package.el + DVCS for security and convenience (was: ELPA security)

[Ted Zlatanov <tzz@lifelogs.com>]

I propose to require signatures for ELPA packages and make package.el
aware of signatures:

http://doc.bazaar.canonical.com/beta/en/user-guide/gpg_signatures.html

(the same idea for Git: http://git-scm.com/book/en/Git-Basics-Tagging)

The key is to make package.el talk to a repository, not to a web site.

Then, package.el can verify the history of the package as a series of
revisions and verify their signatures.  That would require much better
integration with Bazaar and Git for package.el, but I actually think
that's a good thing and would give users convenient tools like seeing
the history of a package with all the commits.

Maybe `vc-dir' already has code to do this, so package.el can simply
ride on top of it.

This has several benefits:

- doesn't introduce new infrastructure or ELPA/Emacs packages

- is entirely optional to package.el, so repositories and individual
  packages within them can choose to use this mechanism

- does not depend on a central authority like SSL

- if the tools to verify the GPG signature are not available, we can
  fall back to warning the user instead of failing altogether

Ted