820 research outputs found
Secure aggregation of distributed information: How a team of agents can safely share secrets in front of a spy
We consider the generic problem of Secure Aggregation of Distributed
Information (SADI), where several agents acting as a team have information
distributed among them, modeled by means of a publicly known deck of cards
distributed among the agents, so that each of them knows only her cards. The
agents have to exchange and aggregate the information about how the cards are
distributed among them by means of public announcements over insecure
communication channels, intercepted by an adversary "eavesdropper", in such a
way that the adversary does not learn who holds any of the cards. We present a
combinatorial construction of protocols that provides a direct solution of a
class of SADI problems and develop a technique of iterated reduction of SADI
problems to smaller ones which are eventually solvable directly. We show that
our methods provide a solution to a large class of SADI problems, including all
SADI problems with sufficiently large size and sufficiently balanced card
distributions
Perfectly secure data aggregation via shifted projections
We study a general scenario where confidential information is distributed
among a group of agents who wish to share it in such a way that the data
becomes common knowledge among them but an eavesdropper intercepting their
communications would be unable to obtain any of said data. The information is
modelled as a deck of cards dealt among the agents, so that after the
information is exchanged, all of the communicating agents must know the entire
deal, but the eavesdropper must remain ignorant about who holds each card.
Valentin Goranko and the author previously set up this scenario as the secure
aggregation of distributed information problem and constructed weakly safe
protocols, where given any card , the eavesdropper does not know with
certainty which agent holds . Here we present a perfectly safe protocol,
which does not alter the eavesdropper's perceived probability that any given
agent holds . In our protocol, one of the communicating agents holds a
larger portion of the cards than the rest, but we show how for infinitely many
values of , the number of cards may be chosen so that each of the agents
holds more than cards and less than
Unconditionally Secure Cryptography: Signature Schemes, User-Private Information Retrieval, and the Generalized Russian Cards Problem
We focus on three different types of multi-party cryptographic protocols. The first is in the area of unconditionally secure signature schemes, the goal of which is to provide users the ability to electronically sign documents without the reliance on computational assumptions needed in traditional digital signatures. The second is on cooperative protocols in which users help each other maintain privacy while querying a database, called user-private information retrieval protocols. The third is concerned with the generalized Russian cards problem, in which two card players wish to communicate their hands to each other via public announcements without the third player learning the card deal. The latter two problems have close ties to the field of combinatorial designs, and properly fit within the field of combinatorial cryptography. All of these problems have a common thread, in that they are grounded in the information-theoretically secure or unconditionally secure setting
Crossing Hands in the Russian Cards Problem
When communicating using an unconditionally secure protocol, a sender and receiver is able to transmit secret information over a public, insecure channel without fear of the secret being intercepted by a third party. The Russian cards problem is an example of an unconditionally secure protocol where the communication is fully understandable for everyone listening in. Even though everyone can understand what is being said, only the sender and receiver are able to uncover the secrets being transmitted. In this thesis we investigate the interaction among the communicating parties. By extending existing problem-specific software we are able to more efficiently analyze protocols, and we are therefore able to provide an answer to an open problem in the literature. We provide a completely new solution to the Russian cards protocol and show that it fulfills all requirements by the problem. Discovering this new solution provides the person initiating the protocol two new strategies to choose from when constructing the initial announcement of the protocol.Masteroppgave i informasjonsvitenskapINFO39
Hash Families and Cover-Free Families with Cryptographic Applications
This thesis is focused on hash families and cover-free families and their application to
problems in cryptography. We present new necessary conditions for generalized separating
hash families, and provide new explicit constructions. We then consider three cryptographic
applications of hash families and cover-free families. We provide a stronger de nition of
anonymity in the context of shared symmetric key primitives and give a new scheme with
improved anonymity properties. Second, we observe that nding the invalid signatures
in a set of digital signatures that fails batch veri cation is a group testing problem, then
apply and compare many group testing algorithms to solve this problem e ciently. In
particular, we apply group testing algorithms based on cover-free families. Finally, we
construct a one-time signature scheme based on cover-free families with short signatures
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