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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();
}
}
}
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