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Coldcard Mk4

Latest Release: v5.4.0 12th September 2024

Our wallet review process

We examine wallets starting at the code level and continue all the way up to the finished app that lives on your device. Provided below is an outline of each of these steps along with security tips for you and general test results.

Developer

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Custody

Private keys generated and held by user

As part of our Methodology, we ask: Is the provider ignorant of the keys?

The answer is "yes". Private keys are generated by the user on the wallet.
Read more

Source code

Public on github

Released

1st May 2022

Application build

The binary provided was reproducible from the code provided.

See test result
Tested 1st October 2024

Platform notes

There is no globally accepted definition of a hardware wallet. Some consider a paper with 12 words a hardware wallet - after all paper is a sort of hardware or at least not software and the 12 words are arguably a wallet(‘s backup). For the purpose of this project we adhere to higher standards in the hardware wallet section. We only consider a hardware wallet if dedicated hardware protects the private keys in a way that leaves the user in full and exclusive control of what transactions he signs or not. That means:

  • The device allows to create private keys offline

  • The device never shares private key material apart from an offline backup mechanism

  • The device displays receive addresses for confirmation
  • The device shares signed transactions after informed approval on the device without reliance on insecure external hardware

Passed all 12 tests

We answered the following questions in this order:

Is this product the original?

The answer is "yes".
If the answer was "no", we would mark it as "Fake" and the following would apply:

The answer is "no". We marked it as "Fake".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "Fake" and the following would apply:

The bigger wallets often get imitated by scammers that abuse the reputation of the product by imitating its name, logo or both.

Imitating a competitor is a huge red flag and we urge you to not put any money into this product!

The product cannot be independently verified. If the provider puts your funds at risk on purpose or by accident, you will probably not know about the issue before people start losing money. If the provider is more criminally inclined he might have collected all the backups of all the wallets, ready to be emptied at the press of a button. The product might have a formidable track record but out of distress or change in management turns out to be evil from some point on, with nobody outside ever knowing before it is too late.
Can we expect the product to ever be released?

The answer is "yes".
If the answer was "no", we would mark it as "Announced but never delivered" and the following would apply:

The answer is "no". We marked it as "Announced but never delivered".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "Announced but never delivered" and the following would apply:

Some products are promoted with great fund raising, marketing and ICOs, to disappear from one day to the other a week later or they are one-man side projects that get refined for months or even years to still never materialize in an actual product. Regardless, those are projects we consider “vaporware”.

Is this product available yet?

The answer is "yes".
If the answer was "no", we would mark it as "Un-Released" and the following would apply:

The answer is "no". We marked it as "Un-Released".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "Un-Released" and the following would apply:

We focus on products that have the biggest impact if things go wrong and while pre-sales sometimes reach many thousands to buy into promises that never materialize, the damage is limited and there would be little definite to be said about an unreleased product anyway.

If you find a product in this category that was released meanwhile, please contact us to do a proper review!

Is it a wallet?

The answer is "yes".
If the answer was "no", we would mark it as "Not a wallet" and the following would apply:

The answer is "no". We marked it as "Not a wallet".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "Not a wallet" and the following would apply:

If it’s called “wallet” but is actually only a portfolio tracker, we don’t look any deeper, assuming it is not meant to control funds. What has no funds, can’t lose your coins. It might still leak your financial history!

If you can buy Bitcoins with this app but only into another wallet, it’s not a wallet itself.

Is it for bitcoins?

The answer is "yes".
If the answer was "no", we would mark it as "A wallet but not for Bitcoin" and the following would apply:

The answer is "no". We marked it as "A wallet but not for Bitcoin".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "A wallet but not for Bitcoin" and the following would apply:

At this point we only look into wallets that at least also support BTC.

Is the provider ignorant of the keys?

The answer is "yes".
If the answer was "no", we would mark it as "Provided private keys" and the following would apply:

The answer is "no". We marked it as "Provided private keys".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "Provided private keys" and the following would apply:

The best hardware wallet cannot guarantee that the provider deleted the keys if the private keys were put onto the device by them in the first place.

There is no way of knowing if the provider took a copy in the process. If they did, all funds controlled by those devices are potentially also under the control of the provider and could be moved out of the client’s control at any time at the provider’s discretion.

The product cannot be independently verified. If the provider puts your funds at risk on purpose or by accident, you will probably not know about the issue before people start losing money. If the provider is more criminally inclined he might have collected all the backups of all the wallets, ready to be emptied at the press of a button. The product might have a formidable track record but out of distress or change in management turns out to be evil from some point on, with nobody outside ever knowing before it is too late.
Does the device hide your keys from other devices?

The answer is "yes".
If the answer was "no", we would mark it as "Leaks Keys" and the following would apply:

The answer is "no". We marked it as "Leaks Keys".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "Leaks Keys" and the following would apply:

Some people claim their paper wallet is a hardware wallet. Others use RFID chips with the private keys on them. A very crucial drawback of those systems is that in order to send a transaction, the private key has to be brought onto a different system that doesn’t necessarily share all the desired aspects of a hardware wallet.

Paper wallets need to be printed, exposing the keys to the PC and the printer even before sending funds to it.

Simple RFID based devices can’t sign transactions - they share the keys with whoever asked to use them for whatever they please.

There are even products that are perfectly capable of working in an air-gapped fashion but they still expose the keys to connected devices.

This verdict is reserved for key leakage under normal operation and does not apply to devices where a hack is known to be possible with special hardware.

The product cannot be independently verified. If the provider puts your funds at risk on purpose or by accident, you will probably not know about the issue before people start losing money. If the provider is more criminally inclined he might have collected all the backups of all the wallets, ready to be emptied at the press of a button. The product might have a formidable track record but out of distress or change in management turns out to be evil from some point on, with nobody outside ever knowing before it is too late.
Can the user verify and approve transactions on the device?

The answer is "yes".
If the answer was "no", we would mark it as "Bad Interface" and the following would apply:

The answer is "no". We marked it as "Bad Interface".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "Bad Interface" and the following would apply:

These are devices that might generate secure private key material, outside the reach of the provider but that do not have the means to let the user verify transactions on the device itself. This verdict includes screen-less smart cards or USB-dongles.

The wallet lacks either a screen or buttons or both. In consequence, crucial elements of approving transactions is being delegated to other hardware such as a general purpose PC or phone which defeats the purpose of a hardware wallet. For big exit scams, a companion app could always request two signatures - one for the coffee you are paying and a second to empty your wallet completely. The former could be broadcast while the latter only gets collected for later use.

Another consquence of a missing screen is that the user is faced with the dilemma of either not making a backup or having to pass the backup through an insecure device for display or storage.

The software of the device might be perfect but this device cannot be recommended due to this fundamental flaw.

The product cannot be independently verified. If the provider puts your funds at risk on purpose or by accident, you will probably not know about the issue before people start losing money. If the provider is more criminally inclined he might have collected all the backups of all the wallets, ready to be emptied at the press of a button. The product might have a formidable track record but out of distress or change in management turns out to be evil from some point on, with nobody outside ever knowing before it is too late.
Is the source code publicly available?

The answer is "yes".
If the answer was "no", we would mark it as "No source for current release found" and the following would apply:

The answer is "no". We marked it as "No source for current release found".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "No source for current release found" and the following would apply:

A wallet that claims to not give the provider the means to steal the users’ funds might actually be lying. In the spirit of “Don’t trust - verify!” you don’t want to take the provider at his word, but trust that people hunting for fame and bug bounties could actually find flaws and back-doors in the wallet so the provider doesn’t dare to put these in.

Back-doors and flaws are frequently found in closed source products but some remain hidden for years. And even in open source security software there might be catastrophic flaws undiscovered for years.

An evil wallet provider would certainly prefer not to publish the code, as hiding it makes audits orders of magnitude harder.

For your security, you thus want the code to be available for review.

If the wallet provider doesn’t share up to date code, our analysis stops there as the wallet could steal your funds at any time, and there is no protection except the provider’s word.

“Up to date” strictly means that any instance of the product being updated without the source code being updated counts as closed source. This puts the burden on the provider to always first release the source code before releasing the product’s update. This paragraph is a clarification to our rules following a little poll.

We are not concerned about the license as long as it allows us to perform our analysis. For a security audit, it is not necessary that the provider allows others to use their code for a competing wallet. You should still prefer actual open source licenses as a competing wallet won’t use the code without giving it careful scrutiny.

The product cannot be independently verified. If the provider puts your funds at risk on purpose or by accident, you will probably not know about the issue before people start losing money. If the provider is more criminally inclined he might have collected all the backups of all the wallets, ready to be emptied at the press of a button. The product might have a formidable track record but out of distress or change in management turns out to be evil from some point on, with nobody outside ever knowing before it is too late.
Is the decompiled binary legible?

The answer is "yes".
If the answer was "no", we would mark it as "Obfuscated" and the following would apply:

The answer is "no". We marked it as "Obfuscated".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "Obfuscated" and the following would apply:

When compiling source code to binary, usually a lot of meta information is retained. A variable storing a masterseed would usually still be called masterseed, so an auditor could inspect what happens to the masterseed. Does it get sent to some server? But obfuscation would rename it for example to _t12, making it harder to find what the product is doing with the masterseed.

In benign cases, code symbols are replaced by short strings to make the binary smaller but for the sake of transparency this should not be done for non-reproducible Bitcoin wallets. (Reproducible wallets could obfuscate the binary for size improvements as the reproducibility would assure the link between code and binary.)

Especially in the public source cases, obfuscation is a red flag. If the code is public, why obfuscate it?

As obfuscation is such a red flag when looking for transparency, we do also sometimes inspect the binaries of closed source apps.

As looking for code obfuscation is a more involved task, we do not inspect many apps but if we see other red flags, we might test this to then put the product into this red-flag category.

The product cannot be independently verified. If the provider puts your funds at risk on purpose or by accident, you will probably not know about the issue before people start losing money. If the provider is more criminally inclined he might have collected all the backups of all the wallets, ready to be emptied at the press of a button. The product might have a formidable track record but out of distress or change in management turns out to be evil from some point on, with nobody outside ever knowing before it is too late.
Can the product be built from the source provided?

The answer is "yes".
If the answer was "no", we would mark it as "Failed to build from source provided!" and the following would apply:

The answer is "no". We marked it as "Failed to build from source provided!".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "Failed to build from source provided!" and the following would apply:

Published code doesn’t help much if the app fails to compile.

We try to compile the published source code using the published build instructions into a binary. If that fails, we might try to work around issues but if we consistently fail to build the app, we give it this verdict and open an issue in the issue tracker of the provider to hopefully verify their app later.

The product cannot be independently verified. If the provider puts your funds at risk on purpose or by accident, you will probably not know about the issue before people start losing money. If the provider is more criminally inclined he might have collected all the backups of all the wallets, ready to be emptied at the press of a button. The product might have a formidable track record but out of distress or change in management turns out to be evil from some point on, with nobody outside ever knowing before it is too late.
Does the published binary match the published source code?

The answer is "yes".
If the answer was "no", we would mark it as "Not reproducible from source provided" and the following would apply:

The answer is "no". We marked it as "Not reproducible from source provided".

We did not ask this question because we failed at a previous question.
If the answer was "no", we would mark it as "Not reproducible from source provided" and the following would apply:

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.

The product cannot be independently verified. If the provider puts your funds at risk on purpose or by accident, you will probably not know about the issue before people start losing money. If the provider is more criminally inclined he might have collected all the backups of all the wallets, ready to be emptied at the press of a button. The product might have a formidable track record but out of distress or change in management turns out to be evil from some point on, with nobody outside ever knowing before it is too late.

Application build test result

Update 2024-10-01: There are no binary misnaming for tag 2024-09-12T1734-v5.4.0. We execute the ws coldcard script:

$ ./scripts/test/hardware/coldCard.sh 2024-09-12T1734-v5.4.0 mk4

Asciicast

Results

Comparing against: /tmp/checkout/firmware/releases/2024-09-12T1734-v5.4.0-mk4-coldcard.dfu
test -n "/tmp/checkout/firmware/releases/2024-09-12T1734-v5.4.0-mk4-coldcard.dfu" -a -f /tmp/checkout/firmware/releases/2024-09-12T1734-v5.4.0-mk4-coldcard.dfu
rm -f -f check-fw.bin check-bootrom.bin
signit split /tmp/checkout/firmware/releases/2024-09-12T1734-v5.4.0-mk4-coldcard.dfu check-fw.bin check-bootrom.bin
start 293 for 942080 bytes: Firmware => check-fw.bin
signit check check-fw.bin
     magic_value: 0xcc001234
       timestamp: 2024-09-12 17:34:31 UTC
  version_string: 5.4.0
      pubkey_num: 1
 firmware_length: 942080
   install_flags: 0x0 =>
       hw_compat: 0x8 => Mk4
         best_ts: b'\x00\x00\x00\x00\x00\x00\x00\x00'
          future: 0000000000000000 ... 0000000000000000
       signature: 895ad7fd1c7cf46b ... 172be2679b6db566
sha256^2: 120e84880289f61c9eae0fe5182a180425ed7bea9016ee3c836e5481ef77ba92
 ECDSA Signature: CORRECT
signit check firmware-signed.bin
     magic_value: 0xcc001234
       timestamp: 2024-10-01 01:25:37 UTC
  version_string: 5.4.0
      pubkey_num: 0
 firmware_length: 942080
   install_flags: 0x0 =>
       hw_compat: 0x8 => Mk4
         best_ts: b'\x00\x00\x00\x00\x00\x00\x00\x00'
          future: 0000000000000000 ... 0000000000000000
       signature: c0fbe3997d069c18 ... bfbedea87fa85475
sha256^2: 5a2923ba8f4059143f194d405289e6dbe4ead833c4698743b07a9f2381d6b1ec
 ECDSA Signature: CORRECT
hexdump -C firmware-signed.bin | sed -e 's/^00003f[89abcdef]0 .*/(firmware signature here)/' > repro-got.txt
hexdump -C check-fw.bin | sed -e 's/^00003f[89abcdef]0 .*/(firmware signature here)/' > repro-want.txt
diff repro-got.txt repro-want.txt

SUCCESS.

The most pertinent part of the review:

You have built a bit-for-bit identical copy of Coldcard firmware for v5.4.0
+ set +ex

Hash of non-signature parts downloaded/compiled:
04114bc10eaebf4a7296823561e966bdf871bb8cbbc77617f2f0714c89ff95d5  2024-09-12T1734-v5.4.0-mk4-nosig.bin
04114bc10eaebf4a7296823561e966bdf871bb8cbbc77617f2f0714c89ff95d5  firmware-nosig.bin

Hash of the signed firmware:
237cfcb3fdf9217550eae1d9ea6fc828c1c8d09470bd60c9f72f9b00a3bb2d11  /tmp/firmware/releases/2024-09-12T1734-v5.4.0-mk4-coldcard.dfu
4ca2a537cb0cd2ffb1227bd7b6bd19f9c3ec1f510d4a743dd1bafe1ee860ff56  /tmp/firmware/stm32/built/firmware-signed.dfu

ColdCard advertises its products as verifiable, we can confirm that firmware version: 2024-09-12T1734-v5.4.0 is reproducible.

Old Analysis

Product Description

The ColdCard Mark 4 is CoinKite’s latest iteration of the ColdCard series. At the time of this writing, the Mark 4 is still in pre-order. The current product in the series is the Coldcard Mk3      .

Claimed features of the Coldcard Mark 4:

  • USB-C Connector
  • Unlimited Memory, no Bitcoin Transaction size restrictions
  • NFC Tap for all data types, PSBT, Address, etc…
  • Slide Cover
  • Even more security, Dual SE (Secure Elements)
  • Extensive duress PIN optionality
  • Multi-vendor SE
  • USB Virtual Disk mode
  • New 2x secure elements design (multi vendor)
  • New plastic
  • Faster Processor

Specs:

  • Speed: 120 Mhz main CPU (was 80Mhz)
  • Memmory: 840kb + 8M RAM (was only 360kb) - This is where we process transactions.
  • Flash memory: for firmware doubled! (now ~1.5M, was ~700M)
  • Settings memory: now 512kb (was 4kb)
  • PSRAM used instead of flash to hold PSBT and Transaction (faster workspace)
  • Replaceable OLED display (same size, resolution but better supplier)
  • Hardware SHA256 & AES engine (faster encryption/decription)
  • Multi-vendor dual Secure Element [SE] new design (Microchip 608A + )
  • New USB LED flashes when USB is active
  • USB-C connector
  • NFC V capability and exposed trace for permanent disable

Functions:

  • Unlimited transaction size
  • More multisig wallets possible
  • Firmware upgrade more secure, faster: 15 seconds using USB vs. 2 minutes
  • Nearly same great price when you add inflation!
  • Boots much faster
  • New “trick pins” allow for endless duress labyrinth. Instant wipe or brick or wipe and continue into duress, etc…
  • Sliding case cover protects screen when COLDCARD is hidden and not in use
  • NFC communications integrated
  • USB disk emulation for simple use w/ web browsers and other PSBT sources
  • Bootrom contains anti-chip shouter/glitching protections which reduce timing certainty
  • Countdown to login feature improved: fast wipe External settings chip removed. Setting now internal to MCU (faster, more space for settings)
  • Kill-key feature: press key N while phishing words shown -> fast wipe+stop (not silent)
  • Debug serial port moved to pins, rather than being virtual over USB

Reproducibility

We have added the test script for ColdCard wallets which is based on the build script that ColdCard provides in their Github.

Here are the test results for the latest version:

$ ./scripts/test/hardware/coldCard.sh "2023-04-07T1330-v5.1.2" 4

...

Hash of non-signature parts downloaded/compiled:
254bcf59c776902603f78310160e8edf2573bc7dcb934282acff8561bd9a173f  2023-04-07T1330-v5.1.2-mk4-nosig.bin
254bcf59c776902603f78310160e8edf2573bc7dcb934282acff8561bd9a173f  firmware-nosig.bin

Hash of the signed firmware:
7aefd5bcce533f15337e83618ebbd42925d336792c82a5ca19a430b209b30b8a  /tmp/firmware/releases/2023-04-07T1330-v5.1.2-mk4-coldcard.dfu
390b2cbc4053a1ab7e3949ee83b7d2008ae214e008a8f7a74688989d52de2d27  /tmp/firmware/stm32/built/firmware-signed.dfu

which shows this firmware is reproducible.

Tests performed by Daniel Andrei R. Garcia, Leo Wandersleb, mohammad

Previous application build tests

15th August 2024 v5.3.3  
8th October 2023 v5.1.4  
22nd June 2023 v5.1.2  
Show more

Disclaimer

Our Analysis is not a full code review! We plan to make code reviews available in the future but even then it will never be a stamp of approval but rather a list of incidents and questionable coding practice. Nasa sends probes to space that crash due to software bugs despite a huge budget and stringent scrutiny.

Do your own research

In addition to reading our analysis, it is important to do your own checks. Before transferring any bitcoin to your wallet, look up reviews for the wallet you want to use. They should be easy to find. If they aren't, that itself is a reason to be extra careful.