How is Marcus’ giving Van his passwords important to our understanding of Van, of Marcus and of their relationship?

Marcus trusts Van in a world that is full of distrust and paranoia. Vanessa Pak is the girl in the trio of guys. She acts as a kind of foil to Marcus, offering her opinions an all of his ideas and putting them in perspective. She is from Vietnam, so she knows about harsh governments and doesn't want Marcus to become a victim of something that he can't possibly beat. Van also helps give Marcus many of the great ideas that make his rebellion succesful. She disappears for the majority of the middle of the book, bailing because she doesn't want to see Marcus fail. Even though she is gone, Marcus still thinks about her frequently. After hastily confessing her love for Marcus, she comes through for him in the end. On a side note, Darryl has had a crush on her for a long time but nothing happens in this book.