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.
But it’s different!
NO specialized software required. It looks like a hard drive, so you can drag and drop files into it. NO companion ‘app’ on your computer, works with the major wallets already.
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.
A full-sized numeric keypad makes entering a 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 the private keys.
Participate in multi-sig wallets, with other signers.
Encrypt/decrypt secret messages (stored on MicroSD or otherwise).
We are still deciding on the PCB color, stay tuned.
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 the 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 “secondary” 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.
We find it a little scary that existing Bitcoin wallets trust the main microprocessor with their valuable secrets.
The Coinkite Coldcard will use Microchip’s ATSHA204 to store the critical master secret (for the root BIP32 HD wallet). This little chip is very powerful and does SHA-256 hashing and has an internal true random number generator (TRNG). Combining those features, and it’s 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
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 in a white paper will come out when the product is finished. We will include code so that you can check we are doing what we say we are.
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, and continuously during operation, 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 later. 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 on 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 specialty crypto coins. It should help that all of the firmware is written in MicroPython.
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.
*Don't ever purchase used Hardware Wallets. Don't accept hardware wallets that have they're sealed open, or their box open.
*Always check that the unit is authentic with the manufacture. Every unit has a security chip to make sure the item is safe.
*There is always a risk when dealing with cryptocurrency, please understand this risk before purchasing. We will not be liable for any losses.
*As this is a high-security item, no returns will be accepted under any circumstances.