Blockchain Commons Sharded Secret Key Reconstruction (SSKR)

by Leonardo Custodio

bc-sskr-ts splits a secret into shares across one or more groups, and reconstructs it from any sufficient quorum.

Sharded Secret Key Reconstruction (SSKR) is a protocol for splitting a secret into a set of shares across one or more groups, such that the secret can be reconstructed from any combination of shares totaling or exceeding a threshold number of shares within each group and across all groups. SSKR is a generalization of Shamir's Secret Sharing (SSS) that allows for multiple groups and multiple thresholds.

Installation Instructions

@blockchaincommons/sskr is published to npm. Install it with your package manager of choice:

npm install @blockchaincommons/sskr
# or
pnpm add @blockchaincommons/sskr
# or
yarn add @blockchaincommons/sskr
# or
bun add @blockchaincommons/sskr

Usage Instructions

import { Secret, GroupSpec, Spec, generateShares, combineShares, shareBytes, SskrError } from "@blockchaincommons/sskr";

const secret = Secret.fromText("my secret belongs to me."); // 16–32 bytes, even
const spec = Spec.from({
  groupThreshold: 2,
  groups: [GroupSpec.parse("2-of-3"), GroupSpec.from({ memberThreshold: 3, memberCount: 5 })],
});

const groups = generateShares(spec, secret); // SskrShare[][], secure RNG by default
const wire = groups.map((g) => g.map(shareBytes)); // the BCR-2020-011 bytes

const recovered = combineShares([groups[0][0], groups[0][2], groups[1][0], groups[1][1], groups[1][4]]);
recovered.equals(secret); // true

try {
  combineShares([groups[0][0], groups[1][0]]);
} catch (e) {
  if (SskrError.isSskrError(e)) console.log(e.code); // "NotEnoughGroups"
}

// Library validation failures throw SskrError; branch with `is`. Spec fields are usize values
// (a number, or a bigint up to 2^64 - 1) and header fields integers in their width, never coerced:
try {
  GroupSpec.from({ memberThreshold: 1.5, memberCount: 3 });
} catch (e) {
  if (SskrError.isSskrError(e) && e.is("InvalidParameter")) {
    console.log(e.details.parameter, e.message);
    // "memberThreshold", "memberThreshold must be an integer in [0, 18446744073709551615] (a number or a bigint), got 1.5"
  }
}

// Values are immutable: `secret.bytes` is a copy; specs, generated shares and parsed shares are frozen.
Object.isFrozen(groups[0][0]); // true

Runnable examples live in the examples/ directory.

Status - Beta

bc-sskr-ts is currently under active development and in beta testing. It should not be used for production tasks until it has had further testing and auditing. See Blockchain Commons' Development Phases.

Version History

• 1.0.0-beta.3 (September 14, 2026) - A zero member threshold is accepted at construction and fails at generation, as in the reference; spec fields accept bigint and integer-valued numbers up to 2^64; every argument is type-checked before anything else, share objects are checked as their bytes would be, equals on specs, and the identifier draw goes through @blockchaincommons/rand.
• 1.0.0-beta.2 (September 12, 2026) - GroupSpec.parse reports the reference's code for a count or threshold between 2^53 and 2^64;
• 1.0.0-beta.1 (September 9, 2026) - Initial beta implementation.

Roadmap

• Continued testing and auditing on the path from beta to a stable 1.0.0 release.

Dependencies

@blockchaincommons/sskr depends on @blockchaincommons/rand, @blockchaincommons/shamir at runtime.

To build and work on this library, you'll need the following tools:

• Node.js >= 22.12 - JavaScript runtime.
• Bun - used to install dependencies and run scripts (any node package manager works).
• TypeScript >= 5.7 - language and type checker.

Derived from ...

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

• BlockchainCommons/bc-sskr-rust - The reference Rust implementation, by Wolf McNally.
• paritytech/bcts - A TypeScript port of many Blockchain Commons' specs, by Parity Technologies.

Financial Support

bc-sskr-ts 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 bc-sskr-ts 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.

Contributing

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

Discussions

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

Gordian Developer Community. For standards and open-source developers who want to talk about interoperable wallet specifications, please use the Discussions area of the Gordian Developer Community repo. This is where you talk about Gordian specifications such as Gordian Envelope, bc-shamir, Sharded Secret Key Reconstruction, and bc-ur as well as the larger Gordian Architecture, its Principles of independence, privacy, resilience, and openness, and its macro-architectural ideas such as functional partition (including airgapping, the original name of this community).

Gordian User Community. For users of the Gordian reference apps, including Gordian Coordinator, Gordian Seed Tool, Gordian Server, Gordian Wallet, and SpotBit as well as our whole series of CLI apps. This is a place to talk about bug reports and feature requests as well as to explore how our reference apps embody the Gordian Principles.

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 those covered by the Gordian Developer Community or the Gordian User Community.

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.

Credits

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

| Name | Role | Github | Email | GPG Fingerprint | | ----------------- | ------------------- | ------------------------------------------------- | ------------------------------------- | -------------------------------------------------- | | Christopher Allen | Principal Architect | @ChristopherA | <[email protected]> | FDFE 14A5 4ECB 30FC 5D22 74EF F8D3 6C91 3574 05ED | | Wolf McNally | Lead Researcher/Engineer | @wolfmcnally | <[email protected]> | 9436 52EE 3844 1760 C3DC 3536 4B6C 2FCF 8947 80AE | | Leonardo Custodio | Software Engineer | @leonardocustodio | <[email protected]> | 59DA D997 67EF 3BAB 2B90 D057 5384 DEF3 B582 450D |

Contributing Sponsor

Blockchain Commons Sharded Secret Key Reconstruction (SSKR) for TypeScript was produced as a collaboration between Blockchain Commons and one of our patrons, Parity Technologies: Parity wrote the wrappers based on Blockchain Commons' specifications and reference libraries. Blockchain Commons is dedicated to not just creating open infrastructure on our own, but also coordinating the work of other companies in benefiting the Commons. Thanks to Parity for working directly with us in this manner.

Responsible Disclosure

We want to keep all of 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 [email protected] (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.