u2f-zero

There’s the U2F Zero https://github.com/conorpp/u2f-zero/wiki/Building-a-U2F-Toke... but of course there’s always a reflections-on-trusting-trust issue: you’ve got to get your CPU, CPU design, compiler, firmware and chip programmer somewhere! Of course, an accidental software bug is probably more likely than intentionally backdoored hardware targeting you personally...

The open-source U2F Zero claims ~$3 of parts and a ~$2 PCB [1] ordering a single unit. Making a large volume, that price is only going to come down. Admittedly you'd have to pay for a plastic case, assembly costs, an envelope and stamps. But if I can get a 16GB flash drive for $8 with free shipping [2] the plastic case, assembly etc can't be that expensive! [1] https://github.com/conorpp/u2f-zero [2] https://www.amazon.com/SanDisk-Cruzer-Low-Profile-Drive-SDCZ...

lol no. this is almost not even worth a response. the key managed here https://github.com/conorpp/u2f-zero/blob/master/firmware/src... and here https://github.com/conorpp/u2f-zero/blob/master/firmware/src... just means that the "actual key" (unmasked) only lives in MCU memory for a short time -- the time from when the mask is applied and then until return to caller and memory is cleared, in the enrollment case I linked. In the authenticate case, it lives quite a bit longer because the stack space used for key storage isn't zero'd. The atecc508 doesn't use or know how to use the mask. The actual key used for the encryption is passed in the clear over i2c. (note that the key derivation you suggest is wrong because of the extra xor masking.)

The one in the pictures uses a EFM32 Jade/Pearl [1]. More details are in the discussion on github: [2]. [1] https://www.silabs.com/products/mcu/32-bit/efm32-pearl-gecko [2] https://github.com/conorpp/u2f-zero/issues/76

> The ATECC508A is not used correctly. It is used as a RNG and for it's crypto functions, but not for key storage. Where did you get that idea from? Preparing a device consists of the following steps: - Flash temporary configuration firmware - Send keys to the device, which are stored on ATECC508A - Flash actual u2f-zero firmware So on the second step (configuring the device), the host writes keys on the device, and those keys are stored on ATECC508A. It happens there: https://github.com/conorpp/u2f-zero/blob/master/firmware/src... I do agree that the code is bad though, but alas. I did consider reimplementing it properly, also on a more powerful chip, but I don't think I'll be able to find time for that. Anyway, dirty code doesn't mean that the device is insecure. From what I see, among other things, ATECC508A is used properly.

There are at least two U2F keys I was able to find on Amazon which were under $10 USD: https://www.amazon.com/dp/B01N6XNC01 https://www.amazon.com/dp/B01L9DUPK6 The latter is an open source / open hardware design: https://github.com/conorpp/u2f-zero

The Github page has this to say: "The token should be durable enough to survive on a key chain for years, even after going through the wash." [0] I'd guess covering it all with hot glue would provide sufficient protection. [0] https://github.com/conorpp/u2f-zero/

If you're feeling crafty, you can create your own: https://github.com/conorpp/u2f-zero/wiki/Building-a-U2F-Toke...

How does something like the U2F Zero[1] compare? As I understand it, the u2f zero acts as an HID device and not as a smartcard provider, but could one modify the firmware to do that? Isn't this basically an open source yubikey you can make yourself for < $25? 1. https://github.com/conorpp/u2f-zero

It's a good question. It's definitely not been through years of testing yet but in the past few months me and some friends have had no problems. All of the parts have a low center of mass with respect to the PCB and are unlikely to catch on anything. Water and/or sweat won't hurt it as long as it's dry when you use it. I've tested it works fine after putting it through a washer and dryer. However, making your own casing or 3D printing something like this [1] is always best [1]: https://github.com/conorpp/u2f-zero/blob/master/hardware/cas...

For those confused, see https://github.com/conorpp/u2f-zero/commit/dd71758a

There is a 3d-printable case included in the repo! https://github.com/conorpp/u2f-zero/blob/master/hardware/cas...