Michal Zalewski - Silence on the Wire: A Field Guide to Passive Reconnaissance and Indirect Attacks

For Maja

What does it take to write a novel book on computer security? Or rather, what does it take to write a novel on modern computing?

A young yet highly experienced author with talents in many areas including many aspects of computing, mathematics, and electronics (and perhaps a hobby in robotics), as well as other seemingly unrelated interests (including, lets say, fatalistic erotic photography), and indeed with a talent and desire to write.

Once upon a time in a dark and largely unexplored forest, the magic chemistry of (brain cell) trees gave birth to a bit of information, only to let him sail his way down a quick river, into the vast sea (of the Internet), and ultimately find his new home, grave, or maybe a place in a museum .

And so the tale begins. Whether our little bit is good or evil, at a young age he will reach the stream flowing into a shiny castle made out of white-colored foil (yet regarded by many as a black box). He will pass through the entrance and approach the counter to check in. If he werent so naive and short-sighted, he could notice a group of evil-looking bits staring at the counter from a distance, taking note of the time bits check in and out; he would have no choice but to proceed to sign in, though .

Once rested, our hero might be asked to team up with his siblings or to join a group of other bits and bitesses, and together they would pack their bodies tightly onto a used inflatable boat. A careful bit could notice bits of garbage (or is that garbage?) in the boat, presumably left by a previous group .

Observing the traffic lights and squeezing through traffic jams, our bits enter a safe harbor and sail to the wharf. Will they be seen from nearby castles and lighthouses? Will someone track the traffic light switches to determine just when our group sailed? Will someone turn on lights at the wharf and take pictures? Will those other evil bits assume the identity of ours and sail away to the sea first? Our bits wouldnt know .

And so they change boats at the wharf and sail to the sea... The journey of our pet bits proceeds, with many dangers yet to come .

No, Michals book does not hide technical detail behind a fairy tale as I have above. Rather, while a very entertaining read, it gets all the facts straight and promptly gives answers to most challenges introduced at the beginning of each chapter.

Silence on the Wire is unique in many aspects, but two stand out: First, it provides in-depth coverage of almost all essential stages of data processing that enable todays internetworkingfrom a keypress to the intended end result of that keypress. Second, it outlines the largely overlooked, under-researched, and inherent security issues associated with each stage of networking and with the process as a whole. The security issues covered serve well to demonstrate the art of vulnerability research from both the attackers and the defenders perspective, and will encourage further research on the part of the reader.

Clearly, a computer security book cant be comprehensive. In SotW , Michal has provocatively chosen to leave out all the well known yet highly dangerous and widespread vulnerabilities and attacks being discussed and worked on today by most in the information security community. He will teach you about subtle keystroke timing attacks, but you will not be reminded that trojan horse software with key logging capabilities is currently both more common and easier to use than any of such attacks could ever be.

Why mention keystroke timings while leaving the trojans out? Because timing attacks are largely underappreciated and misunderstood even by information security professionals, whereas trojans are a widely known and obvious threat. Vulnerability to timing attacks is a property of the design of many components involved, whereas to implant a trojan requires either a software bug or an end-user error.

Similarly, and with few exceptions, you wont find the slightest mention in SotW of the widely exploited software bugsor even generic software bug classes such as buffer overflows. If you are not already familiar with the common computer security threats and would like to gain that knowledge, you will need to accompany yourself on your journey through this book with the perusal of less exciting material available on the Internet and in other books, and in particular with material pertaining to the specific operating systems that you use.

Why study silence, you may wonderisnt that a nothing? Yes, in a sense. A zero is a nothing in that sense, too. But it is also a number, a concept we cannot really understand the world without.

Enjoy the silencethe best you can.

Alexander Peslyak

Founder and CTO

Openwall, Inc.

better known as

Solar Designer

Openwall Project leader

January 2005