ATECC608A datasheet(39/81 Pages) MICROCHIP

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Table 5-37. Asymmetric Cryptography Commands

Command Name Opcode

Description

ECDH

0x43

Generates an ECDH pre-master secret using the stored private key and input public

key.

GenKey

0x40

Generates an ECC private key or optionally generates an ECC public key from the

stored private key.

Sign

0x41

Signs an internal or external message digest using an ECC private key with an

ECDSA signature calculation.

Verify

0x45

Verifies an internal or external message digest using an ECC public key with an

ECDSA verify calculation.

5.2.1

ECDH Command

The ECDH command is used to generate a shared secret between two devices. By passing an ECC public key from

another device and combining with the ECC private key stored in a slot or with an ephemeral key stored in TempKey

and doing the reverse on the other device, both devices will generate the same shared master secret. This can then

be further combined with other common data in both sides to generate a shared session key between the devices.

The KDF command is often used with TLS sessions to further diversify the shared secret.

5.2.1.1

ECDH - Stored Key

The ECDH command may use an internal data slot as its ECC private key source. The slot must have its access

policies configured such that the slot is an ECC private key and that the ECDH command is allowed. Access policies

may also specify whether or not the output will be stored, encrypted or allow the command itself to determine whether

the output is stored or encrypted. The IO protection key is used when encryption is required. Encryption can only

occur when data is output to the output buffer.

For the ATECC608A-TNGLoRaWAN, the ECDH command may be run using the ECC private keys stored in Slot 1.

Table 5-38. Input Parameters ECDH Stored Key

Opcode

(1 Byte)

Mode

(1 Byte)

KeyId

(2 Bytes)

Data

Description

Data 1

(32 Bytes)

Data 2

(32 Bytes)

0x43

0x0C

0x00 0[Slot] X component of

public key

Y component of

public key

• Results go to the output buffer

• Output is in the clear(1)

0x0E

0x00 0[Slot] X component of

public key

Y component of

public key

• Results go to the output buffer

• Output is encrypted

0x08

0x00 0[Slot] X component of

public key

Y component of

public key

• Results stored in TempKey

• Output is available for other

operations but is not directly

accessible.

Note:

When the ChipOptions.ECDHPROT value is 1, then the output of the ECDH command will be encrypted in this

mode. For the ATECC608A-TNGLoRaWAN the ECDHPROT field is set to 0 and encryption will be dependent

upon the mode of the ECDH command.

Table 5-39. Output Response ECDH Stored Key

Name

Mode

Size

Description

Response

0x0C or 0x0E

1 byte

Error code if command fails

ATECC608A-TNGLoRaWAN

Device Commands

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