A system includes circuitry for rewriting blockchains in a non-tamper-evident or tamper-evident operation by a selected trusted party during a rewrite-permissive phase for the selected trusted party. During a rewrite-embargoed phase for the selected trusted party, rewrite access may pass to at least one second trusted party in a turn-based scheme. In some implementations, rewrite access may be implemented by controlling access to combination of a turn-control key secret portion with respective key secret portions controlled the by the individual trusted parties. Using the access to combination with the turn-control key secret portion, the trusted parties may preform rewrites to the blockchain.