You can do that using Multi Party Computation. There are a bunch of MPC protocols for generating Eliptic Curve private keys and doing DSA where the whole privat

You can do that using Multi Party Computation. There are a bunch of MPC protocols for generating Eliptic Curve private keys and doing DSA where the whole private key is never assembled. It uses Shamir Sharings as part of the magic, it's quite neat :)