  In this paper we generalize results of P. Le Duff to genus n hyperelliptic
curves. More precisely, let C/Q be a hyperelliptic genus n curve and let J(C)
be the associated Jacobian variety. Assume that there exists a prime p such
that J(C) has semistable reduction with toric dimension 1 at p. We provide an
algorithm to compute a list of primes l (if they exist) such that the Galois
representation attached to the l-torsion of J(C) is surjective onto the group
GSp(2n, l). In particular we realize GSp(6, l) as a Galois group over Q for all
primes l in [11, 500000].
