Coldcard: Coinkite's Bitcoin-Only Hardware Wallet, Models and the 2026 Seed Flaw

Coinkite Inc. designs and sells COLDCARD. The company's sales terms give a Toronto address, are governed by Ontario law, and send disputes to arbitration in Toronto ⁸. Coinkite says it was founded in 2012 and labels its products "Made in Canada" ⁷. Besides COLDCARD, it makes TAPSIGNER (an NFC key card), OPENDIME (a physical Bitcoin bearer device), SEEDPLATE (a metal seed backup) and the BLOCKCLOCK mini display ⁶⁷.

Prices shown are Coinkite's own listings and change often ⁶. Coinkite says its sales are final and the product is sold "as-is" ⁸. Resellers handle their own orders ⁸. To avoid tampered devices, buy only from store.coinkite.com or a reseller listed on coinkite.com, and update the firmware before you create a seed ⁶⁹.

COLDCARD only does Bitcoin. It doesn't support Ethereum, tokens or other chains ⁶. The device generates and stores your seed. A desktop or mobile wallet app, such as Sparrow, Nunchuk or Electrum, builds the transaction as a PSBT (Partially Signed Bitcoin Transaction, BIP-174). The COLDCARD then signs it ⁶. A typical air-gapped flow:

1. Your wallet app creates an unsigned transaction and saves it to a microSD card or shows it as a QR code.
2. You move it to the COLDCARD, check the amount and destination on the device screen, and sign.
3. You return the signed transaction to the app, which broadcasts it.

The seed is protected by a PIN and two secure-element chips from different vendors (Microchip and Maxim) ⁶. Coinkite also builds in anti-coercion tools: a duress PIN that opens a decoy wallet, a "brick me" PIN, and login countdowns. Advanced backup options include BIP-85 child seeds, Seed XOR, multisig co-signing, and Codex32 and Shamir backups since firmware 5.6.3/1.5.3Q ¹⁶. Coinkite says the firmware is open source and reproducible, so anyone can check that a release matches the published code ⁶. Background: what a hardware wallet is and how to set one up.

What went wrong. A good seed needs strong randomness. TRM Labs says a build configuration error, dating from firmware released in March 2021, made some COLDCARD devices fall back to a weak software random number generator instead of the hardware source when creating seeds. On older devices, that cut the effective key strength from 128 bits to as little as about 40 bits, which is low enough to brute-force without touching the device ². Coinkite says attackers recreated private keys offline. Devices weren't hacked remotely ¹.

Which devices. Coinkite's advisory says the older Mk2/Mk3 path was "more severely weakened." It also covers seeds made on the Mk4, Mk5 and Q before the fixed releases, and it warns owners of newer hardware not to assume they're safe ¹.

Losses. The thefts began on July 30, 2026. The first wave took about 594 BTC (about $38 million) from roughly 500 wallets in 25 minutes ². Galaxy Research counted 1,778 BTC (about $112 million) taken by August 14 ³. TRM cited a running tally of about 1,816 BTC (about $116 million) across more than 5,200 addresses ². Some of the funds went through Wasabi and Tornado Cash ². No attacker had been publicly identified in the sources reviewed, and law enforcement is investigating ²⁴.

Coinkite's fixes.

• A firmware fix for new seeds shipped on July 31, 2026 ³.
• The August releases (Mk4/Mk5 5.6.1, Q 1.5.1Q) require you to add your own randomness when creating a seed: at least 65 key presses, 50 dice rolls or 128 coin flips. They also replaced the backup random generator with SHA-256 Hash_DRBG, added hardware-RNG checks, and re-verify transactions just before signing ³⁴.
• As of October 1, 2026, the recommended versions are 5.6.3 and 1.5.3Q ¹.
• Coinkite says the fixed releases have had targeted outside review, not a complete independent audit. A full postmortem is still "in preparation" ¹.

What owners need to do. Updating the firmware doesn't fix a seed that was already created ¹. Coinkite's advice for anyone whose seed was generated on affected firmware:

1. Verify and install the current firmware.
2. Create a new seed, adding your own entropy.
3. For meaningful balances, consider a strong BIP-39 passphrase that you back up separately.
4. Move the funds to the new seed.

The only exception is a seed created from at least 50 fair, private dice rolls that were never recorded ¹. Coinspect has released a free tool, "Unlukey," that checks whether addresses may come from weak seeds ³. Nunchuk also advises migrating multisig wallets that use only COLDCARD keys ⁵. Never type your seed into a website that claims to "check" it.