· · · Repository hosted by TU Delft Library

We extend our work from the 2010 WIC symposium on ternary codes withthe Manhattan distance. We state a simple observation relating theparity of the Manhattan distance between two vectors and the parities of their weights, and use it to improve on a known Plotkin-like bound. Next, we concentrate on codes with minimum Manhattan distance three. We recall an explicit construction of such codes, and derive an upper bound on the size of such a code that is the solution of a linear programming (LP) bound. We analytically derive the behaviour of this LP bound for large n and evaluate it numerically for small n. A table of lower and upper bounds on the size of short codes ofwith minimum Manhattan distance 3 is presented.

We generalize the Gilbert-Varshamov lower bound on the maximum sizeof a code with given minimum Hamming distance. By using the Delsarteinequalities, it is shown that no improvement is obtained in the asymptotic case. A further improvement is given as well; it is undecided if this improvement can beat the asymptotic Gilbert-Varshamov bound or not.

In [1], Chow et al. provide an implementation of AES as a series oflookups in key-dependenttables. The tables depend not only on a key,but also on randomly chosen permutations ofthe set of 8-bits bytes.The idea is that many pairs of keys and permutations may give riseto the same table, thus obfuscating the key. The cryptanalysis of Billet et al. [2] shows how to reconstruct the used byte permutations.The most time consuming part of their method deals with finding theused byte permutationup to an affine mapping; it has a time-complexity of at most 2^24, thus essentially cracking the given AES implementation. In this paper, we provide a variation on this part of the attack, reducing the time complexity even further, viz. to at most 2^14.

Lighting is a major part of energy consumption in buildings. Lighting systems will thus be one of the important component systems of a smart grid for dynamic load management services like demand response.In the scenario considered in this paper, under a demand response request, lighting systems in a building react by executing dimming control based on their load shedding flexibilities. Load shedding flexibility reflects the amount of power reduction that can be achievedby an individual controller without violating minimum illumination requirements of occupants in that area. We consider different methodsfor distributing load reduction across multiple controllers employing their respective load shedding flexibilities.

Usually a communication link is secured by means of a symmetric-keyalgorithm. For that, a method is required to securely establish a symmetric-key for that algorithm.This old problem is still relevant and of paramount importance both in existing computernetworks and newlarge-scale ubiquitous systems comprising resource-constrained devices. Identity-based pairwise key agreement allows for the generationof a common key betweentwo parties given secret keying material owned by the first party and the identity of thesecond one. However, existing methods are prone to collusion attacks. In this paper we discuss a new class of key establishment scheme aiming at full collusionresistant identity-based symmetric-key agreement and propose a specific scheme, the HIMMO lgorithm, relying on two design concepts: Hiding Information and Mixing Modular Operations. Collusion attacks on schemes from literature cannot readily be applied to HIMMO. Also, thesimple logic of the HIMMO algorithm allows for very efficient implementations in terms of both speed and memory. Finally, being an identity-based symmetric-key establishment scheme, HIMMO allows for efficient real-world key-exchange protocols.

The famous max-flow min-cut theorem states that a source node can send information through a network ( ) to a sink node at a rate determined by the min-cut separating and . Recently, it has been shown that this rate can also be achieved for multicasting to several sinks provided that the intermediate nodes are allowed to re-encode the information they receive. We demonstrate examples of networks where theachievable rates obtained by coding at intermediate nodes are arbitrarily larger than if coding is not allowed. We give deterministic polynomial time algorithms and even faster randomized algorithms fordesigning linear codes for directed acyclic graphs with edges of unit capacity. We extend these algorithms to integer capacities and tocodes that are tolerant to edge failures.