COLDCARD Security Advisory A seed-generation defect affected releases beginning with firmware 4.0.1. Fixed firmware is available. Existing affected seeds still require migration. Check status
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About Coldcard

Written by Coinkite Team

Coldcard is made by Coinkite Inc., a Bitcoin security company founded in 2012. We build tools for people who want full ownership and custody of their Bitcoin. Our hardware devices keep private keys offline and sign Bitcoin transactions without those keys ever touching the internet. They are Bitcoin-only, can operate air-gapped, and run firmware whose source and reproducible-build process are public.

Who We Are

Coinkite was founded in Toronto, Canada in 2012. The team is made up of security engineers, product designers, and Bitcoiners who share a common philosophy of security-first.

We are a Bitcoin-only company by design. Staying focused on Bitcoin means a simpler, more auditable codebase, a smaller attack surface, and a team whose full attention stays on one problem: securing Bitcoin.

Security and convenience are not the same thing. COLDCARD publishes its firmware source and reproducible-build process so technical users can inspect and reproduce important software claims. Hardware, supply-chain, and operational claims require their own evidence and checks.

Coldcard devices are designed and assembled in Canada.

What We Believe

Sovereignty is the foundation of freedom. Sovereignty is the ability to hold, verify, and transact your wealth without depending on any person, government, or company. Secure self-custody of Bitcoin is how you pursue sovereignty and Coldcard is built on the principles that make that possible.

  • Bitcoin-only. A Bitcoin-only architecture keeps the codebase focused and auditable, with the team's full attention on one problem. It is a security decision, not a limitation.

  • Air-gapped signing. QR or MicroSD signing removes a live USB, Bluetooth, or Wi-Fi data channel between COLDCARD and an internet-connected coordinator. The device still parses the transferred transaction, so the user must verify destination, amount, fee, and change on the COLDCARD screen.

  • Open and verifiable. COLDCARD firmware source and reproducible-build instructions are public. Advanced users can inspect the source, reproduce a release build, and verify firmware hashes and signatures. Open source makes those checks possible; it does not mean the code cannot contain a defect.

  • Self-custody is a practice, not a product. Custody is never a solved problem. It requires ongoing attention as threats evolve and a willingness to revise your approach. Coldcard operates the same way, in a never-ending pursuit of better, more secure custody solutions.

What We Make

Coldcard Q

The Coldcard Q is our most capable signing device, featuring a full QWERTY keyboard, large color display, built-in QR code scanner, NFC, MicroSD, USB-C, and battery operation via USB-C power bank or AAA batteries. It supports the full range of Coldcard security and custody options and is designed for anyone who wants the most complete air-gapped signing experience available.

Coldcard Mk5

The Coldcard Mk5 is built on the same security foundation as the Q, in a more portable and low-profile form factor. It's credit card-sized and fits in your pocket for convenient and discreet storage and transportation. It supports MicroSD and NFC tap signing and handles the full range of custody and multisig configurations, making it the right device when portability is the priority.

The Coinkite Ecosystem

Beyond Coldcard, Coinkite builds a range of Bitcoin tools for every layer of a self-custody setup:

  • Opendime: a Bitcoin bearer instrument on a USB stick for spending Bitcoin physically, like cash
  • Tapsigner: an NFC card that stores a private key for mobile Bitcoin signing
  • Satscard: an NFC bearer card with ten independent slots for physically giving and receiving Bitcoin
  • Seedplate: a stainless steel plate for a durable seed phrase backup
  • Blockclock: a Bitcoin clock that displays real-time network data

Open Source

COLDCARD firmware source is available at github.com/Coldcard/firmware. The repository applies MIT terms plus the Commons Clause, documents reproducible builds, and is under active development. You can inspect the code, build a release from source, and compare the result with the published firmware binary.

Review COLDCARD security and verification.

Public code and reproducible builds let users independently check important software claims instead of relying only on vendor promises. They do not prove that the code has no defects or that every hardware claim is correct.

Editorial Team

COLDCARD technical articles are published under the Coinkite Team byline. The byline identifies Coinkite's internal contributors without inventing individual writers or exposing private employee information.

Article bylines and review dates are published visibly and in the page's structured data. Product comparisons and security claims also describe their methodology and link to the primary evidence used for the review.

Use these official properties when checking product information, firmware, documentation, or support:

Before downloading firmware, confirm that the browser address is on an official domain and verify the download using the firmware verification procedure. Coinkite support will not ask for seed words, passphrases, dice-roll sequences, private keys, or wallet backup files.

Coldcard is made by Coinkite Inc., Toronto, Canada. Bitcoin-only. Air-gapped. Open source.