Looks good. Alternatively, we can have a Vec<Vec<u8>>, but not a big deal since the query is meant to be serialized and passed along to the server.

I did [] because we don't want the array to be tampered with. Is my thinking here wrong?

The fields will be non-mutable by definition (Rust things :) ) if that's what you mean. In order to change the values of a struct field, you'd need to wrap it in a Box or RefCell - similar to what we have in the Storage:

 struct Storage {                                                                        
  secret_key: SecretKey,                                                              
  size: usize,                                                                        
  store: RefCell<Vec<Scalar>>,                                                        
}    

If store was defined as store: Vec<Scalar>,, the contents of the vector could not be changed.