Crypto-pointers for secure data storage
The present invention relates to pairing of a different cryptographic key with each pointer in a data structure to form a crypto-pointer. The cryptographic key is used to encrypt the contents of all data stored at the physical location on the storage device indicated by the pointer. Preferably the only data accessible in an unencrypted form is contained in cells that are reachable from root-set crypto-pointers. Once the crypto-pointer associated with a particular memory cell is deleted, normally by overwriting or explicitly zeroing the crypto-pointer, the contents of the memory cell become inaccessible because the data stored at that cell is in encrypted form (cipher text) and the crypto-pointer that included the cryptographic key for decrypting the cipher text has been deleted from the system.
1. In a hierarchical digital data structure comprising a plurality of memory cells, a method of preventing recovery of deleted data comprising the steps of:
obtaining a first address of a first memory cell in the data structure;
providing a first cryptographic key;
associating the first address and the first cryptographic key with one another so as to form a first logical entity defining a first crypto-pointer to the first memory cell;
obtaining a second address of a second memory cell in the data structure;
providing a second cryptographic key different from the first cryptographic key;
associating the second address and the second cryptographic key with one another so as to form a second logical entity defining a second crvpto-pointer to the second memory cell;
encrypting first data and the second crypto-pointer using the first cryptographic key to form first cipher-data;
storing the first cipher-data in the first memory cell; and
when the first data is no longer needed, deleting the first crypto-pointer, thereby rendering the first data unrecoverable at the moment it becomes inaccessible.
2. The method of preventing recovery of deleted data according to claim 1 wherein said deleting the first crypto-pointer comprises physically overwriting both the first address and the first cryptographic key.
3. The method of preventing recovery of deleted data according to claim 1 wherein said deleting the first crypto-pointer comprises physically overwriting both the first address and the first cryptographic key by zeroing both fields.
4. The method of preventing recovery of deleted data of claim 1 further comprising creating a copy of the second crypto-pointer, the copy of the second crypto-pointer not being encrypted using the first cryptographic key and serving as an additional reference to the second memory cell.
5. The method of preventing recovery of deleted data of claim 1 further comprising creating an additional reference to the first memory cell by copying the first crypto-pointer.
6. The method of preventing recovery of deleted data of claim 1 wherein the data structure comprises a file directory.