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Skycoin hardware wallet

Build Status

Table of contents


This repo contains the firmware and bootloader for the Skywallet as well as tools to test and develop for the Skywallet. The firmware can be found in /tiny-firmware. The firmware has been modified from Trezor.

The skycoin-api folder contains the definition of the functions implementing the Skycoin features. The Skywallet Go CLI defines Golang functions that communicate with the firmware/bootloader.


Frequently Asked Question

Install tools

Get the development dependencies and tools from the tiny-firware/ first, before continuing with the build instructions.

Build instructions:

After cloning this repository, make sure the submodules are up-to-date by executing the following command:

git submodule update --init --recursive

Should you find any issues while running any of the commands that follow please consult FAQ before reporting a bug.

Build a bootloader

make bootloader # Your firmware is skybootloader-no-memory-protect.bin

Build a bootloader with memory protection enabled

Careful if you flash and run that bootloader on the device it will activate a memory protection that will close access to flash memory.

You won't be able to flash your device with an st-link again.

make bootloader-mem-protect # Your firmware is bootloader-memory-protected.bin

Build a firmware

make firmware  # Your firmware is tiny-firmware/skyfirmware.bin

Sign firmware

Signs the firmware with the private key corresponding to the PubKeys that were registered in the bootloader during building. The PubKeys can be found in the project Makefile

make sign # Your firmware is tiny-firmware/skyfirmware.bin

Sign on MacOS with docker

Currently, the firmware cannot be signed on MacOS straight away. In order to sign the firmware on MacOS nonetheless, you can use the script which requires a stable Docker release to be installed.


Combine bootloader and firmware

This creates a combined firmware without memory protection.

make full-firmware # this will create a full-firmware-no-mem-protect.bin file

Combine a memory protected bootloader and firmware

Caution: This combined firmware has memory protection enabled and therefore cannot be re-flashed.

make full-firmware-mem-protect # this will create a full-firmware-memory-protected.bin file

Build and run emulator

make clean && make run-emulator

In case of needing special compiler flags for the SDL library it is possible to provide them in SDL_CFLAGS variable. For instance , if SDL was installed with brew on Mac OS X then the following command execution would force searching for header files at the right location.

make clean && make run-emulator SDL_CFLAGS=-I$(brew --prefix sdl2)/include/SDL2

However for the default brew installation in practice this should not be needed since the value of SDL_CFLAGS defaults to $(shell sdl2-config --cflags | sed 's/-D_THREAD_SAFE//g').

Development guidelines

Code added in this repository should comply with the development guidelines documented in the Skycoin wiki.

This project has two branches: master and develop.

  • develop is the default branch and will always have the latest code.
  • master will always be equal to the current stable release on the website, and should correspond with the latest release tag.

Versioning policies

Firmware version scheme

The firmware follows Semver.

The firmware binary filename is skywallet-firmware-v$(VERSION_FIRMWARE).bin e.g. skywallet-firmware-v1.0.0.bin .

Bootloader version scheme

The bootloder versioning is independent of the firmware versioning, but follows Semver as well.

The bootloader binary filename is skywallet-bootloader-mem-protect-v$(VERSION_BOOTLOADER).bin if compiled with memory protection enabled it is skywallet-bootloader-no-memory-protect-v$(VERSION_BOOTLOADER).bin. For instance, skywallet-bootloader-mem-protect-v1.0.2.bin or skywallet-bootloader-no-memory-protect-v1.0.2.bin could be bootloader file names.

Versioning libraries

In order to identify at first sight the features supported by a particular release of a client library, its major and minor version numbers should match the corresponding values of the version of the firmware they were built (tested) for. It is expected that the aforementioned library will be able to communicate to any firmware, as long as both versions (client and firmware) have the same major version number and firmware minor number is greater than the one of the library.

Running tests

The project includes a test suite. In order to run it just execute the following command

make clean && make test

Generating tests code coverage

To generate code coverage html report you need to have lcov available in your PATH, in a debian based system you can run apt install lcov, lcov can be available using brew on osx too, but in the most general case you can follow the the official install instructions. After having this tool you can run make check-coverage, if not errors found you can find the result in coverage/index.html.


Skycoin firmware releases

The Skywallet firmware is composed of two parts: the bootloader and the firmware.

Upon startup, the bootloader checks the validity of the firmware installed on the device. It checks whether the signatures of the firmware correspon to the PubKeys registered in the bootlaoder. The firmware is expected to have a header with proper MAGIC number and three signature slots.

If the firmware does not have a valid signature in its header it is considered "not official". A warning will be displayed but the user can still skip it and use it anyway.

Update the version

  1. If the master branch has commits that are not in develop (e.g. due to a hotfix applied to master), merge master into develop (and fix any build or test failures)
  2. Switch to a new release branch named release-X.Y.Z for preparing the release.
  3. Update tiny-firmware/VERSION and tiny-firmware/bootloader/VERSION with corresponding version numbers
  4. Run make build to make sure that the code base is up to date
  5. Update move the "unreleased" changes to the version and add the date.
  6. Follow the steps in pre-release testing
  7. Make a PR merging the release branch into master
  8. Ensure changes needed in protobuffer specs are merged into its master branch
  9. Ensure protobuf specs sub-module will track changes from its master branch after merge
  10. Review the PR and merge it
  11. Tag the master branch with the version number. Version tags start with v, e.g. v0.20.0. Sign the tag. If you have your GPG key in github, creating a release on the Github website will automatically tag the release. It can be tagged from the command line with git tag -as v0.20.0 $COMMIT_ID, but Github will not recognize it as a "release".
  12. Tag the changeset of the protob submodule checkout with the same version number as above.
  13. Release builds are created and uploaded by travis. To do it manually, checkout the master branch and follow the create release builds instructions.
  14. Checkout develop branch and bump tiny-firmware/VERSION and tiny-firmware/bootloader/VERSION to next dev version number.

Pre-release testing

Once the candidate release build artifacts have been downloaded it is necessary to check once again that they behave according to specifications. The followinfg steps are aimed at ensuring this is the case. Execute

  1. Flash the device with latest versions of bootloader and firmware
  2. Ensure you have a recent version of Skycoin desktop software in one of the following ways
  1. Open desktop wallet
  2. Recover a test wallet with nonzero balance from seed to confirm wallet loading works
  3. Send coins to another wallet to confirm spending works
  4. Check that transferred amounts reported in transaction history are correct
  5. Add a PIN to the hardware wallet
  6. Use the same recovery seed of the wallet configured in the Skywallet device and to load a wallet directly in desktop wallet
  7. Send coins to another wallet again
  8. Check transaction history once again
  9. Wipe the wallet
  10. Set up the hardware wallet with a random seed and write down the first address
  11. Create a seed backup
  12. Wipe the wallet and restore the seed. Check if the first address is equal to the one previously written
  13. Repeat steps from the top but using combined bootloader + firmware image to flash the hardware wallet device.

Creating release builds

The following instruction creates a full release:

make release

Firmware version will be retrieved automatically from git, and bootloader version will be take from tiny-firmware/VERSION.

Responsible Disclosure

Security flaws in Skywallet source code or infrastructure can be sent to Bounties are available for accepted critical bug reports.

PGP Key for signing:



Key ID: 0x913BBD5206B19620

The fingerprint for this key is:

pub   ed25519 2019-09-17 [SC] [expires: 2023-09-16]
uid           [ultimate] iketheadore skycoin <>
sub   cv25519 2019-09-17 [E] [expires: 2023-09-16] account: