(Not saying auditing truecrypt is bad; I'll probably donate some $ once I get back to the US) This problem already exists, and is actually something Mac App St

(Not saying auditing truecrypt is bad; I'll probably donate some $ once I get back to the US) This problem already exists, and is actually something Mac App Store, iOS/iTunes store, and Google Play do a pretty good job of solving; I assume there are some similar solutions for Windows (I don't really know the windows consumer software distribution space). The extensions improvements in Chrome/Firefox (and I guess other browsers, but I don't follow them) also are a great step forward toward this. Ubuntu/Debian do a pretty good job of locking down main repositories, too. It's really just a matter of training users that downloading random code from random URLs is risky. Once locked-down distribution hits critical mass, you can probably get away with making it even more difficult and obvious-to-the-user-he-is-doing-something-risky in "sideloading" applications. You can also have corp/org security policies which prohibit this kind of thing. Obviously there are sacrifices for this -- it becomes possible for a platform owner to restrict availability of apps based on non-security considerations, like being anti-porn (Apple), complying with the union of laws of all countries, etc. Or just outright commercial anti-competitiveness (again, mostly Apple...)