ATSHA204A datasheet(48/93 Pages) MICROCHIP

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Name

Size Notes

0: Slot<SlotID>

1: TempKey

Bit 0:

Source of the second 32-bytes of the SHA message.

0: ClientChal parameter

1: TempKey

Param2 SlotID

Which internal slot is to be used to generate the response. Only bits 3-0 are used.

Data1

ClientChal

Challenge sent to Client. (Must appear in the input stream).

Data2

ClientResp

Response generated by the Client.

Data3

OtherData

Remaining constant data needed for response calculation.

Table 8-9. Output parameter

Name Size Notes

Result

Returns a 1-byte value of zero if ClientResp matches the internally computed digest, one if there is a

mismatch.

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

32 bytes

key<SlotID> or TempKey (depending on the mode)

32 bytes

ClientChal or TempKey (depending on the mode)

4 bytes

OtherData<0:3>

8 bytes

OTP<0:7> or zeros (depending on the mode)

3 bytes

OtherData<4:6>

1 byte

SN<8>

4 bytes

OtherData<7:10>

2 bytes

SN<0:1>

2 bytes

OtherData<11:12>

The purpose of OtherData is to construct a SHA-256 message that matches identically to the MAC

message that was used to produce ClientResp. By comparing the message used for the SHA-256 of the

MAC command, OtherData is parsed as follows:

Table 8-10. OtherData

Size CheckMac

MAC

Notes

OtherData<0>

OpCode

MAC OpCode = 0x08

OtherData<1>

Mode

Mode used for MAC command.

OtherData<2:3>

SlotID

SlotID used for MAC command.

OtherData<4:6>

OTP<8:10>

OTP<8:10> used for MAC command. (Useful for Legacy.)

OtherData<7:10>

SN<4:7>

SN<4:7> used for MAC command. (Unique per Client.)

OtherData<11:12>

SN<2:3>

SN<2:3> used for MAC command. (Unique per Client.)

ATSHA204A

Security Commands

DS40002025A-page 48

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