As a quick workaround, there is a library file which I think ships in Openacs3.2.5 which contains Tcl routines to encode/decode base 64 which is lying around in the /tcl directory, it was used by the bulkmail package that Greg Haverkamp wrote at one point. This is non-optimal because it is written in Tcl and thus some orders of magnitude slower than a native C routine.
