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Coinkite Coldcard Mk 2

Latest release: v2.0.2 ( 26th August 2019 ) 🔍 Last analysed 19th May 2022 . Not reproducible from source provided Not updated in a long time
6th April 2019

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Try out searching for "lost bitcoins", "stole my money" or "scammers" together with the wallet's name, even if you think the wallet is generally trustworthy. For all the bigger wallets you will find accusations. Make sure you understand why they were made and if you are comfortable with the provider's reaction.

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The Analysis 

Background

The Coinkite Coldcard Mk 2 has been obsoleted by the manufacturer and is no longer available commercially.

Ledger disclosed that the Mk2 may be susceptible to a Laser Fault Injection attack.

The security scheme of the Coldcard Mk2 wallet is well designed and relies mainly on the ATECC508A secure memory, which is a smart design decision. The equipment required to perform the physical attack of the ATECC508A is expensive: about $200k, which limits the potential attackers.

Above they briefly state how the attack is performed:

We physically injected a fault during the execution of the secure memory to bypass the access conditions verification of a targeted data slot. This is an invasive attack which requires physical access to the secure memory die:

Product Description

Firmware Version 2.0.2

  • BIP-39 Passphrase support: enter up to 100 characters to create new wallets from your existing seed words. Each is a completely independent wallet to Electrum and PSBT files, so please make note of the extended master fingerprint (eight hex digits).
  • Support for Mark2 hardware, with membrane keypad replacing touch interface.
  • Adds activity light during MicroSD card read/write (Mk2 only)
  • New command: “Lock down seed” which converts BIP-39 seed words and passphrase into the master xprv and saves that as new wallet secret. Locks in the passphrase, deletes seed words.
  • New bootrom, version 1.2.1 with Mk2 hardware support and improved one-wire bus MitM defences.
  • Bugfix: extra keypress occurs during certain interactions involving key repeat.
  • (in 2.0.1) bugfix: underscore/space indicator shown on Settings > Idle Timeout menu
  • (in 2.0.2) Page up/down on long text displays with 7/9 keys
  • (in 2.0.2) Public summary file now includes extended master key fingerprint near top of file.
  • (in 2.0.2) Bugfix: signing larger transactions could fail due to lack of memory

Analysis

As mentioned above, the Coinkite Coldcard Mk 2 has been obsoleted by the manufacturer, further analysis would be moot and academic.

(dg)

Verdict Explained

We could not verify that the provided code matches the binary!

As part of our Methodology, we ask:

Is the published binary matching the published source code? If not, we tag it Unreproducible!

Published code doesn’t help much if it is not what the published binary was built from. That is why we try to reproduce the binary. We

  1. obtain the binary from the provider
  2. compile the published source code using the published build instructions into a binary
  3. compare the two binaries
  4. we might spend some time working around issues that are easy to work around

If this fails, we might search if other revisions match or if we can deduct the source of the mismatch but generally consider it on the provider to provide the correct source code and build instructions to reproduce the build, so we usually open a ticket in their code repository.

In any case, the result is a discrepancy between the binary we can create and the binary we can find for download and any discrepancy might leak your backup to the server on purpose or by accident.

As we cannot verify that the source provided is the source the binary was compiled from, this category is only slightly better than closed source but for now we have hope projects come around and fix verifiability issues.

But we also ask:

Was the product updated during the last two years? If not, we tag it Obsolete!

Bitcoin wallets are complex products and Bitcoin is a new, advancing technolgy. Projects that don’t get updated in a long time are probably not well maintained. It is questionable if the provider even has staff at hands that is familiar with the product, should issues arise.

This verdict may not get applied if the provider is active and expresses good reasons for not updating the product.