3 files changed, 13 insertions, 3 deletions
diff --git a/crypto/src/crypto/agreement/DHAgreement.cs b/crypto/src/crypto/agreement/DHAgreement.cs
index b5af104f9..e988c0d53 100644
--- a/crypto/src/crypto/agreement/DHAgreement.cs
+++ b/crypto/src/crypto/agreement/DHAgreement.cs
@@ -85,7 +85,11 @@ namespace Org.BouncyCastle.Crypto.Agreement
 
             BigInteger p = dhParams.P;
 
-            BigInteger result = pub.Y.ModPow(privateValue, p);
+            BigInteger peerY = pub.Y;
+            if (peerY == null || peerY.CompareTo(BigInteger.One) <= 0 || peerY.CompareTo(p.Subtract(BigInteger.One)) >= 0)
+                throw new ArgumentException("Diffie-Hellman public key is weak");
+
+            BigInteger result = peerY.ModPow(privateValue, p);
             if (result.Equals(BigInteger.One))
                 throw new InvalidOperationException("Shared key can't be 1");
 
diff --git a/crypto/src/crypto/agreement/DHBasicAgreement.cs b/crypto/src/crypto/agreement/DHBasicAgreement.cs
index d6f017e32..6c3fe6595 100644
--- a/crypto/src/crypto/agreement/DHBasicAgreement.cs
+++ b/crypto/src/crypto/agreement/DHBasicAgreement.cs
@@ -56,7 +56,13 @@ namespace Org.BouncyCastle.Crypto.Agreement
             if (!pub.Parameters.Equals(dhParams))
                 throw new ArgumentException("Diffie-Hellman public key has wrong parameters.");
 
-            BigInteger result = pub.Y.ModPow(key.X, dhParams.P);
+            BigInteger p = dhParams.P;
+
+            BigInteger peerY = pub.Y;
+            if (peerY == null || peerY.CompareTo(BigInteger.One) <= 0 || peerY.CompareTo(p.Subtract(BigInteger.One)) >= 0)
+                throw new ArgumentException("Diffie-Hellman public key is weak");
+
+            BigInteger result = peerY.ModPow(key.X, p);
             if (result.Equals(BigInteger.One))
                 throw new InvalidOperationException("Shared key can't be 1");
 
diff --git a/crypto/src/crypto/parameters/DHPublicKeyParameters.cs b/crypto/src/crypto/parameters/DHPublicKeyParameters.cs
index 1704c47dc..e7aeeff19 100644
--- a/crypto/src/crypto/parameters/DHPublicKeyParameters.cs
+++ b/crypto/src/crypto/parameters/DHPublicKeyParameters.cs
@@ -46,7 +46,7 @@ namespace Org.BouncyCastle.Crypto.Parameters
             this.y = Validate(y, parameters);
         }
 
-        public BigInteger Y
+        public virtual BigInteger Y
         {
             get { return y; }
         }