Different ways to connect your Coldcard – OFF, by default 😎
The industry-standard for transmitting both data and power over a single cable.
Maximum security when transferring data between devices
Secure & very short-range wireless transmission that sends data to your phone easily
Mk4 can emulate a USB disk drive, so sending PSBT files can be a drag-n-drop.
Trick PIN Features
Mk4 has even more tricks up its sleeve!
You may define an optional "duress PIN code". If anyone enters 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 duress wallet. 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.
Countdown to Brick PIN
This is a covert variation of the BRICK ME PIN mode. It forces a time delay (of minutes/hours/days) when logging into the Coldcard.
But once set, unlike the normal countdown, this special mode covertly bricks the Coldcard (or, optionally merely wipes the seed). Again, this may form some part of your game-theory for duress situations, but is completely optional.
The goal of this mode is to provide plausible deniability of a required time delay (similar to Bank’s safes), while denying the attacker a functional device in case they take it away.
BIP39 Passphrases (25th word)
We support BIP39 passphrases so you can also create an unlimited supply of distraction wallets. This feature is also useful for your own organization of funds or accounts. Unlike the single duress PIN, an unlimited number of related wallets can be created using BIP39.
Brick Me PIN
Another PIN can also be defined, which we call the “Brick Me” PIN. Using that PIN code at any PIN prompt, will destroy the dual secure element and render your Coldcard worthless. Again, this may form some part of your game-theory for duress situations, but is completely optional.
Force a time delay when logging into the Coldcard. Once enabled, you must enter the PIN correctly, and then wait out a forced delay (of minutes/hours/days) while a countdown is shown on-screen. Then enter your PIN correctly, a second time, to get in.
Rugged and sleek protective cover
Like the classic calculators from our childhoods: slide the protective
cover down, reverse, and slide back onto the rear. Saves your screen
Level up on your USB P.P.E. and power your Coldcard or other low power USB devices from a standard 9-volt battery without any USB data concerns. Makes a great gift for the cypherpunk in your life. (5volts, 500mA max current)
Interoperation between Bitcoin signing devices (a.k.a. hardware wallets) is now possible, thanks to BIP174 which introduces a binary file format that all signing devices can use. Coldcard has been based on BIP174 from day one, and uses it exclusively.
Most Trusted and Secure Bitcoin Signing Device (Hardware Wallet)
Dual Secure Element for Key Storage
We find it quite scary that some signing devices trust the main microprocessor with their most valuable secrets. Instead, Coldcard uses two Secure Elements, from different vendors,
to protect your Bitcoin.
Specifically, the Coldcard (Mk4) uses Microchip's ATECC608A and Maxim's DS28C36B,
to store the critical master secret: the 24-word seed phrase for your BIP39 wallet.
These little chips are very powerful. Communication is
controlled by complex challenges and SHA-256 responses which
prevent replay and eavesdropping. The dual secure element
the attacker must know the PIN to access the secrets. An attacker
cannot brute-force combinations or replay a previous login sequence.
This remains true even if they removed the chip from the board or
fully-replaced the firmware in the main microprocessor. In fact,
even with the secure element removed from the system, and all the
secrets of the main micro fully-known (and all the secrets held in
the second Secure Element, DS28C36B), the attacker would still only
get 13 tries before the ATECC608B bricks itself. (Don’t worry,
this counter is reset every time you login correctly.)
Even if there was some critical security bug in the dual secure element that completely exposed the secrets it holds, your bitcoin would still be safe, because we encrypt the contents of the dual secure element with a one-time pad known only to the main micro.
To resist Evil Maids, and other sneaky people with physical access to your Coldcard, we sign our firmware with a factory key. During boot-up, the firmware's signature, and nearly every byte of flash memory, will be verified and the appropriate Green/Red light set. Changing that light's status is actually controlled by dedicated circuitry connected directly to a Secure Element, so a rogue bit of software cannot override it. The circuit for the lights is exposed on the top surface of the product, so any physical tampering by those maids will be visible as well.
The PIN code on Coldcard is divided into two parts, such as 1234-5678. You first enter 1234 and then you will be shown two words on-screen. Those words are unique for all PIN prefixes, and for each Coldcard ever made. (The secrets used to enforce that come from inside the secure element, and are unknown to the rest of the world.)
Your job is to memorize those two words, keep them secret, and every time you use the Coldcard, check them before entering the final 5678 part of your PIN. This protects you against a trojan-horse Coldcard that might look like yours but it cannot know those two words.
Both secure elements and critical parts of the main micro are covered by epoxy at the factory. Our clear case is part of our security model too, so you can look and see if a "hardware implant" has been inserted inside your device.
Because of the in-depth use of the secure elements, there is no "factory reset" for the Coldcard. If you forget your Coldcard PIN, there is nothing we can do except remind you to recycle your e-waste responsibly!
We've even put a label, "SHOOT THESE", for more effective device destruction... When the time comes.
Air Gap Operation
Coldcard never needs to touch a computer. It can work entirely from a USB power pack or AC power adapter. This includes everything you need to do in the whole life of the product:
Initial PIN choosing and setup.
Pick your 24-seed words using our TRNG, import existing secrets, or use your dice rolls.
Export skeleton wallet files, for setup of Electrum or other desktop/mobile wallets.
Advanced users can even setup a multisig wallet between multiple cosigners, entirely on-device, and air gapped
Using our industrial grade MicroSD Cards or any standard MicroSD card, for each of the above steps that require data to come in and out. Sneakernet for the win! If you want to reach the next level paranoia, you can use different cards for the data coming into versus out of the Coldcard, and/or use cards a single time only.
Dice Roll and Provable Bitcoin Seed Generation
If you don't trust our random number generator, you can generate the BIP39 seed phrase using dice rolls. We help with this process: you just have to press 1–6 for each roll (99 rolls recommended). At the end of that process, you'll have a properly-encoded seed phrase based solely on the dice rolls. Learn how to verify COLDCARD's dice-rolls math here.
Great multisig support and advanced defenses
Unparalleled Bitcoin Core support with output descriptors
Unique ColdCard Features
Endless Security to Help Reduce Your Risk
We have a convenient backup feature: just a few clicks and an encrypted file is written to MicroSD with everything you would need to restore a lost or broken Coldcard. Because it's a simple text file (inside the encryption), it would also be all you need to switch vendors and avoid any lock-in.
Learn more in our on-line docs about Backups. You can even verify our encryption, using any desktop 7z program. On the Coldcard itself, you can perform quick check that the file is not truncated, and a simple checksum applies.
If you don't like the idea of encrypted backups, because passphrases can get lost, we do offer clear-text backup file output.
One risk with signing devices (a.k.a. hardware wallets) is malicious software tricking them into displaying incorrect details of a transaction. Coldcard is therefore very careful analyzing the content of the PSBT file and the transaction itself. These checks include:
Verify UTXO details of inputs being spent (plus leverages advantages of new SegWit-style transactions in this area).
Change outputs, which should be coming back to the same wallet, are carefully studied. In particular, we’ve found other wallets are not being detailed enough in this process.
The Coinkite team has been in the Bitcoin space long enough to know that we shouldn’t expect you to trust us! (Since 2012, BTW.)
Here are some of the features we offer to support that goal:
Open source software, every byte
Provable dice rolls to generate your seed
Clear plastic case
Open standards for file formats: BIP174 (PSBT), 7z encrypted archives, simple JSON/text files when possible, etc.
Tamper-resistant shipping bags
NFC interface can be mechanically disabled
We are the only hardware wallet addressing the problem of substitute devices, and other trojan, by using a dual secure element. In effect you are verifying the Coldcard’s dual secure element every time you login.
Firmware Upgradable and Expandable
This product is firmware upgradable in the field. Updated firmware must be signed by the factory private key. The Mk4 has considerable memory resources available for power new features and to support advances to Bitcoin in the furture
As a developer, you can also download the source and compile it yourself to personalize your Coldcard, but we also have a one-step reproducable build process so your know what's in the factory release too.
Running your own custom firmware is possible but a warning is shown every boot, and the correct PIN code must be used to install it in the first place.
We use a unique tamper-evident plastic bag to package your new Coldcard.
Each bag is unique and coded with a serial number. That "bag number" is written into
the Coldcard's as it's put into its bag. That value cannot be changed,
and we ask your to verify the bag number when you power-up the Coldcard for
the first time.
The clear plastic case on Coldcard is an important feature as well. There have been demonstrations of inserting custom hardware inside a competitor's hardware wallet to capture key-presses.
Epoxy Globs of Love
We cover the secure selement, and other sensitive parts of the Coldcard with epoxy. This makes it harder to remove those chips, or change the wiring around them.