  In peer-to-peer systems, attrition attacks include both traditional,
network-level denial of service attacks as well as application-level attacks in
which malign peers conspire to waste loyal peers' resources. We describe
several defenses for LOCKSS, a peer-to-peer digital preservation system, that
help ensure that application-level attacks even from powerful adversaries are
less effective than simple network-level attacks, and that network-level
attacks must be intense, wide-spread, and prolonged to impair the system.
