1 files changed, 9 insertions, 5 deletions
diff --git a/crypto/src/crypto/agreement/ECDHCBasicAgreement.cs b/crypto/src/crypto/agreement/ECDHCBasicAgreement.cs
index 1c9ae45f9..f0b5d1e02 100644
--- a/crypto/src/crypto/agreement/ECDHCBasicAgreement.cs
+++ b/crypto/src/crypto/agreement/ECDHCBasicAgreement.cs
@@ -50,15 +50,19 @@ namespace Org.BouncyCastle.Crypto.Agreement
         public virtual BigInteger CalculateAgreement(
             ICipherParameters pubKey)
         {
-            ECPublicKeyParameters pub = (ECPublicKeyParameters) pubKey;
-            ECDomainParameters parameters = pub.Parameters;
-            if (!parameters.Equals(privKey.Parameters))
+            ECPublicKeyParameters pub = (ECPublicKeyParameters)pubKey;
+            ECDomainParameters dp = privKey.Parameters;
+            if (!dp.Equals(pub.Parameters))
                 throw new InvalidOperationException("ECDHC public key has wrong domain parameters");
 
-            BigInteger hd = parameters.H.Multiply(privKey.D).Mod(parameters.N);
+            BigInteger hd = dp.H.Multiply(privKey.D).Mod(dp.N);
 
-            ECPoint P = pub.Q.Multiply(hd).Normalize();
+            // Always perform calculations on the exact curve specified by our private key's parameters
+            ECPoint pubPoint = ECAlgorithms.CleanPoint(dp.Curve, pub.Q);
+            if (pubPoint.IsInfinity)
+                throw new InvalidOperationException("Infinity is not a valid public key for ECDHC");
 
+            ECPoint P = pubPoint.Multiply(hd).Normalize();
             if (P.IsInfinity)
                 throw new InvalidOperationException("Infinity is not a valid agreement value for ECDHC");