ATSHA204 datasheet(46/65 Pages) ATMEL

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Atmel ATSHA204 [DATASHEET]

8740D

−CRYPTO−3/12

8.8

MAC Command

Computes a SHA-256 digest of a key stored in the device, a challenge, and other information on the device. The output of this

command is the digest of this message. If the message includes the serial number of the device, the response is said to be

diversified.

The normal command flow to use this command is as follows:

Run Nonce command to load input challenge and optionally combine it with a generated random number. The result

of this operation is a nonce stored internally on the device.

Optionally run GenDig command to combine one or more stored EEPROM locations in the device with the nonce.

The result is stored internally in the device. This capability permits two or more keys to be used as part of the

response generation.

Run this MAC command to combine the output of step one (and step two if desired) with an EEPROM key to

generate an output response (or digest).

Alternatively, data in any slot (which does not have to necessarily even be secret) can be accumulated into the response

through the same GenDig mechanism. This has the effect of authenticating the value stored in that location.

Table 8-22. Input Parameters

Name

Size

Notes

Opcode

MAC

0x08

Param1

Mode

Controls which fields within the device are used in the message.

Param2

KeyID

Which internal key is to be used to generate the response.

Bits 0:3 only are used to select a slot but all 16 bits are used in the SHA-256 message.

Data

Challenge

0 or 32

Input portion of message to be digested, ignored if Mode:0 is one.

Table 8-23. Output Parameter

Name

Size

Notes

Response

SHA-256 digest

The message that will be hashed with the SHA-256 algorithm consists of the following information:

32 bytes key[KeyID] or TempKey (See Table 8-24)

32 bytes Challenge or TempKey (See Table 8-24)

1 byte

Opcode (always 0x08)

1 byte

Mode

2 bytes Param2

8 bytes OTP[0:7] (or zeros, see Table 8-24)

3 bytes OTP[8:10] (or zeros, see Table 8-24)

1 byte

SN[8] bits (never zeroed out)

4 bytes SN[4:7] bits (or zeros, see Table 8-24)

2 bytes SN[0:1] (never zeroed out)

2 bytes SN[2:3] (or zeros, see Table 8-24)

ATSHA204 Datasheet(PDF) 46 Page - ATMEL Corporation

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