1 files changed, 71 insertions, 0 deletions
diff --git a/Crypto/src/crypto/agreement/kdf/ECDHKekGenerator.cs b/Crypto/src/crypto/agreement/kdf/ECDHKekGenerator.cs
new file mode 100644
index 000000000..7d55aa485
--- /dev/null
+++ b/Crypto/src/crypto/agreement/kdf/ECDHKekGenerator.cs
@@ -0,0 +1,71 @@
+using System;
+
+using Org.BouncyCastle.Asn1;
+using Org.BouncyCastle.Asn1.X509;
+using Org.BouncyCastle.Crypto.Generators;
+using Org.BouncyCastle.Crypto.Parameters;
+
+namespace Org.BouncyCastle.Crypto.Agreement.Kdf
+{
+	/**
+	* X9.63 based key derivation function for ECDH CMS.
+	*/
+	public class ECDHKekGenerator
+		: IDerivationFunction
+	{
+		private readonly IDerivationFunction kdf;
+
+		private DerObjectIdentifier	algorithm;
+		private int					keySize;
+		private byte[]				z;
+
+		public ECDHKekGenerator(
+			IDigest digest)
+		{
+			this.kdf = new Kdf2BytesGenerator(digest);
+		}
+
+		public void Init(
+			IDerivationParameters param)
+		{
+			DHKdfParameters parameters = (DHKdfParameters)param;
+
+			this.algorithm = parameters.Algorithm;
+			this.keySize = parameters.KeySize;
+			this.z = parameters.GetZ(); // TODO Clone?
+		}
+
+		public IDigest Digest
+		{
+			get { return kdf.Digest; }
+		}
+
+		public int GenerateBytes(
+			byte[]	outBytes,
+			int		outOff,
+			int		len)
+		{
+			// TODO Create an ASN.1 class for this (RFC3278)
+			// ECC-CMS-SharedInfo
+			DerSequence s = new DerSequence(
+				new AlgorithmIdentifier(algorithm, DerNull.Instance),
+				new DerTaggedObject(true, 2, new DerOctetString(integerToBytes(keySize))));
+
+			kdf.Init(new KdfParameters(z, s.GetDerEncoded()));
+
+			return kdf.GenerateBytes(outBytes, outOff, len);
+		}
+
+		private byte[] integerToBytes(int keySize)
+		{
+			byte[] val = new byte[4];
+
+			val[0] = (byte)(keySize >> 24);
+			val[1] = (byte)(keySize >> 16);
+			val[2] = (byte)(keySize >> 8);
+			val[3] = (byte)keySize;
+
+			return val;
+		}
+	}
+}