1 files changed, 82 insertions, 0 deletions
diff --git a/Crypto/src/crypto/digests/ShortenedDigest.cs b/Crypto/src/crypto/digests/ShortenedDigest.cs
new file mode 100644
index 000000000..9e4d99e7b
--- /dev/null
+++ b/Crypto/src/crypto/digests/ShortenedDigest.cs
@@ -0,0 +1,82 @@
+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();
+		}
+	}
+}