Add SecretKeyUtil to help with key cleanup

Author: peterdettman

tls/src/main/jdk1.5/org/bouncycastle/tls/crypto/impl/jcajce/SecretKeyUtil.java

@@ -0,0 +1,21 @@
+package org.bouncycastle.tls.crypto.impl.jcajce;
+
+import javax.crypto.SecretKey;
+import javax.security.auth.Destroyable;
+
+abstract class SecretKeyUtil
+{
+    static void destroy(SecretKey secretKey)
+    {
+        if (secretKey instanceof Destroyable)
+        {
+            try
+            {
+                ((Destroyable)secretKey).destroy();
+            }
+            catch (Exception e)
+            {
+            }
+        }
+    }
+}

tls/src/main/jdk1.9/org/bouncycastle/tls/crypto/impl/jcajce/SecretKeyUtil.java

@@ -0,0 +1,21 @@
+package org.bouncycastle.tls.crypto.impl.jcajce;
+
+import javax.crypto.SecretKey;
+import javax.security.auth.Destroyable;
+
+abstract class SecretKeyUtil
+{
+    static void destroy(SecretKey secretKey)
+    {
+        if (secretKey != null)
+        {
+            try
+            {
+                ((Destroyable)secretKey).destroy();
+            }
+            catch (Exception e)
+            {
+            }
+        }
+    }
+}