ATECC508A datasheet(72/109 Pages) MICROCHIP

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Table 9-23. Input Parameters

Name Size

Notes

Opcode HMAC

0x11

Param1 Mode

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

Param2 KeyID

The internal key is to be used to generate the response. Bits 3:0 are only used to select a

slot; however, all 16 bits are used in the HMAC message.

Data

—

Table 9-24. Output Parameter

Name

Size

Notes

Response

HMAC digest.

The HMAC digest is computed using the key at KeyID as the HMAC key over a message consisting of

the following information:

32 bytes

Zeros

32 bytes

TempKey

1 byte

Opcode (always 0x11)

1 byte

Mode

2 bytes

KeyID

8 bytes

Zeros

3 bytes

Zeros

1 byte

SN<8> (never zeroed out)

4 bytes

SN<4:7> (or zeros, see Mode Encoding)

2 bytes

SN<0:1> (never zeroed out)

2 bytes

SN<2:3> (or zeros, see Mode Encoding)

Table 9-25. Mode Encoding

Bits Meaning

Must be zero.

0 =

48 Message bits corresponding to SN<2:3> and SN<4:7> are set to zero.

1 =

Include the 48 bits SN<2:3> and SN<4:7> in the message.

5–3 Must be zero.

The value of this bit must match the value in TempKey.SourceFlag or the command will return an error.

1–0 Must be zero.

ATECC508A

Security Commands

Datasheet Complete

DS20005927A-page 72

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