Use utility method

Author: peterdettman

prov/src/main/java/org/bouncycastle/jcajce/provider/asymmetric/dh/KeyAgreementSpi.java

@@ -37,6 +37,7 @@
 import org.bouncycastle.jcajce.spec.DHUParameterSpec;
 import org.bouncycastle.jcajce.spec.MQVParameterSpec;
 import org.bouncycastle.jcajce.spec.UserKeyingMaterialSpec;
+import org.bouncycastle.util.BigIntegers;
 
 /**
  * Diffie-Hellman key agreement. There's actually a better way of doing this
@@ -104,30 +105,9 @@ protected byte[] bigIntToBytes(
         //
         int expectedLength = (p.bitLength() + 7) / 8;
 
-        byte[]    tmp = r.toByteArray();
-
-        if (tmp.length == expectedLength)
-        {
-            return tmp;
-        }
-
-        if (tmp[0] == 0 && tmp.length == expectedLength + 1)
-        {
-            byte[]    rv = new byte[tmp.length - 1];
-            
-            System.arraycopy(tmp, 1, rv, 0, rv.length);
-            return rv;
-        }
-
-        // tmp must be shorter than expectedLength
-        // pad to the left with zeros.
-        byte[]    rv = new byte[expectedLength];
-
-        System.arraycopy(tmp, 0, rv, rv.length - tmp.length, tmp.length);
-
-        return rv;
+        return BigIntegers.asUnsignedByteArray(expectedLength, r);
     }
-    
+
     protected Key engineDoPhase(
         Key     key,
         boolean lastPhase)