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Assets/BestHTTP/SecureProtocol/crypto/agreement/ECDHBasicAgreement.cs

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+#if !BESTHTTP_DISABLE_ALTERNATE_SSL && (!UNITY_WEBGL || UNITY_EDITOR)
+
+using System;
+
+using Org.BouncyCastle.Math;
+using Org.BouncyCastle.Math.EC;
+using Org.BouncyCastle.Crypto;
+using Org.BouncyCastle.Crypto.Parameters;
+
+namespace Org.BouncyCastle.Crypto.Agreement
+{
+    /**
+     * P1363 7.2.1 ECSVDP-DH
+     *
+     * ECSVDP-DH is Elliptic Curve Secret Value Derivation Primitive,
+     * Diffie-Hellman version. It is based on the work of [DH76], [Mil86],
+     * and [Kob87]. This primitive derives a shared secret value from one
+     * party's private key and another party's public key, where both have
+     * the same set of EC domain parameters. If two parties correctly
+     * execute this primitive, they will produce the same output. This
+     * primitive can be invoked by a scheme to derive a shared secret key;
+     * specifically, it may be used with the schemes ECKAS-DH1 and
+     * DL/ECKAS-DH2. It assumes that the input keys are valid (see also
+     * Section 7.2.2).
+     */
+    public class ECDHBasicAgreement
+        : IBasicAgreement
+    {
+        protected internal ECPrivateKeyParameters privKey;
+
+        public virtual void Init(
+            ICipherParameters parameters)
+        {
+            if (parameters is ParametersWithRandom)
+            {
+                parameters = ((ParametersWithRandom)parameters).Parameters;
+            }
+
+            this.privKey = (ECPrivateKeyParameters)parameters;
+        }
+
+        public virtual int GetFieldSize()
+        {
+            return (privKey.Parameters.Curve.FieldSize + 7) / 8;
+        }
+
+        public virtual BigInteger CalculateAgreement(
+            ICipherParameters pubKey)
+        {
+            ECPublicKeyParameters pub = (ECPublicKeyParameters) pubKey;
+            if (!pub.Parameters.Equals(privKey.Parameters))
+                throw new InvalidOperationException("ECDH public key has wrong domain parameters");
+
+            ECPoint P = pub.Q.Multiply(privKey.D).Normalize();
+
+            if (P.IsInfinity)
+                throw new InvalidOperationException("Infinity is not a valid agreement value for ECDH");
+
+            return P.AffineXCoord.ToBigInteger();
+        }
+    }
+}
+
+#endif