Secure file erasure

• US 5,265,159 A
• Filed: 06/23/1992
• Issued: 11/23/1993
• Est. Priority Date: 06/23/1992
• Status: Expired due to Term

• Current Assignee: Hughes Electronics Corporation (AT&T, Inc.)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Kung, Kenneth C.
• Primary Examiner(s): Cain, David C.
• Application Number:
  US07/902,607
• Time in Patent Office: 518 Days
• Field of Search: 380/4
• US Class Current: 713/193
• CPC Class Codes: G06F 21/6209 to a single file or object, e.g. in a secure envelope, encrypted and accessed using a key, or with access control rules appended to the object itself
• CPC Class Codes: G06F 2221/2143 Clearing memory, e.g. to prevent the data from being stolen
• CPC Class Codes: H04L 9/0897 involving additional devices, e.g. trusted platform module [TPM], smartcard or USB

Abstract

A method of securely deleting a file on a storage medium of a computer system so that it is not readable, wherein an encryption algorithm is used to encrypt the data in the stored file prior to a conventional deletion process. The present invention permits a user to erase files from a permanent storage space and in a manner that makes the file totally unreadable by others. When a user requests deletion of a stored file, the file is encrypted so that it is not readable. The user has an option to undelete the file by decrypting the file as long as this operation is done before the storage space is used by another program. When the secure deletion method is used, no utility program can recover any information from the deleted file. To an intruder, the storage space is encrypted to look like random bits. Therefore, no information can be retrieved nor derived from the encrypted, deleted file. If the user does not expect to undelete the information, a one-way encryption algorithm is used to increase the speed of secure deletion of the file. If the user does not destroy the key, he or she may recover the file. This method restores the file directory pointer to the file, and decrypts the encrypted stored file using the random key to permit access to the data contained in the stored file.

Claims

1. A method of deleting a file stored on a permanent storage medium of a computer system under the control of an operating system, said operating system identifying the location of said file by means of a file directory pointer, said method comprising the steps of:

selecting a stored file for deletion;

encrypting the stored file using a random key;

deleting the file director pointer to the stored file.

2. A method of deleting a file stored on a permanent storage medium of a computer system under the control of an operating system, said operating system identifying the location of said file by means of a file directory pointer, said method comprising the steps of:

selecting a stored file for deletion;

encrypting the stored file using a random key;

destroying the random key; and

deleting a file director pointer to the stored file.

3. A method of processing a file stored on a permanent storage medium of a computer system to eliminate access to the file by unauthorized persons, said computer system being under the control of an operating system, said operating system identifying the location of said file by means of a file directory pointer, said method comprising the steps of:

selecting a stored file for deletion;

encrypting the stored file using a random key;

deleting a file director pointer to the stored file

at a time prior to overwriting of storage locations of the encrypted data file, restoring the file directory pointer to the stored file; and

decrypting the encrypted stored file using the random key to permit access to the data contained in the stored file.