ATSGA204A View Datasheet(PDF) - Microchip Technology
Part Name
Description
MFG CO.
'ATSGA204A' PDF : 93 Pages View PDF
ATSHA204A
Security Commands
If zone is Data and SlotConfig<SlotID>.CheckOnly is one, the SHA-256 message body used to create the
resulting new TempKey consists of the following bytes:
32 bytes
4 bytes
1 byte
2 bytes
25 bytes
32 bytes
Slot<SlotID>
OtherData
SN<8>
SN<0:1>
Zeros
TempKey.value
In all other cases, the message use to create TempKey is as follows:
32 bytes
1 byte
1 byte
2 bytes
1 byte
2 bytes
25 bytes
32 bytes
Config<SlotID> or OTP<SlotID> or Data.slot<SlotID> or TransportKey<SlotID>
Opcode
Param1
Param2
SN<8>
SN<0:1>
Zeros
TempKey.value
8.5.9
HMAC Command
The HMAC command computes an HMAC/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 output of the HMAC algorithm
computed over this key and 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:
1. Run the 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.
2. Optionally run the GenDig command to combine one or more stored EEPROM locations in the
device with the nonce. The result is stored internally in the device.
3. Run this HMAC command to combine the output of step one (and Step 2 if desired) with an
EEPROM key to generate an output response.
Step 2 addresses multiple use models. If the data in the EEPROM is a key, GenDig has the effect of
authenticating the challenge with multiple secret keys. Alternatively, if the contents of the slot are data
(which do not have to necessarily even be secret), GenDig has the effect of authenticating the value
stored in that location.
Table 8-17. Input Parameters
Name Size Notes
Opcode HMAC 1 0x11.
Param1 Mode
Param2 SlotID
1 Controls which fields within the device are used in the message.
2 Which key is to be used to generate the response.
© 2018 Microchip Technology Inc.
DS40002025A-page 53
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