PDFBOX-5660: optimize, as suggested by Valery Bokov; closes #432

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/branches/2.0@1932893 13f79535-47bb-0310-9956-ffa450edef68

Author: THausherr

pdfbox/src/main/java/org/apache/pdfbox/pdmodel/encryption/StandardSecurityHandler.java

@@ -511,13 +511,15 @@ private void prepareEncryptionDictRev2345(String ownerPassword, String userPassw
         COSArray idArray = document.getDocument().getDocumentID();
 
         //check if the document has an id yet.  If it does not then generate one
+        byte[] userPasswordBytes = userPassword.getBytes(Charsets.ISO_8859_1);
+        byte[] ownerPasswordBytes = ownerPassword.getBytes(Charsets.ISO_8859_1);
         if (idArray == null || idArray.size() < 2)
         {
             MessageDigest md = MessageDigests.getMD5();
             BigInteger time = BigInteger.valueOf(System.currentTimeMillis());
             md.update(time.toByteArray());
-            md.update(ownerPassword.getBytes(Charsets.ISO_8859_1));
-            md.update(userPassword.getBytes(Charsets.ISO_8859_1));
+            md.update(ownerPasswordBytes);
+            md.update(userPasswordBytes);
             md.update(document.getDocument().toString().getBytes(Charsets.ISO_8859_1));
 
             byte[] id = md.digest(this.toString().getBytes(Charsets.ISO_8859_1));
@@ -532,15 +534,16 @@ private void prepareEncryptionDictRev2345(String ownerPassword, String userPassw
         COSString id = (COSString) idArray.getObject(0);
 
         byte[] ownerBytes = computeOwnerPassword(
-                ownerPassword.getBytes(Charsets.ISO_8859_1),
-                userPassword.getBytes(Charsets.ISO_8859_1), revision, length);
+                ownerPasswordBytes,
+                userPasswordBytes, revision, length);
 
+        byte[] idBytes = id.getBytes();
         byte[] userBytes = computeUserPassword(
-                userPassword.getBytes(Charsets.ISO_8859_1),
-                ownerBytes, permissionInt, id.getBytes(), revision, length, true);
+                userPasswordBytes,
+                ownerBytes, permissionInt, idBytes, revision, length, true);
 
-        setEncryptionKey(computeEncryptedKey(userPassword.getBytes(Charsets.ISO_8859_1), ownerBytes,
-                null, null, null, permissionInt, id.getBytes(), revision, length, true, false));
+        setEncryptionKey(computeEncryptedKey(userPasswordBytes, ownerBytes,
+                null, null, null, permissionInt, idBytes, revision, length, true, false));
 
         encryptionDictionary.setOwnerKey(ownerBytes);
         encryptionDictionary.setUserKey(userBytes);