The World Needs An Open, Cheap & Ultrasecure Hardware Wallet!

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What is the Coinkite Coldcard? It's a Bitcoin hardware wallet, so it signs transactions and can be used offline.

• BIP39 based, which means you can backup the secret words onto paper, and have lots of sub-accounts and unlimited independent payment addresses.

• It knows how to understand transactions, so you can see what you are approving.

• The first PSBT (BIP 174) native wallet which can be used completely offline for it's entire lifecycle.

But it's different!

• NO specialized software required. It accepts standard PSBT transaction (BIP 174) stored on an MicroSD card. NO companion 'app' on your computer, works with the major wallets already (Electrum, and more to come).

• It's cheap! Simple packaging, plain design, no fancy boxes, no redundant cables.

• It's ultrasecure! Real crypto security chip. Your private key is stored in a dedicated security chip, not the main micro's flash.

• Easy back-up! MicroSD card slot for backup and data storage. This allows truly offline signing, by transferring the unsigned/signed transactions on sneakernet.

• Open source software design runs Micropython and you can change it.

Other features:

• Full-sized numeric keypad makes entering PIN easy and quick.

• Larger 128x64 OLED screen.

It's an open platform, and we expect other "apps" in time, like:

• Sign text messages to prove control over private key.

• Participate in multisig wallets, with other signers.

• Encrypt/decrypt secret messages (stored on MicroSD or otherwise).

Available For Purchase

We deliver, as with all the other projects. We always deliver!

You can buy the Coldcard now, and a large number of early birds have already bought up the first batch.

These units shipped in August 2018.

Prices are subject to change, get in now!

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We reserve the right to change the features and prices at anytime without notice.

Bulk orders

If you are already a Opendime reseller or NEW and interested in reselling, reach out to support for orders over 50 quantity.

How It Works

Duress/Secondary Wallet Feature

To limit the damage from rubber-hose attacks...

We provide an optional "secondary PIN code". If you enter that PIN code, instead of the "real" PIN code, nothing special is shown on the screen and everything operates as normal... However, the bitcoin key generated is not the main key. It is effectively a completely separate wallet!

To take best advantage of this feature, you should put some Bitcoin into the secondary accounts. How much you are willing to lose or what you need to make it plausible, we don't know.

The "duress" wallet will still be derived from the original BIP39 words, so you don't need to back it up separately, but there will be no way to get from that wallet back to the original wallet with the real funds in it.

Key Storage

We find it a little scary that existing Bitcoin wallets trust the main microprocessor with their valuable secrets.

The Coinkite Coldcard uses Microchip's ATECC508A to store the critical master secret (for the root BIP32 HD wallet). This little chip is very powerful: it does SHA-256 hashing and includes an internal true random number generator (TRNG). Combining those features, and with careful protocol design, we can enforce cryptographically, that the attacker must know the PIN to access the secret. An attacker cannot brute-force all 10,000 combinations of a four-digit numeric code: the search space is 2**256 not 10**4. This remains true even if they removed the chip from the board or fully-replaced the firmware in the main microprocessor.

More details are available in this white paper and the complete source code is available as well.

Genuine vs. Caution Lights

To resist Evil Maids, and other sneaky people with physical access to your Coldcard, we will sign our firmware with a factory key. During boot-up, the firmware's signature will be verified and the appropriate Green/Red light set. Changing that light's status is actually controlled by dedicated circuitry, so a rogue bit of software cannot override it. The control circuit for this is exposed on the top surface of the product, so any physical tampering by those maids will be visible as well.

Firmware Upgradable and Expandable

This product will be firmware upgradable in the field. Updated firmware must be signed by the factory, but we will allow third party software to run as well.

We have internal protection on the master secret, so we feel it's safe to allow potentially hostile firmware onto this platform. If you don't feel safe doing that, then it's a choice you can make.

We're hopeful that altcoin proponents will be able to take our system and extend it to support their speciality crypto coins. It should help that all of the firmware is written in MicroPython.

Debug Mode

Upon entering the unlock code (PIN) and selecting the appropriate menu item, we will even support REPL access over USB. This means you can type python commands directly into the product! You might use this to develop new features, create special transactions, or do special signing requests.

As a developer, you can also download the source and compile it yourself to personalize your Coldcard.

Online Docs

Our documentation is now online here!.

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