ATECC508A datasheet(84/109 Pages) MICROCHIP

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HMACstart: Initialization of the HMAC calculation engine and initialization of the SHA context in

memory. A stored key legal for use with SHA operations must be specified. This mode does not

accept any message bytes.

Update: Along with SHA(Public), identical to SHA-256.

HMACend: The HMAC calculation is completed re-using the key value from HMACstart, and the

resulting digest is placed into the output buffer. It is also stored in the TempKey register. From 0

bytes to 63 bytes may be passed to the device for this mode.

Table 9-47. Input Parameters

Name

Size

Notes

Opcode SHA

0x47

Param1 Mode

Bits

7-3:

Must be zero.

Bits

2-0:

000 (Start) = Load TempKey with the initialization value for SHA2-56. No

message bytes are accepted (Length must be zero).

001 (Update) = Add 64 bytes in the message parameter to the SHA context.

010 (End) = Complete the SHA-256 computation and load the digest into

TempKey and the output buffer. Up to 63 message bytes are accepted

(Length must be 0 through 63 inclusive.)

011 (Public) = Add 64 bytes of a public key stored in one of the Data zone

slots to the SHA context. Param2 should contain the slot ID of the public key,

and the command will return an error if the slot contains anything other than a

public key. No further bytes should appear in the input stream (Message size

is zero).

100 (HMACstart) = Load TempKey with the initialization value for SHA2-56.

Length field specifies the key to be used for the HMAC calculation. No

message bytes are accepted.

101 (HMACend) = Complete the HMAC/SHA-256 computation and load the

digest into TempKey and the output buffer. Up to 63 message bytes are

accepted (Length must be 0 through 63 inclusive.)

Param2 Length

Number of bytes in the Message parameter.

KeyID for the HMAC key if Mode is “HMACstart”.

Data

Message 0 – 64 Up to 64 bytes of data to be included into the hash operation.

Table 9-48. Output Parameter

Name

Size

Notes

Response 1 or 32 The SHA256 digest if Mode is End(0x02) or HMACend(0x05), otherwise 0x00 for success or

an error code.

9.18

Sign Command

The Sign command generates a signature using the ECDSA algorithm. The ECC private key in the slot

specified by KeyID is used to generate the signature.

The message may be externally or internally generated, as noted below:

ATECC508A

Security Commands

Datasheet Complete

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