A system includes circuitry for rewriting blockchains in a non-tamper-evident or tamper-evident operation by a trusted party during a rewrite-permissive phase. During a rewrite-embargoed phase, at least one trusted party with rewrite access during the rewrite-permissive phase may have rewrite access revoked. In some implementations, rewrite access may be implemented by controlling access to a key secret for the blockchain. In some cases, access to the key secret may be changed by deleting the key secret or by changing access permissions for a particular device.