ICs & Semiconductors
field upgrades, but transmission of the code can expose it to copying. A hardware security device can support authentication and encryption of the code using either a common distribution model or custom images for each individual system.
(2) Secure Identification: Serial numbers
are useful for controlling help-centre costs, identifying a system owner, managing maintenance records and many other uses. Usually, this just means putting the serial number in an EEPROM. An authentication chip can provide
numerous advantages over an EEPROM: it ships from the chip fab with a guaranteed unique serial number, and it supports an easy to use protocol that can identify any attempt at duplication.
(3) Encrypted Communication: When the information transmitted over the network is sensitive (as in medical systems) or prone to fraud (whenever money is involved) it’s best to encrypt the data. While many standard microprocessors include AES encryption blocks, there’s no easy way to protect the encryption key. An authentication device can be used to confidentially store these secret keys or to exchange a volatile session key with a host system.
Figure 1: Consumable authentication process
Authentication is the process of identifying a system peripheral (daughter card, network card, etc.) or replaceable item (battery pack, ink cartridge, other consumable) as genuine, authorised for connection to or insertion in the system being protected. Figure 1 illustrates the process of validating a consumable item. A small authentication device is embedded in the consumable client product and when connected, acts as a slave to the microprocessor (in the host
system). Using a secure challenge- response process, the host microprocessor issues a challenge to the client which encrypts a response back to the host. The same secret contained in the authentication device is stored in the host microcontroller to enable it to calculate an expected response which it compares to the actual response and if successful, validates the client (permitting its operation in the system). Modern microprocessor-based systems
always include system firmware and often include an electronic interface to a PC, network, USB flash drive, daughter card, replaceable battery or consumable item. In all these situations, and more, including a hardware security chip on the system board can provide a host of additional benefits which include: preventing unauthorised firmware copying; implementing secure identification and enabling encrypted communication. (1) Embedded Software Clone Prevention: Usually firmware development is the most costly and time consuming part of embedded system development. An authentication device can help prevent fraudulent cloning of that firmware – only systems that contain a device with the correct OEM secret will function properly. The basic operation of this security model is displayed in Figure 2. At periodic intervals, an instruction is inserted in the source code to issue a challenge to the authentication device. The response from the device is then compared to the expected response and the program continues only if the response is correct. By providing a large number of challenges and hiding or cleverly placing them in the code, the source becomes extremely difficult to reverse engineer. Finding and removing all the inserted authentication commands is a very difficult challenge.
Figure 2: Embedded software protection process
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Also, if source code is stored in flash memory, then the system designer can offer the benefit of
An example of such authentication ICs is the CryptoAuthentication family of devices. These chips from Atmel are designed to securely authenticate any item to which they are attached. Each device can also be used to exchange session keys with a remote entity enabling the system microprocessor to securely encrypt/decrypt data. The devices are housed in small 3-lead SOT-23 packages with a tiny footprint, making it simple to incorporate these devices into even the tightest of spaces. The family of devices is believed to be the only low cost authentication chips which implement SHA-256, and advanced encryption algorithm. Rapid advances in crypto analysis mean that older weaker algorithms may not offer an acceptable product lifetime. Using SHA-256 ensures the designer that the obsolescence of the product will not be caused by its security system.
But using the latest algorithms doesn’t matter if an attacker can microprobe the chip or attack it in other ways to get the secret out. Consequently any authentication device needs to be fully protected from such attacks. For example, Atmel’s devices feature a metal shield over the entire chip, internally generated clocks, onboard voltage regulation, and a host of other defences. For legitimate manufacturers of embedded systems and peripherals, it is easy to justify the cost of enhancing the security of their products against the losses of add-on and replacement revenue, losses in confidence in their company’s products, and damage to the company or brand reputation from inferior “clones” invading their markets. Authentication devices offer inexpensive, easily implemented solutions to accomplish this – and it means that enhanced security can be surprisingly affordable.
Atmel |
www.atmel.com
Alexander Kurz is Marketing Manager Memories and Crypto at Atmel Corporation
Components in Electronics October 2011 45
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