NYMBLE BLOCKING

 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

 Existing users’ credentials must be updated, making it
impractical. Verifier-local revocation (VLR) fixes this
shortcoming by requiring the server (“verifier”) to
perform only local updates during revocation.
 Unfortunately, VLR requires heavy computation at the
server that is linear in the size of the blacklist.

 We present a secure system called Nymble, which provides
all the following properties: anonymous authentication,
backward unlink ability, subjective blacklisting, fast
authentication speeds, rate-limited anonymous
connections, revocation auditability, and also addresses the
Sybil attack to make its deployment practical .
 Our system ensures that users are aware of their blacklist
status before they present a nymble, and disconnect
immediately if they are blacklisted.

Nymble Manager
Pseudonym Manager
Blacklisting a user
Nymble-authenticated connection

 Servers can therefore blacklist anonymous users
without knowledge of their IP addresses while allowing
behaving users to connect anonymously.
 Our system ensures that users are aware of their
blacklist status before they present a nymble, and
disconnect immediately if they are blacklisted.
 Although our work applies to anonymizing networks in
general, we consider Tor for purposes of exposition.
 In fact, any number of anonymizing networks can rely
on the same Nymble system, blacklisting anonymous
users regardless of their anonymizing network(s) of
choice.

 The user must first contact the Pseudonym Manager
(PM) and demonstrate control over a resource; for IP-
address blocking, the user must connect to the PM
directly (i.e., not through a known anonymizing
network), ensuring that the same pseudonym is
always issued for the same resource.

 Users who make use of anonymizing networks expect their
connections to be anonymous.
 If a server obtains a seed for that user, however, it can link
that user’s subsequent connections.
 It is of utmost importance, then,that users be notified of
their blacklist status before they present a nymble ticket to
a server.
 In our system, the user can download the server’s blacklist
and verify her status. If blacklisted, the user disconnects
immediately.
 IP-address blocking employed by Internet services. There
are, however, some inherent limitations to using IP
addresses as the scarce resource.
 If a user can obtain multiple addresses she can circumvent
both nymble-based and regular IP-address blocking.

 Blacklistability:
Assures that any honest server can indeed block
misbehaving users. Specifically, if an honest server
complains about a user that misbehaved in the
current linkability window, the complaint will be
successful and the user will not be able to “nymble-
connect,” i.e., establish a Nymble-authenticated
connection, to the server successfully in subsequent
time periods (following the time of complaint) of that
linkability window.

 Assures any honest server that no user can successfully
nymble-connect to it more than once within any single
time period. Non-frameability guarantees that any honest
user who is legitimate according to an honest server can
nymble-connect to that server. This prevents an attacker
from framing a legitimate honest user, e.g., by getting the
user blacklisted for someone else’s misbehavior. This
property assumes each user has a single unique identity.
 When IP addresses are used as the identity, it is possible
for a user to “frame” an honest user who later obtains the
same IP address. Non-frameability holds true only against
attackers with different identities (IP addresses).
 A user is legitimate according to a server if she has not
been blacklisted by the server, and has not exceeded the
rate limit of establishing Nymble-connections. Honest
servers must be able to differentiate between legitimate
and illegitimate users.

Hardware Requirements:
System : Pentium IV 2.4 GHz.
Hard Disk : 40 GB.
Floppy Drive : 1.44 Mb.
Monitor : 15 VGA Colour.
Mouse : Logitech.
Ram : 256 Mb.

Software Requirements:
Operating system : Windows XP Professional/7
Front End :SOCKET,REMOTE
SERVER :SQLSERVER
Tool :VS2008

 Serverscan blacklist misbehavingusers while maintainingtheir
privacy, and we show how these propertiescan be attainedin a way
that is practical, efficient, and sensitiveto needs of both users and
services.
 We hope that our work will increasethe mainstreamacceptance of
anonymzingnetworks such asTor, which has thus far been completely
blocked by several services becauseof users who abuse their
anonymity.

THANK YOU..!!
DONE BY,
B.SONIKA(08P71A0587)
A.SURENDRANATH REDDY(08P71A05A4)
VATSALYA ERANKY(08P71A05B2)

NYMBLE BLOCKING

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