✨ SecretSharingDotNet ✨

A C# implementation of Shamir's Secret Sharing.

Build & Test Status Of Default Branch 👷

Status	Solution	Project Format	.NET Version
	SecretSharingDotNet.slnx	SDK	Standard 2.0
			Standard 2.1
			FX 4.7
			FX 4.7.1
			FX 4.7.2
			FX 4.8
			.NET 8
			.NET 9
			.NET 10

NuGet 📦

Supported Target Frameworks

Build And Test Status	NuGet Version	Git Tag	Target Frameworks
			Standard 2.0
			Standard 2.1
			FX 4.7
			FX 4.7.1
			FX 4.7.2
			FX 4.8
			.NET 8
			.NET 9
			.NET 10

Install SecretSharingDotNet package 📥

1. Open a console and switch to the directory, containing your project file.

2. Use the following command to install version 0.14.0 of the SecretSharingDotNet package:

   dotnet add package SecretSharingDotNet -v 0.14.0 -f <FRAMEWORK>
   

3. After the completion of the command, look at the project file to make sure that the package is successfully installed.

   You can open the .csproj file to see the added package reference:

   <ItemGroup>
     <PackageReference Include="SecretSharingDotNet" Version="0.14.0" />
   </ItemGroup>

Remove SecretSharingDotNet package 📤

1. Open a console and switch to the directory, containing your project file.

2. Use the following command to remove the SecretSharingDotNet package:

   dotnet remove package SecretSharingDotNet
   

3. After the completion of the command, look at the project file to make sure that the package is successfully removed.

   You can open the .csproj file to check the deleted package reference.

Usage 🔧

Important

Breaking Change in v0.14.0: The string encoding in SecretSharingDotNet with text secrets is UTF-8.

Basics

Use the function MakeShares to generate the shares, based on a random or pre-defined secret. Afterwards, use the function Reconstruction to re-construct the original secret.

The length of the shares is based on the security level. It is possible to pre-define a security level by ctor or the SecurityLevel property. The pre-defined security level will be overriden, if the secret size is greater than the Mersenne prime, which is calculated by means of the security level. It is not necessary to define a security level for a re-construction.

Using the SecretSharingDotNet library with DI in a .NET project.

This guide will demonstrate how to use the SecretSharingDotNet library with Dependency Injection (DI) in a .NET project.

Firstly, add the following dependencies:

using Microsoft.Extensions.DependencyInjection;
using SecretSharingDotNet.Cryptography;
using SecretSharingDotNet.Cryptography.ShamirsSecretSharing;
using SecretSharingDotNet.Math;
using System.Numerics;

Next, initialize a ServiceCollection instance and add dependencies to the DI container:

var serviceCollection = new ServiceCollection();
serviceCollection.AddSingleton<IExtendedGcdAlgorithm<BigInteger>, ExtendedEuclideanAlgorithm<BigInteger>>();
serviceCollection.AddSingleton<IMakeSharesUseCase<BigInteger>, SecretSplitter<BigInteger>>();
serviceCollection.AddSingleton<IReconstructionUseCase<BigInteger>, SecretReconstructor<BigInteger>>();
using var serviceProvider = serviceCollection.BuildServiceProvider();

In the code above, the ServiceCollection registers an implementation for each of the main components of the SecretSharingDotNet library.

Next, create an instance of the IMakeSharesUseCase<BigInteger>:

var makeSharesUseCase = serviceProvider.GetRequiredService<IMakeSharesUseCase<BigInteger>>();

Using this instance, it is possible to create shares from a secret:

var shares = makeSharesUseCase.MakeShares(3, 7, "Hello!");
Console.WriteLine(shares);

Similarly, an instance of IReconstructionUseCase<BigInteger> can be created to rebuild the original secret:

var reconstructionUseCase = serviceProvider.GetRequiredService<IReconstructionUseCase<BigInteger>>();
var reconstruction = reconstructionUseCase.Reconstruction(shares.Where(p => p.IsIndexEven).ToArray());
Console.WriteLine(reconstruction);

The code above reconstructs the original secret from the shares, and then outputs it.

Random secret 🎲

Create a random secret in conjunction with the generation of shares. The length of the generated shares and of the secret are based on the security level. Here is an example with a pre-defined security level of 127:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;

using SecretSharingDotNet.Cryptography;
using SecretSharingDotNet.Cryptography.ShamirsSecretSharing;
using SecretSharingDotNet.Math;

namespace Example1
{
  public class Program
  {
    public static void Main(string[] args)
    {
      //// Create Shamir's Secret Sharing instance with BigInteger
      var splitter = new SecretSplitter<BigInteger>();

      //// Minimum number of shared secrets for reconstruction: 3
      //// Maximum number of shared secrets: 7
      //// Security level: 127 (Mersenne prime exponent)
      var shares = splitter.MakeShares(3, 7, 127, out var secret);

      //// Secret as big integer number
      Console.WriteLine((BigInteger)secret);

      //// Secret as base64 string
      Console.WriteLine(secret.ToBase64());

      var gcd = new ExtendedEuclideanAlgorithm<BigInteger>();
      //// The 'shares' instance contains the shared secrets
      var combiner = new SecretReconstructor<BigInteger>(gcd);
      var subSet1 = shares.Where(p => p.IsIndexEven).ToList();
      var recoveredSecret1 = combiner.Reconstruction(subSet1.ToArray());
      var subSet2 = shares.Where(p => p.IsIndexOdd).ToList();
      var recoveredSecret2 = combiner.Reconstruction(subSet2.ToArray());

      //// String representation of all shares
      Console.WriteLine(shares);

      //// 1st recovered secret as big integer number
      Console.WriteLine((BigInteger)recoveredSecret1);

      //// 2nd recovered secret as big integer number
      Console.WriteLine((BigInteger)recoveredSecret2);

      //// 1st recovered secret as base64 string
      Console.WriteLine(recoveredSecret1.ToBase64());

      //// 2nd recovered secret as base64 string
      Console.WriteLine(recoveredSecret2.ToBase64());
    }
  }
}

Pre-defined secret: text 📄

Use a text as secret, which can be divided into shares. The length of the generated shares is based on the security level. Here is an example with auto-detected security level:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;

using SecretSharingDotNet.Cryptography;
using SecretSharingDotNet.Cryptography.ShamirsSecretSharing;
using SecretSharingDotNet.Math;

namespace Example2
{
  public class Program
  {
    public static void Main(string[] args)
    {
      //// Create Shamir's Secret Sharing instance with BigInteger
      var splitter = new SecretSplitter<BigInteger>();

      string password = "Hello World!!";
      //// Minimum number of shared secrets for reconstruction: 3
      //// Maximum number of shared secrets: 7
      //// Attention: The password length can change the security level set by the ctor
      //// or SecurityLevel property.
      var shares = splitter.MakeShares(3, 7, password);

      var gcd = new ExtendedEuclideanAlgorithm<BigInteger>();
      //// The 'shares' instance contains the shared secrets
      var combiner = new SecretReconstructor<BigInteger>(gcd);
      var subSet1 = shares.Where(p => p.IsIndexEven).ToList();
      var recoveredSecret1 = combiner.Reconstruction(subSet1.ToArray());
      var subSet2 = shares.Where(p => p.IsIndexOdd).ToList();
      var recoveredSecret2 = combiner.Reconstruction(subSet2.ToArray());

      //// String representation of all shares
      Console.WriteLine(shares);

      //// 1st recovered secret as string (not base64!)
      Console.WriteLine(recoveredSecret1);

      //// 2nd recovered secret as string (not base64!)
      Console.WriteLine(recoveredSecret2);
    }
  }
}

Pre-defined secret: number 🔢

Use an integer number as secret, which can be divided into shares. The length of the generated shares is based on the security level. Here is an example with a pre-defined security level of 521:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;

using SecretSharingDotNet.Cryptography;
using SecretSharingDotNet.Cryptography.ShamirsSecretSharing;
using SecretSharingDotNet.Math;

namespace Example3
{
  public class Program
  {
    public static void Main(string[] args)
    {
      //// Create Shamir's Secret Sharing instance with BigInteger
      //// and 
      var splitter = new SecretSplitter<BigInteger>();

      BigInteger number = 20000;
      //// Minimum number of shared secrets for reconstruction: 3
      //// Maximum number of shared secrets: 7
      //// Security level: 521 (Mersenne prime exponent)
      //// Attention: The size of the number can change the security level set by the ctor
      //// or SecurityLevel property.
      var shares = splitter.MakeShares (3, 7, number, 521);

      var gcd = new ExtendedEuclideanAlgorithm<BigInteger>();
      ////  The 'shares' instance contains the shared secrets
      var combiner = new SecretReconstructor<BigInteger>(gcd);
      var subSet1 = shares.Where(p => p.IsIndexEven).ToList();
      var recoveredSecret1 = combiner.Reconstruction(subSet1.ToArray());
      var subSet2 = shares.Where(p => p.IsIndexOdd).ToList();
      var recoveredSecret2 = combiner.Reconstruction(subSet2.ToArray());

      //// String representation of all shares
      Console.WriteLine(shares);

      //// 1st recovered secret as big integer number
      Console.WriteLine((BigInteger)recoveredSecret1);

      //// 2nd recovered secret as big integer number
      Console.WriteLine((BigInteger)recoveredSecret2);
    }
  }
}

Pre-defined secret: byte array ▦

Use a byte array as secret, which can be divided into shares. The length of the generated shares is based on the security level. Here is an example with auto-detected security level:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;

using SecretSharingDotNet.Cryptography;
using SecretSharingDotNet.Cryptography.ShamirsSecretSharing;
using SecretSharingDotNet.Math;

namespace Example4
{
  public class Program
  {
    public static void Main(string[] args)
    {
      //// Create Shamir's Secret Sharing instance with BigInteger
      var splitter = new SecretSplitter<BigInteger>();

      byte[] bytes = { 0x1D, 0x2E, 0x3F };
      //// Minimum number of shared secrets for reconstruction: 4
      //// Maximum number of shared secrets: 10
      //// Attention: The password length changes the security level set by the ctor
      var shares = splitter.MakeShares(4, 10, bytes);

      var gcd = new ExtendedEuclideanAlgorithm<BigInteger>();
      //// The 'shares' instance contains the shared secrets
      var combiner = new SecretReconstructor<BigInteger>(gcd);
      var subSet = shares.Where(p => p.IsIndexEven).ToList();
      var recoveredSecret = combiner.Reconstruction(subSet.ToArray()).ToByteArray();

      //// String representation of all shares
      Console.WriteLine(shares);

      //// The secret bytes.
      Console.WriteLine($"{recoveredSecret[0]:X2}, {recoveredSecret[1]:X2}, {recoveredSecret[2]:X2}");
    }
  }
}

Shares 🔑

The following example shows three ways to use shares to reconstruct a secret:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;

using SecretSharingDotNet.Cryptography;
using SecretSharingDotNet.Cryptography.ShamirsSecretSharing;
using SecretSharingDotNet.Math;

namespace Example5
{
  public class Program
  {
    public static void Main(string[] args)
    {
      //// One way to use shares
      string shares1 = "02-665C74ED38FDFF095B2FC9319A272A75" + Environment.NewLine +
                       "05-CDECB88126DBC04D753E0C2D83D7B55D" + Environment.NewLine +
                       "07-54A83E34AB0310A7F5D80F2A68FD4F33";

      //// A 2nd way to use shares
      string[] shares2 = {"02-665C74ED38FDFF095B2FC9319A272A75",
                          "07-54A83E34AB0310A7F5D80F2A68FD4F33",
                          "05-CDECB88126DBC04D753E0C2D83D7B55D"};

      //// Another way to use shares
      var share1 = new Share<BigInteger>("05-CDECB88126DBC04D753E0C2D83D7B55D");
      var share2 = new Share<BigInteger>("07-54A83E34AB0310A7F5D80F2A68FD4F33");
      var share3 = new Share<BigInteger>("02-665C74ED38FDFF095B2FC9319A272A75");

      var gcd = new ExtendedEuclideanAlgorithm<BigInteger>();
      var combiner = new SecretReconstructor<BigInteger>(gcd);
 
      var recoveredSecret1 = combiner.Reconstruction(shares1);
      //// Output should be 52199147989510990914370102003412153
      Console.WriteLine((BigInteger)recoveredSecret1);

      var recoveredSecret2 = combiner.Reconstruction(shares2);
      //// Output should be 52199147989510990914370102003412153
      Console.WriteLine((BigInteger)recoveredSecret2);

      //// Output should be 52199147989510990914370102003412153
      var recoveredSecret3 = combiner.Reconstruction(share1, share2, share3);
      Console.WriteLine((BigInteger)recoveredSecret3);
    }
  }
}

CLI building instructions

Prerequisites

For the following instructions, please make sure that you are connected to the internet. If necessary, NuGet will try to restore the xUnit packages.

If you start the unit tests on Linux, you must install the mono-complete package in case of the .NET Frameworks 4.7, 4.7.1, 4.7.2, 4.8 and 4.8.1. You can find the Mono installation instructions here.

The .NET Frameworks 4.7, 4.7.1, 4.7.2, 4.8 and 4.8.1 can be found here.

The .NET SDKs 8.0, 9.0 and 10.0 can be found here.

Build and test the solution

You can use the SecretSharingDotNet.sln solution file with the dotnet command to build the SecretSharingDotNet library in the Debug or Release configuration. You can also use the dotnet command to start the unit tests.

1. Restore NuGet packages

dotnet restore SecretSharingDotNet.sln

2. Build the solution

dotnet build -c Debug --no-restore SecretSharingDotNet.sln

or

dotnet build -c Release --no-restore SecretSharingDotNet.sln

3. Test the solution

dotnet test -c Debug --no-restore --no-build SecretSharingDotNet.sln -- RunConfiguration.TargetPlatform=x64 RunConfiguration.MaxCpuCount=1  xUnit.AppDomain=denied xUnit.ParallelizeAssembly=false xUnit.ParallelizeTestCollections=false

or

dotnet test -c Release --no-restore --no-build SecretSharingDotNet.sln -- RunConfiguration.TargetPlatform=x64 RunConfiguration.MaxCpuCount=1  xUnit.AppDomain=denied xUnit.ParallelizeAssembly=false xUnit.ParallelizeTestCollections=false