8,364 research outputs found
On structure constants with two spinning twist-two operators
I consider three-point functions of one protected and two unprotected
twist-two operators with spin in N=4 SYM at weak coupling. At one loop I
formulate an empiric conjecture for the dependence of the corresponding
structure constants on the spins of the operators. Using such an ansatz and
some input from explicit perturbative results, I fix completely various
infinite sets of one-loop structure constants of these three-point functions.
Finally, I determine the two-loop corrections to the structure constants for a
few fixed values of the spins of the operators.Comment: 21 page
A note on three-point functions of unprotected operators
Given the recent progress in computing three-point functions in N=4 SYM via
integrability, I provide here a novel direct calculation of some structure
constants at weak coupling. The main focus is on correlators involving more
than one unprotected operator, at two-loop order in the perturbative expansion.Comment: 17 page
Coding with Scrambling, Concatenation, and HARQ for the AWGN Wire-Tap Channel: A Security Gap Analysis
This study examines the use of nonsystematic channel codes to obtain secure
transmissions over the additive white Gaussian noise (AWGN) wire-tap channel.
Unlike the previous approaches, we propose to implement nonsystematic coded
transmission by scrambling the information bits, and characterize the bit error
rate of scrambled transmissions through theoretical arguments and numerical
simulations. We have focused on some examples of Bose-Chaudhuri-Hocquenghem
(BCH) and low-density parity-check (LDPC) codes to estimate the security gap,
which we have used as a measure of physical layer security, in addition to the
bit error rate. Based on a number of numerical examples, we found that such a
transmission technique can outperform alternative solutions. In fact, when an
eavesdropper (Eve) has a worse channel than the authorized user (Bob), the
security gap required to reach a given level of security is very small. The
amount of degradation of Eve's channel with respect to Bob's that is needed to
achieve sufficient security can be further reduced by implementing scrambling
and descrambling operations on blocks of frames, rather than on single frames.
While Eve's channel has a quality equal to or better than that of Bob's
channel, we have shown that the use of a hybrid automatic repeat-request (HARQ)
protocol with authentication still allows achieving a sufficient level of
security. Finally, the secrecy performance of some practical schemes has also
been measured in terms of the equivocation rate about the message at the
eavesdropper and compared with that of ideal codes.Comment: 29 pages, 10 figure
Increasing Physical Layer Security through Scrambled Codes and ARQ
We develop the proposal of non-systematic channel codes on the AWGN wire-tap
channel. Such coding technique, based on scrambling, achieves high transmission
security with a small degradation of the eavesdropper's channel with respect to
the legitimate receiver's channel. In this paper, we show that, by implementing
scrambling and descrambling on blocks of concatenated frames, rather than on
single frames, the channel degradation needed is further reduced. The usage of
concatenated scrambling allows to achieve security also when both receivers
experience the same channel quality. However, in this case, the introduction of
an ARQ protocol with authentication is needed.Comment: 5 pages, 4 figures; Proc. IEEE ICC 2011, Kyoto, Japan, 5-9 June 201
A Physical Layer Secured Key Distribution Technique for IEEE 802.11g Wireless Networks
Key distribution and renewing in wireless local area networks is a crucial
issue to guarantee that unauthorized users are prevented from accessing the
network. In this paper, we propose a technique for allowing an automatic
bootstrap and periodic renewing of the network key by exploiting physical layer
security principles, that is, the inherent differences among transmission
channels. The proposed technique is based on scrambling of groups of
consecutive packets and does not need the use of an initial authentication nor
automatic repeat request protocols. We present a modification of the scrambling
circuits included in the IEEE 802.11g standard which allows for a suitable
error propagation at the unauthorized receiver, thus achieving physical layer
security.Comment: 9 pages, 7 figures. Accepted for publication in IEEE Wireless
Communications Letters. Copyright transferred to IEE
Improving the efficiency of the LDPC code-based McEliece cryptosystem through irregular codes
We consider the framework of the McEliece cryptosystem based on LDPC codes,
which is a promising post-quantum alternative to classical public key
cryptosystems. The use of LDPC codes in this context allows to achieve good
security levels with very compact keys, which is an important advantage over
the classical McEliece cryptosystem based on Goppa codes. However, only regular
LDPC codes have been considered up to now, while some further improvement can
be achieved by using irregular LDPC codes, which are known to achieve better
error correction performance than regular LDPC codes. This is shown in this
paper, for the first time at our knowledge. The possible use of irregular
transformation matrices is also investigated, which further increases the
efficiency of the system, especially in regard to the public key size.Comment: 6 pages, 3 figures, presented at ISCC 201
- …