init commit

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

@@ -0,0 +1,56 @@
+using System;
+using Org.BouncyCastle.Crypto.Parameters;
+using Org.BouncyCastle.Math;
+
+namespace Org.BouncyCastle.Crypto.Agreement;
+
+public class DHBasicAgreement : IBasicAgreement
+{
+	private DHPrivateKeyParameters key;
+
+	private DHParameters dhParams;
+
+	public virtual void Init(ICipherParameters parameters)
+	{
+		if (parameters is ParametersWithRandom)
+		{
+			parameters = ((ParametersWithRandom)parameters).Parameters;
+		}
+		if (!(parameters is DHPrivateKeyParameters))
+		{
+			throw new ArgumentException("DHEngine expects DHPrivateKeyParameters");
+		}
+		key = (DHPrivateKeyParameters)parameters;
+		dhParams = key.Parameters;
+	}
+
+	public virtual int GetFieldSize()
+	{
+		return (key.Parameters.P.BitLength + 7) / 8;
+	}
+
+	public virtual BigInteger CalculateAgreement(ICipherParameters pubKey)
+	{
+		if (key == null)
+		{
+			throw new InvalidOperationException("Agreement algorithm not initialised");
+		}
+		DHPublicKeyParameters dHPublicKeyParameters = (DHPublicKeyParameters)pubKey;
+		if (!dHPublicKeyParameters.Parameters.Equals(dhParams))
+		{
+			throw new ArgumentException("Diffie-Hellman public key has wrong parameters.");
+		}
+		BigInteger p = dhParams.P;
+		BigInteger y = dHPublicKeyParameters.Y;
+		if (y == null || y.CompareTo(BigInteger.One) <= 0 || y.CompareTo(p.Subtract(BigInteger.One)) >= 0)
+		{
+			throw new ArgumentException("Diffie-Hellman public key is weak");
+		}
+		BigInteger bigInteger = y.ModPow(key.X, p);
+		if (bigInteger.Equals(BigInteger.One))
+		{
+			throw new InvalidOperationException("Shared key can't be 1");
+		}
+		return bigInteger;
+	}
+}