Yet another strange blog

There is security flaw in computer systems called Side Channel Leaks. Basically it consists in taking an available piece of information and inferring the rest based on a previous knowledge of the system.

To make this notion clearer, imagine a system which is composed by two pieces (client and server) and the internet is connecting those parts (SaaS). Imagine also that someone, let’s call this person Holmes, has access to all the network traffic on the client side. Holmes wants to know the data the client, let’s call this client Porlock, is passing to the server side. As we said, Holmes has access to the network, but it’s almost impossible for him to find out exactly what is going on, for the traffic is all encrypted. And there we have it: The Side Channel Leak.

Suppose Holmes has used the system before and he knows that there is a part of the system which, if used, makes the packets transmitted in the network be really large. Suppose also that this is a part of the system that Porlock is not suppose to have access to. If Holmes see some specific packets being transmitted, then he is able to know that Porlock is doing something wrong. And guess what, the more Holmes knows about the timing between packets, as their size, and how the system works, the more knowledge he has of what exactly Porlock is doing without even trying decrypt those packets. That is Side Channel Leak.

Until here, we’ve been talking about computers systems, but there is something more for us to learn from this hypothetical scenario.

Lets take a look at another hypothetical scenario in the beginning of the book “The Valley of Fear”. In this particular part of the book, Sherlock Holmes receives a letter containing an encrypted message from Porlock. The means to decrypt the message would be sent later to Holmes, but Porlock got scared and decided not to give it to Holmes. And that was enough for Holmes to successfully decrypt the message. How cool is that?!

You see, in this case Holmes knew some specific information about the system, which in this case is both Porlock and the letters. Facts about the system that he knew:

1. The key to decipher the message was a book. Of two methods commonly used by thieves to send encrypted messages, this could be only this one.
2. A part of the encrypted message was referring to the page of the book, 534. Such a big book wouldn’t be sent to Holmes so he could decipher the message, therefore it was a book he probably already had. The problem still has several possibilities, but in a limited number.
3. Another part of the message seems to refer to the column of the book (C2). So this book must have two columns.
4. As this book is supposed to be the key to decipher several messages, he must have lots of words per page. Now we have even less and less possibilities for this odd book.
5. He then grabs an Almanac and there we have it. He is able to decipher the message.
6. To know more about how the story ends this theory won’t work, I’m afraid. You will have to read the book.

You see, humans are also a system, and you can use Side Channel Leaks theory to know much more than what you see. Of course this is nothing new, cops, investigators, managers, artists, mothers, sons use that all the time. At a first glance I was surprised to see that applied to humans as well, but then, I should be surprised to see something like that applied to computers.