Coinkite’s new firmware adds hand-entered entropy and stricter transaction checks to its Coldcard wallets.
Weeks after a randomness flaw exposed Coldcard hardware wallets to a +$100M BTC theft, Coinkite has released firmware 5.6.1 for Mk4/Mk5 devices and 1.5.1Q for the Q model. This update stemmed from of an AI-assisted security sweep that dug into far more than the original bug.
What’s the Scoop?
- Root cause: A configuration mistake baked into Coldcard’s 2021 firmware quietly downgraded its randomness source, so seeds meant to carry 128 bits of entropy sometimes shipped with as few as ~40, which was weak enough for attackers to guess private keys with no physical access required.
- What changed: New seeds now must draw on randomness the owner supplies by hand, namely dice rolls, coin flips, or an unpredictable string of key presses. These inputs are layered atop the device’s hardware entropy, and a fresh SHA-256-based generator now backs it up. Coldcard also rechecks transaction contents right before signing, closing off a compromised computer’s chance to tamper post-approval.
- The catch: Seeds generated between 2021 and this July are still considered burned regardless of the update. Any owners from that period still have to create a new one on patched firmware and migrate their funds if they haven’t already.
