I look forward to struggling to comprehend the crypto magic involved in "ring multisignature."
Don't worry, I drank too much Vanilla Latte earlier and solved this on a napkin.
Basically, you need to stop thinking of it as a 'ring' multisignature, or else you would need multiple overlapping rings in a two-dimensional cryptospace. That quickly causes infinite conflicts.
What we will do is create a cryptographic 'sphere' signature scheme (vs ring), and then our multi-sig rings can freely rotate around in 3D cryptospace.
At this point the collisions become desired multi-sig targets. Basically what we will do is allow transactions to mix freely on a potentially infinite amount of rings, and if you wish to have a multisig on your address then the program will find (or force) a collision between rings. It might seem impossible to force different rings to intersect if they don't naturally, but (and I don't mean to blow your mind) the different cryptographic rings are also rotating around the cryptocore simulataneously. A collision might be impossible to find for a human, but for a powerful computing network it will be trivial (or at least possible).
You might also say, "But what if Bob and Alice both want to do a multisig and need to move a shared-ring in opposing ways to have their transaction process?". Well, this is where transaction fees come into play in the Monero economy. Either Bob can bid more than Alice in the fee department, or get in line and wait for a fortunate collision that allows his multisig crypto transaction to process. This video can help you visualize the mathemagic that will be involved:
https://youtu.be/T2OnfBGkcyw Anyway, it's not like anyone is *forcing* him to use Cryptonote multisig. He can just use a single key transaction and his transaction will happen much quicker.
Bottom line: multisig is possible with Cryptonote but there will be potential speed tradeoffs. Fortunately as the multisig multidimensional cryptospace grows the potential intersections of rotating cryptographic rings around the central sphere will increase and it will become easier and cheaper to execute multisig address actions.
My napkin proved all this, and was going to serve as my white paper, but the fucking barista at Starbucks threw it away with my coffee and I don't really feel like writing it all down again.
So the proof is left as a trivial exercise for the intrepid reader. Now if you'll excuse me, I'm off to browse the clearance racks at Ross.
