Chapter 21. Network Attack and Defense

Whoever thinks his problem can be solved using cryptography, doesn't understand his problem and doesn't understand cryptography.

— Attributed by Roger Needham and Butler Lampson to Each Other

If you spend more on coffee than on IT security, then you will be hacked. What's more, you deserve to be hacked.

— Richard Clarke, Former U.S. Cybersecurity Tsar


So far we've seen a large number of attacks against individual computers and other devices. But attacks increasingly depend on connectivity. Consider the following examples.

  1. An office worker clicks on an attachment in email. This infects her PC with malware that compromises other machines in her office by snooping passwords that travel across the LAN.

  2. The reason she clicked on the attachment is that the email came from her mother. The malware had infected her mother's machine and then sent out a copy of a recent email, with itself attached, to everyone in mum's address book.

  3. Her mother in turn got infected by an old friend who chose a common password for his ISP account. When there are many machines on a network, the bad guys don't have to be choosy; rather than trying to guess the password for a particular account, they just try one password over and over for millions of accounts. Given a webmail account, they can send out bad email to the whole contact list.

  4. Another attack technique that makes sense only in a network context is Google hacking. Here, the bad guys use search engines to find ...

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