MultiSig Account

[ChihChengLiang]

With the BLS support, we already have built-in n-n multi-sig.

It would also be interesting to have k-n multi-sig support. But we need to think about how to commit such n keys in the public key tree.

• We could use a Merkle tree to do it. commit a Merkle root in the public key tree, then use Merkle proof in the fraud-proof.
• We could consider a polynomial commitment to commit public keys since they don't require a future update.