Recovery from malicious transactions

Preventive measures sometimes fail to deflect malicious attacks. In this paper, we adopt an information warfare, perspective, which assumes success by the attacker in achieving partial, but not complete, damage. In particular, we work in the database context and consider recovery from malicious but committed transactions. Traditional recovery mechanisms do not address this problem, except for complete rollbacks, which undo the work of benign transactions as well as malicious ones, and compensating transactions, whose utility depends on application semantics. Recovery is complicated by the presence of benign transactions that depend, directly or indirectly, on the malicious transactions. We present algorithms to restore only the damaged part of the database. We identify the information that needs to be maintained for such algorithms. The initial algorithms repair damage to quiescent databases; subsequent algorithms increase availability by allowing new transactions to execute concurrently with the repair process. Also, via a study of benchmarks, we show practical examples of how off line analysis can efficiently provide the necessary data to repair the damage of malicious transactions.