1 files changed, 60 insertions, 0 deletions
diff --git a/Crypto/src/crypto/agreement/DHBasicAgreement.cs b/Crypto/src/crypto/agreement/DHBasicAgreement.cs
new file mode 100644
index 000000000..5a5277049
--- /dev/null
+++ b/Crypto/src/crypto/agreement/DHBasicAgreement.cs
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+using System;
+
+using Org.BouncyCastle.Crypto.Parameters;
+using Org.BouncyCastle.Math;
+using Org.BouncyCastle.Security;
+
+namespace Org.BouncyCastle.Crypto.Agreement
+{
+	/**
+	 * a Diffie-Hellman key agreement class.
+	 * <p>
+	 * note: This is only the basic algorithm, it doesn't take advantage of
+	 * long term public keys if they are available. See the DHAgreement class
+	 * for a "better" implementation.</p>
+	 */
+	public class DHBasicAgreement
+		: IBasicAgreement
+	{
+		private DHPrivateKeyParameters	key;
+		private DHParameters			dhParams;
+
+		public void Init(
+			ICipherParameters parameters)
+		{
+			if (parameters is ParametersWithRandom)
+			{
+				parameters = ((ParametersWithRandom) parameters).Parameters;
+			}
+
+			if (!(parameters is DHPrivateKeyParameters))
+			{
+				throw new ArgumentException("DHEngine expects DHPrivateKeyParameters");
+			}
+
+			this.key = (DHPrivateKeyParameters) parameters;
+			this.dhParams = key.Parameters;
+		}
+
+		/**
+		 * given a short term public key from a given party calculate the next
+		 * message in the agreement sequence.
+		 */
+		public BigInteger CalculateAgreement(
+			ICipherParameters pubKey)
+		{
+			if (this.key == null)
+				throw new InvalidOperationException("Agreement algorithm not initialised");
+
+			DHPublicKeyParameters pub = (DHPublicKeyParameters)pubKey;
+
+			if (!pub.Parameters.Equals(dhParams))
+			{
+				throw new ArgumentException("Diffie-Hellman public key has wrong parameters.");
+			}
+
+			return pub.Y.ModPow(key.X, dhParams.P);
+		}
+	}
+
+}