Nymble: Blocking Misbehaving Users in Anonymizing Networks –
JAVA/J2EE

ABSTRACT
Anonymizing networks such as Tor allow users to access Internet services privately by using a series of routers to
hide the client's IP address from the server. The success of such networks, however, has been limited by users
employing this anonymity for abusive purposes such as defacing popular Web sites. Web site administrators
routinely rely on IP-address blocking for disabling access to misbehaving users, but blocking IP addresses is not
practical if the abuser routes through an anonymizing network. As a result, administrators block all known exit
nodes of anonymizing networks, denying anonymous access to misbehaving and behaving users alike. To address
this problem, we present Nymble, a system in which servers can “blacklist” misbehaving users, thereby blocking
users without compromising their anonymity. Our system is thus agnostic to different servers' definitions of
misbehavior-servers can blacklist users for whatever reason, and the privacy of blacklisted users is maintained.