3,683 research outputs found
Secure two-party quantum evaluation of unitaries against specious adversaries
We describe how any two-party quantum computation, specified by a unitary
which simultaneously acts on the registers of both parties, can be privately
implemented against a quantum version of classical semi-honest adversaries that
we call specious. Our construction requires two ideal functionalities to
garantee privacy: a private SWAP between registers held by the two parties and
a classical private AND-box equivalent to oblivious transfer. If the unitary to
be evaluated is in the Clifford group then only one call to SWAP is required
for privacy. On the other hand, any unitary not in the Clifford requires one
call to an AND-box per R-gate in the circuit. Since SWAP is itself in the
Clifford group, this functionality is universal for the private evaluation of
any unitary in that group. SWAP can be built from a classical bit commitment
scheme or an AND-box but an AND-box cannot be constructed from SWAP. It follows
that unitaries in the Clifford group are to some extent the easy ones. We also
show that SWAP cannot be implemented privately in the bare model
On the Efficiency of Classical and Quantum Secure Function Evaluation
We provide bounds on the efficiency of secure one-sided output two-party
computation of arbitrary finite functions from trusted distributed randomness
in the statistical case. From these results we derive bounds on the efficiency
of protocols that use different variants of OT as a black-box. When applied to
implementations of OT, these bounds generalize most known results to the
statistical case. Our results hold in particular for transformations between a
finite number of primitives and for any error. In the second part we study the
efficiency of quantum protocols implementing OT. While most classical lower
bounds for perfectly secure reductions of OT to distributed randomness still
hold in the quantum setting, we present a statistically secure protocol that
violates these bounds by an arbitrarily large factor. We then prove a weaker
lower bound that does hold in the statistical quantum setting and implies that
even quantum protocols cannot extend OT. Finally, we present two lower bounds
for reductions of OT to commitments and a protocol based on string commitments
that is optimal with respect to both of these bounds
Multi-party Quantum Computation
We investigate definitions of and protocols for multi-party quantum computing
in the scenario where the secret data are quantum systems. We work in the
quantum information-theoretic model, where no assumptions are made on the
computational power of the adversary. For the slightly weaker task of
verifiable quantum secret sharing, we give a protocol which tolerates any t <
n/4 cheating parties (out of n). This is shown to be optimal. We use this new
tool to establish that any multi-party quantum computation can be securely
performed as long as the number of dishonest players is less than n/6.Comment: Masters Thesis. Based on Joint work with Claude Crepeau and Daniel
Gottesman. Full version is in preparatio
Can relativistic bit commitment lead to secure quantum oblivious transfer?
While unconditionally secure bit commitment (BC) is considered impossible
within the quantum framework, it can be obtained under relativistic or
experimental constraints. Here we study whether such BC can lead to secure
quantum oblivious transfer (QOT). The answer is not completely negative. On one
hand, we provide a detailed cheating strategy, showing that the
"honest-but-curious adversaries" in some of the existing no-go proofs on QOT
still apply even if secure BC is used, enabling the receiver to increase the
average reliability of the decoded value of the transferred bit. On the other
hand, it is also found that some other no-go proofs claiming that a dishonest
receiver can always decode all transferred bits simultaneously with reliability
100% become invalid in this scenario, because their models of cryptographic
protocols are too ideal to cover such a BC-based QOT.Comment: Published version. This paper generalized some results in Sec. V of
arXiv:1101.4587, and pointed out the limitation of the proof in
arXiv:quant-ph/961103
- …