A system includes circuitry for rewriting blockchains in a non-tamper-evident or tamper-evident operation using a key secret held by a trusted party. The blockchains may include a series of blocks secured integrity codes that may prevent non-tamper-evident rewrites by non-trusted parties that are not in possession of the key secret. In some cases, the key may allow valid but tamper-evident rewrites of the blockchain by trusted entities. Integrity outputs may be generated from the integrity codes based on the content of the previous blocks in the series such that attempts by untrusted parties to replace a block may be detected through coding-inconsistencies with other blocks.