ATECC608A datasheet(36/81 Pages) MICROCHIP

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Table 5-27. Input Parameters SHA HMAC Mode

Opcode

(1 Byte)

Mode

(1 Byte)

Param2

(2 Bytes)

Data

(Varies by Mode)

Description

0x47

0x04

0x00 0[slot]

0 bytes

HMAC Start mode and include a key from a data slot

0x04

0xFF FF

0 bytes

HMAC Start mode and include a key from TempKey

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 5-28. Output Response SHA256 Standard

Name

Mode

Size

Description

Response

0x04, 0x01

1 byte

0x00 if successful, otherwise an error code is received

0x02, 0x42, 0xC2

1 byte

32 bytes

If Error Code

HMAC Digest upon success

5.1.8.3

SHA - Context Switching

Context switching allows for the generation of a digest to be interrupted to do other functions or to generate other

digests. Context switching can be used only in the SHA256 Digest mode, so it can only occur after a SHA Start has

been issued and prior to a SHA Finalize command. Context switching may happen multiple times during the

course of a digest generation.

Context switching involves two phases:

Read_Context - Reads a variable length context from the ATECC608A-TNGLoRaWAN while leaving the

context valid within the chip. The total length of the output data parameter is always from 40 to 99 bytes and

can either be determined from the length field in the output packet or computed as 40 plus the Least

Significant six bits of the first byte in the output.

Write_Context - Writes a SHA256 context from the host to the ATECC608A-TNGLoRaWAN to allow

subsequent update operations to be completed. This context must have previously been read from the chip

with the Read_Context mode. The ATECC608A-TNGLoRaWAN determines the size of the context from the

first 4 bytes of the data parameter.

After the context has been read, the device may perform any other operations as required. Upon completion of the

other operations, the context may be written back to the ATECC608A-TNGLoRaWAN and the SHA256 Digest

generation process may continue until it has completed.

Table 5-29. Input Parameters SHA Context Switching

Opcode

(1 Byte)

Mode

(1 Byte)

Param2

(2 Bytes)

Data

(Varies by Mode)

Description

0x47

0x06

0x00 00

0 bytes

Read the current context

0x07

0x00 [ByteCount]

40 to 99 bytes

Restore the current context from the prior session

ATECC608A-TNGLoRaWAN

Device Commands

Complete Datasheet

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