack that cannot be completely repelled. Recovery is thus crucial during the exploration and exploitation phases of intrusion. Recovery strategies in use today include replication of critical information and services, use of fault-tolerant designs, and incorporation of backup systems for hardware and software.