ATECC508A datasheet(9/109 Pages) MICROCHIP

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be used to combine two keys with the challenge, which is useful when there are multiple layers of

authentication to be performed.

In a host-client configuration where the host (for instance, a mobile phone) needs to verify a client (for

instance, an OEM battery), there is a need to store the secret in the host in order to validate the response

from the client. The CheckMac command(see Section CheckMac Command) allows the device to

securely store the secret in the host system and hides the correct response value from the pins, returning

only a yes or no answer to the system.

Finally, the hash combination of a challenge and secret key can be kept on the device and XORed with

the contents of a slot to implement an encrypted Read command(see Section Read Command), or it can

be XORed with encrypted input data to implement an encrypted Write command(see Section Write

Command).

All hashing functions are implemented using the industry-standard SHA-256 secure hash algorithm,

which is part of the latest set of high-security cryptographic algorithms recommended by various

government agencies and cryptographic experts(see Section SHA-256 and Section HMAC/SHA-256).

The ATECC508A employs full-sized 256-bit secret keys to prevent any kind of exhaustive attack.

1.4

Commands

The ATECC508A is a command-based device which receives commands from the system, executes

those commands, and then returns a result or error code. Within this document, the following

nomenclature is used to describe the various commands:

•

Security Commands:

Described in Section Security Commands. This group of commands generally access the EEPROM

space and/or perform cryptographic computation. These commands are indicated with a special

font in this document (e.g. GenDig) and are available from all interfaces.

•

Cryptographic Commands:

This subset of the security commands includes all the ECC commands which access the hardware

ECC accelerator (GenKey, Sign, ECDH, and Verify) and the SHA commands which access the

hardware SHA accelerator (CheckMac, DeriveKey, GenDig, HMAC, MAC, SHA, and Nonce).

ATECC508A

Introduction

Datasheet Complete

DS20005927A-page 9

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