How can i loop all nodes in an XML document in objective-c and change their values then save the xml?

Question

Hiya - I am really struggling here - I want to load an XML document in objective-c and loop each node and encrypt the string value of that node. Then encryption bit i have sorted but when i run the following code it just changes the root node and every other node and not the values of the nodes.

e.g. - i want to go from:

<root>
      <node1>some text</node1>
      <node2>
        <node3>some more text</node3>
       </node2>
    </root>

to something like:

    <root>
      <node1>encrypted text here</node1>
      <node2>
        <node3>encrypted text here</node3>
       </node2>
    </root>

but my code below just returns:

    <root>
      encrypted text here
    </root>

Code is currently:

    NSString *filenameStr = @"/Users/blah/Documents/project/filetestIN.xml";

    //OPEN XML
    NSXMLDocument *xmlDoc;
    NSError *err=nil;
    NSURL *furl = [NSURL fileURLWithPath:filenameStr];
    if (!furl) {
        NSLog(@"Can't create a URL from file %@.", filenameStr);
    }
    xmlDoc = [[NSXMLDocument alloc] initWithContentsOfURL:furl options:(NSXMLNodePreserveWhitespace|NSXMLNodePreserveCDATA) error:&err];
    if (xmlDoc == nil) {
        xmlDoc = [[NSXMLDocument alloc] initWithContentsOfURL:furl options:NSXMLDocumentTidyXML error:&err];
    }


    //ENCRYPT IT NODE BY NODE

    StringEncryption *crypto = [[[StringEncryption alloc] init] autorelease];


    NSArray *nodes = [xmlDoc nodesForXPath:@"//*" error:&err];

    for (NSXMLElement *categoryElement in nodes) {
        [crypto encryptXMLNode:categoryElement];
    }


    //SAVE XML
    NSData *xmlData = [xmlDoc XMLData];
    NSString *filenameStrOUT = @"/Users/blah/Documents/project/output/filetestOUT.xml";

    NSURL *furlOUT = [NSURL fileURLWithPath:filenameStrOUT];
    if (!furlOUT) {
        NSLog(@"Can't create an URL from file %@.", filenameStrOUT);
    }                
    [xmlData writeToURL:furlOUT atomically:YES];

    //and the ecnrptionbit:

    - (void)encryptXMLNode:(NSXMLNode *)node
    {
        if ([node kind] == NSXMLElementKind)
        {
            NSString *name = [node name];

            NSString *strval = [node stringValue];
            NSLog(@"old:%@=%@", name, strval);
                    //in time the actual encryption of strval will go here:
            NSString *newVal = @"encrypted text here";
            [node setStringValue:newVal];
            name = [node name];
            strval = [node stringValue];
            NSLog(@"new:%@=%@", name, strval);
        }
    }

Many thanks for any help at all!