760 research outputs found
The Sender-Excited Secret Key Agreement Model: Capacity, Reliability and Secrecy Exponents
We consider the secret key generation problem when sources are randomly
excited by the sender and there is a noiseless public discussion channel. Our
setting is thus similar to recent works on channels with action-dependent
states where the channel state may be influenced by some of the parties
involved. We derive single-letter expressions for the secret key capacity
through a type of source emulation analysis. We also derive lower bounds on the
achievable reliability and secrecy exponents, i.e., the exponential rates of
decay of the probability of decoding error and of the information leakage.
These exponents allow us to determine a set of strongly-achievable secret key
rates. For degraded eavesdroppers the maximum strongly-achievable rate equals
the secret key capacity; our exponents can also be specialized to previously
known results.
In deriving our strong achievability results we introduce a coding scheme
that combines wiretap coding (to excite the channel) and key extraction (to
distill keys from residual randomness). The secret key capacity is naturally
seen to be a combination of both source- and channel-type randomness. Through
examples we illustrate a fundamental interplay between the portion of the
secret key rate due to each type of randomness. We also illustrate inherent
tradeoffs between the achievable reliability and secrecy exponents. Our new
scheme also naturally accommodates rate limits on the public discussion. We
show that under rate constraints we are able to achieve larger rates than those
that can be attained through a pure source emulation strategy.Comment: 18 pages, 8 figures; Submitted to the IEEE Transactions on
Information Theory; Revised in Oct 201
Rate-Distortion Theory for Secrecy Systems
Secrecy in communication systems is measured herein by the distortion that an
adversary incurs. The transmitter and receiver share secret key, which they use
to encrypt communication and ensure distortion at an adversary. A model is
considered in which an adversary not only intercepts the communication from the
transmitter to the receiver, but also potentially has side information.
Specifically, the adversary may have causal or noncausal access to a signal
that is correlated with the source sequence or the receiver's reconstruction
sequence. The main contribution is the characterization of the optimal tradeoff
among communication rate, secret key rate, distortion at the adversary, and
distortion at the legitimate receiver. It is demonstrated that causal side
information at the adversary plays a pivotal role in this tradeoff. It is also
shown that measures of secrecy based on normalized equivocation are a special
case of the framework.Comment: Update version, to appear in IEEE Transactions on Information Theor
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
Secret-Key Generation using Correlated Sources and Channels
We study the problem of generating a shared secret key between two terminals
in a joint source-channel setup -- the sender communicates to the receiver over
a discrete memoryless wiretap channel and additionally the terminals have
access to correlated discrete memoryless source sequences. We establish lower
and upper bounds on the secret-key capacity. These bounds coincide,
establishing the capacity, when the underlying channel consists of independent,
parallel and reversely degraded wiretap channels. In the lower bound, the
equivocation terms of the source and channel components are functionally
additive. The secret-key rate is maximized by optimally balancing the the
source and channel contributions. This tradeoff is illustrated in detail for
the Gaussian case where it is also shown that Gaussian codebooks achieve the
capacity. When the eavesdropper also observes a source sequence, the secret-key
capacity is established when the sources and channels of the eavesdropper are a
degraded version of the legitimate receiver. Finally the case when the
terminals also have access to a public discussion channel is studied. We
propose generating separate keys from the source and channel components and
establish the optimality of this approach when the when the channel outputs of
the receiver and the eavesdropper are conditionally independent given the
input.Comment: 29 Pages, Submitted IEEE Trans. Information Theor
Lists that are smaller than their parts: A coding approach to tunable secrecy
We present a new information-theoretic definition and associated results,
based on list decoding in a source coding setting. We begin by presenting
list-source codes, which naturally map a key length (entropy) to list size. We
then show that such codes can be analyzed in the context of a novel
information-theoretic metric, \epsilon-symbol secrecy, that encompasses both
the one-time pad and traditional rate-based asymptotic metrics, but, like most
cryptographic constructs, can be applied in non-asymptotic settings. We derive
fundamental bounds for \epsilon-symbol secrecy and demonstrate how these bounds
can be achieved with MDS codes when the source is uniformly distributed. We
discuss applications and implementation issues of our codes.Comment: Allerton 2012, 8 page
Secret Key Generation from Correlated Sources and Secure Link
In this paper, we study the problem of secret key generation from both
correlated sources and a secure channel. We obtain the optimal secret key rate
in this problem and show that the optimal scheme is to conduct secret key
generation and key distribution jointly, where every bit in the secret channel
will yield more than one bit of secret key rate. This joint scheme is better
than the separation-based scheme, where the secure channel is used for key
distribution, and as a result, every bit in the secure channel can only provide
one bit of secret key rate.Comment: 5 pages, 1 figur
- …