In this master thesis we introduce algebraic geometry codes (AG codes). Be- sides basic definitions, properties and attributes of AG codes and algebraic ge- ometry we show how to encode AG codes that has nontrivial Abelian group of permutation automorphisms and how to decode one-point AG codes. We also present Hermitian codes, which are example of one-point AG codes with nontriv- ial Abelian group of permutation automorphisms. We demonstrate the method for encoding and the method for decoding on specific Hermitian code. 1

FAPEMIG - Fundação de Amparo a Pesquisa do Estado de Minas Gerais / Neste trabalho, estudamos conceitos de geometria algébrica relacionados a teoria de códigos de Goppa algebricos geometricos (códigos AG). Vimos como o cálculo do semi- grupo de Weierstrass pode ser aplicado na obtencao dos parâmetros de certos cádigos AG. Em particular, calculamos o semigrupo de Weierstrass em dois pontos da curva Xq2r dada pela equacao afim yq + y = xq+1 sobre Fq2r, onde r e um inteiro positivo ímpar e q á uma potencia de um numero primo, e construímos um cádigo AG bipontual sobre Xq2r, cujos parâmetros relativos sao melhores que cádigos AG pontuais comparâveis tambem construídos sobre esta curva. A principal referencia deste trabalho foi [8]. / In this work we study basics concepts of the algebraic geometry related to Algebraic Geometric Goppa codes theory (AG codes). We have seen how the calculation of the Weierstrass semigroup can be applied in obtaining the parameters of certain AG codes. In particular, we calculated the Weierstrass semigroup at two points on the curve Xq2r defined by afim equation yq + y = xq +1 over Fq2r, where r is a positive odd integer and q is a prime power, and construct a two-point AG code over Xq2r whose relative parameters are better than comparable one-point AG code. The main reference of this work was [8]. / Dissertação (Mestrado)