1 files changed, 40 insertions, 0 deletions
diff --git a/Crypto/src/crypto/modes/gcm/BasicGcmExponentiator.cs b/Crypto/src/crypto/modes/gcm/BasicGcmExponentiator.cs
new file mode 100644
index 000000000..98049e1db
--- /dev/null
+++ b/Crypto/src/crypto/modes/gcm/BasicGcmExponentiator.cs
@@ -0,0 +1,40 @@
+using System;
+
+using Org.BouncyCastle.Utilities;
+
+namespace Org.BouncyCastle.Crypto.Modes.Gcm
+{
+	public class BasicGcmExponentiator
+		: IGcmExponentiator
+	{
+		private byte[] x;
+
+		public void Init(byte[] x)
+		{
+			this.x = Arrays.Clone(x);
+		}
+
+		public void ExponentiateX(long pow, byte[] output)
+		{
+			// Initial value is little-endian 1
+			byte[] y = GcmUtilities.OneAsBytes();
+
+			if (pow > 0)
+			{
+				byte[] powX = Arrays.Clone(x);
+				do
+				{
+					if ((pow & 1L) != 0)
+					{
+						GcmUtilities.Multiply(y, powX);
+					}
+					GcmUtilities.Multiply(powX, powX);
+					pow >>= 1;
+				}
+				while (pow > 0);
+			}
+
+			Array.Copy(y, 0, output, 0, 16);
+		}
+	}
+}