The Internet is afflicted by unwelcome "requests", defined broadly as
claims on a scarce resource, such as a server's CPU (in the case of
spurious traffic whose purpose is to deny service) or a human's
attention (in the case of spam). Traditional responses to these problems
apply heuristics: they try to identify "bad" requests based on their
content (e.g., in the way that spam filters analyze an email's text).
This talk argues that heuristic attempts at filtering are inherently
gameable and instead presents two systems that limit request volumes
directly. The first is a denial-of-service mitigation in which clients
are encouraged to automatically send *more* traffic to a besieged
server. The "good" clients can thereby compete equally with the "bad"
ones. The second is a system for enforcing *per-sender email quotas* to
control spam. This system scales to a workload of millions of requests
per second, tolerates Byzantine faults in its constituent hosts, and
resists a variety of attacks.
Michael Walfish is a Ph.D. student in computer science at M.I.T. He
received his B.A. from Harvard in 1998 and then worked for four years,
three of those at Digital Fountain, Inc. His research interests are in
networked systems, with sub-interests in security, performance, and