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You might not think that the typical family operates any secure systems. But just stop and think.

1 You probably use some of the systems I've already described. You may use a web-based electronic banking system to pay bills, and you may have online access to your doctor's surgery so you can order repeat prescriptions. If you're diabetic then your insulin pump may communicate with a docking station at your bedside. Your home burglar alarm may send an encrypted ‘all's well’ signal to the security company every few minutes, rather than waking up the neighborhood when something happens.

2 Your car probably has an electronic immobilizer. If it was made before about 2015, the car unlocks when you press a button on the key, which sends an encrypted unlock command. If it's a more recent model, where you don't have to press any buttons but just have the key in your pocket, the car sends an encrypted challenge to the key and waits for the right response. But eliminating the button press meant that if you leave your key near the front door, a thief might use a radio relay to steal your car. Car thefts have shot up since this technology was introduced.

3 Your mobile phone authenticates itself to the network by a cryptographic challenge-response protocol similar to the ones used in car door locks and immobilizers, but the police can use a false base station (known in Europe as an IMSI-catcher, and in America as a Stingray) to listen in. And, as I mentioned above, many phone companies are relaxed about selling new SIM cards to people who claim their phones have been stolen; so a crook might steal your phone number and use this to raid your bank account.

4 In over 100 countries, households can get prepayment meters for electricity and gas, which they top up using a 20-digit code that they buy from an ATM or an online service. It even works off-grid; in Kenyan villages, people who can't afford $200 to buy a solar panel can get one for $2 a week and unlock the electricity it generates using codes they buy with their mobile phones.

5 Above all, the home provides a haven of physical security and seclusion. This is changing in a number of ways. Burglars aren't worried by locks as much as by occupants, so alarms and monitoring systems can help; but monitoring is also becoming pervasive, with many households buying systems like Alexa and Google Home that listen to what people say. All sorts of other gadgets now have microphones and cameras as voice and gesture interfaces become common, and the speech processing is typically done in the cloud to save battery life. By 2015, President Obama's council of advisers on science and technology was predicting that pretty soon every inhabited space on earth would have microphones that were connected to a small number of cloud service providers. (The USA and Europe have quite different views on how privacy law should deal with this.) One way or another, the security of your home may come to depend on remote systems over which you have little control.

Over the next few years, the number of such systems is going to increase rapidly. On past experience, many of them will be badly designed. For example, in 2019, Europe banned a children's watch that used unencrypted communications to the vendor's cloud service; a wiretapper could download any child's location history and cause their watch to phone any number in the world. When this was discovered, the EU ordered the immediate safety recall of all watches [903].

This book aims to help you avoid such outcomes. To design systems that are safe and secure, an engineer needs to know about what systems there are, how they work, and – at least as important – how they have failed in the past. Civil engineers learn far more from the one bridge that falls down than from the hundred that stay up; exactly the same holds in security engineering.