Add validation to DSA public key constructor

1 files changed, 17 insertions, 1 deletions

diff --git a/crypto/src/crypto/parameters/DsaPublicKeyParameters.cs b/crypto/src/crypto/parameters/DsaPublicKeyParameters.cs

index f11f858f3..3a81bfdd0 100644
--- a/crypto/src/crypto/parameters/DsaPublicKeyParameters.cs
+++ b/crypto/src/crypto/parameters/DsaPublicKeyParameters.cs
@@ -7,6 +7,22 @@ namespace Org.BouncyCastle.Crypto.Parameters
     public class DsaPublicKeyParameters
 		: DsaKeyParameters
     {
+        private static BigInteger Validate(BigInteger y, DsaParameters parameters)
+        {
+            // we can't validate without params, fortunately we can't use the key either...
+            if (parameters != null)
+            {
+                if (y.CompareTo(BigInteger.Two) < 0
+                    || y.CompareTo(parameters.P.Subtract(BigInteger.Two)) > 0
+                    || !y.ModPow(parameters.Q, parameters.P).Equals(BigInteger.One))
+                {
+                    throw new ArgumentException("y value does not appear to be in correct group");
+                }
+            }
+
+            return y;
+        }
+
         private readonly BigInteger y;
 
 		public DsaPublicKeyParameters(
@@ -17,7 +33,7 @@ namespace Org.BouncyCastle.Crypto.Parameters
 			if (y == null)
 				throw new ArgumentNullException("y");
 
-			this.y = y;
+			this.y = Validate(y, parameters);
         }
 
 		public BigInteger Y