ATECC508A datasheet(33/109 Pages) MICROCHIP

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signature calculated using the corresponding private key calculated over the nonce stored in

TempKey. This signature is then validated.

Depending upon the configuration of the slot containing the authorizing secret, a token can be externally

stored, which can be repeatedly used for key authorization. If the authorizing slot is configured to require

a random nonce (KeyConfig.ReqRandom is one), then a stored authorizing token will not work, and the

authorizing digest or signature will have to be computed on the fly by the authorizing agent using the

random nonce generated by the device.

3.3

Security Features

3.3.1

Physical Security

The ATECC508A incorporates a number of physical security features designed to protect the EEPROM

contents from unauthorized exposure. The security measures include:

•

Active Shield Circuitry

•

Internal Memory Encryption

•

Glitch Protection

•

Voltage Tamper Detection

Pre-programmed transport keys stored on the ATECC508A are encrypted in such a way as to make

retrieval of their values using outside analysis very difficult.

Both the logic clock and logic supply voltage are internally generated, thus preventing any direct attack on

these two signals using the pins of the device.

3.3.2

Random Number Generator (RNG)

The ATECC508A includes a high-quality RNG which returns 32 random bytes to the system. See https://

csrc.nist.gov/projects/cryptographic-algorithm-validation-program/validation/validation-list/drbg for further

documentation on NIST CAVP certification of this RNG. The RNG of the ATECC508A is identical to that

of the ATECC108A. The device generally combines this generated number with a separate input number

to form a nonce that is stored within the device in TempKey and may be used by subsequent commands.

The system may use this RNG for any purpose. The device provides a special Random command for

such purposes that do not affect the internally stored nonce.

Random numbers are generated from a combination of the output of a hardware RNG and an internal

seed value, which is not externally accessible. The internal seed is stored in the EEPROM and is

normally updated once after every power-up or sleep/wake cycle. After the update, this seed value is

retained in registers within the device that are invalidated if the device enters Sleep mode, or the power is

removed.

To simplify system testing, prior to Config Locking the RNG always returns the following value:

ff ff 00 00 ff ff 00 00 …

where ff is the first byte read from the device and the first byte into the SHA message.

ATECC508A

Security Information

Datasheet Complete

DS20005927A-page 33

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