ShortenedDigest.cs :  » PDF » iTextSharp » Org » BouncyCastle » Crypto » Digests » C# / CSharp Open Source

using System;
using Org.BouncyCastle.Crypto;

namespace Org.BouncyCastle.Crypto.Digests{
  /**
  * Wrapper class that reduces the output length of a particular digest to
  * only the first n bytes of the digest function.
  */
  public class ShortenedDigest
    : IDigest
  {
    private IDigest  baseDigest;
    private int    length;

    /**
    * Base constructor.
    *
    * @param baseDigest underlying digest to use.
    * @param length length in bytes of the output of doFinal.
    * @exception ArgumentException if baseDigest is null, or length is greater than baseDigest.GetDigestSize().
    */
    public ShortenedDigest(
      IDigest  baseDigest,
      int    length)
    {
      if (baseDigest == null)
      {
        throw new ArgumentNullException("baseDigest");
      }

      if (length > baseDigest.GetDigestSize())
      {
        throw new ArgumentException("baseDigest output not large enough to support length");
      }

      this.baseDigest = baseDigest;
      this.length = length;
    }

    public string AlgorithmName
    {
      get { return baseDigest.AlgorithmName + "(" + length * 8 + ")"; }
    }

    public int GetDigestSize()
    {
      return length;
    }

    public void Update(byte input)
    {
      baseDigest.Update(input);
    }

    public void BlockUpdate(byte[] input, int inOff, int length)
    {
      baseDigest.BlockUpdate(input, inOff, length);
    }

    public int DoFinal(byte[] output, int outOff)
    {
      byte[] tmp = new byte[baseDigest.GetDigestSize()];

      baseDigest.DoFinal(tmp, 0);

          Array.Copy(tmp, 0, output, outOff, length);

      return length;
    }

    public void Reset()
    {
      baseDigest.Reset();
    }

    public int GetByteLength()
    {
      return baseDigest.GetByteLength();
    }
  }
}