Orientador: Fernando Eduardo Torres Orihuela / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Cientifica / Made available in DSpace on 2018-08-10T07:01:07Z (GMT). No. of bitstreams: 1 SepulvedaCastellanos_Alonso_D.pdf: 783003 bytes, checksum: 2af4bba938cd5b7d31fcd02a5c79ac85 (MD5) Previous issue date: 2008 / Resumo: Estudamos os códigos de Goppa (códigos GH) sobre certos corpos de funções algébricas com muitos lugares racionais. Estes códigos generalizam os bem conhecidos códigos Hermitianos; portanto podemos esperar que estes códigos tenham bons parâmetros. Bulygin (IEEE Trans. Inform. Theory 52 (10), 4664¿4669 (2006)) inicia o estudo dos códigos GH; enquanto Bulygin considerou somente característica par, nosso trabalho 'e feito em qualquer característica. Em qualquer caso, nosso trabalho é fortemente influenciado pelo de Bulygin. A seguir, listamos alguns dos nossos resultados com respeito aos códigos GH. ¿ Calculamos ¿distâncias mínimas exatas¿, em particular, melhoramos os resultados de Bulygin; ¿ Encontramos cotas para os pesos generalizados de Hamming, al'em disso, mostramos um algoritmo para aplicar estes cálculos na criptografia; ¿ Calculamos um subgrupo de Automorfismos; ¿ Consideramos códigos em determinados subcorpos dos corpos usados para construir os códigos GH / Abstract: We study Goppa codes (GH codes) based on certain algebraic function fields whose number of rational places is large. These codes generalize the well-known Hermitian codes; thus we might expect that they have good parameters. Bulygin (IEEE Trans. Inform. Theory 52 (10), 4664¿4669 (2006)) initiate the study of GH-codes; while he considered only the even characteristic, our work is done regardless the characteristic. In any case our work was strongly influenced by Bulygin¿s. Next we list some of the results of our work with respect to GH-codes. ¿ We calculate ¿true minimum distances¿, in particular, we improve Bulygin¿s results; ¿ We find bounds on the generalized Hamming weights, moreover, we show an algorithm to apply these computations to the cryptography; ¿ We calculate an Automorphism subgroup; ¿ We consider codes on certain subfields of the fields used for to construct GH-codes / Doutorado / Algebra (Geometria Algebrica) / Doutor em Matemática

Probabilistic simultaneous polynomial reconstruction algorithm of Bleichenbacher-Kiayias-Yung is extended to the polynomials whose degrees are allowed to be distinct. Furthermore, it is observed that probability of the algorithm can be increased. Specifically, for a finite field $F$, we present a probabilistic algorithm which can recover polynomials $p_1,ldots, p_r in F[x]$ of degree less than $k_1,k_2,ldots,k_r$, respectively with given field evaluations $p_l(z_i) = y_{i,l}$ for all $i in I$, $|I|=t$ and $l in [r]$ with probability at least $1 - (n - t)/|F|$ and with time complexity at most $O((nr)^3)$. Next, by using this algorithm, we present a probabilistic decoder for interleaved Reed-Solomon codes. It is observed that interleaved Reed-Solomon codes over $F$ with rate $R$ can be decoded up to burst error rate $frac{r}{r+1}(1 - R)$ probabilistically for an interleaving parameter $r$. It is proved that a Reed-Solomon code RS$(n / k)$ can be decoded up to error rate $frac{r}{r+1}(1 - R&#039 / )$ for $R&#039 / = frac{(k-1)(r+1)+2}{2n}$ when probabilistic interleaved Reed-Solomon decoders are applied. Similarly, for a finite field $F_{q^2}$, it is proved that $q$-folded Hermitian codes over $F_{q^{2q}}$ with rate $R$ can be decoded up to error rate $frac{q}{q+1}(1 - R)$ probabilistically. On the other hand, it is observed that interleaved codes whose subcodes would have different minimum distances can be list decodable up to radius of minimum of list decoding radiuses of subcodes. Specifically, we present a list decoding algorithm for $C$, which is interleaving of $C_1,ldots, C_b$ whose minimum distances would be different, decoding up to radius of minimum of list decoding radiuses of $C_1,ldots, C_b$ with list size polynomial in the maximum of list sizes of $C_1,ldots, C_b$ and with time complexity polynomial in list size of $C$ and $b$. Next, by using this list decoding algorithm for interleaved codes, we obtained new list decoding algorithm for $qh$-folded Hermitian codes for $q$ standing for field size the code defined and $h$ is any positive integer. The decoding algorithm list decodes $qh$-folded Hermitian codes for radius that is generally better than radius of Guruswami-Sudan algorithm, with time complexity and list size polynomial in list size of $h$-folded Reed-Solomon codes defined over $F_{q^2}$.

Submitted by isabela.moljf@hotmail.com (isabela.moljf@hotmail.com) on 2016-08-15T15:24:51Z No. of bitstreams: 1 oscarjhoanpalaciomarin.pdf: 723203 bytes, checksum: d8ac71f1e1162340ce21f336196d0070 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-08-16T13:02:45Z (GMT) No. of bitstreams: 1 oscarjhoanpalaciomarin.pdf: 723203 bytes, checksum: d8ac71f1e1162340ce21f336196d0070 (MD5) / Made available in DSpace on 2016-08-16T13:02:45Z (GMT). No. of bitstreams: 1 oscarjhoanpalaciomarin.pdf: 723203 bytes, checksum: d8ac71f1e1162340ce21f336196d0070 (MD5) Previous issue date: 2016-06-23 / Nesse trabalho, estamos interessados, especialmente, nas propriedades de duas classes de Códigos Corretores de Erros: os Códigos Hermitianos e os Códigos Hermitianos Generalizados. O primeiro é definido a partir de lugares do corpo de funções Hermitiano clássico sobre um corpo finito de ordem quadrada, já o segundo é definido a partir de uma generalização desse mesmo corpo de funções. Como base para esse estudo, apresentamos ainda resultados da teoria de corpos de funções e outras construções de Códigos Corretores de Erros. / Inthisworkweinvestigatepropertiesoftwoclassesoferror-correctingcodes,theHermitian Codes and their generalization. The Hermitian Codes are defined using the classical Hermitian curve defined over a quadratic field. The generalized Hermitian Codes are similar, but uses a generalization of this curve. We also present some results of the theory of function fields and other constructions of error-correcting codes which are important to understand this work.