  The "Ring Learning with Errors" (RLWE) problem was formulated as a variant of
the "Learning with Errors" (LWE) problem, with the purpose of taking advantage
of an additional algebraic structure in the underlying considered lattices;
this enables improvements on the efficiency and cipher expansion on those
cryptographic applications which were previously based on the LWE problem. In
Eurocrypt 2010, Lyubashevsky et al. introduced this hardness problem and showed
its relation to some known hardness problems over lattices with a special
structure. In this work, we generalize these results and the problems presented
by Lyubashevsky et al. to the more general case of multivariate rings,
highlighting the main differences with respect to the security proof for the
RLWE counterpart. This hardness problem is denoted as "Multivariate Ring
Learning with Errors" ($m$-RLWE or multivariate RLWE) and we show its relation
to hardness problems over the tensor product of ideal lattices. Additionally,
the $m$-RLWE problem is more adequate than its univariate version for
cryptographic applications dealing with multidimensional structures.
