Ensuring that a device is authentic without using an overly complex and expensive scheme to do so is one of today’s many embedded design challenges. A chip-based implementation of elliptic curve cryptography can provide a secure solution at the right price.

Protecting electronic systems from counterfeiting is a growing challenge for OEMs. With the move to outsourced manufacturing for consumer electronics and computer peripherals, it is increasingly difficult to protect IP and prevent unauthorized production of devices using an OEM brand.

The problem is bigger than it might appear at first glance. For companies that offer a core system at subsidized prices, expecting to earn profits in aftermarket sale of accessories or consumables, counterfeit devices threaten both the business model and brand reputation. Some companies have even reported incidents of non-OEM accessories such as battery packs reaching end users and creating a potential liability.

Hardware authentication: challenges and selection criteria

Many classes of aftermarket parts and accessories such as notebook AC adapters and batteries are built to be compatible with OEM specifications and standards. In the midst of legitimate accessories manufactured by authorized third parties, there are counterfeit devices that are exact or near-exact replicas of authorized products.

The challenge is enabling a system to distinguish between authorized and unauthorized parts or between the OEM brand and third-party brands. While there are many tactics to address counterfeiting threats, each has its limits. Patents, custom connectors, and proprietary hardware/software solutions are used with varying success rates.

A relatively new approach is the concept of embedded authentication hardware, which can be used to ensure that an accessory or peripheral is authentic for use with a given system. In this type of solution, the authentication hardware is located in the accessory and the software resides in the host system.

The characteristics of a software-to-hardware authentication solution to protect against counterfeiting should address the following questions:

1.  Is the host system immune to attacks?

2.  Is the peripheral or accessory immune to attacks?

3.  Is it possible to break one device and use the information to hack all the systems?

4.  Can the security infrastructure extend to protect legitimate aftermarket parts?

5.  How can one warn about the reuse of expired or unwarranted parts/accessories?

6.  Is the solution cost?effective and easy to implement?

In response to the final question, embedded security using a software?to?hardware authentication solution can meet both cost and ease-of-implementation targets for price-sensitive consumer electronics while still addressing the other questions.

Chip-based product authentication

Infineon Technologies provides chip-based security solutions for many applications, including e?passport, Trusted Platform Module (TPM), and payment and chip card devices. The company recently added the Origa Original Product Authentication Solution (SLE95050FX) to its portfolio, drawing on two decades of security chip experience to address counterfeit protection in cost-limited applications.

The chip supports asymmetric authentication using discrete Elliptic Curve Cryptography (ECC) logarithm implementation, a mathematically complex and highly secure form of ECC. It stores data such as the private key, unique chip ID, and other customer information in a protected memory space secured from modification. Up to 192 bits of read-only data can be written into this space.

Additionally, the chip offers unprotected and freely usable nonvolatile memory of 512 or 704 bits for different purposes such as traceability of the manufacturing and logistics chain, OEM-added data about the accessory, or documentation of end-user behavior such as the charging cycle. One version features an integrated temperature monitoring sensor to simplify the implementation of rechargeable batteries.

As depicted in Figure 1, an authentication solution consists of a host device serving as the master communicating through a Single Wire Interface (SWI) to the accessory containing the SLE95050. The chip can be directly or indirectly powered via the SWI interface, as shown in this illustration.

Symmetric versus asymmetric cryptography

An important consideration in counterfeit protection is the cryptographic system used. In consumer electronics and computers, the shared secret scheme or symmetric solution (in which the host and peripheral share the same secret) falls short. If the host shared secret is exposed, then original devices can be easily replicated into counterfeits guaranteed to work with all host systems.

Asymmetric cryptography uses two different keys for encryption and decryption. The so-called public key can be made public (and therefore used in the software that resides in the host system), as long as the other secret or private key is still in the safe environment of a chip embedded in the peripheral. This concept is illustrated in Figure 2.

Now let’s take a look at how the software-to-hardware system addresses the challenges involved in implementing a robust authentication solution.

1. Is the host system immune to attacks?

Attacks on host systems are typically aimed at retrieving the secret that would allow successful counterfeiting. In software-to-hardware authentication, host code and libraries only contain public information. An attack on the host is therefore futile. From this perspective, the system is immune to attacks.

2. Is the peripheral or accessory immune to attacks?

The authentication chip incorporates physical security to protect its secret. Due to the ECC asymmetric protocol, bus snooping will not reveal any secrets. The chip implementation also includes protection against replay, side channel, and power attacks. Hence, the solution is relatively immune to attacks.

3. Is it possible to break one device and use the information to hack all the systems?

Since the host only contains public parameters and the chip contains the secret key and parameters, it is not possible to extract private information by manipulating the host. Also, hardware personalization at Infineon’s Common Criteria EAL5+ certified facility prevents secret leakage from accessory manufacturing sites.

4. Can the security infrastructure extend to protect legitimate aftermarket parts?

The security system offers a personalization step that takes place in a secure Infineon facility. Personalization is possible for each particular customer or for each stock-keeping unit or subgroup of products for the same customer. Personalized devices are supplied only to customer?designated manufacturing sites and are not available for purchase by any other entities. The secure personalization process serves several purposes:

·    Protects from a purchase of blank chips in the open market that are then personalized to produce a counterfeit.

·    Prevents possible secret leakage from manufacturing or ODM sites.

·    Eases the manufacturing process, eliminating key or secret injection and key management logistics at the production site, thus saving costs and reducing production time.

5. How can one warn about the reuse of expired parts/accessories?

Each chip has a countdown-only lifespan indicator that can be used to warn or permanently retire any part or accessory. A combination of unique ID, nonvolatile memory data, and lifespan indicator can be used for this purpose as well.

6. Is it cost-effective and easy to implement?

The solution is architected and designed to achieve a balance between cost, degree of security, and ease of implementation. It can meet stringent security requirements while allowing easy implementation with a reasonable cost structure. Infineon provides the code library package that also contains the ECC library, simplifying the implementation process and saving time.

Protection worth the cost

As noted, the goal in designing for counterfeit protection is to achieve an efficient level of security while limiting the impact on the Bill-Of-Materials (BOM) cost. For example, printer cartridge manufacturers and cell phone manufacturers want to protect revenue streams and ensure device reliability.

The software-to-hardware solution described herein addresses the requirements for secure product authentication at a BOM cost – in relatively high product volume, well under one dollar. Additional applications including unique platform identification, remote peripheral authentication and reporting for warranty and services, binding application or firmware to a particular platform, multifactor authentication, and machine-to-machine authentication are also economically viable. With its low-power single-wire implementation, the device is particularly suited for embedded systems.

Robert Rozario is a technical marketing and application engineering manager for the Chip Card and Security Business Unit at Infineon Technologies. He primarily focuses on Infineon TPM and hardware authentication solutions. Robert holds an MS in Electrical Engineering from the University of Utah.

Infineon Technologies
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www.infineon.com