Deletion of content in digital storage systems

Patent metadata

Field	Value
Publication number	US-9548866-B2
Application number	US-201615046673-A
Country	US
Kind code	B2
Filing date	Feb 18, 2016
Priority date	Nov 20, 2013
Publication date	Jan 17, 2017
Grant date	Jan 17, 2017

Abstract

A data processing and storage apparatus has a hardware security module and a data storage medium storing encrypted data objects and a hierarchical data maintenance structure of encrypted partition tables and hash-nodes forming a rooted tree, where a given partition table comprises a first reference to a given encrypted data object and a first cryptographic key for decryption thereof, where a given hash-node comprises a second reference to a partition tables or hash-node and a second cryptographic key being suitable for decryption thereof, and where the root node is decipherable using a master cryptographic key stored in the hardware security module, the given data object being assigned to the root node via the first and second references of the given partition table and the given hash-nodes forming a set of successive nodes in the rooted tree.

First claim

What is claimed is:

1. A computer-implemented method of secure data deletion, comprising:
providing a master cryptographic key securely stored on an internal storage of a hardware security module of an apparatus;
providing a plurality of data objects individually encrypted and stored on a storage medium of the apparatus, the storage medium further storing a hierarchical data-maintenance structure comprising a tree having successive nodes including a root node, a plurality of hash-nodes, and a plurality of partition tables, the root node decipherable via the master cryptographic key;
responsive to receiving an instruction specifying to delete a first of the plurality of data objects, wherein the first object is assigned to a first of the partition tables, wherein the first object is decipherable via a first cryptographic key stored in the first partition table, traversing successive nodes in the tree by successively decrypting one or more of the plurality of hash-nodes, and the first partition table starting from the root node and using cryptographic keys obtained by decrypting each of the traversed nodes; and
recursively traversing and re-encrypting successive nodes starting from the first partition table and with new cryptographic keys, by operation of one or more computer processors, wherein the first cryptographic key is removed from the first partition table or disregarded in re-encrypting the first partition table, thereby effecting secure deletion of the first data object.

2. The computer-implemented method of claim 1 , wherein the hardware security module is configured to exclusively perform any encryption involving the master cryptographic key stored in the internal storage.

3. The computer-implemented method of claim 1 , wherein the hardware security module is configured to exclusively perform any decryption involving the master cryptographic key stored in the internal storage.

4. The computer-implemented method of claim 1 , wherein the apparatus comprises a data processing and storage apparatus, wherein the storage medium comprises a data storage medium, wherein the apparatus includes an application program, wherein the successive nodes are recursively traversed by the application program, wherein each partition table and each hash-node is individually encrypted.

5. The computer-implemented method of claim 4 , wherein the first partition table contains a first reference assigning the first data object to the first partition table, wherein the second partition table contains a second reference assigning the first partition table to the first hash-node, wherein the first data object is effectively assigned to the root node via the first and second references, wherein the first partition table and the first hash node form a first set of successive nodes in the tree.

6. The computer-implemented method of claim 5 , further comprising:
rebalancing the hierarchical data-maintenance structure of the hash-nodes and the partition tables, thereby distributing data from a source hash-node of the hash-nodes or a source partition table of the partition tables to a target hash-node of the hash nodes or a target partition-table of the partition tables;
wherein the source hash node or the source partition table is assigned to the root node via hash-node references, wherein the source partition table and associated hash-nodes form a second set of successive nodes in the tree;
wherein the target hash node or the target partition table is assigned to the root node via hash-node references, wherein the target partition table and associated hash-nodes form a third set of successive nodes in the tree.

7. The computer-implemented method of claim 6 , wherein rebalancing the hierarchical data-maintenance structure comprises, by the apparatus:
traversing the second set of successive nodes in the tree by successively decrypting all nodes starting from the root node using second cryptographic keys obtained by decrypting each of the nodes, thereby resulting in a decrypted source partition table or decrypted source hash-node; and
traversing the third set of successive nodes in the tree by successively decrypting all hash-nodes and the partition table starting from the root node using the second cryptographic keys obtained by decrypting each of the nodes, thereby resulting in a decrypted target partition table or decrypted target hash-node.

8. The computer-implemented method of claim 7 , wherein rebalancing the hierarchical data-maintenance structure further comprises:
adding at least a part of the references and cryptographic keys comprised in the decrypted source partition table or decrypted source hash-node to the decrypted target partition table or decrypted target hash-node; and
removing the moved part from the respective decrypted given partition table or decrypted source hash-node.

9. The computer-implemented method of claim 8 , wherein rebalancing the hierarchical data-maintenance structure further comprises:
recursively traversing and re-encrypting the second set of successive nodes starting from the source partition table or the source hash-node, and with new second cryptographic keys; and
recursively traversing and re-encrypting the third set of successive nodes starting from the target partition table or the target hash-node, and with new second cryptographic keys.

10. The computer-implemented method of claim 9 , wherein each data object is assigned a unique identifier, wherein the first hash-node has an associated hash-function description that provides a mapping of the unique identifier to a reference assigning one of the partition tables or one of the hash-nodes to the first hash-node, wherein rebalancing the hierarchical data-maintenance structure further comprises:
replacing the hash-function description in each of the source and target hash-nodes in order to reflect a change in cardinality of references of the respective hash-node.

11. The computer-implemented method of claim 10 , wherein the hardware security module is configured to perform encryption and decryption in a manner that confines the master cryptographic key and the first and second cryptographic keys and any decrypted plain-text representation of data objects involved in the decryption or encryption to the internal storage, wherein the hardware security module is configured to:
exclusively perform the encryption and decryption in case the encryption and decryption are purely performed using the master cryptographic key stored in the internal storage; and
perform the encryption and decryption on a first portion of data readable from the data storage medium, wherein the apparatus includes a further processing module configured to execute the encryption and decryption on a second portion of the data readable from the data storage medium.

12. The computer-implemented method of claim 11 , wherein the hardware security module is configured to:
in a first instance, perform the encryption and decryption on the data readable from the data storage medium only to an extent of encrypting, decrypting, and re-encrypting the first and second cryptographic keys; and
in a second instance, perform the encryption and decryption on the data readable from the data storage medium only to an extent of encrypting, decrypting, and re-encrypting the hash-nodes and the partition tables;
wherein the hardware security module is configured to create a public-private-key pair for asymmetric encryption of the plurality of data objects, the public-private-key pair including a public key and a private key, wherein the private key is embedded into the first partition table as the first cryptographic key, wherein the public key is provided

Assignees

• IBM

Inventors

• Barney Jonathan M
• Lebutsch David
• Mega Cataldo
• Schleipen Stefan
• Waizenegger Tim

Classifications

• G06F21/78 Primary

  to assure secure storage of data (address-based protection against unauthorised use of memory G06F12/14; record carriers for use with machines and with at least a part designed to carry digital markings G06K19/00) · CPC title

• H04L9/3242 Primary

  involving keyed hash functions, e.g. message authentication codes [MACs], CBC-MAC or HMAC · CPC title

• G06F21/6218 Primary

  to a system of files or objects, e.g. local or distributed file system or database · CPC title

• H04L2209/24

  Key scheduling, i.e. generating round keys or sub-keys for block encryption · CPC title

• G06F2221/2143

  Clearing memory, e.g. to prevent the data from being stolen · CPC title