Security Engineering. Ross Anderson

Чтение книги онлайн.

СКАЧАТЬ people didn't really bother. The first computer systems were isolated, serving a single company or university. Students might try to hack the system to get more resources and sysadmins would try to stop them, but it was mostly a game. When dial-up connections started to appear, pranksters occasionally guessed passwords and left joke messages, as they'd done at university. The early Internet was a friendly place, inhabited by academics, engineers at tech companies, and a few hobbyists. We knew that malware was possible but almost nobody took it seriously until the late 1980s when PC viruses appeared, followed by the Internet worm in 1988. (Even that was a student experiment that escaped from the lab; I tell the story in section 21.3.2.)

Things changed once everyone started to get online. The mid-1990s saw the first spam, the late 1990s brought the first distributed denial-of-service attack, and the explosion of mail-order business in the dotcom boom introduced credit card fraud. To begin with, online fraud was a cottage industry; the same person would steal credit card numbers and use them to buy goods which he'd then sell, or make up forged cards to use in a store. Things changed in the mid-2000s with the emergence of underground markets. These let the bad guys specialise – one gang could write malware, another could harvest bank credentials, and yet others could devise ways of cashing out. This enabled them to get good at their jobs, to scale up and to globalise, just as manufacturing did in the late eighteenth century. The 2000s also saw the world's governments putting in the effort to ‘Master the Internet’ (as the NSA put it) – working out how to collect data at scale and index it, just as Google does, to make it available to analysts. It also saw the emergence of social networks, so that everyone could have a home online – not just geeks with the skills to create their own handcrafted web pages. And of course, once everyone is online, that includes not just spies and crooks but also jerks, creeps, racists and bullies.

      Over the past decade, this threat landscape has stabilised. We also know quite a lot about it. Thanks to Ed Snowden and other whistleblowers, we know a lot about the capabilities and methods of Western intelligence services; we've also learned a lot about China, Russia and other nation-state threat actors. We know a lot about cybercrime; online crime now makes up about half of all crime, by volume and by value. There's a substantial criminal infrastructure based on malware and botnets with which we are constantly struggling; there's also a large ecosystem of scams. Many traditional crimes have gone online, and a typical firm has to worry not just about external fraudsters but also about dishonest insiders. Some firms have to worry about hostile governments, some about other firms, and some about activists. Many people have to deal with online hostility, from kids suffering cyber-bullying at school through harassment of elected politicians to people who are stalked by former partners. And our politics may become more polarised because of the dynamics of online extremism.

      One of the first things the security engineer needs to do when tackling a new problem is to identify the likely opponents. Although you can design some specific system components (such as cryptography) to resist all reasonable adversaries, the same is much less true for a complex real-world system. You can't protect it against all possible threats and still expect it to do useful work at a reasonable cost. So what sort of capabilities will the adversaries have, and what motivation? How certain are you of this assessment, and how might it change over the system's lifetime? In this chapter I will classify online and electronic threats depending on motive. First, I'll discuss surveillance, intrusion and manipulation done by governments for reasons of state, ranging from cyber-intelligence to cyber-conflict operations. Second, I'll deal with criminals whose motive is mainly money. Third will be researchers who find vulnerabilities for fun or for money, or who report them out of social conscience – compelling firms to patch their software and clean up their operations. Finally, I'll discuss bad actors whose reasons are personal and who mainly commit crimes against the person, from cyber-bullies to stalkers.

      The big service firms, such as Microsoft, Google and Facebook, have to worry about all four classes of threat. Most firms and most private individuals will only be concerned with some of them. But it's important for a security engineer to understand the big picture so you can help clients work out what their own threat model should be, and what sort of attacks they should plan to forestall.

2.2 Spies

      Governments have a range of tools for both passive surveillance of networks and active attacks on computer systems. Hundreds of firms sell equipment for wiretapping, for radio intercept, and for using various vulnerabilities to take over computers, phones and other digital devices. However, there are significant differences among governments in scale, objectives and capabilities. We'll discuss four representative categories – the USA and its allies, China, Russia and the Arab world – from the viewpoint of potential opponents. Even if spies aren't in your threat model today, the tools they use will quite often end up in the hands of the crooks too, sooner or later.

      2.2.1 The Five Eyes

      Just as everyone in a certain age range remembers where they were when John Lennon was shot, everyone who's been in our trade since 2013 remembers where they were when they learned of the Snowden revelations on Friday 7th June of that year.

       2.2.1.1 Prism

I was in a hotel in Palo Alto, California, reading the Guardian online before a scheduled visit to Google where I'd been as a scientific visitor in 2011, helping develop contactless payments for Android phones. The headline was ‘NSA Prism program taps in to user data of Apple, Google and others’; the article, written by Glenn Greenwald and Ewen MacAskill, describes a system called Prism that collects the Gmail and other data of users who are not US citizens or permanent residents, and is carried out under an order from the FISA court [818]. After breakfast I drove to the Googleplex, and found that my former colleagues were just as perplexed as I was. They knew nothing about Prism. Neither did the mail team. How could such a wiretap have been built? Had an order been served on Eric Schmidt, and if so how could he have implemented it without the mail and security teams knowing? As the day went on, people stopped talking.

It turned out that Prism was an internal NSA codename for an access channel that had been provided to the FBI to conduct warranted wiretaps. US law permits US citizens to be wiretapped provided an agency convinces a court to issue a warrant, based on ‘probable cause’ that they were up to no good; but foreigners could be wiretapped freely. So for a foreign target like me, all an NSA intelligence analyst had to do was click on a tab saying they believed I was a non-US person. The inquiry would be routed automatically via the FBI infrastructure and pipe my Gmail to their workstation. According to the article, this program had started at Microsoft in 2007; Yahoo had fought it in court, but lost, joining in late 2008; Google and Facebook had been added in 2009 and Apple finally in 2012. A system that people thought was providing targeted, warranted wiretaps to law enforcement was providing access at scale for foreign intelligence purposes, and according to a slide deck leaked to the Guardian it was ‘the SIGAD¹ most used in NSA reporting’.

      The following day we learned that the source of the story was Edward Snowden, an NSA system administrator who'd decided to blow the whistle. The story was that he'd smuggled over 50,000 classified documents out of a facility in Hawaii on a memory stick and met Guardian journalists in Hong Kong [819]. He tried to fly to Latin America on June 21st to claim asylum, but after the US government cancelled his passport he got stuck in Moscow and eventually got asylum in Russia instead. A consortium of newspapers coordinated a series of stories describing the signals intelligence capabilities of the ‘Five Eyes’ countries – the USA, the UK, Canada, Australia and New Zealand – as well as how these capabilities were not just used but also abused.

      The first story based on the leaked documents had actually appeared two days before the Prism story; it was about how the FISA court had ordered Verizon to hand over all call data records (CDRs) to the NSA in February that year [815]. This hadn't got much attention from security professionals as СКАЧАТЬ