 I am a geek, and I want to talk to you about a geeky subject that applies to all of us, but a subject that is such a passion of mine. I want to talk to you about cryptography, hiding information in secret codes to make sure that anyone but the intended recipient can't access it. Now, it surprises me that so few people know about cryptography when you consider that it's been made sexy by every spy novel that any of you have ever read in every movie. When you consider that it has turned the tides of war, such as the Enigma Machine in World War II, and when you consider that it underpins all of our modern infrastructure, every time you make a payment online, every time you post something embarrassing on Facebook that you wish you hadn't. But encryption can be used for bad as well as for good. Take this computer virus. Here is a file I created, could just as easily be pictures of a firstborn child or something like that, and here is a nasty email from a cyber criminal. Now, I stupidly run the attachment, which then puts up a message saying, my files have been encrypted with the RSA 1024 algorithm. If I look at my data now, we can see all of my documents are encrypted, and I can no longer access them. They're literally holding my data to ransom on my own computer. How terrifying is that? Now, encryption isn't new. Roman generals use the Caesar cipher to send information to each other. A very simple cipher where, if the key was two, you would change A to C and a like. But it was very easy to break that cipher. You could enumerate all of the different possibilities and quickly figure out the answer. So modern computers have to be much, much smarter. The problem is, surely if something between A and B is done by a computer, a computer can undo it as well. You need something that is easy in one direction and hard in another. And here comes the elegant mathematical trick that powers the modern world. If you take two prime numbers, 19 and 31, and you multiply them together, most of you could do this quite easily, some of you might need more time or a calculator, but nonetheless, you could do it fast. However, if I gave you the number 589 and asked you to find the two prime numbers, that constituted together, multiplied, to give this, you'd find it really hard. And so does a computer. It's like unmixing paint. This can take seconds in one direction and years in another. Now imagine that number is absolutely huge, just like an encryption. For the parties A and B that know the secret, this takes mere seconds, but for the attacker, it takes forever. You now understand cryptography, or at least the basis of it, that keeps most of our computers safe today. But unfortunately, computers are getting more powerful. So there's lots of research going on into new areas, like quantum key distribution, using light to send information from A to B, using a wonderful law of quantum mechanics that says, if you look at the photons of light between A and B, the photons being the pasta here, made a lot of mess in my kitchen, then if you look at them when they arrange at the other end, they'll be fundamentally different. It's a system that is designed by nature to be proofed from tampering. Now there's another important concept to encryption that we have to consider. The art of being random. Now it sounds easy, but being random is actually really hard. If you say to a computer, be random, it has a program to do that, which is quite logical and not very random. So we have to look at other ways to get that stuff. So I went out on a little mission to build some of these devices, and I'm gonna share one of them with you now. I took a smoke alarm, and a smoke alarm contains a lovely little radioactive source, and nature provides these wonderfully random, radioactive emissions. So I took this and using an incredibly expensive high-tech containment device, I connected it to my computer with a Geiger counter and collected data from this wonderful source. And the net result, okay, I'm the only one that's excited about that, right? To a cryptographer, that is brilliant. It's pure randomness, okay? Now, I'm taking all of these devices. I've built lots of others, some from vacuum cleaners and other strange things, and plugging them into my website, where you'll be able to go online and you'll be able to use these to generate some random data to make yourselves more secure online. But most critically, my hope is this. Encryption, cryptography, is one of the most critical pillars of our infrastructure today. It's the guardian of your privacy and your security. I hope that my passion and this talk inspires you to learn more about how to keep yourself safe and how this fascinating subject works. Thank you.