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Leaks from Edward Snowden, a system’s administrator turned whistleblower at the National Security Agency(NSA), America’s signals

admin2016-09-24  25
问题     Leaks from Edward Snowden, a system’s administrator turned whistleblower at the National Security Agency(NSA), America’s signals-intelligence agency, have confirmed that the Internet is insecure, and that modern spy agencies can—and do, on an industrial scale—tap virtually any form of online communication. But perhaps the most acute embarrassment so far has been caused by the revelation that the NSA may have been listening to phone calls made by the leaders of America’s allies, most notably those of the German chancellor, Angela Merkel. But how exactly is it done?
    A mobile phone is essentially a telephone with a radio attached. Anyone can listen in on the radio waves travelling between a handset and the base station to which it is connected. To prevent casual eavesdropping, phones often(although not always)use encryption, which disarranges the data so that only the intended recipient can make sense of it. But not all encryption is created equal. The encryption used in second-generation(2G)phones—a technology that dates back to 1991—is weak, and readily cracked by modern computers. The 3G standard includes stronger disarranging, although it is still not perfect. 4G, the newest standard, currently being used around the world, likewise offers more competent encryption—although documents leaked by Edward Snowden suggest that the spies are pressuring manufacturers to put secret "back doors" into their products.
    But getting involved in cryptography isn’t always necessary. Spy agencies can obtain details from telephone companies, either by asking them to cooperate or forcing them to. Another option is to impersonate the mobile network itself, by setting up a fake base-station and persuading the target’s phone to connect to it. At a hacker conference in 2010, a security researcher called Chris Paget gave a detailed demonstration of how this works, using less than $ 2, 000 of off-the-shelf equipment(a fake base-station can instruct phones that connect to it to do all sorts of things, such as turn off their encryption). Police forces around the world use a similar gear to silently listen in on calls made by their targets. A recent book describes how the FBI has quietly removed several such fake base-stations— run by foreign embassies—from around Washington, D. C.
    Nor is it just calls. Text messages can also be snatched. Modern smartphones are general-purpose computers. Users store e-mails on them, fix their position with satellite navigation systems, and even use them for banking, making them very juicy targets indeed. Even if the phones themselves are secure, it is far from clear how secure the behind-the-scenes servers run by Google and Apple, which control the Android and iOS platforms respectively, really are. For the non-spies, there are cheaper, simpler options that often work, too. This week several journalists in Britain are standing trial for hacking the voicemail messages of everyone from serving politicians to murdered schoolchildren. Their methods were low-tech but effective: they smooth-talked employees of mobile-phone companies into handing over the four-digit pass codes that protect their customers’ voicemail accounts. Or else they simply guessed them, betting that the phone owners either hadn’t changed them from default settings or had chosen easy-to-remember ones, such as 1 — 2 — 3 — 4. Whether the NSA used low-or high-tech methods to tap Mrs. Merkel’s phone remains a mystery—for now, at least.
How can encryption prevent casual eavesdropping?
选项 A、By stopping the usual radio waves.
B、By disconnecting a telephone to a radio.
C、By making the information incomprehensible.
D、By creating equal code pages.
答案C
解析 加密金钥如何防止偶然的窃听?使信息无法理解。根据第二段第三句，为了防止偶然的窃听，电话往往(尽管并非总是如此)使用加密金钥，即一种特殊的代码，代码将数据打乱，只让蓄意的接收者理解数据。
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