Skip to content


Switch branches/tags

Latest commit


Git stats


Failed to load latest commit information.
Latest commit message
Commit time

🔑 Blockchain Commons SSKR

by Wolf McNally and Christopher Allen

Blockchain Commons SSKR is an implementation of Sharded Secret Key Reconstruction (SSKR) for use in Blockchain Commons Software Projects.


  • If bc-crypto-base is not installed, the configure step below will fail.
  • If bc-shamir is not installed, the configure step below will fail.

Installation Instructions

MacOS and Linux

$ ./configure
$ make check
$ sudo make install

This sequence runs the module's unit tests.


Warning: This is an experimental feature!

  1. Install and activate Emscripten:
  2. After setting up the environment variables for the toolchain $ source $HOME/emsdk/ run ./ This will build the wasm/sskr.wasm and wasm/sskr.js files
  3. cd into wasm and run ./ and navigate to http://localhost:8888/sskr.html
  4. You can edit sskr.html, save and refresh browser

Usage Instructions

  1. Link against libbc-sskr.a, libbc-shamir.a and libbc-crypto-base.a.
  2. Include the umbrella header in your code:
#include <bc-sskr/bc-sskr.h>

Design Notes

The Blockchain Commons implementation of Shamir's Secret Sharing makes a decision to incorporate fragments of the hashed secret to reduce complexity and share size for sharding, and to allow the detection of malicious shares, but it comes at the cost of reducing the Information-Theoretic Security of Shamir's Secret Sharing to Computational Security.This was a thoughtful and purposeful decision that has also been adopted by others in the industry. We believe that it offers advantages to the secret-sharing scheme while maintaining a level of security congruent with any services that bc-sskr is likely to be used with, such as Bitcoin and other cryptocurrencies. Read the SSKR security review for more information.

Maintainer Notes

Before accepting a PR that can affect build or unit tests, make sure the following sequence of commands succeeds:

$ ./configure
$ make lint
$ make distcheck
$ make distclean

make lint uses Cppcheck to perform static analysis on the code. All PRs should pass with no warnings.

make distcheck builds a distribution tarball, unpacks it, then configures, builds, and runs unit tests from it, then performs an install and uninstall from a non-system directory and makes sure the uninstall leaves it clean. make distclean removes all known byproduct files, and unless you've added files of your own, should leave the directory in a state that could be tarballed for distribution. After a make distclean you'll have to run ./configure again.

Status - Released & Reviewed

This released project has received a security review.

Origin, Authors, Copyright & Licenses

Unless otherwise noted (either in this / or in the file's header comments) the contents of this repository are Copyright © 2020 by Blockchain Commons, LLC, and are licensed under the spdx:BSD-2-Clause Plus Patent License.

In most cases, the authors, copyright, and license for each file reside in header comments in the source code. When it does not we have attempted to attribute it accurately in the table below.

This table below also establishes provenance (repository of origin, permalink, and commit id) for files included from repositories that are outside of this repository. Contributors to these files are listed in the commit history for each repository, first with changes found in the commit history of this repo, then in changes in the commit history of their repo of their origin.

File From Commit Authors & Copyright (c) License
exception-to-the-rule.c or exception-folder 2020 Exception Author MIT

Used with…

These are other projects that work with or leverage bc-sskr:

  • Gordian SeedTool — iPhone app for storing cryptographic seeds.
  • LetheKit — Open source DIY hardware box for offline cryptographic tools.
  • seedtool — Tool for generating and transforming cryptographic seeds.

Derived from…

bc-sskr project is either derived from or was inspired by:

  • SLIP-39: Shamir's Secret-Sharing for Mnemonic Codes


To build the bc-sskr you'll need to use the following tools:

  • autotools - Gnu Build System from Free Software Foundation (intro).
  • bc-crypto-base - base cryptography library
  • bc-shamir - Shamir's Secret Sharing library

Financial Support

Blockchain Commons SSKR is a project of Blockchain Commons. We are proudly a "not-for-profit" social benefit corporation committed to open source & open development. Our work is funded entirely by donations and collaborative partnerships with people like you. Every contribution will be spent on building open tools, technologies, and techniques that sustain and advance blockchain and internet security infrastructure and promote an open web.

To financially support further development of Blockchain Commons SSKR and other projects, please consider becoming a Patron of Blockchain Commons through ongoing monthly patronage as a GitHub Sponsor. You can also support Blockchain Commons with bitcoins at our BTCPay Server.


We encourage public contributions through issues and pull-requests! Please review for details on our development process. All contributions to this repository require a GPG signed Contributor License Agreement.


The best place to talk about Blockchain Commons and its projects is in our GitHub Discussions areas.

Wallet Standard Discussions. For standards and open-source developers who want to talk about wallet standards, please use the Discussions area of the Airgapped Signing repo. This is where you can talk about projects like our LetheKit and command line tools such as seedtool, both of which are intended to testbed wallet technologies, plus the libraries that we've built to support your own deployment of wallet technology such as bc-bip39, bc-slip39, bc-shamir, Sharded Secret Key Reconstruction, bc-ur, and the bc-crypto-base. If it's a wallet-focused technology or a more general discussion of wallet standards,discuss it here.

Blockchain Commons Discussions. For developers, interns, and patrons of Blockchain Commons, please use the discussions area of the Community repo to talk about general Blockchain Commons issues, the intern program, or topics other than the Gordian System or the wallet standards, each of which have their own discussion areas.

Other Questions & Problems

As an open-source, open-development community, Blockchain Commons does not have the resources to provide direct support of our projects. Please consider the discussions area as a locale where you might get answers to questions. Alternatively, please use this repository's issues feature. Unfortunately, we can not make any promises on response time.

If your company requires support to use our projects, please feel free to contact us directly about options. We may be able to offer you a contract for support from one of our contributors, or we might be able to point you to another entity who can offer the contractual support that you need.


The following people directly contributed to this repository. You can add your name here by getting involved — the first step is to learn how to contribute from our documentation.

Name Role Github Email GPG Fingerprint
Christopher Allen Principal Architect @ChristopherA <> FDFE 14A5 4ECB 30FC 5D22 74EF F8D3 6C91 3574 05ED
Wolf McNally Project Lead @WolfMcNally <> 9436 52EE 3844 1760 C3DC  3536 4B6C 2FCF 8947 80AE

Responsible Disclosure

We want to keep all our software safe for everyone. If you have discovered a security vulnerability, we appreciate your help in disclosing it to us in a responsible manner. We are unfortunately not able to offer bug bounties at this time.

We do ask that you offer us good faith and use best efforts not to leak information or harm any user, their data, or our developer community. Please give us a reasonable amount of time to fix the issue before you publish it. Do not defraud our users or us in the process of discovery. We promise not to bring legal action against researchers who point out a problem provided they do their best to follow the these guidelines.

Reporting a Vulnerability

Please report suspected security vulnerabilities in private via email to (do not use this email for support). Please do NOT create publicly viewable issues for suspected security vulnerabilities.

The following keys may be used to communicate sensitive information to developers:

Name Fingerprint
Christopher Allen FDFE 14A5 4ECB 30FC 5D22 74EF F8D3 6C91 3574 05ED

You can import a key by running the following command with that individual’s fingerprint: gpg --recv-keys "<fingerprint>" Ensure that you put quotes around fingerprints that contain spaces.