44 research outputs found
Limitations of Quantum Coset States for Graph Isomorphism
It has been known for some time that graph isomorphism reduces to the hidden
subgroup problem (HSP). What is more, most exponential speedups in quantum
computation are obtained by solving instances of the HSP. A common feature of
the resulting algorithms is the use of quantum coset states, which encode the
hidden subgroup. An open question has been how hard it is to use these states
to solve graph isomorphism. It was recently shown by Moore, Russell, and
Schulman that only an exponentially small amount of information is available
from one, or a pair of coset states. A potential source of power to exploit are
entangled quantum measurements that act jointly on many states at once. We show
that entangled quantum measurements on at least \Omega(n log n) coset states
are necessary to get useful information for the case of graph isomorphism,
matching an information theoretic upper bound. This may be viewed as a negative
result because highly entangled measurements seem hard to implement in general.
Our main theorem is very general and also rules out using joint measurements on
few coset states for some other groups, such as GL(n, F_{p^m}) and G^n where G
is finite and satisfies a suitable property.Comment: 25 page
Quantum Fourier sampling, Code Equivalence, and the quantum security of the McEliece and Sidelnikov cryptosystems
The Code Equivalence problem is that of determining whether two given linear
codes are equivalent to each other up to a permutation of the coordinates. This
problem has a direct reduction to a nonabelian hidden subgroup problem (HSP),
suggesting a possible quantum algorithm analogous to Shor's algorithms for
factoring or discrete log. However, we recently showed that in many cases of
interest---including Goppa codes---solving this case of the HSP requires rich,
entangled measurements. Thus, solving these cases of Code Equivalence via
Fourier sampling appears to be out of reach of current families of quantum
algorithms.
Code equivalence is directly related to the security of McEliece-type
cryptosystems in the case where the private code is known to the adversary.
However, for many codes the support splitting algorithm of Sendrier provides a
classical attack in this case. We revisit the claims of our previous article in
the light of these classical attacks, and discuss the particular case of the
Sidelnikov cryptosystem, which is based on Reed-Muller codes
Flow Secure Message in Parity Matrix
The goal of security is confidential ,integrity and availability to decrypt the messages.In recent years,many researchers has said about how to secure high-value data on hard disk.proposed system explains about the high grade cryptosystem one which even an attacker possessing both a copy of your encryption engine and knowledge of your operation.
DOI: 10.17762/ijritcc2321-8169.15014
The Optimal Single Copy Measurement for the Hidden Subgroup Problem
The optimization of measurements for the state distinction problem has
recently been applied to the theory of quantum algorithms with considerable
successes, including efficient new quantum algorithms for the non-abelian
hidden subgroup problem. Previous work has identified the optimal single copy
measurement for the hidden subgroup problem over abelian groups as well as for
the non-abelian problem in the setting where the subgroups are restricted to be
all conjugate to each other. Here we describe the optimal single copy
measurement for the hidden subgroup problem when all of the subgroups of the
group are given with equal a priori probability. The optimal measurement is
seen to be a hybrid of the two previously discovered single copy optimal
measurements for the hidden subgroup problem.Comment: 8 pages. Error in main proof fixe
Quantum game players can have advantage without discord
The last two decades have witnessed a rapid development of quantum
information processing, a new paradigm which studies the power and limit of
"quantum advantages" in various information processing tasks. Problems such as
when quantum advantage exists, and if existing, how much it could be, are at a
central position of these studies. In a broad class of scenarios, there are,
implicitly or explicitly, at least two parties involved, who share a state, and
the correlation in this shared state is the key factor to the efficiency under
concern. In these scenarios, the shared \emph{entanglement} or \emph{discord}
is usually what accounts for quantum advantage. In this paper, we examine a
fundamental problem of this nature from the perspective of game theory, a
branch of applied mathematics studying selfish behaviors of two or more
players. We exhibit a natural zero-sum game, in which the chance for any player
to win the game depends only on the ending correlation. We show that in a
certain classical equilibrium, a situation in which no player can further
increase her payoff by any local classical operation, whoever first uses a
quantum computer has a big advantage over its classical opponent. The
equilibrium is fair to both players and, as a shared correlation, it does not
contain any discord, yet a quantum advantage still exists. This indicates that
at least in game theory, the previous notion of discord as a measure of
non-classical correlation needs to be reexamined, when there are two players
with different objectives.Comment: 15 page