Little Brother

then everyone who uses them has to keep them a secret too, and if someone changes sides, you have to find a new cipher.
    The Nazi cipher was called Enigma, and they used a little mechanical computer called an Enigma Machine to scramble and unscramble the messages they got. Every sub and boat and station needed one of these, so it was inevitable that eventually the Allies would get their hands on one.
    When they did, they cracked it. That work was led by my personal all-time hero, a guy named Alan Turing, who pretty much invented computers as we know them today. Unfortunately for him, he was gay, so after the war ended, the stupid British government forced him to get shot up with hormones to "cure" his homosexuality and he killed himself. Darryl gave me a biography of Turing for my 14th birthday — wrapped in twenty layers of paper and in a recycled Batmobile toy, he was like that with presents — and I've been a Turing junkie ever since.
    Now the Allies had the Enigma Machine, and they could intercept lots of Nazi radio-messages, which shouldn't have been that big a deal, since every captain had his own secret key. Since the Allies didn't have the keys, having the machine shouldn't have helped.
    Here's where secrecy hurts crypto. The Enigma cipher was flawed. Once Turing looked hard at it, he figured out that the Nazi cryptographers had made a mathematical mistake. By getting his hands on an Enigma Machine, Turing could figure out how to crack any Nazi message, no matter what key it used.
    That cost the Nazis the war. I mean, don't get me wrong. That's good news. Take it from a Castle Wolfenstein veteran. You wouldn't want the Nazis running the country.
    After the war, cryptographers spent a lot of time thinking about this. The problem had been that Turing was smarter than the guy who thought up Enigma. Any time you had a cipher, you were vulnerable to someone smarter than you coming up with a way of breaking it.
    And the more they thought about it, the more they realized that anyone can come up with a security system that he can't figure out how to break. But no one can figure out what a smarter person might do.
    You have to publish a cipher to know that it works. You have to tell as many people as possible how it works, so that they can thwack on it with everything they have, testing its security. The longer you go without anyone finding a flaw, the more secure you are.
    Which is how it stands today. If you want to be safe, you don't use crypto that some genius thought of last week. You use the stuff that people have been using for as long as possible without anyone figuring out how to break them. Whether you're a bank, a terrorist, a government or a teenager, you use the same ciphers.
    If you tried to use your own cipher, there'd be the chance that someone out there had found a flaw you missed and was doing a Turing on your butt, deciphering all your "secret" messages and chuckling at your dumb gossip, financial transactions and military secrets.
    So I knew that crypto would keep me safe from eavesdroppers, but I wasn't ready to deal with histograms.

    I got off the BART and waved my card over the turnstile as I headed up to the 24th Street station. As usual, there were lots of weirdos hanging out in the station, drunks and Jesus freaks and intense Mexican men staring at the ground and a few gang kids. I looked straight past them as I hit the stairs and jogged up to the surface. My bag was empty now, no longer bulging with the ParanoidXbox discs I'd been distributing, and it made my shoulders feel light and put a spring in my step as I came up the street. The preachers were at work still, exhorting in Spanish and English about Jesus and so on.
    The counterfeit sunglass sellers were gone, but they'd been replaced by guys selling robot dogs that barked the national anthem and would lift their legs if you showed them a picture of Osama bin Laden. There was probably some cool stuff going on in their little brains and I made a mental note to pick a couple of them up and take them apart later. Face-recognition was pretty new in toys, having only recently made the leap from the military to casinos trying to find cheats, to law enforcement.
    I started down 24th Street toward Potrero Hill and home, rolling my shoulders and smelling the burrito smells wafting out of the restaurants and thinking about dinner.
    I don't know why I happened to glance back over my shoulder, but I did. Maybe it was a little bit of subconscious