added check for null private exponent with CRT key.

Author: dghgit

core/src/main/java/org/bouncycastle/crypto/engines/RSACoreEngine.java

@@ -221,6 +221,13 @@ public BigInteger processBlock(BigInteger input)
 
                 return m;
             }
+            else
+            {
+                if (key.getExponent() == null)
+                {
+                    throw new IllegalStateException("null exponent, should \"org.bouncycastle.rsa.no_lenstra_check\" be enabled?");
+                }
+            }
         }
 
         return input.modPow(key.getExponent(), key.getModulus());

core/src/test/java/org/bouncycastle/crypto/test/RSABlindedTest.java

@@ -435,6 +435,20 @@ public void performTest()
         bEng.init(true, privParameters);
 
         bEng.processBlock(new byte[]{ 1 }, 0, 1);
+
+        privParameters = new RSAPrivateCrtKeyParameters(mod, null, null, p, q, pExp, qExp, crtCoef);
+        
+        bEng.init(true, privParameters);
+
+        try
+        {
+            bEng.processBlock(new byte[]{1}, 0, 1);
+            fail("no exception");
+        }
+        catch (IllegalStateException e)
+        {
+            // ignore - expected.
+        }
     }