International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

Seung Geol Choi

Affiliation: US Naval Academy

Publications

Year
Venue
Title
2019
JOFC
(Efficient) Universally Composable Oblivious Transfer Using a Minimal Number of Stateless Tokens
We continue the line of work initiated by Katz (Eurocrypt 2007) on using tamper-proof hardware tokens for universally composable secure computation. As our main result, we show an oblivious-transfer (OT) protocol in which two parties each create and transfer a single, stateless token and can then run an unbounded number of OTs. We also show a more efficient protocol, based only on standard symmetric-key primitives (block ciphers and collision-resistant hash functions), that can be used if a bounded number of OTs suffice. Motivated by this result, we investigate the number of stateless tokens needed for universally composable OT. We prove that our protocol is optimal in this regard for constructions making black-box use of the tokens (in a sense we define). We also show that nonblack-box techniques can be used to obtain a construction using only a single stateless token.
2018
JOFC
2015
EPRINT
2014
CRYPTO
2014
TCC
2014
EPRINT
2013
PKC
2013
TCC
2013
ASIACRYPT
2012
TCC
2011
ASIACRYPT
2009
TCC
2009
ASIACRYPT
2009
ASIACRYPT
2008
TCC
2008
EPRINT
Fair Traceable Multi-Group Signatures
This paper presents fair traceable multi-group signatures (FTMGS), which have enhanced capabilities, compared to group and traceable signatures, that are important in real world scenarios combining accountability and anonymity. The main goal of the primitive is to allow multiple groups that are managed separately (managers are not even aware of the other ones), yet allowing users (in the spirit of the Identity 2.0 initiative) to manage what they reveal about their identity with respect to these groups by themselves. This new primitive incorporates the following additional features. - While considering multiple groups it discourages users from sharing their private membership keys through two orthogonal and complementary approaches. In fact, it merges functionality similar to credential systems with anonymous type of signing with revocation. - The group manager now mainly manages joining procedures, and new entities (called fairness authorities and consisting of various representatives, possibly) are involved in opening and revealing procedures. In many systems scenario assuring fairness in anonymity revocation is required. We specify the notion and implement it in the random oracle model.
2007
ASIACRYPT