Abstract Logical investigations of the notion of secrecy are typically concentrated on tools for deducing whether private information is well hidden from unauthorized, direct, or indirect access attempts. This paper proposes a multi-agent, normal multi-modal logic to capture salient features of secrecy’s intentions. Specifically, we focus on the intentions, beliefs and knowledge of secret keepers and, more generally, of all the actors involved in secret-keeping scenarios. In particular, we investigate intentions underlying the keeping of a true secret, namely a secret concerning information known (and so true) by the secret keeper. The resulting characterization of intending to keep a true secret provides valuable insights into conditions ensuring or undermining secrecy depending on agents’ attitudes and links between secrets and their surrounding context. We present the proposed logical system’s soundness, completeness and decidability results. Furthermore, we outline some theorems with potential applications to several fields, e.g. computer science and the social sciences.

Salp Swarm Algorithm (SSA) is a novel swarm technique using to optimize design problems. SSA is inspired by the swarming behavior of salp observed in the deep area of sea. In spite of its application versatility, SSA suffers from mediocre convergence rate and limited exploratory capabilities. In this paper, a Fitness Dependent Salp Swarm Algorithm (FDSSA) is proposed. The novelties of the proposed approach are the definition of a fitness coefficient able to enhance the exploration, the introduction of a novel mathematical model to describe the trajectory of salps and a mutation mechanism to increase the convergence speed. The designed algorithm is tested on unimodal and multimodal benchmark functions and then compared with well-known heuristic algorithms. The results show the superiority of FDSSA with respect to the comparison algorithms in terms of optimization and convergence performances according to their computational complexity.

A new efficient design of second-order spectralnull (2-OSN) codes is presented. The new codes are obtained by applying the technique used to design parallel decoding balanced (i.e., 1-OSN) codes to the random walk method introduced by some of the authors for designing 2-OSN codes. This gives new non-recursive efficient code designs, which are less redundant than the code designs found in the literature. In particular, if k ∈ IIN is the length of a 1-OSN code then the new 2-OSN coding scheme has length n = k + r ∈ IIN with an extra redundancy of r ≃ 2 log2k + (1/2) log2log2k - 0.174 check bits, with k and r even and n multiple of 4. The whole coding process requires O(k log k) bit operations and O(k) bit memory elements.

A new efficient coding scheme is given for second-order spectral-null (2-OSN) codes. The new method applies the Knuth's optimal parallel decoding scheme for balanced (i.e., 1-OSN) codes to the random walk method introduced by Tallini and Bose to design 2-OSN codes. If k ∈ IN is the length of a 1-OSN code then the new 2-OSN coding scheme has length n = k+r ∈ IN with an extra redundancy of r ≳ 2 log2k + (1/2) log2log2k - 0.674 check bits. The whole coding process requires O(n log n) bit operations and 0(n) bit memory elements.

A symbol permutation invariant balanced (SPI-balanced) code over the alphabet Zopfm= {0, 1, ..., m - 1} is a block code over Zopfmsuch that each alphabet symbol occurs as many times as any other symbol in every codeword. For this reason, every permutation among the symbols of the alphabet changes an SPI-balanced code into an SPI-balanced code. This means that SPI-balanced words are "the most balanced" among all possible m-ary balanced word types and this property makes them very attractive from the application perspective. In particular, they can be used to achieve m-ary DC-free communication, to detect/correct asymmetric/unidirectional errors on the m-ary asymmetric/unidirectional channel, to achieve delay-insensitive communication, to maintain data integrity in digital optical disks, and so on. This paper gives some efficient methods to convert (encode) m-ary information sequences into m-ary SPI-balanced codes whose redundancy is equal to roughly double the minimum possible redundancy rmin. It is proven that rminsime [(m - 1)/2]logmn - (1/2)[1 - (1/log2pim)]m - (1/log2pim) for any code which converts k information digits into an SPI-balanced code of length n = k + r. For example, the first method given in the paper encodes k information digits into an SPI-balanced code of length n = k + r, with r = (m - 1) logmk + O(m logmlogmk). A second method is a recursive method, which uses the first as base code and encodes k digits into an SPI-balanced code of length n = k + r, with r sime (m - 1) logmn - logm[(m - 1)!]

Let /spl Phi//sub m//spl sube/ /spl Copf/ be the set of all mth roots of unity, m/spl isin/ IN. A balanced code over /spl Phi//sub m/ is a block code over the alphabet /spl Phi//sub m/ such that each code word is balanced; that is, the complex sum of its components (or weight) is equal to 0. Let B/sub m/(n) be the set of all balanced words of length n over /spl Phi//sub m/. In this correspondence, it is shown that when m is a prime number, the set B/sub m/(n) is not empty if, and only if, m divides n. In this case, the minimum redundancy for a balanced code over /spl Phi//sub m/ of length n is. On the other hand, it is shown that when m=4, the set B/sub 4/(n) is not empty if, and only if, n is even, and in this case, the minimum redundancy for a balanced code over /spl Phi//sub 4/ of length n is. Further, this correspondence completely solves the problem of designing efficient coding methods for balanced codes over /spl Phi//sub m/, when m=4. In fact, it reduces the problem of designing efficient coding schemes for balanced codes over /spl Phi//sub 4/ to the design of efficient balanced codes over the usual bipolar alphabet /spl Phi//sub 2/={-1,+1}.

A symbol permutation invariant balanced (SPI-balanced) code over the alphabet ZZm= {0, 1,....,m - 1} is a block code over ZZmsuch that each alphabet symbol occurs as many times as any other symbol in every codeword. For this reason every permutation among the symbols of the alphabet changes a SPI-balanced code into a SPI-balanced code. This means that SPI-balanced words are "the most balanced" among all possible m-ary balanced word types, and this property makes them very attractive from the application perspective. In particular, they can be used to achieve m-ary DC-free communication, to detect/correct asymmetric/unidirectional errors on the m-ary asymmetric/unidirectional channel, to achieve delay-insensitive communication, to maintain data integrity in digital optical disks, and so on. The paper gives some efficient methods to convert (encode) m-ary information sequences into m-ary SPI-balanced codes whose redundancy is equal to roughly double the minimum possible redundancy rminsime [(m - 1)/2] logmn - (1/2)[1 $(1/log2pim)] m - (1/log2pim) for SPI-balanced code with k information digits and length n = k + r. For example, the first method given in the paper encodes k information digits into a SPI-balanced code of length n = k + r, with r = (m - 1) logmk + O(m logmk). A second method is a recursive method, which uses the first as base code, and encodes k digits into a SPI-balanced code of length n = k + r, with r sime (m - 1) logmn $logm[(m - 1)!]