SPEAKER:
Sherman S. M. Chow
NYU

TITLE: 
Ring Signatures without Random Oracles

ABSTRACT:
Ring signatures, first introduced by Rivest, Shamir, and Tauman,
enable a user to sign a message so that a ring of possible signers (of
which the user is a member) is identified, without revealing exactly
which member of that ring actually generated the signature. In
contrast to group signatures, ring signatures are completely
``ad-hoc'' and do not require any central authority or coordination
among the various users (indeed, users do not even need to be aware of
each other); furthermore, ring signature schemes grant users
fine-grained control over the level of anonymity associated with any
particular signature.

In this talk, I will discuss some new results in ring signature
schemes.  I will go over the hierarchy of formal security definitions
identified by Bender, Katz and Morselli. Then I will show three new
constructions of ring signature schemes in the standard model. One is
a generic scheme based on standard signature, public-key encryption
and ZAP proof system; and a second, more efficient ring signature
scheme but supporting only 2 users. The last one is an independent
work by Chow, Liu, Wei and Yuen without utilizing encryption and ZAP. 
These are the first constructions of ring signature that do not rely 
on random oracles or ideal ciphers; the generic scheme is proven to be
secure under the strongest definitions of security.