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CoinKite Coldcard Mk 1

Latest release: v1.2.1 ( 19th December 2019 ) 🔍 Last analysed 19th May 2022 . Not reproducible from source provided Not updated in a long time
25th July 2018

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The Analysis 

Background

Announced on December 8, 2017, the CoinKite Coldcard Mk 1 is the first iteration of Coinkite’s series of devices. It is now obsoleted by the manufacturer and is no longer for sale.

Product Specifications

  • Can sign transactions and can be used offline
  • BIP39 based: backup passphrase, sub-accounts, unlimited payment addresses
  • No specialized hardware required
  • Private key is secured in a dedicated security chip
  • MicroSD card slot of backup and data storage
  • Open source using Micropython
  • Full-sized numeric keypad
  • 128x64 OLED screen

Firmware Updates

v1.0.2

  • Add support for SLIP-132
  • yprv/zprv keys can now be imported
  • public.txt file includes both SLIP-132 and BIP-32 values where needed (segwit cases)
  • test cases added to match
  • Can create Electrum skeleton wallet for Segwit Native and Segwit P2SH now.
  • caveat: the plugin is not ready yet for P2SH/Segwit, but Segwit native is fine
  • Improvements in ‘public.txt’ output:
  • add SLIP-132 values where we can
  • correct names when used for Litecoin
  • Improvements to backup and restore
  • can now restore cleartext backups (for devs only!)
  • fix “Unable to open … /sd/backup.7z” error

v1.1.0

  • Allow setting max network fee to a number of possible levels, or disable it (was previously fixed to 10%). Thanks to @crwatkins for this suggestion.
  • Touch improvements: two new setting, which are between the old ‘Least Sensitive’ and ‘Most Sensitive’ settings. New menu text.
  • Touch sensitivity preference is applied before login, so PIN entry is easier.
  • Although we do not use the bech32_decode() function recently found to have an buffer overflow bug, we’ve included the fix into our fork of the affected library. This change, and the original bug, does not affect the Coldcard firmware in any way.
  • Correctly include witness data in transactions when signing based on witness UTXO data (thanks to @SomberNight)
  • Bugfix: Fix divide-by-zero if transaction sends zero amount out (only possible if network fee equals 100% of inputs).

Analysis

The product is no longer commercially available and is obsoleted by the manufacturer.

(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.