942 research outputs found
Enhancement of Secrecy of Block Ciphered Systems by Deliberate Noise
This paper considers the problem of end-end security enhancement by resorting
to deliberate noise injected in ciphertexts. The main goal is to generate a
degraded wiretap channel in application layer over which Wyner-type secrecy
encoding is invoked to deliver additional secure information. More
specifically, we study secrecy enhancement of DES block cipher working in
cipher feedback model (CFB) when adjustable and intentional noise is introduced
into encrypted data in application layer. A verification strategy in exhaustive
search step of linear attack is designed to allow Eve to mount a successful
attack in the noisy environment. Thus, a controllable wiretap channel is
created over multiple frames by taking advantage of errors in Eve's
cryptanalysis, whose secrecy capacity is found for the case of known channel
states at receivers. As a result, additional secure information can be
delivered by performing Wyner type secrecy encoding over super-frames ahead of
encryption, namely, our proposed secrecy encoding-then-encryption scheme. These
secrecy bits could be taken as symmetric keys for upcoming frames. Numerical
results indicate that a sufficiently large secrecy rate can be achieved by
selective noise addition.Comment: 11 pages, 8 figures, journa
Concatenation of convolutional and block codes Final report
Comparison of concatenated and sequential decoding systems and convolutional code structural propertie
Toward Photon-Efficient Key Distribution over Optical Channels
This work considers the distribution of a secret key over an optical
(bosonic) channel in the regime of high photon efficiency, i.e., when the
number of secret key bits generated per detected photon is high. While in
principle the photon efficiency is unbounded, there is an inherent tradeoff
between this efficiency and the key generation rate (with respect to the
channel bandwidth). We derive asymptotic expressions for the optimal generation
rates in the photon-efficient limit, and propose schemes that approach these
limits up to certain approximations. The schemes are practical, in the sense
that they use coherent or temporally-entangled optical states and direct
photodetection, all of which are reasonably easy to realize in practice, in
conjunction with off-the-shelf classical codes.Comment: In IEEE Transactions on Information Theory; same version except that
labels are corrected for Schemes S-1, S-2, and S-3, which appear as S-3, S-4,
and S-5 in the Transaction
Computable Lower Bounds for Capacities of Input-Driven Finite-State Channels
This paper studies the capacities of input-driven finite-state channels,
i.e., channels whose current state is a time-invariant deterministic function
of the previous state and the current input. We lower bound the capacity of
such a channel using a dynamic programming formulation of a bound on the
maximum reverse directed information rate. We show that the dynamic
programming-based bounds can be simplified by solving the corresponding Bellman
equation explicitly. In particular, we provide analytical lower bounds on the
capacities of -runlength-limited input-constrained binary symmetric and
binary erasure channels. Furthermore, we provide a single-letter lower bound
based on a class of input distributions with memory.Comment: 9 pages, 8 figures, submitted to International Symposium on
Information Theory, 202
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