GWT: Decrypt GAE-JDO key to access parent

In the GAE-JDO docs it is possible to get parent keys from child keys:

Note also that the string representation of the string is not encrypted: the user can decode the key string to retrieve its components, including the species and identifiers of the object and its ancestors.

REF: "Objects, Properties and Keys"

I am generating keys using the following:

@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
@Extension(vendorName = "datanucleus", key = "gae.encoded-pk", value = "true")
private String id;

      

        
        
        
      

    

When validating the datastore, the entity keys look like this:

parent.id = agpzfnZpdmVlbGFichQLEgdTZXNzaW9uGICAgICgwMsIDA
child1.id = agpzfnZpdmVlbGFiciYLEgdTZXNzaW9uGICAgICgwMsIDAsSBVN0YWdlGICAgICAwK8KDA
...

      

        
        
        
      

    

(where the parent has children of type Child). So, I'm looking for a GWT function like this:

String getParentIdFromChildId(String childId) {
    String parentId = ...        
    return parentId;
}

      

        
        
        
      

    

so from the client (GWT) I can refer to the child object (by first discovering its parent):

Child child = data.getParent(getParentIdFromChildId(childId)).getChild(childId);

      

        
        
        
      

    

I could solve this by also tracking the parent id, but if the parent information is already embedded in the child id, this is inefficient.

Thanks in advance.

~ Owen