International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

Yacov Yacobi

Publications

Year
Venue
Title
2010
EPRINT
Towards a Theory of Trust Based Collaborative Search
Yacov Yacobi
Trust Based Collaborative Search is an interactive metasearch engine, presenting the user with clusters of results, based not only on the similarity of content, but also on the similarity of the recommending agents. The theory presented here is broad enough to cover search, browsing, recommendations, demographic profiling, and consumer targeting. We use the term search as an example. We developed a novel general trust theory. In this context, as a special case, we equate trust between agents with the similarity between their search-behaviors. The theory suggests that clusters should be close to maximal similarity within a tolerance dictated by the amount of uncertainty about the vectors of probabilities of attributes representing queries, pages and agents. In addition, we give a new theoretical analysis of clustering tolerances, enabling more judicial decisions about optimal tolerances. Specifically, we show that tolerances should at least be divided by a constant>1 as we descend from one layer in the hierarchical clustering to the next. We also show a promising connection between collaborative search and cryptography: A query plays the role of a cryptogram, the search engine is the cryptanalyst, and the user's intention is the cleartext. Shannon's unicity distance is the length of the search. It is needed to quantify the clustering-tolerance.
2010
EPRINT
Quantifying Trust
Trust is a central concept in public-key cryptography infrastruc- ture and in security in general. We study its initial quantification and its spread patterns. There is empirical evidence that in trust-based reputation model for virtual communities, it pays to restrict the clusters of agents to small sets with high mutual trust. We propose and motivate a mathematical model, where this phenomenon emerges naturally. In our model, we separate trust values from their weights. We motivate this separation using real examples, and show that in this model, trust converges to the extremes, agreeing with and accentuating the observed phenomenon. Specifically, in our model, cliques of agents of maximal mutual trust are formed, and the trust between any two agents that do not maximally trust each other, converges to zero. We offer initial practical relaxations to the model that preserve some of the theoretical flavor.
2008
EPRINT
On the economic payoff of forensic systems when used to trace Counterfeited Software and content
Yacov Yacobi
We analyze how well forensic systems reduce counterfeiting of soft- ware and content. We make a few idealized assumptions, and show that if the revenues of the producer before the introduction of forensics (Ro) are non-zero then the payoff of forensics is independent of the overall market size, it declines as the ratio between the penalty and the crime (both monetized) goes up, but that this behavior is reversed if Ro = 0. We also show that the payoff goes up as the ratio between success probability with and without forensics grows; however, for typical parameters most of the payoff is already reached when this ratio is 5.
2005
PKC
2002
EPRINT
A Note on the Bilinear Diffie-Hellman Assumption
Yacov Yacobi
Abstract. The Bi-linear Diffie-Hellman (BDH) intractability assumption is required to establish the security of new Weil-pairing based cryptosystems. BDH is reducible to most of the older believed-to-be-hard discrete-log problems and DH problems, but there is no known reduction from any of those problems to BDH. Let the bilinear mapping be e:G1 X G1->G2, where G1 and G2 are cyclic groups. We show that a many-one reduction from any of the relevant problems to BDH has to include an efficient mapping \phi:G2 ->G1 where \phi(g^{x})=f(x)P. Here g, and P are generators of the corresponding cyclic groups. The function \phi must be used in the reduction either before or after the call to oracle BDH. We show that if f(x)=ax^n+b for any constants a,b,n, then \phi could be used as an oracle for a probabilistic polynomial time solution for Decision Diffie-Hellman in G2. Thus such a reduction is unlikely.
1997
JOFC
1995
CRYPTO
1994
ASIACRYPT
1993
JOFC
1992
EUROCRYPT
1992
EUROCRYPT
1991
EUROCRYPT
1990
CRYPTO
1990
CRYPTO
1990
EUROCRYPT
1989
CRYPTO
1987
CRYPTO
1987
CRYPTO
1987
EUROCRYPT

Program Committees

Crypto 2001
Crypto 1992