Codes -- The Order Bound for Toric Codes -- An Extension of the Order Bound for AG Codes -- Sparse Numerical Semigroups -- From the Euclidean Algorithm for Solving a Key Equation for Dual Reed-Solomon Codes to the Berlekamp-Massey Algorithm -- Rank for Some Families of Quaternary Reed-Muller Codes -- Optimal Bipartite Ramanujan Graphs from Balanced Incomplete Block Designs: Their Characterizations and Applications to Expander/LDPC Codes -- Simulation of the Sum-Product Algorithm Using Stratified Sampling -- A Systems Theory Approach to Periodically Time-Varying Convolutional Codes by Means of Their Invariant Equivalent -- On Elliptic Convolutional Goppa Codes -- The Minimum Hamming Distance of Cyclic Codes of Length 2p s -- There Are Not Non-obvious Cyclic Affine-invariant Codes -- On Self-dual Codes over Z 16 -- Cryptography -- A Non-abelian Group Based on Block Upper Triangular Matrices with Cryptographic Applications -- Word Oriented Cascade Jump ??LFSR -- On Some Sequences of the Secret Pseudo-random Index j in RC4 Key Scheduling -- Very-Efficient Anonymous Password-Authenticated Key Exchange and Its Extensions -- Efficient Constructions of Deterministic Encryption from Hybrid Encryption and Code-Based PKE -- Algebra -- Noisy Interpolation of Multivariate Sparse Polynomials in Finite Fields -- New Commutative Semifields and Their Nuclei -- Spreads in Projective Hjelmslev Geometries -- On the Distribution of Nonlinear Congruential Pseudorandom Numbers of Higher Orders in Residue Rings -- Rooted Trees Searching for Cocyclic Hadamard Matrices over D 4t -- Extended Abstracts -- Interesting Examples on Maximal Irreducible Goppa Codes -- Repeated Root Cyclic and Negacyclic Codes over Galois Rings -- Construction of Additive Reed-Muller Codes -- Gröbner Representations of BinaryMatroids -- A Generalization of the Zig-Zag Graph Product by Means of the Sandwich Product -- Novel Efficient Certificateless Aggregate Signatures -- Bounds on the Number of Users for Random 2-Secure Codes.

This book constitutes the refereed proceedings of the 18th International Symposium on Applied Algebra, Algebraic Algorithms and Error-Correcting Codes, AAECC-18, held in Tarragona, Spain, in June 2009. The 22 revised full papers presented together with 7 extended absstracts were carefully reviewed and selected from 50 submissions. Among the subjects addressed are block codes, including list-decoding algorithms; algebra and codes: rings, fields, algebraic geometry codes; algebra: rings and fields, polynomials, permutations, lattices; cryptography: cryptanalysis and complexity; computational algebra: algebraic algorithms and transforms; sequences and boolean functions.