init commit

output/Libraries/BouncyCastle.Crypto/Org/BouncyCastle/Crypto/Agreement/ECDHCBasicAgreement.cs

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+using System;
+using Org.BouncyCastle.Crypto.Parameters;
+using Org.BouncyCastle.Math;
+using Org.BouncyCastle.Math.EC;
+
+namespace Org.BouncyCastle.Crypto.Agreement;
+
+public class ECDHCBasicAgreement : IBasicAgreement
+{
+	private ECPrivateKeyParameters privKey;
+
+	public virtual void Init(ICipherParameters parameters)
+	{
+		if (parameters is ParametersWithRandom)
+		{
+			parameters = ((ParametersWithRandom)parameters).Parameters;
+		}
+		privKey = (ECPrivateKeyParameters)parameters;
+	}
+
+	public virtual int GetFieldSize()
+	{
+		return (privKey.Parameters.Curve.FieldSize + 7) / 8;
+	}
+
+	public virtual BigInteger CalculateAgreement(ICipherParameters pubKey)
+	{
+		ECPublicKeyParameters eCPublicKeyParameters = (ECPublicKeyParameters)pubKey;
+		ECDomainParameters parameters = privKey.Parameters;
+		if (!parameters.Equals(eCPublicKeyParameters.Parameters))
+		{
+			throw new InvalidOperationException("ECDHC public key has wrong domain parameters");
+		}
+		BigInteger b = parameters.H.Multiply(privKey.D).Mod(parameters.N);
+		ECPoint eCPoint = ECAlgorithms.CleanPoint(parameters.Curve, eCPublicKeyParameters.Q);
+		if (eCPoint.IsInfinity)
+		{
+			throw new InvalidOperationException("Infinity is not a valid public key for ECDHC");
+		}
+		ECPoint eCPoint2 = eCPoint.Multiply(b).Normalize();
+		if (eCPoint2.IsInfinity)
+		{
+			throw new InvalidOperationException("Infinity is not a valid agreement value for ECDHC");
+		}
+		return eCPoint2.AffineXCoord.ToBigInteger();
+	}
+}