COLDCARD Mk4 Improvements

Mk4 Preview

As seen in the recent Bitcoin Magazine Article!

The Mk4 COLDCARD® is on its way and packing serious upgrades. Better usability, faster performance, stronger security — all without sacrificing COLDCARD's unparalleled affordability.

Get ready to meet your new self-custody, cold storage solution.

Mk4 Highlights

  • USB-C connector
  • Unlimited memory: no Bitcoin transaction size restrictions!
  • Expanded multisig capabilities: handle bigger, more complex transactions.
  • NFC-V compatible: tap to transmit all data types, including PSBTs, addresses, and XPUBs.
  • Protective sliding cover shields screen and keypad when not in use.
  • Two Secure Elements for even more security:
    • Many new and extensive duress PIN options (Trick PINs)
    • Two Secure Elements, two manufacturers; minimizes unknown vulnerability risks.
  • USB Virtual Disk Mode: emulates a 4MB disk when connected to macOS, Windows, iPhone, etc.
  • Tougher case: upgraded with new plastic and cleaner edges.
  • Faster processor and substantially higher memory capacity.

Mk3 vs. Mk4 Fact Sheet

A side-by-side comparison of some of the improvements you can look forward to:

Mk4 Mk3
Connector USB-C Micro USB
# of Secure Elements 2 1
CPU Speed 120 MHz 80 MHz
Memory 840 kB + 8 MB RAM 360 kB
Flash Memory (Firmware) ≈ 1.5 MB ≈ 700 kB
Settings Memory 512 kB 4 kB
Additional Secure Storage 216 (3 x 72) bytes
External Settings Chip
USB-In-Use LED
Debug Serial Port Physical (Pins) Virtual (USB)
Sliding Cover
NFC-V Compatible
PSBT Location PSRAM Flash
Trick PINs
USB Virtual Disk Mode
Firmware Upgrade Time 15 seconds 2 minutes
Bitcoin Transaction Size Limit 2 MB 384 kB

New Features for COLDCARD Mk4

NFC-V Compatibility

NFC is the technology behind tap-to-pay and keyless entry. You'll soon be able to sign a transaction with a tap of your COLDCARD, but only if you choose to.

The NFC feature is turned off by default and can be rendered unusable — permanently — by cutting a trace on the board. No other functions use the destructible trace.

Those who opt to enable NFC can use it for all PSBT, transaction, address sharing, and similar data.

USB Virtual Disk Mode

Another data transfer option is Virtual Disk Mode: connect the Mk4 to a computer or mobile phone and it sees the Mk4 as a 4 MB USB stick. Using your COLDCARD Mk4 with web browsers and other PSBT sources is effortless because you can save directly to your Mk4.

Increased Performance and Security

The Mk4 takes advantage of its new hardware to provide faster and more secure transactions:

  • MCU implements SHA-256 and AES natively for quicker encryption/decryption.
  • PSRAM provides a faster workspace than flash memory. PSBTs and other transaction data are now held in PSRAM.
  • Boot ROM incorporates anti-chip shouting/glitching protections which reduce timing certainty.
  • Settings are now in the MCU, rather than an external settings chip, allowing more space for settings and quicker response times.
  • Second Secure Element expands the duress labyrinth to keep your secrets safe:
  • Highly customizable Trick PINs can be configured to temporarily or permanently disable your COLDCARD, or just wipe the stored seed, in an instant.
  • Fast Wipe (immediate clearing of seed words) added to Countdown to Login feature.
  • New Kill Key option - select a key to press when anti-phishing words are displayed which will trigger a Fast Wipe during login.

NFC Notes

  • defaults to OFF, must be enabled in Settings > Hardware On/Off > NFC Sharing
  • press 3 after signing to share txn by NFC
  • press 3 on any QR to share same by NFC
  • can share any PSBT/Txt/Transaction file from MicroSD
  • disable forever by cutting trace labeled "NFC", visible in the MicroSD slot.

Todo / Roadmap

  • 216 bytes (3x72) of new super-secure storage alongside main seed phrase

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