82 lines
3.3 KiB
Markdown
82 lines
3.3 KiB
Markdown
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# sha204_playground
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Firmware for ATMEL chips to communicate with ATSHA204 chip interactively
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over Serial. Sources are supplied in two forms:
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- As AVR-GCC project utilizing the [LUFA] library (for USB capable
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ATMEL chips, tested on atmega32U4 and atxmega128a3u).
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- As an [Arduino] sketch.
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Along with this, a python script `talk_to_sha204.py` is provided to
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access some of the functionality of the ATSHA204 chip, talking to
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it via the firmware above (in a binary mode), a-la [hashlet].
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## Usage / Installation
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Please see the READMEs in the individual subdirectories for some info on
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how to use them.
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## Pictures
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The original impetus to write this stuff for me was that I had a couple
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of ATSHA204 breakout boards from [Sparkfun] and I wanted to play with
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them outside Arduino, using just avr-gcc and [LUFA], on some USB sticks
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with ATMEL chips. Here are pics with two of them:
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And matrixstorm's [AVR stick] with the same Sparkfun's ATSHA breakout:
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## Idle thoughts / ramblings
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So, what can be ATSHA204 used for? Well, it performs hashing (SHA256)
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and it can securely store "keys" (32 bytes long blocks of data).
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The important point (for me) is that to verify that a "signature" (hash,
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MAC) was generated on a particular ATSHA requires knowing all the
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"secrets" that were used to generate the signature. This works fine for
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Client/Server-like situations: "Client" ATSHA generates a signature for,
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say, a file, (e.g. on a local computer), which is then sent to "Server"
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for verification. However the "Server" has to know the "secret keys" on
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ATSHA that were used in the signature computation; so either the
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"Server" has a copy of the keys stored in ATSHA, or there's another
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ATSHA on the "Server" with the keys.
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This kind of thing can be used for instance to roll one's own
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authentication service a-la [YubiKey].
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What I wanted to use it for is to securely store encryption keys
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locally, for a "two-factor key storage". This is also possible to do:
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user enters a password, this is passed to ATSHA which generates a hash
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of the user's password, together with one of its "secret keys". This
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hash is then used as an encryption key. So to obtain the
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encryption key, one has to know the password and have the ATSHA along.
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## Notes
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Please see the READMEs in the individual subdirectories for more info
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about the various parts of the project, as well as credits.
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## TODO / Roadmap
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- Make also binary-mode-only versions of the firmware (for smaller than
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32kB chips).
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## License
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My code is (c) flabbergast. MIT license (see LICENSE file). Portions
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of the code come from LUFA demos, this is licensed by LUFA's license.
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The original code from SHA204 library is licensed by Apache V2.0 license.
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[AVRstick]: http://matrixstorm.com/avr/avrstick/
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[LUFA]: http://www.fourwalledcubicle.com/LUFA.php
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[hashlet]: https://github.com/cryptotronix/hashlet
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[YubiKey]: https://www.yubico.com/products/yubikey-hardware/yubikey-2/
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[Arduino]: http://www.arduino.cc/
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[Sparkfun]: https://www.sparkfun.com/products/11551
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[AVR stick]: http://matrixstorm.com/avr/avrstick/
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