  We study the proximity effect between an s-wave superconductor and the
surface states of a strong topological insulator. The resulting two dimensional
state resembles a spinless p_x+ip_y superconductor, but does not break time
reversal symmetry. This state supports Majorana bound states at vortices. We
show that linear junctions between superconductors mediated by the topological
insulator form a non chiral 1 dimensional wire for Majorana fermions, and that
circuits formed from these junctions provide a method for creating,
manipulating and fusing Majorana bound states.
