A system including: memory configured to store a blockchain; and blockchain phase circuitry configured to: initiate a rewrite-permissive phase for a selected trusted party by obtaining, on behalf of the selected trusted party, access that allows combination of a turn-control portion of a key secret with a first portion of the key secret, the first portion controlled by the selected trusted party; combine the turn-control portion and the first portion to generate the key secret; receive from the selected trusted third party a first command to perform a first validity-preserving rewrite to the blockchain, wherein the first command requests an alteration to one or more blocks of the blockchain, the first command received during the rewrite-permissive phase for the selected trusted party; responsive to receiving the first command during the rewrite-permissive phase, cause execution of the first validity-preserving rewrite to the blockchain using the key secret; after the rewrite-permissive phase for the selected trusted party, based on a loss of the access, fail to combine the first portion and the turn-control portion during a rewrite-embargoed phase for the selected trusted party; receive a second command to perform a second validity-preserving rewrite to the blockchain, the second command received during the rewrite-embargoed phase for the selected trusted party; and responsive to receiving the second command during the rewrite-embargoed phase, fail to cause execution of the second validity-preserving rewrite to the blockchain. memory configured to store a blockchain; and blockchain phase circuitry configured to: initiate a rewrite-permissive phase for a selected trusted party by obtaining, on behalf of the selected trusted party, access that allows combination of a turn-control portion of a key secret with a first portion of the key secret, the first portion controlled by the selected trusted party; combine the turn-control portion and the first portion to generate the key secret; receive from the selected trusted third party a first command to perform a first validity-preserving rewrite to the blockchain, wherein the first command requests an alteration to one or more blocks of the blockchain, the first command received during the rewrite-permissive phase for the selected trusted party; responsive to receiving the first command during the rewrite-permissive phase, cause execution of the first validity-preserving rewrite to the blockchain using the key secret; after the rewrite-permissive phase for the selected trusted party, based on a loss of the access, fail to combine the first portion and the turn-control portion during a rewrite-embargoed phase for the selected trusted party; receive a second command to perform a second validity-preserving rewrite to the blockchain, the second command received during the rewrite-embargoed phase for the selected trusted party; and responsive to receiving the second command during the rewrite-embargoed phase, fail to cause execution of the second validity-preserving rewrite to the blockchain. initiate a rewrite-permissive phase for a selected trusted party by obtaining, on behalf of the selected trusted party, access that allows combination of a turn-control portion of a key secret with a first portion of the key secret, the first portion controlled by the selected trusted party; combine the turn-control portion and the first portion to generate the key secret; receive from the selected trusted third party a first command to perform a first validity-preserving rewrite to the blockchain, wherein the first command requests an alteration to one or more blocks of the blockchain, the first command received during the rewrite-permissive phase for the selected trusted party; responsive to receiving the first command during the rewrite-permissive phase, cause execution of the first validity-preserving rewrite to the blockchain using the key secret; after the rewrite-permissive phase for the selected trusted party, based on a loss of the access, fail to combine the first portion and the turn-control portion during a rewrite-embargoed phase for the selected trusted party; receive a second command to perform a second validity-preserving rewrite to the blockchain, the second command received during the rewrite-embargoed phase for the selected trusted party; and responsive to receiving the second command during the rewrite-embargoed phase, fail to cause execution of the second validity-preserving rewrite to the blockchain.