Little Brother

and hanging up after the first ring, three times in a row. A minute later, he was up on Xnet and we were able to have a secure chat. I pointed him to my blog-post on the radio vans and he came back a minute later all freaked out.
    > You sure they're looking for us?
    In response I sent him to the quiz.
    > OMG we're doomed
    > No it's not that bad but we need to figure out who we can trust
    > How?
    > That's what I wanted to ask you — how many people can you totally vouch for like trust them to the ends of the earth?
    > Um 20 or 30 or so
    > I want to get a bunch of really trustworthy people together and do a key-exchange web of trust thing
    Web of trust is one of those cool crypto things that I'd read about but never tried. It was a nearly foolproof way to make sure that you could talk to the people you trusted, but that no one else could listen in. The problem is that it requires you to physically meet with the people in the web at least once, just to get started.
    > I get it sure. That's not bad. But how you going to get everyone together for the key-signing?
    > That's what I wanted to ask you about — how can we do it without getting busted?
    Jolu typed some words and erased them, typed more and erased them.
    > Darryl would know
    I typed.
    > God, this was the stuff he was great at.
    Jolu didn't type anything. Then,
    > How about a party?
    he typed.
    > How about if we all get together somewhere like we're teenagers having a party and that way we'll have a ready-made excuse if anyone shows up asking us what we're doing there?
    > That would totally work! You're a genius, Jolu.
    > I know it. And you're going to love this: I know just where to do it, too
    > Where?
    > Sutro baths!

Chapter
10

    This chapter is dedicated to Anderson's Bookshops, Chicago's legendary kids' bookstore. Anderson's is an old, old family-run business, which started out as an old-timey drug-store selling some books on the side. Today, it's a booming, multi-location kids' book empire, with some incredibly innovative bookselling practices that get books and kids together in really exciting ways. The best of these is the store's mobile book-fairs, in which they ship huge, rolling bookcases, already stocked with excellent kids' books, direct to schools on trucks — voila, instant book-fair!
    Anderson's Bookshops: 123 West Jefferson, Naperville, IL 60540 USA +1 630 355 2665
    What would you do if you found out you had a spy in your midst? You could denounce him, put him up against the wall and take him out. But then you might end up with another spy in your midst, and the new spy would be more careful than the last one and maybe not get caught quite so readily.
    Here's a better idea: start intercepting the spy's communications and feed him and his masters misinformation. Say his masters instruct him to gather information on your movements. Let him follow you around and take all the notes he wants, but steam open the envelopes that he sends back to HQ and replace his account of your movements with a fictitious one. If you want, you can make him seem erratic and unreliable so they get rid of him. You can manufacture crises that might make one side or the other reveal the identities of other spies. In short, you own them.
    This is called the man-in-the-middle attack and if you think about it, it's pretty scary. Someone who man-in-the-middles your communications can trick you in any of a thousand ways.
    Of course, there's a great way to get around the man-in-the-middle attack: use crypto. With crypto, it doesn't matter if the enemy can see your messages, because he can't decipher them, change them, and re-send them. That's one of the main reasons to use crypto.
    But remember: for crypto to work, you need to have keys for the people you want to talk to. You and your partner need to share a secret or two, some keys that you can use to encrypt and decrypt your messages so that men-in-the-middle get locked out.
    That's where the idea of public keys comes in. This is a little hairy, but it's so unbelievably elegant too.
    In public key crypto, each user gets two keys. They're long strings of mathematical gibberish, and they have an almost magic property. Whatever you scramble with one key, the other will unlock, and vice-versa. What's more, they're the only keys that can do this — if you can unscramble a message with one key, you know it was scrambled with the other (and vice-versa).
    So you take either one of these keys (it doesn't matter which one) and you