decided to use JAR files http://en.wikipedia.org/wiki/JAR_(file_format) which already have a well-defined signature mechanism, instead of designing our own bespoke thing yet again (see http://wiki.laptop.org/go/User:Homunq/Activity_bundles_v2 and http://wiki.laptop.org/go/Contents_manifest_specification ). --scott -- ( http://cscott.net/ )