ATSHA204 datasheet(43/65 Pages) ATMEL

43 / 65 page

Atmel ATSHA204 [DATASHEET]

8740D

−CRYPTO−3/12

8.6

HMAC Command

Computes a 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:

Run 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.

Optionally run GenDig command to combine one or more stored EEPROM locations in the device with the nonce.

The result is stored internally in the device.

Run this HMAC command to combine the output of steps one (and step two if desired) with an EEPROM key to

generate an output response.

Step two 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 does 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

0x11

Param1

Mode

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

Param2

KeyID

Which 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 HMAC message.

Data

Table 8-18. 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

OTP[0:7] (or zeros, see Table 8-19)

3 bytes

OTP[8:10] (or zeros, see Table 8-19)

1 byte

SN[8] bits (never zeroed out)

4 bytes

SN[4:7] bits (or zeros, see Table 8-19)

2 bytes

SN[0:1] (never zeroed out)

2 bytes

SN[2:3] (or zeros, see Table 8-19)

ATSHA204 Datasheet(PDF) 43 Page - ATMEL Corporation

ATSHA204 Datasheet(HTML) 43 Page - ATMEL Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

Datasheet Download

Link URL