I wanted to find out how hard it is to manipulate the @SeedSigner
. It was easy as expected. Never give it out of hand! Simple swap to a manipulated sd-card and it logs your seed to it. Later the attacker can collect the sd-card and get your seed words.
Total lines added to the code are six.
Needless to say, it writes the seed also to sd-card if you scan your backup seed.
I strongly prefer HWW's with anti-exfil. Right now that's only Jade and Bitbox over USB/BLE. QR anti-exfil would be possible but it would need a new standard to be invented with an extra round trip making it annoying to use. I personally trust anti-exfil over USB more than anything else. Stealing from it requires both HWW and host to be exploited which might be harder to pull off.
https://medium.com/blockstream/anti-exfil-stopping-key-exfiltration-589f02facc2e
IMHO USB is worst than exfil, you can deal with the nonce issues with deterministic builds.
