Adding DKG to Polkadot/Substrate

[coax1d]

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Description

This is the implementation of the a-DKG pvss scheme for Polkadot. This allows for validators to enact a Distributed Key Generation Protocol ontop of the Barreto-Lynn-Scott curve BLS-381. Validators can via a gossip protocol setup a shared Public key with which all validators contain a share of the secret key. Validators can engage in a signing process using their secret share s with which they can sign a message m with aggregated secret key SK if threshold t (2/3 of validators) is met. This message can verified against aggregate public key PK. The aggregation of shares is done by collators of the Bridge Hub System Parachain. Validators will post shares to the BridgeHub Collator set.

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