  In this paper we present a novel class of convolutional codes and investigate
its use in a variant of the McEliece cryptosystem that possesses several
interesting properties, including a reduction of the public key for a given
security level. In contrast to the classical McEliece cryptosystems, where
block codes are used, we propose the use of a convolutional encoder to be part
of the public key. The secret key is constituted by a Generalized Reed-Solomon
encoder and two Laurent polynomial matrices that contain large parts that are
generated completely at random. Instead of multiplying on the right the GRS
encoder by a permutation matrix, it is multiplied by a polynomial matrix with
columns having weight zero or at least two. In this setting the message is a
sequence of messages instead of a single block message and the errors are added
randomly throughout the sequence. We conclude the paper studying its security
and presenting several examples.
