System and method for securely deleting plaintext data

Details System and method for securely deleting plaintext data System and method for securely deleting plaintext data

1998-07-22

2003-01-14

Decady, Albert (Department: 2132)

Electrical computers and digital processing systems: support

Data processing protection using cryptography

By stored data protection

Reexamination Certificate

active

06507911

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates generally to data deletion systems and methods, and more particularly to data deletion systems and methods employing data overwrite techniques and/or data encryption.
When deleting data, such as computer files or other information, today's computer systems typically require a user to manually select data, such as a file or files, which are to be deleted. Typical deletion systems and methods provide some sort of temporary storage (sometimes referred to as “recycle bins”) to allow later recovery of a deleted file in the event that the user inadvertently deleted the information. The data to be deleted that is identified in the temporary storage or recycle bin may then be “deleted” by a user when a user selects a file deletion process. However typical deletion systems do not actually physically delete the information but instead simply mark what file is no longer needed and the file's location in the file system so that the location is available for new data. The file allocation table (FAT) typically points to a place on a disk where a file is located and the operating system or other management system marks a file allocation table having pointers indicating that the location is free for later storage of other information. Hence the data to be “deleted” is not typically physically removed from the disk when a final delete or deletion process is activated, directly or indirectly by a user. By simply marking the allocated storage as free for use, the overhead on the system is typically minimized. However for sensitive information, this approach may be undesirable because the data can be recovered easily by off the shelf utilities in case of accidental deletion, or by an attacker desiring access to the sensitive information.
To overcome this problem, some encryption systems encrypt a copy of the document, file or data to be “deleted” and stored in the recycle bin so that the information is securely recoverable only by the user to prevent an attacker from readily obtaining sensitive information from the recycle bin. However, such known systems are user invoked secured deletion systems which requires a user to select an individual file, or group of files that need to be securely deleted in interim storage. Such systems may also typically overwrite the original document with random data or fixed data patterns to ensure secure deletion of plaintext data while storing an encrypted copy in the recycle bin for later retrieval if desired. However such stand alone user invoked deletion systems place the burden on the user to invoke a secure deletion process. This becomes a problem when voluminous amounts of data must be deleted. Also, some sensitive files are transparently created by a system in the background and are generated by software applications as they are running so that such files are not typically available to be user selected to be overwritten.
Other known deletion systems and methods overwrite the plaintext data with random data so that no data can be recovered even if it employs a file allocation table pointer system. However, as with other known systems, such data overwriting systems are typically user invoked requiring a user to manually select each file that must be deleted. Therefore, sensitive files may be accidentally missed by a user and files that are automatically generated by a utility or software program may not be selected for deletion.
Consequently, there exists a need for an improved data deletion system and method that facilitates system invoked physical deletion of information either by overwriting the data and/or securely encrypting the data without requiring user invocation.


REFERENCES:
patent: 5193184 (1993-03-01), Belsan et al.
patent: 5835601 (1998-11-01), Shimbo et al.
patent: 5991778 (1999-11-01), Starek et al.
patent: 6016507 (2000-01-01), Carroll et al.
patent: 6070147 (2000-05-01), Starek et al.

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