257,767 research outputs found
Secret-key Agreement with Channel State Information at the Transmitter
We study the capacity of secret-key agreement over a wiretap channel with
state parameters. The transmitter communicates to the legitimate receiver and
the eavesdropper over a discrete memoryless wiretap channel with a memoryless
state sequence. The transmitter and the legitimate receiver generate a shared
secret key, that remains secret from the eavesdropper. No public discussion
channel is available. The state sequence is known noncausally to the
transmitter. We derive lower and upper bounds on the secret-key capacity. The
lower bound involves constructing a common state reconstruction sequence at the
legitimate terminals and binning the set of reconstruction sequences to obtain
the secret-key. For the special case of Gaussian channels with additive
interference (secret-keys from dirty paper channel) our bounds differ by 0.5
bit/symbol and coincide in the high signal-to-noise-ratio and high
interference-to-noise-ratio regimes. For the case when the legitimate receiver
is also revealed the state sequence, we establish that our lower bound achieves
the the secret-key capacity. In addition, for this special case, we also
propose another scheme that attains the capacity and requires only causal side
information at the transmitter and the receiver.Comment: 10 Pages, Submitted to IEEE Transactions on Information Forensics and
Security, Special Issue on Using the Physical Layer for Securing the Next
Generation of Communication System
How Many Queries Will Resolve Common Randomness?
A set of m terminals, observing correlated signals, communicate interactively
to generate common randomness for a given subset of them. Knowing only the
communication, how many direct queries of the value of the common randomness
will resolve it? A general upper bound, valid for arbitrary signal alphabets,
is developed for the number of such queries by using a query strategy that
applies to all common randomness and associated communication. When the
underlying signals are independent and identically distributed repetitions of m
correlated random variables, the number of queries can be exponential in signal
length. For this case, the mentioned upper bound is tight and leads to a
single-letter formula for the largest query exponent, which coincides with the
secret key capacity of a corresponding multiterminal source model. In fact, the
upper bound constitutes a strong converse for the optimum query exponent, and
implies also a new strong converse for secret key capacity. A key tool,
estimating the size of a large probability set in terms of Renyi entropy, is
interpreted separately, too, as a lossless block coding result for general
sources. As a particularization, it yields the classic result for a discrete
memoryless source.Comment: Accepted for publication in IEEE Transactions on Information Theor
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