COLDCARD: keys, security, fees and reviews

In short

Key control: Self-custody: private keys stay offline on the device and transactions are signed without the keys touching the internet.
Fees: Device price: List price COLDCARD Q $369, COLDCARD Mk5 $269 in the official store (as of 31 October 2026); a one-day discount was running.
Risks and caveats: Seeds created on affected firmware before July 2026 remain weak after a firmware update; funds must be moved to a newly generated seed.
Checked: 31 October 2026

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Key facts

Official site: coldcard.com

Key facts checked on 31 October 2026 against official sources.

What is COLDCARD

COLDCARD is a Bitcoin-only hardware wallet made by Coinkite Inc. of Toronto, Canada (founded 2012). The current models are the COLDCARD Q, with a QWERTY keyboard and QR scanner, and the smaller Mk5. It signs transactions air-gapped through MicroSD, QR or NFC and works with third-party wallet software instead of a required companion app.

Who holds the keys

Who holds the keys — COLDCARD
Parameter	Details
Key control	Self-custody: private keys stay offline on the device and transactions are signed without the keys touching the internet.
Account model	No COLDCARD account or companion app needed; works with coordinator software such as Sparrow, Nunchuk or Specter.
Seed phrase	BIP-39 seed words (24); optional passphrase, encrypted MicroSD backups, Seed XOR and, since September 2026, Codex32 and Shamir backups.
Recovery	Support never asks for seed words, passphrases, dice rolls or backup files.

Features and supported networks

Features and supported networks — COLDCARD
Parameter	Details
Supported networks	Bitcoin only.
Connectivity	QR (Q only), MicroSD, NFC, USB-C and virtual disk; all are off by default.
Secure element	Two secure elements from different vendors: Microchip ATECC608 and Maxim DS28C36B.
Display	Q: 3.2-inch LCD with full keyboard and AAA battery option; Mk5: 1.54-inch Gorilla Glass screen with numeric keypad.
Multisig	Multisig, descriptor export, BIP-85 child seeds, duress and brick-me PINs, temporary seeds.

Security and audits

Firmware source is public on GitHub (Coldcard/firmware) under MIT terms plus the Commons Clause, which restricts selling the software; builds are reproducible since firmware 4.0.0 (March 2021).
No Common Criteria or other certification is claimed for the two secure elements (Microchip ATECC608, Maxim DS28C36B).
Coinkite's advisory of 30 July 2026 disclosed a firmware bug that weakened seed generation; attackers regenerated keys of affected seeds offline and stole funds. Mk2/Mk3 firmware 4.0.1-4.1.9 was most affected; Mk4, Mk5 and Q seeds made before the fixes had about 72 bits of entropy instead of 128.
Fixed firmware exists for every model (Mk2/Mk3 4.2.0, Mk4/Mk5 5.6.0, Q 1.5.0Q and later), but updating does not repair an existing affected seed; owners must move funds to a new seed unless the dice-roll exception applies.
Independent reviewers made targeted checks of the fix; Coinkite states this is not a complete audit of every firmware binary.

Security incidents

Security incidents — COLDCARD
Date	What happened	Source
30 July 2026	Exploit: Coinkite disclosed a firmware bug that weakened seed generation (Mk2/Mk3 firmware 4.0.1-4.1.9 most affected; Mk4, Mk5 and Q seeds before the fixes had about 72 bits of entropy). Attackers regenerated private keys of affected seeds offline and stole funds; amounts were not stated. Fixed firmware was released for all models; affected seeds must be migrated. Funds returned: not stated	blog.coinkite.com

Fees

Fees — COLDCARD
Parameter	Details
Device price	List price COLDCARD Q $369, COLDCARD Mk5 $269 in the official store (as of 31 October 2026); a one-day discount was running.
Wallet	No account or subscription; network fees are paid through the chosen coordinator software.

History

History — COLDCARD
Date	Event
2012	Coinkite founded in Toronto, Canada.
24 July 2018	COLDCARD firmware source published; first public release in August 2018.
March 2022	Mk4 firmware line released.
March 2024	COLDCARD Q firmware released.
March 2026	Mk5 source published.
30 July 2026	Security advisory on weakened seed generation; fixed releases published for all firmware tracks.

Risks and caveats

Seeds created on affected firmware before July 2026 remain weak after a firmware update; funds must be moved to a newly generated seed.
Air-gapped signing still requires checking destination, amount, fee and change on the device screen.
Coinkite recommends moving long-term custody off legacy Mk2/Mk3 devices.

About the developer

Developer: Coinkite Inc., Toronto, Canada; devices designed and assembled in Canada.
Founded: 2012 (Coinkite).
Other products: Opendime, Tapsigner, Satscard, Seedplate, Blockclock.

Official links

Website: coldcard.com
Security: coldcard.com/security/status
Docs: coldcard.com/docs
Source code: github.com/Coldcard/firmware
Blog: blog.coinkite.com
Download: store.coinkite.com/store

Questions and answers

Is COLDCARD self-custodial?

Yes. Keys stay offline on the device, no COLDCARD account is needed, and it works with third-party Bitcoin wallet software.

Is COLDCARD open source?

The firmware source is public and reproducible, under MIT terms plus the Commons Clause, which restricts commercial resale of the software.

Which coins does COLDCARD support?

Bitcoin only.

Was COLDCARD hacked?

In July 2026 Coinkite disclosed a firmware bug that weakened seed generation; attackers stole funds from affected seeds offline. Fixed firmware is out, but affected seeds must be replaced.

Who makes COLDCARD?

Coinkite Inc. of Toronto, Canada, founded in 2012.

Sources

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Page updated: 2026-10-31