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();
+ }
+ }
+}
|
