ATECC608A datasheet(35/81 Pages) MICROCHIP

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5.1.8.1

SHA - SHA256 Digest

The SHA command utilizes the SHA256 Hash algorithm for computing the hash of a message. The primary input to

the command is the actual message. The message is submitted to the device in blocks of 1 to 64 bytes. The following

procedure is used when no context switching is required:

Issue the SHA command in Start mode. No message is included.

Issue the SHA command in Update mode with 1 to 64 bytes of the message.

Repeat step 2 until the total number of bytes of the message have been submitted.

Issue the SHA command in End mode to complete the SHA256 calculation.

Table 5-25. Input Parameters SHA Standard Mode

Opcode

(1 Byte)

Mode

(1 Byte)

Param2

(2 Bytes)

Data

(Varies by Mode)

Description

0x47

0x00

0x00 00

0 bytes

Start mode

0x01

0x00 [ByteCount] 1 to 64 bytes

Update mode

0x02

0x00 [ByteCount] 0 to 64 bytes

Finalize mode: Digest placed in Output Buffer and

TempKey

0x42

0x00 [ByteCount]

Finalize mode: Digest placed in Output Buffer and

Message Digest Buffer

0xC2

0x00 [ByteCount]

Finalize mode: Digest placed in Output Buffer only

Table 5-26. Output Response SHA256 Standard

Name

Mode

Size

Description

Response

0x00, 0x01

1 byte

0x00 if successful, otherwise an error code is received

0x02, 0x42, 0xC2

1 byte

32 bytes

If error code

SHA256 Digest

5.1.8.2

SHA - HMAC Digest

The SHA command may be used to calculate an HMAC Digest instead of an SHA256 Digest. The procedure is

essentially the same but requires the use of an internal key and the use of HMAC_START instead of START.

The following procedure is used when no context switching is required:

Issue the SHA command in HMAC_Start mode with key location indicated. No message is included.

Issue the SHA command in Update mode with 1 to 64 bytes of the message.

Repeat step 2 until the total number of bytes of the message has been submitted.

Issue the SHA command in End mode to complete the HMAC Digest calculation.

ATECC608A-TNGLoRaWAN

Device Commands

Complete Datasheet

DS40002154B-page 35

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