Apparatus and method for executing hidden computational functions in a distributed data processing environment. In some embodiments, a trust boundary includes a target device such as a storage device, and a source device such as a client device in a computer network. A storage device processor executes a hidden command function (HCF) routine to accumulate HCF output data in a local cache responsive to an HCF command received from the client device over a data interface. The processor further establishes a smaller retention boundary within the trust boundary that includes the storage device and excludes the client device. The HCF output data are stored locally in a non-volatile memory (NVM) of the storage device while not transferring any portion of the HCF output data outside the retention boundary, including to the client device. The HCF routine can update a block-chain ledger or take some other form to provide data security.