Gr Ruud Pellikaan

List decoding of q-ary Reed-Muller codes

The q-ary Reed-Muller (RM) codes RM/sub q/(u,m) of length n=q/sup m/ are a generalization of Reed-Solomon (RS) codes, which use polynomials in m variables to encode messages through functional encoding. Using an idea of reducing the multivariate case to the univariate case, randomized list-decoding algorithms for RM codes were given in and . The algorithm in Sudan et al. (1999) is an improvement of the algorithm in , it is applicable to codes RM/sub q/(u,m) with u<q/2 and works for up to E<n(1-/spl radic/2u/q) errors. In this correspondence, following , we show that q-ary RM codes are subfield subcodes of RS codes over F/sub q//sup m/. Then, using the list- decoding algorithm in Guruswami and Sudan (1999) for RS codes over F/sub q//sup m/, we present a list-decoding algorithm for q-ary RM codes. This algorithm is applicable to codes of any rates, and achieves an error-correction bound n(1-/spl radic/(n-d)/n). The algorithm achieves a better error-correction bound than the algorithm in , since when u is small. The implementation of the algorithm requires O(n) field operations in F/sub q/ and O(n/sup 3/) field operations in F/sub q//sup m/ under some assumption.

On decoding by error location and dependent sets of error positions

We generalize the existing decoding algorithms by error location for BCH and algebraic-geometric codes to arbitrary linear codes. We investigate the number of dependent sets of error positions. A received word with an independent set of error positions can be corrected.

On a decoding algorithm for codes on maximal curves

A decoding algorithm for algebraic geometric codes that was given by A.N. Skorobogatov and S.G. Vladut (preprint, Inst. Problems of Information Transmission, 1988) is considered. The author gives a modified algorithm, with improved performance, which he obtains by applying the above algorithm a number of times in parallel. He proves the existence of the decoding algorithm on maximal curves by showing the existence of certain divisors. However, he has so far been unable to give an efficient procedure of finding these divisors. >

Decoding geometric Goppa codes using an extra place

Decoding geometric Goppa codes can be reduced to solving the key congruence of a received word in an affine ring. If the codelength is smaller than the number of rational points on the curve, then this method can correct up to 1.2 (d*-L)/2-s errors, where d* is the designed minimum distance of the code and s is the Clifford defect. The affine ring with respect to a place P is the set of all rational functions which have no poles except at P, and it is somehow similar to a polynomial ring. For a special kind of geometric Goppa code, namely C/sub Omega /(D,mP), the decoding algorithm is reduced to solving the key equation in the affine ring, which can be carried out by the subresultant sequence in the affine ring with complexity O(n/sup 3/), where n is the length of codewords. >

The Newton Polygon of Plane Curves with Many Rational Points

This curve has the points (1 : 0 : 0) and (0 : 1 : 0) at infinity over any field. The affine equation is XY +Y +X = 0. The origin is a point of this curve. If (x, y) ∈ F8 is a point of this curve with nonzero coordinates, then x = 1. So 0 = xy + y + x = xy + xy + x = x[(xy) + (xy) + 1]. Let t = xy. Then t + t+ 1 = 0. So the Klein quartic has 3.7 = 21 rational points over F8 with nonzero coordinates. ∗Department of Mathematics and Computing Science, Technical University of Eindhoven , P.O. Box 513, 5600 MB Eindhoven, The Netherlands.

On the existence of order functions

The notions of well-behaving sequences and order functions is fundamental in the elementary treatment of geometric Goppa codes. The existence of order functions is proved with the theory of Grobner bases.

Error-correcting pairs for a public-key cryptosystem

Code-based Cryptography (CBC) is a powerful and promising alternative for quantum resistant cryptography. Indeed, together with lattice-based cryptography, multivariate cryptography and hash-based cryptography are the principal available techniques for post-quantum cryptography. CBC was first introduced by McEliece where he designed one of the most efficient Public-Key encryption schemes with exceptionally strong security guarantees and other desirable properties that still resist to attacks based on Quantum Fourier Transform and Amplitude Amplification. The original proposal, which remains unbroken, was based on binary Goppa codes. Later, several families of codes have been proposed in order to reduce the key size. Some of these alternatives have already been broken. One of the main requirements of a code-based cryptosystem is having high performance t-bounded decoding algorithms which is achieved in the case the code has a t-error-correcting pair (ECP). Indeed, those McEliece schemes that use GRS codes, BCH, Goppa and algebraic geometry codes are in fact using an error-correcting pair as a secret key. That is, the security of these Public-Key Cryptosystems is not only based on the inherent intractability of bounded distance decoding but also on the assumption that it is difficult to retrieve efficiently an error-correcting pair. In this paper, the class of codes with a t-ECP is proposed for the McEliece cryptosystem. Moreover, we study the hardness of distinguishing arbitrary codes from those having a t-error correcting pair.

A polynomial time attack against algebraic geometry code based public key cryptosystems

We give a polynomial time attack on the McEliece public key cryptosystem based on algebraic geometry codes. Roughly speaking, this attacks runs in O(n4) operations in Fq, where n denotes the code length. Compared to previous attacks, the present one allows to recover a decoding algorithm for the public key even for codes from high genus curves.

A symmetric Roos bound for linear codes

The van Lint-Wilson AB-method yields a short proof of the Roos bound for the minimum distance of a cyclic code. We use the AB-method to obtain a different bound for the weights of a linear code. In contrast to the Roos bound, the role of the codes A and B in our bound is symmetric. We use the bound to prove the actual minimum distance for a class of dual BCH codes of length q2 - 1 over Fq. We give cyclic codes [63, 38, 16] and [65, 40, 16] over F8 that are better than the known [63, 38, 15] and [65, 40, 15] codes.

The Quadratic Extension Extractor for (Hyper)Elliptic Curves in Odd Characteristic

We propose a simple and efficient deterministic extractor for the (hyper)elliptic curve