Coldcard: seeds generated on affected firmware are weak
A firmware bug weakened seeds generated on the device. Mk4, Mk5 and Q seeds have about 72 bits of entropy instead of 128; Mk2 and Mk3 seeds are weaker still. Attackers regenerated private keys from weak seeds offline; the devices themselves were not hacked.
Affected: Mk2/Mk3 firmware 4.0.1 to 4.1.9; Mk4/Mk5 before 5.6.0 (Edge before 6.6.0X); Q before 1.5.0Q (Edge before 6.6.0QX). TAPSIGNER, OPENDIME and SATSCARD are not affected.
Seeds created with at least 50 private dice rolls are not at risk. A strong passphrase reduces the risk but does not repair the seed.
What to do
- Install the fixed firmware: Mk2/Mk3 4.2.0+, Mk4/Mk5 5.6.0+ (Edge 6.6.0X+), Q 1.5.0Q+ (Edge 6.6.0QX+).
- Generate a new seed on the fixed firmware, verify the backup and a receive address, and send a small test amount.
- Then move the rest of your funds, and keep the old backup until the move is confirmed. Updating alone does not fix an existing seed.
Affected: Coldcard Mk5, Coldcard Q