You miss the point. The Byzantine generals situation would be akin to completely cut. communication, no technology will help here.
See my reply to MPOE-PR. Use of simple HTTP requests is a bit too fragile: any network congestion can leave order in a dangling state where it can arrive to server at any time. And checking that won't help you, as you're checking current state, but you cannot remove packets which are already in flight.
And colored coins are still vulnerable to doublespend attacks if not done properly.
Colored coin exchange will be based on "atomic coin swap" transactions. Double-spend can only cancel such transaction if it is included into blockchain faster, but it won't be possible to steal anybody's coins.
There is a lot of other useful traits:
- after you've got counter-party's signatures you'll be able to demonstrate that he isn't trustworthy if he double-spends
- transaction is either included into a block or it is not, there is no dangling state
- you can chain several transactions together, if one fails due to double-spend dependent transactions will get canceled automatically
GPG has years of development and fixes behind it and allows for immediate verification without waiting for blochchain confirmations.
Um, what? GPG is simply a digital signature/encryption software. Bitcoin transactions are also digitally signed, but they are also included into blockchain to ensure there are no double-spends. It's an extra protection on top of what GPG can provide.