CryptoMemory. Application Note. Programming the CryptoMemory Device for Embedded Applications

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1 Programming the ryptomemory Device for Embedded pplications ryptomemory provides a cost-effective solution for securing sensitive data in nonvolatile memory within any system. Various security features are built into rypto- Memory, and the user has the option of defining which features will be used for different data elements that may be stored. o prepare ryptomemory for use, several registers are programmed to indicate the selected security features to be used, and the appropriate passwords and keys are loaded into the device. Very little programming is needed to initialize the device. Depending on the options selected, only a few bytes up to a maximum of 2 bits of the configuration zone need to be programmed. his application note describes the process of organizing data and determining security settings and the proper sequence for writing to ryptomemory. his initial programming, or initialization, is typically done before the device is mounted to the board in the final application. he design of the application will determine what data is written during this initialization of the ryptomemory device. ryptomemory pplication Note 5051 MEM 01/04 1

2 Default Device onfiguration Determine Initial Data and ecurity ettings Initial Data ecurity ettings ryptomemory devices are fully tested at tmel. ll functions are verified, and all memory locations are tested and then set to default values. hese values are: User Zones ll user zones (4, 8, or 16) are programmed to all ones ($FF) throughout the entire zone. onfiguration Zone: nswer to Reset his field of the configuration zone is programmed to a preset value. he value programmed includes two bytes that indicate the memory density. onfiguration Zone: Fab ode his field is programmed to a preset value. onfiguration Zone: Lot History ode his field is programmed to a preset value. his field is locked and cannot be changed after leaving tmel. onfiguration Zone: ecure ode his field, also known as the Write 7 Password, is programmed to a preset value. Remaining onfiguration Zone ll remaining fields in the configuration zone are programmed to all ones ($FF). his includes all access and password key registers, all encryption keys, and all passwords except the secure code. In this configuration, access to all user zones is open and free. he first step in initializing ryptomemory is to determine what data will be stored in the device and the structure for that data. Data may be thought of as different files, and these files will need to be organized within the various user zones of ryptomemory. he security requirements for each file should be determined. Files with identical security requirements may be placed in the same user zone. If a file or group of files requires more than one user zone, multiple user zones may be set with the same security requirements to accommodate the large data files. In most cases, the design of the application will determine the data structure and security settings for ryptomemory. With the data structure established, determine what data should be written to the device during the initial programming. his is typically data that needs to be in the device before it is installed on the board. In addition to the user zones, there is also a 4-byte card manufacturer code and a 16-byte issuer code that may be programmed in the configuration zone as part of initialization. he next step is to determine the security requirements of the application and how each zone of the ryptomemory needs to be protected. Each user zone has one access register and one password key register, allowing the security requirements for each zone to be set independently. If multiple zones are required to store large data files, they may be set to the same security requirements. ryptomemory offers a variety of security options; these options can be explored using the ryptomemory Evaluation it ( E). ecurity options are also documented in the ryptomemory Embedded pecification, available under ND. Briefly, the available security options are: Open or free access: no restrictions for read or write of a user zone. One-time programmable: the data programmed during initialization is locked and may not be changed. Program only: the data programmed during initialization may only be changed from a logic value "1" to logic "0" on a bit-by-bit basis. his can be used for a countdown function. Write protect: the data programmed during initialization may be protected byte by byte within a user zone. 2 Programming ryptomemory Device 5051 MEM 01/04

3 Programming ryptomemory Device Password protection: separate passwords may be required for read and/or write privileges to the user zone; eight separate password sets are available. uthentication protection: a successful authentication sequence is required for read and/or write privileges to the user zone; four separate key sets are available. Encryption required: after a successful authentication, data is required to be encrypted for both read and write operations to the user zone. he above list is not exhaustive, and various combinations of these security options may be implemented. Writing to ryptomemory Write Data to User Zones Unlock onfiguration Zone Write Data to onfiguration Zone Once the data structure, initial data, and security settings have been established, this information must be written into the ryptomemory device. his is accomplished by following the sequence below. Once the data is written and the security fuses are set, the device is ready for use in the end application. Details of the commands used and a simple example are included in this document. In the default configuration from tmel, all user zones have free access rights. Writing initial data into the user zones should be done before setting security configurations. Use the et User Zone command and Write User Zone command to write initial data into the user zones. he Read User Zone command may be used to verify the data written. Before any data can be written to the configuration zone, it must be unlocked by presenting the correct security code (Write 7 Password). Use the Verify ecure ode command with the proper password supplied by tmel to unlock the configuration zone. Use the Read onfiguration Zone command to read back the security code at address $E9 for verification that the configuration zone has been unlocked. Data contained in the configuration zone is divided into four types of information: ODE: hese include the answer to reset value, fabrication zone, identification number, card manufacturer zone, and issuer zone. he information programmed in these areas may be used by the application as determined by the application developer. he answer to reset and fabrication zone codes are programmed to default values by tmel but may be modified. hese codes are all write protected once all security fuses have been set. REGIER: For each user zone, there is one 8-bit access register and one 8-bit password/key register. hese registers are used to define the security requirements for each user zone. In addition, there is one device configuration register that determines several options affecting the security of all user zones globally. EY: here are four sets of keys (ecret eeds) used for authentication and four sets of keys (ession eys) used for encryption; each key is 64 bits long. here are also four initial cryptogram values that may be defined and one identification number used with all four sets of keys. PWORD: here are eight sets of passwords; each set consists of a read access password and a write access password. Writing this data is accomplished by performing the Write onfiguration Zone command at the appropriate location. he Read onfiguration Zone command may be used to verify the data written. Please consult the ryptomemory Embedded pecification for proper memory address within the configuration zone for each data field. s soon as 5051 MEM 01/04 3

4 values are written to the registers, keys, and passwords, they become effective in determining the security of the user zones. et ecurity Fuses hree security fuses protect the information contained in the configuration zone. FB FUE: his fuse protects the answer to reset value and the fabrication zone. hese areas are write-protected and cannot be changed once the fab fuse is set. M FUE: his fuse protects the card manufacturer zone. his area is write-protected and cannot be changed once the M fuse is set. PER FUE: his fuse protects the rest of the configuration zone. he issuer code is write-protected and cannot be changed once the PER fuse is set. ll registers, keys, and passwords are write-protected once the PER fuse is set. Modifications to these areas are only permitted by the internal logic; further detail may be found in the ryptomemory Embedded pecification. One exception is the eight password sets. Once a write password is properly presented, only the read and write password in that set can be modified by using the Write onfiguration Zone command. Once the PER fuse is set, the secure code (Write 7 Password) will no longer give access to the configuration zone. hese three fuses must be set in the order listed above (FB, then M, then PER). he Write Fuse command is used to set each of the three fuses individually. he ddress 2 value for setting each fuse is shown in able 1 below. able 1. Write Fuse Fuse ID Fuse ddress 2 FB $06 M $04 PER $00 he Read Fuse Byte command may be used at any time to check the status of all three fuses. able 2. Read Fuse Byte Returned Data Fuse ondition Fuse Byte No Fuses et XXXX 0111 FB et XXXX 0110 FB, M et XXXX 0100 FB, M, PER et XXXX Programming ryptomemory Device 5051 MEM 01/04

5 Programming ryptomemory Device ynchronous ommunications ryptomemory communicates by using a synchronous two-wire serial protocol. his two-wire serial interface is identical to that used on tmel's 24xxx family of serial EEPROMs but with a larger unique command set to support the various security functions. ynchronous communications may be performed with a clock speed of up to 1.5 MHz. ommand et able 3. Initialization ommand et here are a total of 16 commands for communicating with ryptomemory. Only eight commands are required for the initial programming. he command set used for initializing ryptomemory is shown in able 3. ommand ddr 1 ddr2 N Data (N) Write User Zone $B0 addr addr N (1) N bytes Read User Zone $B2 addr addr N ystem Write ystem Read Write onfig Zone $00 addr N (1) Write Fuses $B4 $01 fuse ID $00 et User Zone $03 zone $00 Read onfig Zone $00 addr N $B6 Read Fuse Byte $01 $00 $01 Verify ecure ode $B $07 $00 $03 3-byte password Note: For , N < $10 For , N < $80 ommand Format Each command sent to ryptomemory must have 4 bytes: ommand, ddress 1, ddress 2, and Parameter N. he last byte, N, defines the number of any additional data bytes to be sent to or received from the ryptomemory device. Each command ends with a stop condition, for proper operation acknowledge polling must be performed after each command until the ryptomemory device indicates it is ready for the next command. he formats for the three types of commands used for the initial programming are shown in Figures 1 3. Figure 1. Write ommand with N = 0 (Write Fuses, et User Zone) N bytes R OMMND DDRE 1 DDRE 2 PRMEER N O P Figure 2. Write ommand with N Bytes (Write User Zone, Write onfig Zone, Verify ecure ode) R OMMND DDRE 1 DDRE 2 PRMEER N D (1).... D (N) O P 5051 MEM 01/04 5

6 Figure 3. Read ommand with N Bytes (Read User Zone, Read onfig Zone, Read Fuse Byte) R OMMND DDRE 1 DDRE 2 PRMEER N D (1).... D (N) N O P Initialization Example he is used for this example. small pattern is written into each of the four user zones. ecurity for each of the four user zones and the associated register values are shown in able 4. imple values for codes, keys, and passwords are used. able 4. ecurity ettings ( Example) User Zone Data ecurity Requirements ccess Register Password/ ey Register 0 Zone 0 Data None $FF $FF 1 Zone 1 Data Read/Write Password (et 1) $7F $F9 2 Zone 2 Data Read/Write uthentication (et 2) $DF $BF 3 Zone 3 Data Read/Write Password (et1), Read/Write uthentication (et 2) with Encryption Required $57 $B9 he following example shows the two-wire commands sent to the ryptomemory device for the purpose of initializing the device for use on a board. he flow is consistent with the steps described in this application note, and comments have been added as indicated with an asterisk (*). * Initialization Example *WRIE D O UER ZONE *et User Zone 0 B *Write data = Zone 0 Data B B 5 6F 6E *et User Zone 1 B *Write data = Zone 1 Data B B 5 6F 6E *et User Zone 2 B *Write data = Zone 2 Data B B 5 6F 6E *et User Zone 3 6 Programming ryptomemory Device 5051 MEM 01/04

7 Programming ryptomemory Device B *Write data = Zone 3 Data B B 5 6F 6E *UNLO ONFIGURION ZONE B FF FF FF *WRIE ODE IN ONFIGURION ZONE *Write ard Mfg ode = P001 B4 00 0B *Write Identification Number = B *Write Issuer ode = ION 035 B F 4E *WRIE REGIER IN ONFIGURION ZONE *Write Registers R1/PR1 = 7F F9, R2/PR2 = DF BF, R3/PR3 = 57 B9 B F F9 DF BF 57 B9 *WRIE EY IN ONFIGURION ZONE *Write i for set 2 = B *Write Gc for set 2 = 5B4F9E4B5098BE7 B B 4F 9 E4 B5 09 8B E7 *WRIE PWORD IN ONFIGURION ZONE *Write Passwords, read 7 = , write 7 = B4 00 B FF *RED ENIRE ONFIGURION ZONE O VERIFY B F0 *Device Response: 3B B FF FF 8 D B FF FF FB FF FF 7F F9 DF BF 57 B9 FF FF FF FF FF FF FF FF F 4E FF FF FF FF FF FF FF FF FF 5B 4F 9 E4 B5 09 8B E7 D8 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF MEM 01/04 7

8 *E EURIY FUE *et FB Fuse B *et M Fuse B *et PER Fuse B *Read Fuse Byte = X0 B *Device Response: 00 In-system Programming he process described in this application note and the example given is intended for programming of the ryptomemory device prior to mounting on the board. While this will simplify the operation of ryptomemory in the end application, it is also possible to perform this initial programming in the final system. ll the commands described here may be executed by the system into which ryptomemory is incorporated. But to utilize the security features of ryptomemory, this process of initialization must be performed before any information can be secured within the ryptomemory device. 8 Programming ryptomemory Device 5051 MEM 01/04

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