ATSHA204A datasheet(19/93 Pages) MICROCHIP

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Security Features

3.1

Physical Security

The ATSHA204A incorporates a number of physical security features designed to protect the EEPROM

contents from unauthorized exposure. The security measures include:

•

An Active Shield Over the Part

•

Internal Memory Encryption

•

Secure Test Modes

•

Glitch Protection

•

Voltage Tamper Detection

•

Temperature Tamper Detection

Pre-programmed transport keys stored on the ATSHA204A 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, preventing any direct attack on

these two signals using the pins of the device.

3.2

Random Number Generator (RNG)

The ATSHA204A includes a high-quality RNG that returns a 32-byte random number to the system. The

device 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. One common purpose would be as the input challenge to

the MAC command on a separate CryptoAuthentication device. The device provides a special random

command for such purposes, which does do not affect the internally stored nonce.

To simplify system testing, prior to locking the Configuration zone the RNG always returns the following

32 byte value:

0xFF FF 00 00 FF FF 00 00 …

where 0xFF is the first byte read from the device and is used for the SHA message.

To prevent replay attacks on encrypted data that is passed to or from the ATSHA204A, the device

requires that a new, internally generated nonce be included as part of the encryption sequence used to

protect the data being read or written. To implement this requirement, the data protection key generated

by GenDig and used by the Read or Write command must use the internal RNG during the creation of

the 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 SRAM registers within the device that are invalidated if the device enters sleep mode or the

power is removed.

ATSHA204A

Security Features

DS40002025A-page 19

ATSHA204A Datasheet(PDF) 19 Page - Microchip Technology

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