https://github.com/comodal/secret-shamiracle

Simple builder and utility functions for creating Shamir secret shares and secret reconstruction.
https://github.com/comodal/secret-shamiracle

java-11 shamir shamir-secret-sharing

Last synced: about 1 year ago
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Simple builder and utility functions for creating Shamir secret shares and secret reconstruction.

• Host: GitHub
• URL: https://github.com/comodal/secret-shamiracle
• Owner: comodal
• License: apache-2.0
• Created: 2018-09-12T02:59:11.000Z (almost 8 years ago)
• Default Branch: master
• Last Pushed: 2019-06-12T16:42:29.000Z (about 7 years ago)
• Last Synced: 2025-03-24T15:22:01.725Z (over 1 year ago)
• Topics: java-11, shamir, shamir-secret-sharing
• Language: Java
• Homepage:
• Size: 172 KB
• Stars: 7
• Watchers: 2
• Forks: 1
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

          
# secret-shamiracle [![Build Status](https://travis-ci.org/comodal/secret-shamiracle.svg?branch=master)](https://travis-ci.org/comodal/secret-shamiracle)  [![Download](https://api.bintray.com/packages/comodal/libraries/shamir/images/download.svg)](https://bintray.com/comodal/libraries/shamir/_latestVersion) [![codecov](https://codecov.io/gh/comodal/secret-shamiracle/branch/master/graph/badge.svg)](https://codecov.io/gh/comodal/secret-shamiracle) [![License](http://img.shields.io/badge/license-Apache--2-blue.svg?style=flat)](LICENSE)

> Simple builder and utility functions for creating Shamir secret shares and secret reconstruction.

### Credits

* [Shamir secret sharing wiki](https://en.wikipedia.org/wiki/Shamir%27s_Secret_Sharing#Shamir's_secret-sharing_scheme)

* Credit to Stackoverflow user [JerzySkalski](https://stackoverflow.com/users/4513021/jerzyskalski) for providing a [working example](https://stackoverflow.com/a/34365904/3754157) which limits the finite field with prime modulus division.

### Components

* [Shamir.java](./systems.comodal.shamir/src/main/java/systems/comodal/shamir/Shamir.java#L1): Minimal static methods to facilitate the creation of shares and the reconstruction of a secret.

* [ShamirSharesBuilder.java](./systems.comodal.shamir/src/main/java/systems/comodal/shamir/ShamirSharesBuilder.java#L1): A mutable builder to help coordinate the state needed to create and validate shares.

### Shares Builder Usage

* Required Shares: The minimum number of shares needed to reconstruct the free coefficient secret.

* Total Shares: The total number of shares to generate.

* Prime:

  * Must be supplied directly, or indirectly as a [Mersenne Prime](https://en.wikipedia.org/wiki/Mersenne_prime#List_of_known_Mersenne_primes) exponent.

  * Must be larger than all secrets used.

* Random: Defaults to `new SecureRandom()`

* Secret:

  * May be provided as a byte[] or a BigInteger to `initSecrets(secret)`.

  * Defaults to a random value in the range (0, prime) with a call to `initSecrets()`.

```java

var sharesBuilder = Shamir.buildShares()

  .numRequiredShares(3)

  .numShares(5)

  .mersennePrimeExponent(521)

  .initSecrets("Shamir's Secret".getBytes(UTF_8));

BigInteger[] shares = sharesBuilder.createShares();

// Validate secret reconstruction for all share combinations of size 'numRequiredShares'.

// Throws an IllegalStateException if any reconstructed secret does not equal the original.

sharesBuilder.validateShareCombinations(shares);

// Reconstruct secret.

var coordinates = Map.of(BigInteger.valueOf(1), shares[0],

                         BigInteger.valueOf(3), shares[2],

                         BigInteger.valueOf(5), shares[4]);

var secret = Shamir.reconstructSecret(coordinates, sharesBuilder.getPrime());

var secretString = new String(secret.toByteArray(), UTF_8);

```