Abstract:
A method of secure erase of an electronic device that applies a predetermined voltage to a device. The voltage is selected to be high enough to quickly destroy all data cells of the electronic device, but not high enough to destroy lines to the data cells of the electronic device. Accordingly, since the voltage is too low to destroy the word or bit lines, the predetermined voltage is applied to every data cell using the word or bit lines such that all data is removed. The present invention has the advantage of quickly, reliably, and permanently removing all of the data from the electronic device. The predetermined high voltage can differ for different types of SSDs.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/542,339, filed Oct. 3, 2011, the entirety of which is hereby incorporated by reference into this application. 
    
    
     BACKGROUND OF THE INVENTION 
     Data security is extremely important in many storage applications. When data is no longer needed on an electronic storage device, or in the event of the theft of the device, the data must be permanently removed. This removal process must make it impossible to ever recover the data, and needs to be done very quickly and reliably. In most conventional devices, and in Solid State Drives (SSDs) in particular, just deleting the data only removes its name from the directory or file table. The user data remains until overwritten by new data. Also, reformatting the SSD also leaves data intact. Furthermore, just writing over the data once does not completely erase the previous data as information as to the previous data can still exist as small variations in the bit levels. Indeed, secure erasure techniques, such as those developed by the government require writing over the data multiple times to remove the data. Accordingly, there is a need to erase all user data in allocated blocks, file tables, and data in reallocated defective blocks completely, quickly, and reliably. 
     Conventional techniques for data sanitization have been described. One technique is Secure Erase ATA (Advanced Technology Attachment) command, to a target storage device which overwrites all data in allocated blocks, file tables, and data in reallocated defective blocks. Overwriting can be done to meet a variety of requirements established by different standard organizations, with each organization setting its own method of multiple overwriting with different sequences. However, writing to all blocks multiple times takes a significant amount of time, e.g., 5 seconds per 32 GB of data, which is too long for many applications. 
     Another conventional technique that is much faster is to use a drive with self-encryption, and just overwrite the encryption key. This technique may increase the speed of data sanitization, but the data remains on the drive. Accordingly, although the data may have been encrypted with advantageous encryption algorithms, there is no guarantee that the encryption method may never be broken. 
     Another conventional method that has improved performance speed is to apply a very high voltage to the input of the SSD, thus destroying the SSD. However, applying a very high voltage to the input of the SSD will typically destroy only the input circuitry since this circuitry quickly vaporizes, resulting in broken connections that fail to apply the very high voltage to all the data blocks. Accordingly, there is the potential to read data within blocks of the SSD not having the very high voltage applied. 
     It is desirable to provide a fast, reliable, permanent removal of all data on a storage device. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method of secure erase of data in an electronic device that applies a predetermined voltage to the electronic device. The voltage is selected to be high enough to quickly destroy all data cells of the electronic device, but not high enough to destroy lines of the electronic device. Accordingly, since the voltage is too low to destroy the word or bit lines, the predetermined voltage is applied to every data cell using the word or bit lines such that all data is removed. The present invention has the advantage of quickly, reliably, and permanently removing all of the data from the electronic device. The predetermined high voltage range of voltages can differ for different types of SSDs. 
     In one embodiment, the predetermined voltage is applied to word and/or bit lines of Solid State Drives (SSDs). The predetermined voltage includes, but is not limited to 3.3V, 5.0V, 12V, 24V, 36V, 48V, 60V, 72V, 84V and any other voltage between 3.3V and 84V. Flash memory in SSDs typically uses blocks composed of thousands of non-volatile memory cells, such as NAND cells, with each block using a common word and bit line. The method of the present invention for application of the predetermined voltage to the word or bit line expeditiously applies the voltage to all NAND cells for destruction, and as long as the voltage is selected to be low enough so that the word and bit lines remain intact but high enough to reliably destroy all NAND cells quickly, the method of the present invention reliably and quickly destroys, i.e., securely erases, all data. 
     In another embodiment, an inverted voltage is applied to the electronic device by connecting a NAND ground connect to the predetermined voltage and connecting the NAND VCC to ground. This method also quickly destroys all NAND cells but keeps the word and/or bit lines intact, as well as the IC power supply pin (VCC) and ground lines. 
     The invention will be more fully described by reference to the following drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow diagram illustration of a method of secure erase of an electronic device. 
         FIG. 2  is a schematic diagram of a system for secure erase of an electronic device. 
         FIG. 3  is a schematic diagram of an alternate system for secure erase of an electronic device. 
         FIG. 4  is a schematic diagram of an alternate system for secure erase of an electronic device. 
         FIG. 5  is a schematic circuit diagram of flash memory cells. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in greater detail to a preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like parts. 
       FIG. 1  is a flow diagram illustration of a method of secure erase of an electronic device  10  in accordance with the details of the present invention. In block  12 , a predetermined voltage is selected for an electronic device. The predetermined voltage is selected to be high enough to reliably destroy all data of the electronic device yet low enough to keep electronic connections of the electronic device intact. 
     In one embodiment, the predetermined voltage is applied to word and/or bit lines of Solid State Drives (SSDs). In one embodiment, the predetermined voltages are in the range of about 3.3 V to about 84 V. Suitable predetermined voltages can include, but not be limited to, 3.3V, 5.0V, 12V, 24V, 36V, 48V, 60V, 72V, and 84V. In another embodiment, an inverted voltage is applied to the electronic device by connecting a NAND ground connect to the predetermined voltage and connecting the NAND VCC to ground. 
     In block  14 , application of the predetermined voltage is triggered. 
     Triggering of the application of the predetermined voltage of block  14  is done by any of a number of means including an external switch or button that is manually set when sanitization of an electronic device is required or that is set when the electronic device is removed from a system. 
     Alternatively, triggering the application of the predetermined voltage can be performed automatically such as by a software implementation. For example, the switch can be activated by receiving an input signal or command at a software module. In one embodiment, a mobile phone sends a signal that is received by a software module. If the signal is sent from a particular phone number or with a particular PIN, the switch is set for triggering the application of the predetermined voltage. In an alternate embodiment, a network can forward a signal or command to a software module. In an alternative embodiment, GPS or assisted GPS can be used for triggering the application of the predetermined voltage when the electronic device is moved from a particular location or outside a given area. 
     In an alternate embodiment, a sensor can be used for triggering the application of the predetermined voltage when the sensor detects a shock to the electronic device above a certain level or movement of the electronic device beyond a certain level. In an alternate embodiment, unauthorized tampering or opening of a housing of the electronic device, such as an enclosure of a NAND flash and other non-volatile-memory-based solid state drives, can be used for triggering the application of the predetermined voltage. 
     In block  16 , the predetermined voltage is applied to the electronic device for erasing the data, i.e., destroying the memory cell, yet keeping the electronic connections intact. 
       FIG. 2  is a schematic diagram of a system for secure erase of an electronic device  20 . Electronic device  21  can include host interface logic  22  which interfaces with flash bus controller  23  and voltage generator and controller  24 . Host logic interface  22  can be, for example, a Serial ATA (SATA), micro SATA, integrated drive electronic device (IDE), serial attached SCSI (SAS) and compact flash (CF). Flash bus controller  23  controls a plurality of NAND flash memory cells  25   a - 25   n  over respective channels  26   a - 26   n . Voltage generator and controller  24  applies a selected predetermined voltage to channels  26   a - 26   n  for applying the predetermined selected voltage to flash memory cells  25   a - 25   n  over word lines and bit lines. Switch  28  is coupled to host interface logic  22 . Button  29  can be used to activate switch  28 . 
     Alternatively, switch  28  can be activated by receiving command signal  31  at software module  32  of system for secure erase of an electronic device  30 , as shown in  FIG. 3 . In one embodiment command signal  31  is sent over network  34  to software module  32 . Alternatively, signal  31  is sent by mobile phone  40 . Alternatively, GPS  50  can send signal  31 . 
       FIG. 4  is a schematic diagram of system for secure erase of an electronic device  40 . Sensor  42  can be coupled to electronic device  41 . Sensor  42  can be used for triggering the application of the predetermined voltage when sensor  42  detects a shock to electronic device  41  above a certain level or movement of electronic device  41  beyond a certain level. In an alternate embodiment, unauthorized tampering or opening of a housing  44  of electronic device  41  triggers sensor  42 . 
     Electronic device  31  and electronic device  41  can be a SSD, flash drive or other electronic storage device. 
       FIG. 5  shows the flash memory with the bit and word lines. Channels  26   a - 26   n  connect to bit lines  50  of respective flash memory cells  25   a - 25   n . Bit lines  50  connect to flash memory cells  52 . Word lines  54  are connected to gates  55  of flash memory cells  52 . Current applied to channels  26   a - 26   n  at the predetermined selected voltage flows through memory cells  54  over bit lines  50  and word lines  54 . An inverted voltage is applied to flash memory cells  52  by connecting a NAND ground connect to the predetermined voltage and connecting the NAND VCC to ground. 
     Embodiments of the present invention may be implemented in connection with a special purpose or general purpose computer that include both hardware and/or software components. 
     Embodiments may also include physical computer-readable media and/or intangible computer-readable media for carrying or having computer-executable instructions, data structures, and/or data signals stored thereon. Such physical computer-readable media and/or intangible computer-readable media can be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such physical computer-readable media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, other semiconductor storage media, or any other physical medium which can be used to store desired data in the form of computer-executable instructions, data structures and/or data signals, and which can be accessed by a general purpose or special purpose computer. Within a general purpose or special purpose computer, intangible computer-readable media can include electromagnetic means for conveying a data signal from one part of the computer to another, such as through circuitry residing in the computer. 
     When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a computer, hardwired devices for sending and receiving computer-executable instructions, data structures, and/or data signals (e.g., wires, cables, optical fibers, electronic circuitry, chemical, and the like) should properly be viewed as physical computer-readable mediums while wireless carriers or wireless mediums for sending and/or receiving computer-executable instructions, data structures, and/or data signals (e.g., radio communications, satellite communications, infrared communications, and the like) should properly be viewed as intangible computer-readable mediums. Combinations of the above should also be included within the scope of computer-readable media. 
     Computer-executable instructions include, for example, instructions, data, and/or data signals which cause a general purpose computer, special purpose computer, or special purpose processing device to perform a certain function or group of functions. Although not required, aspects of the invention have been described herein in the general context of computer-executable instructions, such as program modules, being executed by computers, in network environments and/or non-network environments. Generally, program modules include routines, programs, objects, components, and content structures that perform particular tasks or implement particular abstract content types. Computer-executable instructions, associated content structures, and program modules represent examples of program code for executing aspects of the methods disclosed herein. 
     Embodiments may also include computer program products for use in the systems of the present invention, the computer program product having a physical computer-readable medium having computer readable program code stored thereon, the computer readable program code comprising computer executable instructions that, when executed by a processor, cause the system to perform the methods of the present invention. 
     It is to be understood that the above-described embodiments are illustrative of only a few of the many possible specific embodiments, which can represent applications of the principles of the invention. Numerous and varied other arrangements can be readily devised in accordance with these principles by those skilled in the art without departing from the spirit and scope of the invention.