Patent ID: 8887254

Claim:
A database system comprising: a memory containing multiple data records, wherein each of the data records has a data record asymmetric key pair for cryptographic encryption and decryption, wherein each data record asymmetric key pair comprises a data record public key and a data record private key, wherein each of the multiple data records is at least partially encrypted by its data record public key, wherein the data record private key of each asymmetric key pair is encrypted, wherein the memory contains a representation of a directed acyclic graph, wherein paths along the directed acyclic graph each have a starting node and an ending node, forming a chain of nodes; a set of user accounts, wherein each of the user accounts has a user asymmetric key pair for encryption and decryption, wherein each user asymmetric key pair has a user public key and a user private key, wherein the user public key is computed using the user private key; wherein each starting node corresponds to one of the set of user accounts, wherein each ending node corresponds to one of the multiple data records; wherein data is added to a data record by encrypting it with the data record public key, wherein access to the data record is granted to a user account by a cryptographic access key encrypted with the user public key, wherein a directed path formed by the chain of nodes starting at the starting node and ending at the ending node allows decryption of the data record using the cryptographic access key.