WO2008063965A2

WO2008063965A2 - Method and system to provide security implementation for storage devices

Info

Publication number: WO2008063965A2
Application number: PCT/US2007/084446
Authority: WO
Inventors: Sree M. Iyer; Larry L. Jones; Arockiyaswamy Venkidu; Santosh Kumar
Original assignee: Mcm Portfolio Llc
Priority date: 2006-11-14
Filing date: 2007-11-12
Publication date: 2008-05-29
Also published as: WO2008063965A3; KR20090080032A; US20080114994A1; JP2010509690A; CN101484905A; EP2102782A2; TW200823927A; US7876894B2

Abstract

The method comprises providing a separate encryption seed (IV) for each of a plurality of separate addressable blocks (4) of a non-volatile storage device (2), wherein a common encryption method is to encrypt data to be stored on the plurality of separate addressable blocks. In one embodiment, the storage device is a portable storage device. In one embodiment, encryption seed is an Initialization Vector (IV). In one embodiment, the encryption seeds comprise at least one of a media serial number and a logical block address corresponding to the respective block of the non-volatile storage device. In an alternative embodiment, the method further comprises storing at least a part of the separate encryption seed of the separate blocks of the non-volatile storage device within the respective blocks of the storage device.

Description

METHOD AND SYSTEM TO PROVIDE SECURITY IMPLEMENTATION

FOR STORAGE DEVICES

FIELD OF INVENTION

This invention relates to security in non-volatile storage devices.

BACKGROUND OF THE INVENTION Portable digital storage devices are becoming increasing popular. These devices include solid-state storage such as flash memories and hard disks. This popularity extends to the leading flash media, such as CompactFlash, Secure Digital Card, Memory Stick PRO, MultiMediaCard, Flash Drives, and their variants. These devices can easily store gigabytes of data, weigh a few grams, and be no bigger than a credit card. A problem with these devices is they are easily lost. Many people today carry large amounts of vital data on devices, which they keep in their pockets. It is very important that this data be encrypted to ensure that only the owner can read it.

What is needed is a system and a method to use an encryption schemes, to secure the data on non-volatile storage devices, for example portable digital storage devices, with minimal impact on the speed of reading and writing to and from the device, and with minimal additional hardware expense.

SUMMARY

According to the invention, there is provided a method which comprises providing a separate encryption seed for each of a plurality of separate addressable blocks of a non-volatile storage device, wherein a common encryption method is to encrypt data to be stored on the plurality of separate addressable blocks. In one embodiment, the storage device is a portable storage device. In one embodiment, the encryption seed is an Initialization Vector (IV) . In one embodiment, the encryption seeds comprise at least one of a media serial number and a logical block address corresponding to the respective block of the nonvolatile storage device. In an alternative embodiment, the method further comprises storing at least a part of the separate encryption seed of the separate blocks of the non-volatile storage device within the respective blocks of the storage device. In one embodiment, the method, can be performed on a system, and is provided for security implementations for storage devices. There are many encryption schemes, which may be used as the common encryption method. One example is the Advanced Encryption Standard (AES) .

Another aspect of the invention provides a method of decrypting data stored in a data block of a nonvolatile storage device which device comprises a plurality of separately addressable data blocks having respective encryption seeds, the data in all the blocks being encrypted by a common encryption method, the decryption method comprising accessing a desired one of the blocks, generating a decryption code from the encryption seed of that block, and decrypting the data of the desired one of the blocks using the generated decryption code of that block.

In an embodiment, the encryption seed is stored in the data block. Another embodiment comprises generating the decryption code from at least one of a medium serial number and a logical block address of the desired block. A further embodiment comprises generating the decryption code from at least one of a medium serial number and a logical block address of the desired block together with a random number which is stored in the block. The encryption seed may be the decryption code and the decryption code may be an initialization vector.

Another aspect of the invention provides a nonvolatile data store storing data in a plurality of separately addressable data blocks having respective encryption seeds, the data in all the blocks being encrypted by a common encryption method. A further aspect provides a data carrier storing data in a plurality of separately addressable data blocks having respective encryption seeds, the data in all the blocks being encrypted by a common encryption method.

In an embodiment of the said another aspect or of the further aspect yet further aspect the data blocks contain respective encryption seeds used in the encryption of the data of the blocks.

Yet another aspect provides a data processor arranged to decrypt data stored in a data carrier storing data in a plurality of separately addressable data blocks having respective encryption seeds, the data in all the blocks being encrypted by a common encryption method, the data processor being arranged to carry out the method of said another aspect of the invention.

The invention also provides a computer program which, when run on a suitable processor, implements the decryption method of said another aspect of the invention, and a carrier carrying the computer program.

BRIEF DESCRIPTION OF FIGURES

For a better understanding of the present invention, reference will now be made by way of example to the accompanying drawings in which: Figure 1 is a schematic diagram of the data storage area of a Flash memory;

Figure 2 is a schematic diagram of cipher block chaining mode of encryption using AES as the block encryption cipher; Figure 3 is a schematic block diagram of an illustrative system for implementing the invention,

Figure 4 is a schematic block diagram of a decryption process corresponding to the encryption process of Figure 2; Figure 5 presents an example of an IV block, in accordance with one embodiment; Figure 6 presents a simplified block diagram of an asynchronous random generator, in accordance with one embodiment;

Figure 7 shows an illustrative memory page; Figure 8 shows an illustrative memory page with part of the extra data used for error correction data;

Figure 9 shows an illustrative 512-byte page that is to be encrypted, in accordance with one embodiment;

Figure 10 shows a 1024-byte data block, divided in two sectors, in accordance with one embodiment; and

Figure 11 shows a block diagram of an example of an asynchronous random generator, in accordance with one embodiment .

DETAILED DESCRIPTION OF THE INVENTION

Examples of flash memory have a large storage capacity for example several Gigabytes. A flash memory is divided into erase blocks which are portions of the memory which can be erased in one erase operation. An erase block has a storage capacity of for example many pages. As described below a page may have 528 bytes or a multiple thereof.

For the purposes of examples of the invention, and for ease of description, the storage area of a flash memory is divided into segments 4 as shown in Figure 1. Each segment may be for example a page of 528 bytes of which 512 bytes is available for data storage and the other 16 bytes are extra data: see figure 7 below.

In examples of the invention, the data in each segment 4 is encrypted. In the example of Figure 2, the known CBC (Cipher Block Chaining mode) method of encryption is used in which AES (Advanced Encryption Standard) is used as the block cipher encryption method.

The data of a segment 4 is divided into portions of plain text, each portion comprising 128 bits. The first 128-bit portion 61 is logically combined with an initialization vector (IV) 10 in an Exclusive-Or (EX- OR) operation 81. The block cipher operation using AES encrypts the 128 bits using a key 12 to produce 128 bits of cipher text 161. The 128 bits of cipher text are then logically combined in an EX-OR operation 82 with the next 128 bits of plain text, and enciphered in the encryption operation 142 using the same key to produce another 128 bits of cipher text which are used in the next stage of the chain. Subsequent stages in the chain operate in the same manner.

In accordance with examples of the invention, the data segments 4 have respective IVs (IVlO... IV 21... IV 41..), which are different. The data in the segments are encrypted using the same encryption process but with different IVs. Those IVs are stored in the flash memory in some embodiments of the invention as described below. They may be stored in the respective data segments.

Figure 3 shows one example of a system for implementing the process described with reference to Figures 1 and 2.

A flash memory 22 is coupled by an interface (I/F) 24 to a computer. For example the flash memory and interface are those of a well known USB memory device. The computer may be a PC for example. The encryption process is carried out in the computer 26 and the encrypted data stored in the flash memory.

In the example of Figure 3, the computer 26 has a program store 261 and a processor 262 and a non volatile memory 263, for example a disc drive. The encryption process may be applied to the non volatile memory 263 of the computer 26. The computer 26 may be a PC, a PDA, a cell phone or any other device having data storage and data processing.

In this example, decryption is the opposite of encryption as shown in Figure 4. The encryption and decryption processes are symmetrical in that they use the same IVs and keys. The decryption process in this example operates on each segment 4. In this example, the IV of a segment is extracted from the segment and used in the decryption process. As described below, only part of the IV may be stored in the segment and the IV is generated from the stored part. The IV may be generated from a media serial number and/or from a logical segment address optionally together with a random number which may be stored in the segment.

An embodiment of the invention comprises a computer program which when run on a suitable processor implements the decryption method. The computer program may be on a carrier which may be a signal or a recording medium, amongst other possibilities.

As described in more detail below, other encryption and decryption methods can be used.

As described below other sizes of data segments can be used.

The following description gives examples of generating IVs, and other information. IV Generation

In one embodiment, the Advanced Encryption Standard

(AES) specifies several feedback modes for improved encryption of data. Three of these modes, cipher feedback (CFB) mode, cipher block chaining (CBC) mode, and output feedback (OFB) mode, perform an Exclusive

OR (XOR) operation on the data with an initialization vector (IV) . The IV need not be a secret but for CBC and CFB it is to be unpredictable. The IV or seed to generate an IV should be a random number (as used herein IV and seed are used interchangeably) .

In one embodiment, the IV or seed used to generate the IV is stored with the block of data, with which the IV was used. The IV or seed can then be used in the process of decrypting the respective block of data. In one embodiment, the IV is 128 bits of data, or 16 byes of 8 bit data. Alternatively, the IV can be generated from a smaller random number as long as the IV is not repeated in the encryption process. For optimum performance, it is desirable that the IV be unique for every 512 bytes (referred to here forth as the data block) of data, since storage used in almost all devices (personal computers, consumer devices, cell phones, etc.) use 512 bytes as their sector size. This does not preclude using larger data blocks such as 1024 or 2048 bytes.

Flash memories are divided into blocks (this block is different from an data block, discussed previously and is referred to hereinafter as an erase block) . The erase block in flash memory refers to the smallest amount of memory that can be erased at a time so it can be re-written. For example, a typical erase block might consist of 256 pages. To write to the erase block, it must first be erased and then written.

If a block develops too many errors the data can be moved to a new block and the block marked as bad. No matter where the block is located on the flash, it always retains a logical number. In one embodiment, the logical number is used, at least in part, to generate part of the IV for the respective block. As a result, there is a decreased likelihood of a repeating the IV.

Figure 5 shows an example of a 16-byte IV block 100

(128 bits) . However in the extra data area of NAND flash, there is room for only 4 bytes (or 32 bits) .

Therefore from this 32-bit random number, a 128-bit IV block with randomness is generated. In one embodiment, the random number of 32 bits can have appended to it the logical block address and/or the unique serial number of the storage unit.

In the case of when the media does not have a place to store the IV with the data (e.g., hard disk drive), the IV is the logical block number, with or without the serial number of the storage unit. Furthermore, depending on the size of the IV, an additional constant could be also be used in addition to the logical block number, with or without the serial number of the storage unit. Alternative combinations could be used to generate the IV.

Random Number Generation

One way to generate a random number is to have an integrated circuit which includes a register that is not reset to a preset state when power is turned on. As a result, the register has an unpredictable initial seed value after it is turned on. Some controllers have a synchronous design, meaning most of the circuitry gets initialized or preset to the same value at power-up, but a register or hash generator logic can be deliberately designed such that it does not have a preset value at power up. It powers- up in an unpredictable state and is thus a source of randomness.

Referring by way of example to Figure 6, a register 204 has, as its input, the output of a "hash logic" device 203 such as a CRC generator or AES encryptor. This logic device 203 has as its input the outputs of the register and a number based on some internal event, such as, for example a counter and an external event such as the USB frame number. The USB frame number is a pseudo-random number generated by a USB host. This number is periodically updated. One problem is that the event could be predictable. However, if the integrated circuit is connected to a host computer via a port that is not synchronous to the integrated circuit's clock, then the host port can be used to generate a number that is asynchronous to the internally generated number. If these two numbers generated by the internal and external event are fed into the logic block, then a truly random number is generated.

Figure 6 shows a simplified block diagram of such an asynchronous random generator 200, using both an internal random number start value 201 and an external random number start value 202 to feed into its hash logic 203 and the usual sync register 204, providing feedback into the hash logic. The logic of the block diagram in figure 6 could be implemented as hardwired logic or as software or firmware.

IV Storage

Figure 7 shows an example of a memory page 300 (such as a flash memory page) , with 528 bytes of data 301 or its multiple. In one embodiment, the page size is designed to store 512 bytes of data and 16 bytes of extra data 302. Typical page sizes are 528, 2112, 4224, etc. Figure 8 shows an example of a memory page 400 with part of the extra data used for error correction data 403, as is typical, because flash memories are susceptible to random errors. The remaining extra data 402 is used for status. Figure 9 shows an example of a 528-byte page 500 that is to be encrypted. In such a case, it is desirable to store the IV 504 used in encryption in the page for fast access for use in decrypting the data and have only two status bytes 402.

Four bytes (32 bits) of IV data would provide 4,294,967,296 (232) different IV values. Because flash memories can hold gigabytes of data, it is apparent that a larger random number can be used to reduce the chance of repeating the random number.

In one embodiment, an IV comprising 4 bytes of random number is placed at the beginning of a data block, as shown in Figure 9, because if 512 bytes of data is encrypted using a random number, reading the IV first enables the controller to have the IV ahead of the data the controller needs to decrypt. If the number were, for example, placed at the end of data, then the controller would have to read the entire 512 bytes to get to the IV that has been used in the process of encrypting the 512 bytes and then start the decryption. This approach would waste precious cycles during the decryption process.

Figure 10 shows a 1024-byte data block 600, divided in two sectors 601 and 602. One way to reduce the chance of repeating an IV is to associate each IV with make two data blocks or two sectors: in effect increasing the block size. The 512 bytes of data 603a and 603b are still preserved as the smallest chunk of data which is accessible. An IV of 8 bytes 604a and 604b (64-bits) can generate 264, or 18,446,744,073,709,551 616 unique numbers.

In some cases, other portioning may be used. So, for example, in some cases the whole IV could be kept in the first sector, and all error correction in the second. The advantage in this case is that decoding can begin immediately, but the drawback is that the some of it may need to be reworked, once an error has been found (when the second sector is read) . In yet other cases, the error correction may be located up front. That could slow down the writing process (requiring effectively a double write) , but would allow immediate decoding without error. In cases where reads outnumber writes by a large ratio, it still may be an interesting choice. In some instances, a record may be kept of read-to-write ratio, and once a threshold is exceeded, the memory may be dynamically reconfigured.

Look Ahead Error Correction Flash memories have reliability problems: individual bits may go bad from time to time. If the data is encrypted, an error can cause the data to be incapable of being decrypted. If it is not encrypted it can cause the data to be incorrect. It is common to have an error-correction scheme to correct failing bits. These correction schemes can correct one or more errors. The error correction scheme in one embodiment can detect up to 5-byte errors and correct up to 4- byte errors in a 512 byte space.

In some cases, based on a trend (increasing number of bad spots in a sector) , a sector or block may be permanently mapped out (i.e., move the data to a new block) , hence preventing or minimizing disastrous data loss. The information on the correctable errors is stored in the extra area where 10 bytes store the ECC values for the 512 byte data, as shown in Figure 9. The controller puts down the correct ECC value while writing to the flash media and compares original ECC value with the ECC value while reading back the data.

As a result, the controller can determine if the error occurred in the data block and correct it using the ECC data. In addition, the controller can flag an imminent bad block when it corrects 4-byte errors so the controller can undertake a corrective action of mapping this data into a new good area.

In one embodiment, the controller keeps track of available good blocks that can be used to map out (i.e., move the data to a new block) an about-to-go- bad block. For instance, if the host requests to read 128 sectors and sectors 3, 19, 38 were found to have been corrected with 4-byte errors, the controller would keeps these about-to-go-bad sectors in a FIFO while transferring the entire 128 sectors of data to the host. After the data transfer is complete, the firmware would read this FIFO to find out that several sectors have data errors in this block indicating that it is about to go bad. The firmware would then take the corrective action of moving the entire block of sectors to a new, good block. Once the moving is complete, it would then mark the current block as bad, thereby averting data loss. In general a correction scheme capable of correcting N errors would be used to indicate when to move a block when there were N or possibly less than N errors.

Boot Code Encryption/Authentication

Flash memory storage devices often contain so-called boot firmware. This is firmware that is loaded from the flash memory by the flash controller integrated circuit when power is applied. This boot firmware is usually written at the time the device is manufactured; however patches to this firmware may be written at any time during the life of the device. It is desirable that this boot data be encrypted so that the processor can validate that this code is authentic, and is not rogue firmware intended to break the encryption.

In some cases, this method may also be applied to the host boot section in the CD area described below. This approach may prevent viruses from taking over the host boot section.

If the device has been assigned a key as defined in the AES standard, this key can be used to encrypt and decrypt the boot data. Often the device may be sold without a key and only later is the key assigned. The reason for this late key assignment is so the user could keep his password a part of the master key, essentially making the key unique. But at the time of manufacture, a master key is needed to ensure that the boot code can be validated. A unique key can be generated for each device at the time of manufacture for use only by the boot firmware. A unique key can be stored on the controller at manufacture time if the controller has one-time program memory (OTP) . OTP is similar to write once memory, and after this one write, it cannot be modified.

Another approach to changing the key is to store the master key in the flash memory, but change the key every time the device is turned on, using this method according to one embodiment of the present invention:

1. With the current key, decrypt the boot code and load the clear data into the RAM.

2. Generate a new master key, using a method described later in this disclosure, and then erase the current boot block and write a new encrypted boot code using the new master key and write this new boot block into the storage media. A boot block can be located almost anywhere in the media.

Example implementation

The product would be shipped as CD + Public, meaning the storage device, when connected to a PC, would provide a CD icon and a storage icon in the My Computer window, by pretending to the operating system of the host to be or to contain a CD drive. In the CD portion, there would be an application resident to make the device "Secured". When launched, the program prompts the user for a password and then encrypts the secure partition with the master key and IV, as described above.

One method to generate a 32-bit random number in a USB storage system is to use the USB frame number (a random number that is generated by the USB host, such as a PC, every millisecond) and an internal counter in the controller that is incremented every system clock and that has a random starting value that cannot be predicted, as previously discussed in the description of Figure 1.

Figure 11 shows a block diagram of an example of an asynchronous random generator 700, using both a frame number 701 and internal counter 702 to feed into its multiplexer (mux) 703, and the usual sync register and feedback into the hash logic, here shown as a CRC generator 704, generating the random number 705. It is clear that it can be implemented in software, hardware or any combination thereof. Further, in some cases, the CRC generator 704 is not reset at power on and therefore has an undetermined value at every processor power-up .

The processes described above can be stored in a memory of a computer system as a set of instructions to be executed. In addition, the instructions to perform the processes described above could alternatively be stored on other forms of machine- readable media, including magnetic and optical disks. For example, the processes described could be stored on machine-readable media, such as magnetic disks or optical disks, which are accessible via a disk drive (or computer-readable medium drive) . Further, the instructions can be downloaded from a program source, for example a server, into a computing device over a data network in a form of compiled and linked version. Alternatively, the logic to perform the processes as discussed above could be implemented in additional computer and/or machine readable media, such as discrete hardware components as large-scale integrated circuits (LSI's), application-specific integrated circuits (ASIC's), firmware such as electrically erasable programmable read-only memory (EEPROM' s); and electrical, optical, acoustical and other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.); etc.

Claims

1. A method comprising providing respective encryption seeds for a plurality of separately addressable blocks of a non-volatile storage device, wherein a common encryption method is to encrypt data to be stored on the plurality of separately addressable blocks.

2. The method of claim 1, wherein the storage device is a portable storage device.

3. The method of claim 1 or 2, wherein the encryption seed is an Initialization Vector (IV).

4. The method of claim 1, 2 or 3, wherein the common encryption method is Advanced Encryption Standard

(AES) .

5. The method of any preceding claim, wherein each encryption seed comprises at least one of a media serial number and a logical block address corresponding to the respective block of the nonvolatile storage device.

6. The method of any one of claims 1 to 4, wherein the respective encryption seeds each comprise a random number and one or more of the logical block address corresponding to the respective block of the nonvolatile storage device and a media serial number of the storage device.

7. The method of any preceding claim, comprising storing, within the respective blocks of the storage device, at least respective parts of the respective encryption seeds.

8. The method of claim 7, wherein the storing further comprises storing at least a part of the respective encryption seeds within at least a first addressable byte of the respective blocks of the nonvolatile storage device.

9. The method of any preceding claim, wherein at least one or more of the blocks are one of 528 bytes or a multiple of 528 bytes.

10. The method of any one of claims 1 to 9, wherein the storage device comprises a Flash memory storage device .

11. The method of any one of claims 1 to 6, wherein the storage device is a hard-disk drive and the encryption seed is determined from a constant number and one or more of the logical block address corresponding to the respective block of the nonvolatile storage device and a media serial number of the storage device.

12. A method comprising providing respective encryption seeds for a plurality of sets of two or more of separate addressable blocks of a non-volatile storage device, wherein a common encryption method is to encrypt data to be stored on the plurality of separate addressable blocks.

13. The method of claim 12, wherein the two or more separate addressable blocks of each set have sequential logical addresses.

14. The method of claim 12 or 13, wherein each encryption seed comprises at least one of a media serial number and a logical block address corresponding to at least one of the two blocks of a set .

15. The method of claim 14, wherein the storage device is a hard-disk drive, the encryption seed is not stored in the respective block, and the encryption seed further comprises a constant number.

16. The method of claim 14, wherein the encryption seed further comprises a random number, and the method further comprises storing the random number of in a first block of the respective sets of two or more separate addressable blocks of the non-volatile storage device.

17. The method of claim 14, wherein each encryption seed further comprises a random number, and the method further comprises for each seed storing at least part of the random number in a first block of a respective set of two or more separate addressable blocks, and at least part of the random number in a second block of the respective set of two or more separate addressable blocks .

18. The method of claim 17, wherein the storage device is a flash storage device.

19. A machine readable-medium having stored thereon a set of instructions which, when executed, perform a method according to any preceding claim.

20. A computer program which, when run on a suitable processor, implements the method of any one of claims 1 to 1 9 .

21. A carrier carrying a computer program according to claim 20.

22. A carrier according to claim 21 which is a computer readable medium.

23. A carrier according to claim 21 which is an electrical carrier.

24. Apparatus arranged to generate the carrier of claim 23.

25. A data processing apparatus having a data processor, a program store storing the computer program of claim 20, and an interface for communicating with a non-volatile memory device, the processor being operable under the control of the said computer program to encrypt data to be stored in separately addressable blocks of the non-volatile memory and to store the encrypted data in the separately addressable blocks of the non-volatile memory.

26. A data processing apparatus having a data processor, a program store storing the computer program of claim 20, and a non-volatile memory device, the processor being operable under the control of the said computer program to encrypt data to be stored in separately addressable blocks of the non-volatile memory and to store the encrypted data in the separately addressable blocks of the non-volatile memory.

27. A method of decrypting data stored in a data block of a non-volatile storage device which device comprises a plurality of separately addressable data blocks having respective encryption seeds, the data in all the blocks being encrypted by a common encryption method, the decryption method comprising: accessing a desired one of the blocks; generating a decryption code from the encryption seed of that block; and decrypting the data of the desired one of the blocks using the generated decryption code of that block.

28. A decryption method according to claim 27, wherein the encryption seed is stored in the data block.

29. A decryption method according to claim 27, comprising generating the decryption code from at least one of a medium serial number and a logical block address of the desired block.

30. A decryption method according to claim 27 or 28, comprising generating the decryption code from at least one of a medium serial number and a logical block address of the desired block together with a random number which is stored in the block.

31. A decryption method according to claim 27, 28, 29 or 30, wherein the decryption code is an initialization vector.

32. A decryption method according to claim 27, 28, 29, 30 or 31, wherein the encryption seed is the decryption code.

33. A non-volatile data store storing data in a plurality of separately addressable data blocks having respective encryption seeds, the data in all the blocks being encrypted by a common encryption method.

34. A data carrier storing data in a plurality of separately addressable data blocks having respective encryption seeds, the data in all the blocks being encrypted by a common encryption method.

35. A store or carrier according to claim 33 or 34, wherein the data blocks contain respective encryption seeds used in the encryption of the data of the blocks .

36. A store or carrier according to claim 35 wherein the encryption seeds are initialization vectors or parts thereof.

37. A data processor arranged to decrypt data stored in a data carrier storing data in a plurality of separately addressable data blocks having respective encryption seeds, the data in all the blocks being encrypted by a common encryption method, the data processor being arranged to carry out the method of any one of claims 27 to 32.

38. A computer program which, when run on a suitable processor, implements the method of any one of claims

27 to 32.

39. A carrier carrying a computer program according to claim 38.