Abstract:
A system and method which protects a data processing system against encryption key errors by providing redundant encryption keys stored in different locations, and providing the software with the ability to select an alternate redundant key if there is any possibility that the encryption key being used may be corrupted. In the preferred embodiment, a memory control module in the data processing device is configured to accommodate the storage of multiple (for example up to four or more) independent password/key pairs, and the control module duplicates a password key at the time of creation. The redundant passwords and encryption keys are forced into different memory slots for later retrieval if necessary. The probability of redundant keys being corrupted simultaneously is infinitesimal, so the system and method of the invention ensures that there is always an uncorrupted encryption key available.

Description:
FIELD OF INVENTION  
       [0001]     This invention relates to data processing systems. In particular, this invention relates to an encryption system in a data processing device.  
       BACKGROUND OF THE INVENTION  
       [0002]     The use of portable data processing systems has increased significantly in recent years. In addition to so called “laptop” and “tablet” computers, there is a growing popularity in handheld data processing devices, often called a “personal digital assistant” or “PDA.” All of these devices are capable of storing a significant amount of user data, including calendar, address book, tasks and numerous other types of data for business and personal use. Most handheld data processing devices have the ability to connect to a personal computer for data exchange, and many are equipped for wireless communications using, for example, conventional email messaging systems. Depending upon the user&#39;s needs much of this data can be highly sensitive in nature, especially in a government, military or commercial context.  
         [0003]     Portable data processing systems are typically password protected. However, in the hands of a technically sophisticated individual with malicious intent, there are ways to obtain the data stored in memory in such a device if the data is not encrypted. Accordingly the data stored in persistent memory is typically encrypted using an encryption key. This requires that the same encryption key used to encrypt the data be used to decrypt the data.  
         [0004]     In any data storage systems there is a possibility that over time, or because of an event, a portion of the memory will fail. The failure may reveal itself as a single bit error, multiple word errors, or possibly a complete memory failure. When the memory is used to store an encryption key, even a single bit error can corrupt the key sufficiently to render it useless. Should this occur, then the entire volume of data encrypted with the corrupted key becomes undecryptable, and as a result is lost. To prevent this data loss, an uncorrupted encryption key must be available at all times.  
       SUMMARY OF THE INVENTION  
       [0005]     The invention provides a system and method which protects a data processing system against encryption key errors. According to the invention, this is accomplished by providing redundant encryption keys stored in different locations, and providing the software with the ability to select an alternate redundant key if there is any possibility that the encryption key being used may be corrupted.  
         [0006]     In the preferred embodiment, a memory control module in the data processing device is configured to accommodate the storage of multiple (for example up to four or more) independent password/key pairs. When so configured, the control module will duplicate a password key at the time of creation by repeating the ADD_KEY command using the same CURRENT_KEY, KEY_SEED (a random arrangement of bits stored in hardware) and PASSWORD sources. The redundant passwords and encryption keys are forced into different memory slots for later retrieval if necessary.  
         [0007]     The probability of redundant keys being corrupted simultaneously is infinitesimal. The system and method of the invention thus ensures that there is always an uncorrupted encryption key available.  
         [0008]     The present invention thus provides a method of securing data in a data processing device having an encryption device for encrypting and decrypting data using an encryption key-password pair, comprising the steps of: a. generating a first encryption key, b. storing the first encryption key in a first location in a memory, c. generating at least one additional encryption key, d. storing each additional encryption key in a memory in a different location from the location of each other encryption key, and e. creating a register storing the location of each encryption key, wherein to encrypt or decrypt data the first encryption key is retrieved but upon the occurrence of a particular event one of the additional encryption keys is retrieved.  
         [0009]     The present invention further provides a data processing device comprising a system for securing data, comprising an encryption device for encrypting and decrypting data using an encryption key-password pair, at least one key generating device for generating a plurality of encryption keys, and at least one memory for storing the encryption keys in separate locations and for storing a register identifying the location of each encryption key, wherein to encrypt or decrypt data a first encryption key is retrieved but upon the occurrence of a particular event a different encryption key is retrieved.  
         [0010]     The present invention further provides a mobile communications system, comprising a communications subsystem, for receiving and transmitting data, a processor for processing data, having a system for securing data communicated to and from the device comprising an encryption device for encrypting and decrypting data received and transmitted using an encryption key-password pair, comprising at least one key generating device for generating a plurality of encryption keys, and at least one memory for storing the encryption keys in separate locations and for storing a register identifying the location of each encryption key, wherein to encrypt or decrypt data a first encryption key is retrieved but upon the occurrence of a particular event a different encryption key is retrieved. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     In drawings which illustrate by way of example only a preferred embodiment of the system,  
         [0012]      FIG. 1  is a block diagram of a system overview of a conventional mobile data processing device.  
         [0013]      FIG. 2  is a system interface block diagram of a data processor in the data processing device of  FIG. 1 .  
         [0014]      FIG. 3  is a detailed block diagram of the memory controller interface in the data processor of  FIG. 2 .  
         [0015]      FIG. 4  is a detailed block diagram showing the implementation of the encryption and decryption algorithms effected by the AES encryption module in the data processor of  FIG. 2 .  
         [0016]      FIG. 5  is a Configuration Registers Map for the encryption module of  FIG. 4 .  
         [0017]      FIG. 6  is an AES Plaintext Register Field table associated with the Configuration Registers Map of  FIG. 5 .  
         [0018]      FIG. 7  is an AES Ciphertext Register Field table associated with the Configuration Registers Map of  FIG. 5 .  
         [0019]      FIG. 8  is an AES Key Peripheral Register Field table associated with the Configuration Registers Map of  FIG. 5 .  
         [0020]      FIG. 9  is an AES Manual Launch Register table associated with the Configuration Registers Map of  FIG. 5 .  
         [0021]      FIG. 10  is an AES Status Register table associated with the Configuration Registers Map of  FIG. 5 .  
         [0022]      FIG. 11  is an AES Control Register table associated with the Configuration Registers Map of  FIG. 5 .  
         [0023]      FIG. 12  is a State Diagram showing encryption and decryption timing in the encryption module of  FIG. 4 .  
         [0024]      FIG. 13  is a block diagram of the Serial EEPROM Controller in the memory controller interface of  FIG. 3 .  
         [0025]      FIG. 14  is a state diagram for the Serial EEPROM Controller of  FIG. 13 .  
         [0026]      FIG. 15  is a Configuration Registers Map for the Serial EEPROM Controller of  FIG. 13 .  
         [0027]      FIGS. 16A and 16B  are first and second parts of a Control Register table associated with the Configuration Registers Map of  FIG. 15 .  
         [0028]      FIGS. 17A and 17B  are first and second parts of a Status Register table associated with the Configuration Registers Map of  FIG. 15 .  
         [0029]      FIG. 18  is a Password Register Field table associated with the Configuration Registers Map of  FIG. 15 .  
         [0030]      FIG. 19  is a Key Seed Register Field table associated with the Configuration Registers Map of  FIG. 15 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]     A preferred embodiment of the system will be described in detail below, by way of example only, in the context of a hand-held data processing device having wireless communications capabilities as illustrated in FIGS.  1  to  3 . However, it will be appreciated that the principles apply to other data processing devices and the system is not intended to be limited thereby.  
         [0032]     The hand-held data processing devices  10  include a housing, a keyboard  14  and an output device  16 . The output device shown is a display  16 , which is preferably a full graphic LCD. Other types of output devices may alternatively be utilized. A processor  18 , which is shown schematically in  FIG. 1 , is contained within the housing and is coupled between the keyboard  14  and the display  16 . The processor  18  controls the operation of the display  16 , as well as the overall operation of the mobile device  10 , in response to actuation of keys on the keyboard  14  by the user.  
         [0033]     The housing may be elongated vertically, or may take on other sizes and shapes (including clamshell housing structures). The keyboard may include a mode selection key, or other hardware or software for switching between text entry and telephony entry.  
         [0034]     In addition to the processor  18 , other parts of the mobile device  10  are shown schematically in  FIG. 1 . These include a communications subsystem  100 ; a short-range communications subsystem; the keyboard  14  and the display  16 , along with other input/output devices  106 ,  108 ,  110  and  112 ; as well as memory devices  116 ,  118  and various other device subsystems  120 . The mobile device  10  is preferably a two-way RF communication device having voice and data communication capabilities. In addition, the mobile device  10  preferably has the capability to communicate with other computer systems via the Internet.  
         [0035]     Operating system software executed by the processor  18  is preferably stored in a persistent store, such as a flash memory  116 , but may be stored in other types of memory devices, such as a read only memory (ROM) or similar storage element. In addition, system software, specific device applications, or parts thereof, may be temporarily loaded into a volatile store, such as a random access memory (RAM)  118 . Communication signals received by the mobile device may also be stored to the RAM  118 .  
         [0036]     The processor  18 , in addition to its operating system functions, enables execution of software applications  130 A- 130 N on the device  10 . A predetermined set of applications that control basic device operations, such as data and voice communications  130 A and  130 B, may be installed on the device  10  during manufacture. In addition, a personal information manager (PIM) application may be installed during manufacture. The PIM is preferably capable of organizing and managing data items, such as e-mail, calendar events, voice mails, appointments, and task items. The PIM application is also preferably capable of sending and receiving data items via a wireless network  140 . Preferably, the PIM data items are seamlessly integrated, synchronized and updated via the wireless network  140  with the device user&#39;s corresponding data items stored or associated with a host computer system.  
         [0037]     Communication functions, including data and voice communications, are performed through the communication subsystem  100 , and possibly through the short-range communications subsystem. The communication subsystem  100  includes a receiver  150 , a transmitter  152 , and one or more antennas  154  and  156 . In addition, the communication subsystem  100  also includes a processing module, such as a digital signal processor (DSP)  158 , and local oscillators (LOs)  160 . The specific design and implementation of the communication subsystem  100  is dependent upon the communication network in which the mobile device  10  is intended to operate. For example, a mobile device  10  may include a communication subsystem  100  designed to operate with the Mobitex™, Data TAC™ or General Packet Radio Service (GPRS) mobile data communication networks and also designed to operate with any of a variety of voice communication networks, such as AMPS, TDMA, CDMA, PCS, GSM, etc. Other types of data and voice networks, both separate and integrated, may also be utilized with the mobile device  10 .  
         [0038]     Network access requirements vary depending upon the type of communication system. For example, in the Mobitex and DataTAC networks, mobile devices are registered on the network using a unique personal identification number or PIN associated with each device  10 . In GPRS networks, however, network access is associated with a subscriber or user of a device. A GPRS device therefore requires a subscriber identity module, commonly referred to as a SIM card, in order to operate on a GPRS network.  
         [0039]     When required network registration or activation procedures have been completed, the mobile device  10  may send and receive communication signals over the communication network  140 . Signals received from the communication network  140  by the antenna  154  are routed to the receiver  150 , which provides for signal amplification, frequency down conversion, filtering, channel selection, etc., and may also provide analog to digital conversion. Analog-to-digital conversion of the received signal allows the DSP  158  to perform more complex communication functions, such as demodulation and decoding. In a similar manner, signals to be transmitted to the network  140  are processed (e.g. modulated and encoded) by the DSP  158  and are then provided to the transmitter  152  for digital to analog conversion, frequency up conversion, filtering, amplification and transmission to the communication network  140  (or networks) via the antenna  156 .  
         [0040]     In addition to processing communication signals, the DSP  158  provides for control of the receiver  150  and the transmitter  152 . For example, gains applied to communication signals in the receiver  150  and transmitter  152  may be adaptively controlled through automatic gain control algorithms implemented in the DSP  158 .  
         [0041]     In a data communication mode, a received signal, such as a text message or web page download, is processed by the communication subsystem  100  and is input to the processor  18 . The received signal is then further processed by the processor  18  for an output to the display  16 , or alternatively to some other auxiliary I/O device  106 . A device user may also compose data items, such as e-mail messages, using the keyboard  14  and/or some other auxiliary I/O device  106 , such as a touchpad, a rocker switch, a thumb-wheel, or some other type of input device. The composed data items may then be transmitted over the communication network  140  via the communication subsystem  100 .  
         [0042]     In a voice communication mode, overall operation of the device is substantially similar to the data communication mode, except that received signals are output to a speaker  110 , and signals for transmission are generated by a microphone  112 . Alternative voice or audio I/O subsystems, such as a voice message recording subsystem, may also be implemented on the device  10 . In addition, the display  16  may also be utilized in voice communication mode, for example to display the identity of a calling party, the duration of a voice call, or other voice call related information.  
         [0043]     The short-range communications subsystem enables communication between the mobile device  10  and other proximate systems or devices, which need not necessarily be similar devices. For example, the short-range communications subsystem may include an infrared device and associated circuits and components, or a Bluetooth™ communication module to provide for communication with similarly-enabled systems and devices.  
         [0044]     Data stored in the non-volatile memory, in the embodiment shown NAND flash  116 , is encrypted using any suitable encryption algorithm, for example Advanced Encryption Standard (AES), preferably implemented in hardware. In the preferred embodiment the first bits of the basic encryption key are selected randomly and embedded at the time of manufacture of the chip. The user is able to change the basic encryption key, and after doing so all of the encrypted data must be read out of memory, decrypted using the key existing at the time of encryption, re-encrypted with the new key, and written back into memory.  
         [0045]     As the basic encryption key is changed, the components of the prior key(s) and prior password accumulate and form part of the new key. To further increase security, in the preferred embodiment the encryption algorithm uses the address location of the data to modify a portion of the encryption key, so that the same data will be encrypted differently when stored in different locations in memory.  
         [0046]     In the preferred embodiment the encryption system performs a password verification before any data from memory can be decrypted. Also, in the preferred embodiment the encryption key is not derived from the password, so even a weak password will not compromise the key, and before any data from memory can be decrypted a security controller performs a password verification. It is possible to change the value of the key at anytime by transitioning through a state machine that requires successful entry of the password, and once the key is changed, all of the existing data that is encrypted with the old key must be read out using the old key and re-written using the new key.  
         [0047]     According to the preferred embodiment of the invention, multiple address locations in the EEPROM  180  are dedicated as key slots so that the data processing device  10  can store multiple (up to four in the embodiment shown, by way of example only) independent keys. The system software may be configured (by the manufacturer, or if desired the user can be given the option to configure by toggling an enabling command) to automatically use one or more of the extra key slots, either for redundant storage of the master key, or for storing keys dedicated to the encryption and decryption of specific types of data.  
         [0048]     The device  10  may use any available encryption methodology, a conventional AES encryption scheme being illustrated in  FIG. 4  by way of example only. However, encryption could be effected by any other system, such as DES, DESX and triple-DES, and the invention is not limited to any particular encryption system. The encryption module includes interfaces with the EEPROM Control (SEC) block  170  of  FIG. 13  and an interface with an Error Correction Coding (ECC) module and the Read-Write Buffer (RWB). The encryption module encrypts and decrypts in two different modes: a peripheral mode, which allows a programmer to access the encryption module through a peripheral interface and is not used during normal operation of the device  10 ; and a datapath mode used in normal operation of the device  10  which incorporates the encryption module in the chain of functions that bridge the SDRAM memory  118  with NAND flash  116 . The datapath mode happens automatically due to a request from an upstream or downstream block. A peripheral encryption module operation cannot be interrupted by a datapath operation and vice versa. This means that a peripheral operation can be held off by a datapath operation, so a status register is provided for polling.  
         [0049]     In datapath mode it is possible to bypass the encryption module such that the data out remains unchanged. There are two datapath keys supplied, along with bypass and select signals. The high level management of the keys occurs in the Serial EEPROM Control (SEC) block  170  illustrated in  FIG. 13 . The encryption module functions as a peripheral, which can be loaded with a key and plaintext, and then launched. Once the status declares the operation is done, the result can be read from the cipher register. Launch can be done automatically or manually. In the automatic case the encryption module launches once a specific data register is written, and this register can be selected in anticipation of a big or little endian processor.  
         [0050]     Under datapath operation there are two keys to choose from when not in bypass: current key and new key. Although encryption and decryption can be done with either key, in practical terms decryption will always be done with the current key. Encryption will normally be done with the current key, but would be done with the new key during datacopy when the user wants to change over to a new key.  
         [0051]     Communication is through a request and acknowledge protocol. The receiver in the device  10  sends a request for data, along with the address of a sector. The server acknowledges the request and provides data. Both the Ack and Req can be pulled low to stall the flow. The receiver asserts a sector frame signal until it has received all the data.  
         [0052]     Requests to the encryption module will always be a perfect multiple of the encryption module packet size of 128 bits, and in the preferred embodiment one NAND sector, which is 512 bytes. Requests from the encryption module will always be in the encryption module packet size.  
         [0053]     The peripheral bus, which communicates with the encryption module through processor interface  200 , uses a dedicated write clock, which saves power over a scheme which just qualifies the high speed system clock. The dedicated read enable signal, and read data bus allow a simple OR of all the peripheral data return buses since they return zero when not selected.  
         [0054]     The encryption module clock enable is set when a datapath request is in force or a peripheral operation is pending and held until the encryption module state machine has found its way back to idle. The other clock-gating domain lies with the datapath request-acknowledge handshake scheme. The acknowledge can be used to either gate the clock to a register, or qualify that clock. Whoever is sending data in response to an acknowledge has this choice. In the encryption module design the clock is qualified.  
         [0055]     The datapath keys are supplied and managed from the Serial EEPROM Controller (SEC) block  170 . The encryption module block is flanked on two sides by the Read/Write Buffer (RWB) and Error Correction Coding (ECC) block. It follows that there must be input and output data buses to each of these blocks, along with the handshaking signals. Dataflow can be stalled by either Ack or Req going low, so to know that a datapath operation is incomplete, a sector frame signal is used to bracket the entire transaction. The sector address consists of address bit  9  and upwards. A four bit address runs in the opposite direction and is used to select a buffer bank within the RWB. The architecture consists of dedicated combinational logic for a round of encryption and a round of decryption. Their contents are similar in size and function, but they are inverses. A round_companion module accepts plaintext input and works with either Round or InvRound iteratively to produce a result, which is latched in the mux block and is accessible in either peripheral or datapath mode.  
         [0056]      FIG. 5  is a table showing address offsets in the processor  18  for the various register fields and registers utilized in the 128-bit AES encryption process used in the preferred embodiment of the invention. These address offsets are included in the AES base address (AES_BASE) in the host processor Configuration Registers Memory. The register fields and registers are respectively defined in FIGS.  6  to  11 .  
         [0057]     The EEPROM control block  170  implements encryption key management. It interfaces with an integrated EEPROM  180  through EEPROM state machine  210  to store and maintain all keys and passwords; and interfaces with the configuration bus through Key Manager state machine  212  for supplying passwords, key seeds and commands, and to read status. The interface to the EEPROM allocates space for the storage of a plurality of sets of keys and passwords, four in the embodiment illustrated, as defined by the SEC control register bit mnemonic KEY_SELECT[ 1 : 0 ] (bit # 4 : 3  in  FIG. 16 ). The Password Compare block  214  authenticates supplied passwords. The Key Compare block  216  verifies written keys. The XOR blocks  218  provide key generation from a supplied key seed, the current key, and the current password. All operations are under commands to the Key Manager state machine  212 .  
         [0058]      FIG. 12  is a state diagram showing encryption and decryption timing in the encryption module. As illustrated in  FIG. 12 , encryption to NAND takes 11 clocks while decryption takes 23 clocks. The discrepancy arises because the key is expanded to 11 subkeys and the order in which they are generated matches the requirement for them during encryption, but is in the opposite order to the sequence needed for decryption. This means they must be pre-expanded into a dual-port register file, taking 11 clocks. The register file&#39;s output is clocked so there is a clock cycle handoff time between the end of writing and the start of reading. Total decryption time is 11 clocks for expansion plus 1 clock handoff, and finally 11 clocks for actual decryption.  
         [0059]     PseudoCode for the Encryption Module Peripheral Mode is as follows:  
                                   define false = 0x0;       define Manual = 0b1; // Manual ENCRYPTION MODULE launch       define Auto = 0b0; // Auto ENCRYPTION MODULE launch       define le_not_be = 0b10; // If the processor splits a word write into two         halfword writes, with le_not_be       // set the halfword write to the upper address (vs. lower address) will         be the one       // that causes launch. Make your choice such that this is the last write.       define d_not_e = 0b100; // decryption.       define peri_enable = 0b1000; // Enable the clock while you use the         ENCRYPTION MODULE or expect nothing.       define key = 0x000102030405060708090a0b0c0d0e0f;       define plain = 0x00112233445566778899aabbccddeeff;       define cipher = 0x69c4e0d86a7b0430d8cdb78070b4c55a;       // &lt;&gt;&lt; Manual Launch &gt;&lt;&gt;       Configure_encryption module_control_reg(Manual | le_not_be |         d_not_e | peri_enable, ENCRYPTION MODULEbase+0x18);       Load_encryption module_plain_reg(cipher, ENCRYPTION         MODULEbase+0x0); // ENCRYPTION MODULE input data         (encryption or decryption) always goes in the       // plain register       Load_encryption module_key_reg(key, ENCRYPTION         MODULEbase+0x10);       Launch_manual(ENCRYPTION MODULEbase+0x1a);       while (get_status(ENCRYPTION         MODULEbase+0x19)&amp;0x4)==false);       plain = retrieve_cipher(ENCRYPTION MODULEbase+0x8);       // &lt;&gt;&lt; Auto Launch &gt;&lt;&gt;       Configure_encryption module_control_reg(Auto| le_not_be |         d_not_e | peri_enable, ENCRYPTION MODULEbase+0x18);       Load_encryption module_key_reg(key, ENCRYPTION         MODULEbase+0x10);       Load_encryption module_plain_reg(cipher, ENCRYPTION         MODULEbase+0x0); // eighth halfword write causes encryption         module to launch.       while (get_status(ENCRYPTION         MODULEbase+0x19)&amp;0x4)==false);       plain = retrieve_cipher(ENCRYPTION MODULEbase+0x8);                  
 
         [0060]     The user is able to access the Serial EEPROM Controller module  170  through the configuration bus interface, as shown in  FIG. 3 . The configuration bus is controllable from the microprocessor controller unit (MCU)  220 , and from the JTAG interface. When the JTAG interface is used, the ENTER_DEBUG command is permitted, and changing of DIS_ENCRYPT in SEC_CTRL is prohibited.  
         [0061]     The following key commands can be executed in the operation of the Serial EEPROM Controller  170  described above: 
    The GET_KEY command is issued when CMD[ 2 : 0 ]=“000” is written to the SEC-CTRL register. This command retrieves the current key and password set from the EEPROM  180 . The key and password set is determined by KEY_SELECT[ 1 : 0 ] found in the SEC-CTRL register.     The COMPARE_KEYS command is issued when CMD[ 2 : 0 ]=“001” is written to the SEC-CTRL register. This command provides the results of two comparisons. It compares the current password with the test password, and it compared the current key with the previously written key. The results are provided in the SEC-STATUS register.     The ADD_KEY command is issued when CMD[ 2 : 0 ]=“010” is written to the SEC-CTRL register. This command forms the new key from the current password, current key, and the software supplied key seed. This new key can be used in the data copy operations. The new password is also supplied by software and will come into affect when the UPDATE command is executed. The current key and current password are retrieved with the GET_KEY command.     The REMOVE_KEY command is issued when CMD[ 2 : 0 ]=“011” is written to the SEC-CTRL register. This command transitions to the Remove key state where the data copy can be completed.     The CHANGE_KEY command is issued when CMD[ 2 : 0 ]=“100” is written to the SEC-CTRL register. This command forms the new key from the current password, current key, and the software supplied key seed. This new key can be used in the data copy operations. The new password is also supplied by software and will come into effect when the UPDATE command is executed. The current key and current password are retrieved with the GET_KEY command. Reading the SEC_STATUS register provides the current key state status.     The UPDATE_KEY command is issued when CMD[ 2 : 0 ]=“101” is written to the SEC-CTRL register. The generated key and password are written into EEPROM  180  at the KEY_SELECT location.    
 
         [0068]     The following states are possible in the operation of the Serial EEPROM Controller (SEC) block  170  described above: 
    Insecure State: The device is powered up in the Insecure state. In this state, a password in not required, and a key is not used to read and write data to NAND flash.     Get Key: This state is entered with the Get_Key command. The current password and key set is read from the EEPROM  180 . If successful, the current key and current password are updated and control is transferred to the key loaded state. Control will be transferred back to the Insecure state if the EEPROM  180  is busy writing, or if an error is encountered.     Key Loaded: This state is entered upon the successful read of the key and password from the EEPROM  180 . A key comparison can be made by loading the compare keys commands, or a new key can be created by loading the add key command.     Compare: In this state, the current password is compared with the test password, and the current key is compared with the key written. Results are available upon completion. If the passwords match, control will be transferred to the Secure state. If the passwords did not match, control will be transferred back to the Insecure state.     Add Key: In this state, software can read in unencrypted data and write back using the newly generated encryption key. Since reading is done in bypass mode, all previously stored encrypted data is lost. Once the data copy operation is complete, the UPDATE_KEY command is used to write the new key and password to the EEPROM  180 . The Insecure state is entered on completion.     Remove Key: The REMOVE_KEY command allows software to read encrypted data with the current key, and to write data back with no key. Once the data transfer is complete, the UPDATE_KEY command is executed to write the new key into EEPROM  180 .     Change Key: The CHANGE_KEY command allows software to read encrypted data with the current key, and to write data back with the new key. Once the data transfer is complete, the UPDATE_KEY command is executed to write the new key into EEPROM  180 .     Update Key: This state is entered with the Update command. The new password and newly form key are written to the EEPROM  180 . On completion, control is transferred to the Insecure state.     Secure: In the Secure state, encrypted data is written to and read from NAND flash using the current key. In this mode, the COMPARE command must be executed. If the passwords match, the Validate state will be entered. If the passwords do not match, the Insecure state is entered.     Compare 2 : This state is entered from the Secure state. In this state, the current password is compared with the test password, and the current key is compared with the key written. Results are available upon completion. If the passwords match, control will be transferred to the Validate state. If the passwords did not match, control will be transferred back to the Insecure state.     Validate: This state ensures that a valid password is present prior to allowing the change of a key, the removal of a key, or the debugging with keys.     Secure Debug: This state asserts the DEBUG_EN signal, allowing the memory controller interface&#39;s debug functions with the encryption module operational. Executing the EXIT_DEBUG command will transition control to the Insecure state.    
 
         [0081]     EEPROM testing is accommodated with the use of the current key, the key written, and the key compare block. A key can be generated and written into the EEPROM  180 . This key can be read out and compared with the key written using the COMPARE command and monitoring using the KEY_STATUS[ 1 : 0 ] found in the SEC-STATUS register. New keys can be formulated by modifying the key seed. Bits can be inverted by seeding a bit position with a logic 1. At no time is the actual key known by software; only the comparison results.  
         [0082]      FIGS. 16A and 16B  show the Control Register table for the Serial EEPROM Controller  170  of  FIG. 13 .The KEY_SELECT function allows for up to four password/key combinations.  FIG. 14  shows the generation of a new password and new key along with redundant passwords and keys. To generate a new password and a new key, steps (a), (b), and (c) are performed As follows: (a) Starting from the Insecure state, software uses the GET_KEY command, along with a specified KEY as determined by KEY_SELECT, to initialize the current password and the current key from the specified password/key slot in EEPROM  180 . At the end of this task, the state machine passes through the Get_Key state and arrives at the Key_Loaded state. (b) While in the Key_Loaded state, software provides a new password (SEC_PW) and a new key_seed (SEC_KS) and then executes the ADD_KEY command to generate a new encryption key. The state machine then arrives in the Add_Key state, where the data copy function (if required) can be executed by software. (c) Once software has completed the data copy function in the Add_Key state, software can then execute the Update command specifying with KEY_SELECT, the location in EEPROM  180  to store the new password and new encryption key. The state machine passes through the Update_Key state and arrives back in the Insecure state.  
         [0083]     To create a redundant copy of the newly created password and encryption key, where the software is configured to do so (for example by enabling a command for same), after creating the newly created password and encryption key the software performs the same sequence of events, (a), (b), and (c), specifying a different EEPROM location in step (c) from the key slots assigned by KEY_SELECT[ 1 : 0 ] (bit # 4 : 3  in  FIG. 16 ). Namely, the GET_KEY command would be used to initialize the current password and the current key from the same EEPROM slot as in (a) as specified by KEY_SELECT. While in the Key Loaded state, software would provide the same new password (SEC_PW) and same key seed (SEC_KS) as provided in (b). In the Add_Key state, software would specify a different EEPROM location then that specified in (c) by configuring KEY_SELECT with a different redundant slot and executing the UPDATE_KEY command.  
         [0084]     If the system software detects that the current key may be corrupted, a redundant current key and current password are automatically retrieved from one of the other key slots in EEPROM  180  using the GET_KEY command. Software is able to detect a corrupted encryption key by detecting a faulty data signature that could be placed in the data, or by the detection of faulty java script execution. The GET_KEY command is issued when the software automatically writes CMD[ 2 : 0 ]=“000” to the SEC control register, to retrieve the current key and password set. The key and password set is determined by KEY_SELECT[ 1 : 0 ] found in the SEC control register ( FIG. 16 ). All passwords and keys are stored in EEPROM  180 , and optionally the software can be programmed to attempt to overwrite the faulty location.  
         [0085]     The extra key slots in EEPROM  180  could also be used for different purposes; for example, a primary password/key can be stored for decryption of private system data; a third party software application password/key can be stored in another location for suppliers that want to keep data (e.g. JAVA scripts) confidential while at the same time allowing users execute the script; a separate user-selected data password/key for emails, appointments, etc. can be stored in a third location; and any other password/key that may be useful or desirable in any particular situation can be stored in a fourth location. In this embodiment the location of each particular key is mapped and the key-password set invoked by the software when the data associated with the particular key is presented to the EEPROM control block  170 . The system and method of the invention thus provides the additional advantage of allowing for different levels of encryption for different sets of data on a data processing device  10 .  
         [0086]     Various embodiments of the system having been thus described in detail by way of example, it will be apparent to those skilled in the art that variations and modifications may be made without departing from the invention.