In the video above, Bitcoin Magazine reviewed Coinkite’s Coldcard Mk3 bitcoin hardware wallet, evaluating it with a handful of important criteria, including coin control, UTXO selection, Lightning support and more.
Appearance and Feel
As the second version of Coinkite’s hardware wallet, the Mk3 feels almost identical to the earlier model. It features the same full-sized numeric keypad that you would find on a calculator, which, when applied to a bitcoin wallet, feels very convenient in contrast to clicking the same two buttons to confirm actions (often found on other hardware wallets). A notable design feature of the Coldcard Mk3 is the clear plastic casing that highlights the inner workings of the device. This, in my opinion, gives it a really unique, cypherpunk-esque feel.
Security and Usage
The Coldcard can be used by itself without the need to connect to a computer. This means that you can use the Mk3 in an air gapped fashion, which can be a huge plus in the eyes of a security-driven bitcoin user. This is possible thanks to the microSD slot built into the side of the wallet — you can pass along transaction (and other) information to and from a computer by simply putting the chip into the computer and then back into the wallet.
In terms of security, the Mk3 uses Microchip’s ATECC608A to store the critical master secret: the 24-word seed phrase for your BIP 32/BIP 39 wallet.
“This little chip is very powerful,” Coldcard states on its website. “Communication is controlled by complex challenges and SHA-256 responses which prevent replay and eavesdropping. The secure element enforces cryptographically, that the attacker must know the PIN to access the secrets.