ATSHA204A datasheet(51/93 Pages) MICROCHIP

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Figure 8-2. Data Flow for DeriveKey Command

Match

Parent

Key

Target

Key

SHA

(AUTH)

Input MAC

SHA

(Device)

Mode

Source

Key

Nonce

8.5.7

DevRev Command

DevRev command returns a single four-byte word representing the revision number of the device.

Software should not depend upon this value because it may change from time to time.

Table 8-13. Input Parameters

Name

Size

Notes

Opcode

DevRev

0x30.

Param1

Mode

Must be zero.

Param2

—

Must be zero.

Data

—

Table 8-14. Output Parameters

Name

Size

Notes

Success

The current device revision number.

8.5.8

GenDig Command

The GenDig command uses SHA-256 to combine a stored value with the contents of TempKey, which

must have been valid prior to the execution of this command. The stored value can come from one of the

data slots, either of the OTP pages, either of the first two pages of the Configuration zone, or retrieved

from the hardware transport key array. The resulting digest is retained in TempKey and can be used in

one of three ways as follows:

It can be included as part of the message used by the MAC, CheckMac, or HMAC commands.

Because the MAC response output incorporates both the data used in the GenDig calculation and

the secret key from the MAC command, it serves to authenticate the data stored in the Data and/or

OTP zones.

ATSHA204A

Security Commands

DS40002025A-page 51

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