ATSHA204 ATMEL [ATMEL Corporation], ATSHA204 Datasheet - Page 46

• Manufacturer Part Number: ATSHA204
• Description: Atmel CryptoAuthentication
• Manufacturer: ATMEL [ATMEL Corporation]

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:
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
Table 8-23. Output Parameter
The message that will be hashed with the SHA-256 algorithm consists of the following information:
Opcode
Param1
Param2
Data
Name
Response
1.
2.
3.
32 bytes key[KeyID] or TempKey (See Table 8-24)
32 bytes Challenge or TempKey (See Table 8-24)
1 byte
1 byte
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
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)
Run Nonce command to load input challenge and optionally combine it with a generated random number. The result
Optionally run GenDig command to combine one or more stored EEPROM locations in the device with the nonce.
Run this MAC command to combine the output of step one (and step two if desired) with an EEPROM key to
of this operation is a nonce stored internally on the device.
The result is stored internally in the device. This capability permits two or more keys to be used as part of the
response generation.
generate an output response (or digest).
Name
MAC
Mode
KeyID
Challenge
Opcode (always 0x08)
Mode
SN[8] bits (never zeroed out)
0 or 32
Size
Size
32
1
1
2
Notes
0x08
Controls which fields within the device are used in the message.
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.
Input portion of message to be digested, ignored if Mode:0 is one.
Notes
SHA-256 digest
Atmel ATSHA204 [DATASHEET]
8740D−CRYPTO−3/12
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