Originally Posted by noloader
I was reading through Sideload Windows Store Apps. Is it possible to install the 8.0 certificate on an 8.1 device and then side load the needed tools (for example, the debugger)?
Sadly, no, for two reasons. The first is that Windows RT's enforcement of what is allowed to run is enforced by the same kernel driver that enforces what kernel drivers can run, ci.dll. ci.dll has a hard-coded list of certificates that it trusts and there is no way to add additional certificates.
The second is that the certificates aren't really the problem - the object identifiers (OIDs) are. Windows 8.1 didn't invalidate the 8.0 certificates in the ordinary certificate revocation sense; rather, they changed ci.dll to require that a new OID be present in any signature for it to be trusted in 8.1. None of the 8.0 signatures have this OID.
Windows Apps seem to use a different signature system overall. Unsigned Apps can be used if you have a developer certificate, and Apps installed by 8.0 are still valid in 8.1. Similarly, there is something special going on for sideloading. I don't personally know how any of that works, but I do know that sideloading isn't useful, because the privilege level of Apps is too low to be useful for much of anything.
By the way, progress on breaking 8.1: