Statechain
Also · Statecoin · Mercury Layer
A statechain transfers the right to spend a whole UTXO off-chain, by rotating a key shared between the owner and an operator who promises to forget old keys. Spark builds on it.
Proposed by Ruben Somsen in 2018, a statechain moves a coin without a transaction. The UTXO is locked to a key held jointly by its owner and a statechain entity. To transfer it, the current owner and the entity run a protocol that gives the new owner a key share and invalidates the old one, with the entity never able to sign alone and never learning the full key.
Each owner also holds a pre-signed exit transaction with a decreasing timelock, so they can always withdraw to Bitcoin on their own. The trust assumption is explicit. The entity must really delete the previous shares, otherwise it could collude with a past owner. Mercury Layer implemented it for fixed-size coins. Spark generalises the idea with a group of operators and Lightning compatibility.
In French · Statechain
