[Bug] Encrypted QR codes with different i_vector in AES-CBC mode are identical.

selfcustody / krux

Open-source signing device firmware for Bitcoin

https://selfcustody.github.io/krux/

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[Bug] Encrypted QR codes with different i_vector in AES-CBC mode are identical. #477

Open earthdiver opened 1 week ago

earthdiver commented 1 week ago

When creating an encrypted QR code in AES-CBC mode, we are obtaining an additional entropy from the camera, but the generated QR codes are identical for each combination of key, mnemonic_id, and mnemonic. I believe that the first block of data_bytes should not be i_vector (how about replacing it with something like b'x\ff'*16 ?).

odudex commented 1 week ago

Thank you for your important finding! It helped me identify an error in the CBC encryption implementation, which unintentionally "deactivated" i_vector. I'm ashamed of not performing similar test before. We've made a dedicated release for the fix. Thank you again for the catch!

tadeubas commented 1 week ago

Release with the fix: https://github.com/selfcustody/krux/releases/tag/v24.11.1