package org.bouncycastle.crypto.digests;
import org.bouncycastle.crypto.ExtendedDigest;
/**
* Wrapper class that reduces the output length of a particular digest to
* only the first n bytes of the digest function.
*/
public class ShortenedDigest
implements ExtendedDigest
{
private ExtendedDigest baseDigest;
private int length;
/**
* Base constructor.
*
* @param baseDigest underlying digest to use.
* @param length length in bytes of the output of doFinal.
* @exception IllegalArgumentException if baseDigest is null, or length is greater than baseDigest.getDigestSize().
*/
public ShortenedDigest(
ExtendedDigest baseDigest,
int length)
{
if (baseDigest == null)
{
throw new IllegalArgumentException("baseDigest must not be null");
}
if (length > baseDigest.getDigestSize())
{
throw new IllegalArgumentException("baseDigest output not large enough to support length");
}
this.baseDigest = baseDigest;
this.length = length;
}
public String getAlgorithmName()
{
return baseDigest.getAlgorithmName() + "(" + length * 8 + ")";
}
public int getDigestSize()
{
return length;
}
public void update(byte in)
{
baseDigest.update(in);
}
public void update(byte[] in, int inOff, int len)
{
baseDigest.update(in, inOff, len);
}
public int doFinal(byte[] out, int outOff)
{
byte[] tmp = new byte[baseDigest.getDigestSize()];
baseDigest.doFinal(tmp, 0);
System.arraycopy(tmp, 0, out, outOff, length);
return length;
}
public void reset()
{
baseDigest.reset();
}
public int getByteLength()
{
return baseDigest.getByteLength();
}
}