US Patent 11921868 Data access control for user devices using a blockchain

A device configured to provide access to a digital document to a user device and to receive an access request for a first masked data element within the digital document. The device is further configured to generate a first blockchain transaction that identifies a machine learning model that is stored in a blockchain. The device is further configured to publish the first blockchain transaction in a blockchain ledger for the blockchain and to receive a second blockchain transaction from the machine learning model in response to publishing the blockchain transaction in the blockchain ledger. The second transaction indicates whether the user is approved for accessing the masked data element. The device is further configured to provide access to the first masked data element on the user device for the user in response to determining that the user is approved for accessing the masked data element.