Adopt standard code signing in favor of DSA signing

[Andy Matuschak]

We should use code signing for 10.5+ applications; it's in the system, and this way, devs who already sign their apps won't have to do double duty.

[Andy Matuschak (andymatuschak)]

We should investigate the use of CDSA for 10.4 compatibility: http://developer.apple.com/security/cdsaopenssl.html

[James W. Walker (jw-jwwalker)]

When I looked at the code signing stuff, I didn't see any public API to verify a signature, only a command line tool. That might be less convenient for Sparkle.

[Hofman (cmhofman)]

I don't think a command line tool would be a problem, it's easy to run it using NSTask.

The initial reason that code signers don't have to do double work is not true, because what should be signed is the downloaded archive/disk image/package, not the bundle (an installer can be just as malicious, if not more so, than an app).