Overview

This library provides adapters for the missing hashing and base 64 algorithms in the .NET Standard frameworks. Specifically this library provides implementations of ICryptoTransform for HashAlgorithm, ToBase64Transform, and FromBase64Transform.

Problem Statement

Hashing

HashAlgorithm has been available for quite some time as a convenient way to abstract various hashing algorithms such as MD5 and SHA256. It is especially useful in conjunction with CryptoStream that allows you to calculate the hash from a Stream while processing its data.

Stream s = GetStreamFromSomewhere();
 
using (HashAlgorithm hasher = HashAlgorithm.Create("SHA256"))
{
  using (CryptoStream cs = new CryptoStream(s, hasher, CryptoStreamMode.Read) 
  {
    int byteCount;
    byte[] data = new byte[4096];
    while ((byteCount = cs.Read(data, 0, data.Length)) > 0)
    {
      // do something useful with the actual read data
    }

    byte[] hash = hasher.Hash;
    // do something useful with the hash
  }
}

Unfortunatly the definition of HashAlgorithm is not consistent across the different .NET Core frameworks:

• .NET Core 1.0.0 - HashAlgorithm : IDisposable
• .NET Core 1.1.0 - HashAlgorithm : IDisposable
• .NET Core 2.0.0 - HashAlgorithm : ICryptoTransform

This means that HashAlgorithm cannot be used with CryptoStream unless targeting .NET Standard 2.0 which hasn't received much adoption yet.

Base 64

ToBase64Transform : ICryptoTransform
FromBase64Transform : ICryptoTransform

Similarly, if you search for ToBase64Transform and FromBase64Transform using .NET API Browser you will find that these implementations are only available in .NET Standard 2.0 which hasn't received much adoption yet.

This means that any developers wishing to target ealier versions of .NET Standard such as 1.3 cannot use these base 64 transforms with ICryptoTransform or CryptoStream.

Solution

This library provides the following features:

• An adapter implementation of ICryptoTransform for the hashing algorithms already available in .NET Standard
• An adapter implementation of ICryptoTransform for implementations of ToBase64Transform and FromBase64Transform using the base 64 libraries already available in .NET Standard

Adapter Details

Hashing

The following interface and class are provided to represent a cryptographic hash algorithm.

/// <summary>
/// Represents a cryptographic hash algorithm.
/// </summary>
public interface IHashTransform : ICryptoTransform
{
    /// <summary>
    /// Gets the size, in bits, of the computed hash code.
    /// </summary>
    int HashSize { get; }

    /// <summary>
    /// Gets the value of the computed hash code.
    /// </summary>
    byte[] Hash { get; }
}

/// <summary>
/// Provides the implemenation for a cryptographic hash algorithm.
/// </summary>
public class HashTransform : IHashTransform
{
    /// <summary>
    /// Creates an instance of the specified implementation of a hash algorithm.
    /// </summary>
    /// <param name="hashName">The hash algorithm implementation to use.</param>
    public HashTransform(string hashName) { /* ... */ }

    // .NET Core implementation is provided by 'IncrementalHash'
    // .NET Framework implementation is delegated to the existing 'HashAlgorithm' class
}

Base 64

public class ToBase64Transform : ICryptoTransform { /* */ }
public class FromBase64Transform : ICryptoTransform { /* */ }

These classes simply implement the ICryptoTransform interface by using the already existing Convert.FromBase64CharArray and Convert.ToBase64CharArray builtin methods.

Release Notes

• v1.0.0 - Initial release
• v1.0.1 - Refresh the build and add CI using GitHub actions

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