Coldcard

Nobody broke into a Coldcard. What failed was the randomness used to create seeds. In March 2021 Coinkite moved seed generation to a new library, libNgU. The build flag meant to switch off MicroPython's software random generator did not take effect at link time, so seed generation called Yasmarang, a general-purpose PRNG seeded from fixed values, instead of the hardware random number generator the design required. Nobody caught it for five years.

The effect depended on the model. On Mk2 and Mk3 running firmware 4.0.1 to 4.1.9, seeds were weak enough to brute-force: TRM Labs estimates as little as 40 bits instead of 128. On Mk4, Mk5 and Q before the fixed releases Coinkite puts effective strength at about 72 bits, still well short of the target. An attacker only needed to regenerate candidate seeds offline and check which addresses held coins.

Seeds created with at least 50 private dice rolls were not exposed, because the dice added independent randomness. A strong BIP-39 passphrase also put funds out of practical reach, though Coinkite still advises migrating. Updating firmware does not repair an old seed: a new one has to be generated on fixed firmware and the coins moved.

1. 01Check which firmware created your seed and whether you added 50+ private dice rolls when you made it.
2. 02Update the Coldcard to the fixed release for your model and track (Standard or Edge) before creating anything new.
3. 03Generate a new seed on the updated device, back it up, and verify the wallet fingerprint and a receive address.
4. 04Send a small test transaction, then move the rest; keep the old backup until the move is confirmed.

Coinkite has not offered compensation. Its terms contain an arbitration clause, lawyers in Canada and investors including 117 Partners have discussed product-liability and class claims, and at least one Brazilian victim filed a police complaint. No class action had been certified when we checked.

Coinkite announced the first Coldcard in December 2017 with a pitch that still describes the line: Bitcoin only, a numeric keypad, a real security chip, and microSD so transactions can move between computer and device without any cable. Later models kept that and added NFC.

The Mk4 design stores the seed in one secure element and encrypts it with a key that needs the second secure element and the main processor as well. When Ledger's Donjon lab glitched the second chip with a laser in 2023, it reached about half of that chip's memory slots but not the seed. Features like a duress PIN that opens a decoy wallet, a "brick me" PIN and trick PINs are part of why security-focused buyers pick Coldcard.

Our scored review covers the Mk4: Coldcard review.

Coinkite Inc. was set up in Toronto in 2012 by Rodolfo Novak, known as NVK, and began as a bitcoin payments and multisig web wallet before moving to hardware. Besides Coldcard it sells Opendime (a USB bearer stick), Satscard and Tapsigner (NFC cards), Seedplate steel backups and the Blockclock display. Those products run separate code and were not affected by the 2026 bug.

Coinkite publishes Coldcard firmware source on GitHub and ships signed releases in two tracks: Standard, and Edge for newer features. That openness is also how the flaw became visible to anyone looking at the right commit; it took an exploitation wave for it to be found. Since August 2026 Coinkite has said every applicable firmware release should be treated as critical.