155 research outputs found
Information-Theoretically Secure Voting Without an Honest Majority
We present three voting protocols with unconditional privacy and
information-theoretic correctness, without assuming any bound on the number of
corrupt voters or voting authorities. All protocols have polynomial complexity
and require private channels and a simultaneous broadcast channel. Our first
protocol is a basic voting scheme which allows voters to interact in order to
compute the tally. Privacy of the ballot is unconditional, but any voter can
cause the protocol to fail, in which case information about the tally may
nevertheless transpire. Our second protocol introduces voting authorities which
allow the implementation of the first protocol, while reducing the interaction
and limiting it to be only between voters and authorities and among the
authorities themselves. The simultaneous broadcast is also limited to the
authorities. As long as a single authority is honest, the privacy is
unconditional, however, a single corrupt authority or a single corrupt voter
can cause the protocol to fail. Our final protocol provides a safeguard against
corrupt voters by enabling a verification technique to allow the authorities to
revoke incorrect votes. We also discuss the implementation of a simultaneous
broadcast channel with the use of temporary computational assumptions, yielding
versions of our protocols achieving everlasting security
Quantum Cryptography Beyond Quantum Key Distribution
Quantum cryptography is the art and science of exploiting quantum mechanical
effects in order to perform cryptographic tasks. While the most well-known
example of this discipline is quantum key distribution (QKD), there exist many
other applications such as quantum money, randomness generation, secure two-
and multi-party computation and delegated quantum computation. Quantum
cryptography also studies the limitations and challenges resulting from quantum
adversaries---including the impossibility of quantum bit commitment, the
difficulty of quantum rewinding and the definition of quantum security models
for classical primitives. In this review article, aimed primarily at
cryptographers unfamiliar with the quantum world, we survey the area of
theoretical quantum cryptography, with an emphasis on the constructions and
limitations beyond the realm of QKD.Comment: 45 pages, over 245 reference
Universal blind quantum computation
We present a protocol which allows a client to have a server carry out a
quantum computation for her such that the client's inputs, outputs and
computation remain perfectly private, and where she does not require any
quantum computational power or memory. The client only needs to be able to
prepare single qubits randomly chosen from a finite set and send them to the
server, who has the balance of the required quantum computational resources.
Our protocol is interactive: after the initial preparation of quantum states,
the client and server use two-way classical communication which enables the
client to drive the computation, giving single-qubit measurement instructions
to the server, depending on previous measurement outcomes. Our protocol works
for inputs and outputs that are either classical or quantum. We give an
authentication protocol that allows the client to detect an interfering server;
our scheme can also be made fault-tolerant.
We also generalize our result to the setting of a purely classical client who
communicates classically with two non-communicating entangled servers, in order
to perform a blind quantum computation. By incorporating the authentication
protocol, we show that any problem in BQP has an entangled two-prover
interactive proof with a purely classical verifier.
Our protocol is the first universal scheme which detects a cheating server,
as well as the first protocol which does not require any quantum computation
whatsoever on the client's side. The novelty of our approach is in using the
unique features of measurement-based quantum computing which allows us to
clearly distinguish between the quantum and classical aspects of a quantum
computation.Comment: 20 pages, 7 figures. This version contains detailed proofs of
authentication and fault tolerance. It also contains protocols for quantum
inputs and outputs and appendices not available in the published versio
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