By: Rocendo Bracamontes
Atmel’s ATSHA204 CryptoAuthentication™ device allows four different ways to perform symmetric cryptographic authentication on a system:
- Fixed Challenge Authentication
- Fixed Challenge Authentication is an easy way to add security to a product without the expense of added hardware to the host, interactive testing, or extensive software development. With Fixed Challenge Authentication, the client requires an ATSHA204 device programmed with secret keys. The host is able to use any number of pre-calculated challenge/response pairs to validate the presence of a valid ATSHA204 on the client side.
- Random Challenge Authentication
- Random Challenge Authentication improves on the Fixed Challenge method by adding a Random Changing Challenge to each request. This feature enables the system to defend against replay-style attacks.
- By adding an ATSHA204 device to the host, the system can generate a Random Challenge for the client on the fly. In addition, by generating the challenge internally with the host’s ATSHA204 device, the response is unknown to the system, allowing the use of an unsecured processor without the threat that an attacker will be able to learn system secrets. This dramatically limits the ability of an unauthorized device from producing the correct response.
- Unique Challenge Authentication
- Unique Challenge Authentication improves on the Fixed Challenge by adding a Unique Challenge to each request. This authentication feature enables the system to defend against replay-style attacks.
- By adding an ATSHA204 device to the host, the system can generate a challenge for the client on the fly. This allows a unique challenge to be sent for every validation request.
- Diversified Key Authentication
- This method includes the unique serial number of each ATSHA204 as part of the Cryptographic Authentication calculation. Diversified Key Authentication enables the host to identify the specific accessory that is trying to authenticate with it. This approach also enables the use of access lists (black lists) by the system.
With so many different options of authentication models, you can select the approach that best fits your design’s requirements, keeping your valuable intellectual property (IP) safe from malicious attacks or cloning. To learn more about designing with the ATSHA204, including some design tips and tricks, check out this white paper. Also stay tuned for further deep dives into each these models in the weeks to come.
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I am having trouble locating documentation to help me use the ATSHA204.
I have found plenty of marketing material, and Application Notes that tell me what the chip does, but none of them tell me what functions to call, and with what parameters to achieve any specific authentication model.
The Datasheet doesn’t explain usage clearly, it just lists the modes and which bits to set, but doesn’t relate this back to the bigger picture.
I know in some cases I need to combine Nonce, GenDig and CheckMac, but can’t find a decent example.
Is there anyone I can talk to for more information?
I am in Australia.