ATECC508A datasheet(81/109 Pages) MICROCHIP

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Table 9-41. Output Parameter

Name

Size

Notes

Success

Upon successful completion, ATECC508A returns a value of zero.

9.15

Random Command

The Random command generates a random number for use by the system.

Random numbers are generated through a combination of the output of a hardware RNG and an internal

seed value stored in the EEPROM or SRAM. The external system may choose to update the internally

stored EEPROM seed value prior to the generation of the random number as part of the execution of the

Nonce or Random command.

The Random command does not provide a mechanism to integrate an input number with the internal

stored seed. If this functionality is desired, then the system should use the Nonce command and ignore

the generated Nonce.

Prior to the configuration zone being locked, the RNG produces a value of 0xFF, 0xFF, 0x00,

0x00, 0xFF, 0xFF, 0x00, 0x00 to facilitate testing.

Note: The same internal stored seeds are used for both the Nonce and Random commands.

Table 9-42. Input Parameters

Name

Size

Notes

Opcode

RANDOM

0x1B

Param1

Mode

Controls the mechanism of the internal RNG and seed update.

Param2

Zero

Must be 0x0000.

Data

Ignored

—

Table 9-43. Output Parameter

Name

Size

Notes

RandOut

The output of the RNG.

Table 9-44. Mode Encoding

Bits

Meaning

7–1 Must be zero.

0 = Automatically update EEPROM seed only if necessary prior to random number generation.

Recommended for highest security.

1 = Generate random number using existing EEPROM seed, do not update EEPROM seed.

9.16

Read Command

The Read command reads words (one four byte word or an 8-word block of 32 bytes) from one of the

memory zones of the device. The data may optionally be encrypted before being returned to the system.

See Section Address Encoding for data zone byte and word addressing information.

ATECC508A

Security Commands

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