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[Week 10]

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[David J. Malan] [Harvard University]

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[This is CS50.] [CS50.TV]

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>> All right! This is CS50 but not for much longer.

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This is the start of week 10. 

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On Wednesday we have our quiz, and then next Monday we have some celebratory cake 

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as we come full circle all the way back from week zero.

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Today, we talk about one of my favorite topics, truth be told--

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that of security and privacy and the implications of all of the hardware and software

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that we all use these days.

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To be honest, there are a lot of threats out there

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that if you haven't really paused to think about them, 

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they're actually pretty daunting.

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Case in point--if any of you have ever downloaded a piece of software

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off of the Internet and installed it on your computer,

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you've engaged into a significant degree of trust, right?

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There is nothing having prevented Skype, or Chrome, or any piece of software

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you've installed onto your computer, from simply deleting all of the files on your hard drive;

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from uploading all of the files on your hard drive to some bad guy's server;

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from reading all of your emails; from intercepting all of your instant messages.

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Because the reality is today with most modern operating systems

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there really isn't much of a wall between software programs that we install,

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and you and I are pretty much just kind of crossing our fingers and taking on faith

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that that app we downloaded for free, or that thing that's 99 cents,

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is actually completely benign.

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But as we've seen through C, and now PHP and JavaScript, 

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with this ability to express ourselves programatically, 

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you can do most anything you want with a program that a user himself or herself could do.

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>> So, today we focus on that topic--

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not only some threats but also defenses.

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Indeed, in the world of security in general,

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there's kind of this cat-and-mouse game,

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and I daresay the bad guys almost always have a leg up. 

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When it comes to taking advantage of hardware and software on our own personal computers,

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we have to realize that a bad guy simply needs to find one simple mistake--

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one exploit, one bug--in a piece of software we've written or are running

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in order for him or her to take over our whole system.

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By contrast, we--the good guys--need to patch and fix all of those bugs

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and avoid all of those weaknesses.

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And so, I daresay on the whole, the bad guys have the advantage.

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What classes like this and subsequent classes are really about

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are not about teaching you how to wage the battles that these bad guys do,

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but are about how to protect yourself or at least how to make a calculated decision

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that yes, I know this piece of software could indeed read every one of my emails,

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but I'm okay with that because of the value it brings me on the other hand.

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>> I'm very pleased to be joined by 2 of the smartest people I know--

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Rob Bowden and Nate Hardison.

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Rob is about to take us for a tour through the lowest level of security tags--

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that of the compiler which, up until now, we've all come to love and trust. Rob Bowden.

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[applause]

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>> [Rob] All right. David has pretty much taken my whole spiel

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that I was going to introduce with, but--

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Several weeks ago, you saw the example of a buffer-overflow attack

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which is an example of a hacker hacking into some piece of software

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that they are not supposed to be hacking into.

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The other side of this

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is sometimes you have software that is malicious in and of itself.

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It doesn't even need to be hacked.

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The person who wrote the software wants to hack you.

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>> Let's just jump right into code,

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taking a look at "login.c".

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Here, a silly program that validates a username and password combination.

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Here you should definitely be getting comfortable with C again for the quiz.

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First, we are using get strings to describe the username,

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then we're using get string to grab the password, 

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and then we have some trivial checks of just, is the username "rob"?

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And is the password "thisiscs50"?

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Or, is the username "tommy" and the password "i<3javascript"?

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If either of those is the case,

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 then we're just going to print "Success", and then we have access.

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Otherwise, we're going to print "invalid login" and then, of course,

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 since sketch strings malloc's memory, we free username and password.

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This is a trivial login program,

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and if you think about when you log into the appliance,

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it's pretty similar--or even logging in to your computer--

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there's just some login program which is giving you access.

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Here, we happen to have hard-coded 'rob', 'thisiscs50', 'tommy', 'i<3javascript',

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but probably there is some file somewhere on your operating system

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which has a list of usernames who can login to the system

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and a list of passwords associated with those usernames.

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Usually the passwords are not just stored in plaintext like this.

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There is some sort of encryption, but this will do for our example.

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>> Coming over to our compiler--

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it's going to be very straightforward.

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We need to specify at least some file that we want to compile,

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and then here--these lines

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are just reading an A file.

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It reads the entire file into one big buffer,

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and then we null-terminate our buffer as always,

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and finally we just compile the file.

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We're not going to look at how compile is actually implemented,

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but as a hint, it just calls Clang.

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We're going to use this program to compile things instead of Clang.

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One problem we start with is we see we want to compile our compiler,

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but if we're not going to use Clang, I don't know what I'm going to compile with.

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This is a general issue known as bootstrapping.

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So, just this once, I'm going to use Clang to compile our compiler.

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>> If you think of GCC and Clang--

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those programs, those compilers are constantly being updated,

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and those compilers are compiled using GCC and Clang.

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Clang is just one big C or C++ program,

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so the compiler they use to compile that is Clang.

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Here, now, we are just going to be using our compiler to compile our compiler,

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and we can even say--'./compiler', 'compiler.c', 'compile.c', '-o compiler'.

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Notice this is the exact command I ran before--

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just replace Clang with './compiler'.

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And now we have another compiler, but it's exactly the same.

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It just calls Clang.

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>> We're going to use our compiler to compile our login program.

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Okay--"./compiler login.c -o login".

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So, undefined reference to "GetString". 

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Got a "-lcs50". Okay.

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So now I have our login program.

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Running it--receive "Please enter your username".

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One example was rob. Please enter your password--thisiscs50.

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And success! I have access.

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Running it again and entering some invalid password--

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or invalid username and password--

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invalid login.

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Okay. Nothing interesting about this so far.

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But, let's take a look at login again--

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and this is going to be a somewhat trivial example,

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but let's add an else in here and say, else if ((strcmp(username, "hacker") == 0 &&

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strcmp(password, "LOLihackyou") == 0))

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so now, printf("Hacked!! You now have access. \n"); okay.

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Compiling this--compiler login.c -o login -lcs50--

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now running login--and if I use my username hacker 

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and password LOLihackedyou--

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Did I type it wrong in there before?

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At login.c--ihack--I'll do hacked because I think I do that later.

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Okay. Recompiling.

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Re-running--hacker--LOLihackedyou--

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Hacked!! You now have access.

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>> There doesn't seem to be that much of a difference

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because it's the same exact check I was doing for other usernames and passwords.

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Plus, the big thing is that if other people look at this login.c--

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say, if I pass this off to my partner, and they open up this file,

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and they read this, they'll see--okay, why do you have these lines of code here?

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That's obviously not something that should be in your program.

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In some programs--like any proprietary software that is not open-source--

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you may never see these lines of code.

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Something like Skype or something--for all you know,

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Skype is on your computer and there is just some specific username-password combination

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which will login to Skype in some special way.

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We don't know about it, and people don't know about it,

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because they don't get to read the sourcecode to see that there's this hole.

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>> What we call this--

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although this isn't a very clever example--

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this is called a back door.

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If you think of the back door of your house.

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Here, if I validate with the usernames 'rob' or 'tommy,'

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that would be like using the "front door."

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That's the way I'm supposed to securely login.

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But if I enter with this username and password--

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then that's using the "back door."

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It wasn't the intentional way to get into the program,

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but it still works.

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And people in general aren't supposed to know about these back doors.

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We're going to improve this.

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Let's revert this to our original login.c,

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and let's take a look at our new compiler. Okay.

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Everything up here is exactly the same.

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We're reading the entire file into a buffer.

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Everything down here is the same.

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We just compiled the file.

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But now I have this big if in here

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that says, if the file that I happen to be compiling is login.c,

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then I do something special.

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What is that something special?

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I see here some string called 'hack',

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and looking at these lines of code--

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these are the same lines of code--I guess I did use 'ihack' and not 'ihacked' before--

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looking at these lines of code,

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they're the same exact lines of code that I had in login.c before.

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But now, instead of having them in login.c,

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I'm going to put them into my compiler.

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>> These are the lines of code I'm going to want to insert into login.c.

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These lines of code--the buffer that originally held my login.c

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is no longer going to be big enough because now I want to also insert this hack

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into the middle of my program.

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All this is doing is creating a new buffer that's large enough--

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both for the original file and the extra lines of code--the hack--that I want to insert there.

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Here is something to notice--

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char* pattern = "// deny them access!"

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If we look back at login.c,

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we see down here this comment--deny them access!

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In login.c, this comment looks completely innocuous,

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so you wouldn't suspect any malicious intent with just this comment.

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But in our compiler, we are specifically going to look for this line of code,

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and then when we find it--

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these lines of code are inserting our hack into that position.

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So, we are iterating over the entire login.c,

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we are inserting that hack exactly where it says deny them access,

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and then we're compiling--not the original login.c

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but the new login.c with that hack inserted right at 'deny them access.'

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>> Now I want to compile my new compiler with that hack involved.

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I'm not going to use Clang, so let's copy the compiler we used before

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and use that--so, compiler compiler.c compile.c -o evil_compiler.

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Now our evil compiler--

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if we use our evil compiler to compile any other file,

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the file will compile as it should.

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It's completely normal.

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But if we use our evil compiler to compile login--

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so, ./evil_compiler login.c -o login -lcs50--

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looking at login.c again, there's absolutely nothing in here.

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It's our usual 'if it's either rob or tommy we're in, else we're out'.

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But when we run our executable, this will work as usual.

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Running again--hacker, LOLihackyou--

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Hacked!! You now have access.

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Just looking at login.c, you wouldn't think anything is wrong.

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But the compiler that's being used to compile login.c

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is specifically designed to insert this hack into the program.

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We've only moved our original problem.

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Originally, we had these lines of code in login.c that if anyone else looked at them,

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they'd be like, why are these here?

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Now if anyone happens to look at our compiler,

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they'll look at these lines of code and say,

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why are these here?

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So, we haven't completely solved our problem.

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But we can use this idea again.

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>> Taking a look at our third version of the compiler,

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it's the same idea.

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We read the entire file into a buffer up here,

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we compile the file down here,

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and I have some sort of string hack in here, 

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but notice the file that I'm actually hacking now.

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I am hacking compiler.c

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not login.c.

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But what am I inserting into compiler.c?

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I'm inserting this code which is the exact code in our previous compiler,

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which was meant to insert code into login.c.

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Here is our if strcmp file login.c

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and then insert into login.c our hack stuff.

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This new compiler is intended to create a compiler 

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which is intended to compile login maliciously.

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We'll see why that helps us.

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Everything else is the same, so it works exactly as it worked with our previous compiler.

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We are just iterating over our entire compile.c.

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But now instead of looking for 'deny them access,'

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00:16:48,190 --> 00:16:51,490
we're looking for 'compile the file.'

241
00:16:51,490 --> 00:16:53,750
Where is compile the file?

242
00:16:53,750 --> 00:16:57,210
Looking at our completely innocent compiler.c,

243
00:16:57,210 --> 00:17:01,340
it's right down here at the bottom.

244
00:17:01,340 --> 00:17:06,500
This comment--compile the file--again, that looks completely innocuous.

245
00:17:06,500 --> 00:17:11,599
But, in our malicious version of the compiler,

246
00:17:11,599 --> 00:17:16,550
we are going to--right before that comment--insert this code

247
00:17:16,550 --> 00:17:20,690
which is intended to insert code when compiling login.c.

248
00:17:20,690 --> 00:17:25,589
>> There are a lot of levels of indirection here.

249
00:17:25,589 --> 00:17:29,760
Let's actually run it.

250
00:17:29,760 --> 00:17:37,360
Again, we'll copy our original compiler.

251
00:17:37,360 --> 00:17:48,260
Now, compile--compiler compiler.c compile.c -o evilest_compiler--

252
00:17:48,260 --> 00:17:52,640
and now evilest_compiler.

253
00:17:52,640 --> 00:17:59,200
Evilest compiler--if we use that to compile our compiler,

254
00:17:59,200 --> 00:18:01,550
let's actually look.

255
00:18:01,550 --> 00:18:13,230
Evilest_compiler--bringing it over, all the way back to version 1 of our compiler--

256
00:18:13,230 --> 00:18:19,640
version 1 of our compiler which was just read in the file and compile it.

257
00:18:19,640 --> 00:18:24,780
Here, we know that evilest_compiler--when it compiles this file--

258
00:18:24,780 --> 00:18:29,890
is going to insert code right here before compile the file,

259
00:18:29,890 --> 00:18:38,510
and that code is going to look exactly like the code from the second version of our compiler 

260
00:18:38,510 --> 00:18:42,240
which did this.

261
00:18:42,240 --> 00:18:46,450
This code, which is intended to break into login,

262
00:18:46,450 --> 00:18:56,480
is going to be inserted into our compiler by evilest compiler.

263
00:18:56,480 --> 00:19:08,600
Let's use evilest_compiler to compile our compiler.

264
00:19:08,600 --> 00:19:15,040
Now we'll use compiler,

265
00:19:15,040 --> 00:19:19,460
come back over to login,

266
00:19:19,460 --> 00:19:25,280
and remember this login.c has absolutely nothing suspicious in it.

267
00:19:25,280 --> 00:19:35,250
But using our compiler to compile login.c,

268
00:19:35,250 --> 00:19:38,430
rob, thisiscs50, success.

269
00:19:38,430 --> 00:19:44,350
Let's login hacker, LOLihackyou, Hacked!! You now have access.

270
00:19:44,350 --> 00:19:49,710
>> Recognize that this was different from version 2 of our compiler.

271
00:19:49,710 --> 00:20:00,500
The compiler we use--let's move back--copy from login--

272
00:20:00,500 --> 00:20:01,880
let's bring our compiler back in here.

273
00:20:01,880 --> 00:20:06,360
Removing evilest compiler.

274
00:20:06,360 --> 00:20:08,970
All we have left now is compiler.

275
00:20:08,970 --> 00:20:10,950
If we look at compiler.c,

276
00:20:10,950 --> 00:20:16,840
there is absolutely nothing in there that seems malicious in any way.

277
00:20:16,840 --> 00:20:22,390
If we look at login.c,

278
00:20:22,390 --> 00:20:28,790
there is absolutely nothing in here that looks malicious in any way.

279
00:20:28,790 --> 00:20:34,600
But, when we use our compiler to compile login.c,

280
00:20:34,600 --> 00:20:38,840
we get the hackable version of login.c.

281
00:20:38,840 --> 00:20:41,850
When we used our compiler to compile a new version of the compiler,

282
00:20:41,850 --> 00:20:46,620
we get the hackable version of the compiler.

283
00:20:46,620 --> 00:20:51,790
Now if we go out and distribute our compiler executable,

284
00:20:51,790 --> 00:20:59,280
and no one will know that there is anything malicious about it.

285
00:20:59,280 --> 00:21:04,680
>> This is actually so in--I can't remember the year--

286
00:21:04,680 --> 00:21:10,350
Ken Thompson, and he won the Turing Award--

287
00:21:10,350 --> 00:21:15,600
if you are unfamiliar with the Turing Award, it is almost always defined as the 

288
00:21:15,600 --> 00:21:20,160
Nobel Prize of computer science, so that's how I'll define it.

289
00:21:20,160 --> 00:21:24,100
Ken Thompson gave a speech when he received his Turing Award

290
00:21:24,100 --> 00:21:27,150
called "Reflections on Trusting Trust."

291
00:21:27,150 --> 00:21:30,710
Basically, this was the idea of his speech.

292
00:21:30,710 --> 00:21:35,050
Except instead of our compiler, he was talking about GCC--

293
00:21:35,050 --> 00:21:37,250
just another compiler like Clang--

294
00:21:37,250 --> 00:21:45,600
and what he was saying is, like our login.c, our login.c seems relatively useless

295
00:21:45,600 --> 00:21:50,190
but he was talking about the actual UNIX login.c.

296
00:21:50,190 --> 00:21:53,050
When you login to your appliance,

297
00:21:53,050 --> 00:21:56,070
there is some login program that is running.

298
00:21:56,070 --> 00:21:58,080
That was the login that he was talking about.

299
00:21:58,080 --> 00:22:02,420
This was basically his idea.

300
00:22:02,420 --> 00:22:09,080
He said that in GCC, he in theory could have planted a bug--

301
00:22:09,080 --> 00:22:12,290
not a bug but a malicious code--

302
00:22:12,290 --> 00:22:16,860
that when compiling the login function--the login file--

303
00:22:16,860 --> 00:22:23,700
would insert a back door so that he could go to absolutely any UNIX system in the world

304
00:22:23,700 --> 00:22:27,360
and login with some specific username and password.

305
00:22:27,360 --> 00:22:33,710
At the time, GCC was pretty much the compiler that everyone used for anything.

306
00:22:33,710 --> 00:22:36,460
If anyone happened to update GCC,

307
00:22:36,460 --> 00:22:40,880
then they would recompile GCC using GCC,

308
00:22:40,880 --> 00:22:44,500
and you would still get a bad version of GCC 

309
00:22:44,500 --> 00:22:50,140
because it was specifically compiled to recognize that it was recompiling the compiler.

310
00:22:50,140 --> 00:22:57,360
And if you ever use GCC to recompile a login.c file,

311
00:22:57,360 --> 00:23:03,550
then it would insert this back door that he could use to login to any computer.

312
00:23:03,550 --> 00:23:08,750
>> This was all theoretical, but--that particular circumstance was theoretical, 

313
00:23:08,750 --> 00:23:12,440
but the ideas are very real.

314
00:23:12,440 --> 00:23:18,250
In 2003, there was a similar example where--

315
00:23:18,250 --> 00:23:21,290
we'll take a look at this file,

316
00:23:21,290 --> 00:23:25,870
and it has absolutely nothing to actually do with it, but the bug is similar.

317
00:23:25,870 --> 00:23:29,390
This file just defines a function called divide.

318
00:23:29,390 --> 00:23:31,780
It takes an argument a, an argument b,

319
00:23:31,780 --> 00:23:34,270
and the intent is to do a divided by b.

320
00:23:34,270 --> 00:23:37,230
But it does some error checking,

321
00:23:37,230 --> 00:23:40,070
so we know things are weird if b happens to equal zero.

322
00:23:40,070 --> 00:23:44,900
If b is zero, then we split this into 2 cases.

323
00:23:44,900 --> 00:23:46,900
You might already see the bug.

324
00:23:46,900 --> 00:23:51,840
The first case--if a is zero, then we're doing zero divided by zero,

325
00:23:51,840 --> 00:23:54,300
and we just say that's undefined.

326
00:23:54,300 --> 00:23:56,250
The second case--if a is not zero,

327
00:23:56,250 --> 00:24:00,580
then it's something like 1 divided by zero, and we just call that infinity.

328
00:24:00,580 --> 00:24:03,730
Else we return the usual a divided by b.

329
00:24:03,730 --> 00:24:06,390
And so here, we're running those 3 cases,

330
00:24:06,390 --> 00:24:13,740
and we actually run divide--it yells at it for me--

331
00:24:13,740 --> 00:24:21,330
so, ignoring Clang's warnings-- 

332
00:24:21,330 --> 00:24:24,500
end of non-void function--apparently I didn't compile this beforehand.

333
00:24:24,500 --> 00:24:26,500
Return 0.

334
00:24:26,500 --> 00:24:28,900
Make divide--all right.

335
00:24:28,900 --> 00:24:32,470
With ./divide, we see 3, Infinity, Infinity.

336
00:24:32,470 --> 00:24:39,150
Zero divided by zero should not have returned infinity.

337
00:24:39,150 --> 00:24:42,840
And if you haven't figured out the bug yet--or didn't see it before--

338
00:24:42,840 --> 00:24:46,800
we see that we're doing a=0.

339
00:24:46,800 --> 00:24:52,610
Probably we meant a==0. Probably.

340
00:24:52,610 --> 00:24:58,640
>> But, this was actually something that, again, in 2003, the Linux kernel--

341
00:24:58,640 --> 00:25:02,260
so our appliance uses the Linux kernel--

342
00:25:02,260 --> 00:25:05,550
any Linux operating system uses the Linux kernel--

343
00:25:05,550 --> 00:25:11,610
so a bug very similar to this showed up.

344
00:25:11,610 --> 00:25:15,180
The idea behind this bug was--

345
00:25:15,180 --> 00:25:18,820
again, there was just some function that was called, and it did a bit of error checking.

346
00:25:18,820 --> 00:25:24,300
There were some specific inputs that this error checking--

347
00:25:24,300 --> 00:25:30,210
it should have been like, all right, you can't call this function with a divisor of 0.

348
00:25:30,210 --> 00:25:35,070
So, I'm going to just return some error.

349
00:25:35,070 --> 00:25:38,090
Except, it wasn't as innocent as just setting a equal to 0.

350
00:25:38,090 --> 00:25:46,920
Instead, this line of code ended up doing something more like user = administrator.

351
00:25:46,920 --> 00:25:50,500
Or user = superuser.

352
00:25:50,500 --> 00:25:59,170
It was an innocent--at first glance--mistake where it could have just been reasonable

353
00:25:59,170 --> 00:26:01,560
that I only wanted to report something specific

354
00:26:01,560 --> 00:26:05,150
if the user happened to be the superuser administrator.

355
00:26:05,150 --> 00:26:11,220
But then re-thinking about it, the person wanted it to look like a simple typo,

356
00:26:11,220 --> 00:26:14,330
but if this code had actually been released,

357
00:26:14,330 --> 00:26:21,580
then you would have been able to hack into any system by passing a specific flag--

358
00:26:21,580 --> 00:26:25,200
in this case b=0--

359
00:26:25,200 --> 00:26:28,020
and it would automatically make the user the administrator,

360
00:26:28,020 --> 00:26:30,400
and then he has full control.

361
00:26:30,400 --> 00:26:32,540
This happened in 2003.

362
00:26:32,540 --> 00:26:35,700
>> It just so happened that the only reason it was caught

363
00:26:35,700 --> 00:26:39,200
was because there happened to be some automated system

364
00:26:39,200 --> 00:26:41,540
that noticed the change in this file

365
00:26:41,540 --> 00:26:44,560
which never should have been changed by a human.

366
00:26:44,560 --> 00:26:47,580
The file should only have been automatically generated.

367
00:26:47,580 --> 00:26:49,780
It just so happened that someone touched--

368
00:26:49,780 --> 00:26:52,460
well, the person that wanted to hack touched that file,

369
00:26:52,460 --> 00:26:55,450
and the computer caught that touching.

370
00:26:55,450 --> 00:27:01,750
So, they changed this and only later realized what a disaster it would have been

371
00:27:01,750 --> 00:27:04,830
if this had gotten out into the real world.

372
00:27:04,830 --> 00:27:08,220
>> You may be thinking that--coming back to our compiler example--

373
00:27:08,220 --> 00:27:14,290
even though we can't see--looking at the sourcecode--

374
00:27:14,290 --> 00:27:17,490
that anything in particular is wrong,

375
00:27:17,490 --> 00:27:25,460
if we actually look at the binary code of compiler,

376
00:27:25,460 --> 00:27:28,670
we would see that something is wrong.

377
00:27:28,670 --> 00:27:31,260
As an example, if we run the strings function--

378
00:27:31,260 --> 00:27:34,930
which is just going to look over a file and print out all strings it can find--

379
00:27:34,930 --> 00:27:37,990
if we run strings on our compiler,

380
00:27:37,990 --> 00:27:42,400
we see that one string that it finds is this strange--

381
00:27:42,400 --> 00:27:45,500
else if (strcmp(username, "hacker")--blah, blah, blah.

382
00:27:45,500 --> 00:27:52,570
If someone happened to be paranoid enough to not trust their compiler,

383
00:27:52,570 --> 00:27:56,690
they could run strings and see this,

384
00:27:56,690 --> 00:28:00,430
and then they would know that there was something wrong with the actual binary.

385
00:28:00,430 --> 00:28:07,250
But, strings was inevitably something that was  compiled.

386
00:28:07,250 --> 00:28:11,590
So, who's to say that our compiler doesn't just have more special code

387
00:28:11,590 --> 00:28:19,240
that says, if strings is ever run on our compiler, don't output all of that malicious code.

388
00:28:19,240 --> 00:28:23,980
>> The same idea with if we want to dis-assemble the file--

389
00:28:23,980 --> 00:28:30,440
we learned that the assembler brings us from assembly code to a machine code--

390
00:28:30,440 --> 00:28:36,010
we can go in the opposite direction--objdump -d compiler--

391
00:28:36,010 --> 00:28:38,770
will give us the assembly of our code.

392
00:28:38,770 --> 00:28:41,730
Looking at this,

393
00:28:41,730 --> 00:28:47,480
it's pretty cryptic, but if we wanted, we could look through this

394
00:28:47,480 --> 00:28:51,700
and reason, wait, there's something going on in here that shouldn't be going on,

395
00:28:51,700 --> 00:28:59,380
and then we'll recognize that the compiler is doing something malicious.

396
00:28:59,380 --> 00:29:03,950
But, just like strings, who's to say objdump wasn't special-cased.

397
00:29:03,950 --> 00:29:11,380
Basically, it comes down to you can't trust anything.

398
00:29:11,380 --> 00:29:14,310
The point of the paper being called "Trusting Trust" is

399
00:29:14,310 --> 00:29:17,900
in general, we trust our compiler.

400
00:29:17,900 --> 00:29:21,700
You compile your code and expect it to do what you ask it to do.

401
00:29:21,700 --> 00:29:26,440
But, why should you trust the compiler?

402
00:29:26,440 --> 00:29:32,120
You did not write the compiler. You don't know what the compiler is necessarily actually doing.

403
00:29:32,120 --> 00:29:36,870
Who's to say you can trust it?

404
00:29:36,870 --> 00:29:40,050
But even then, well, maybe we can trust the compiler.

405
00:29:40,050 --> 00:29:44,670
There are tens of thousands of people who have looked at this.

406
00:29:44,670 --> 00:29:51,360
Someone must have recognized something was up with the compiler.

407
00:29:51,360 --> 00:29:55,100
>> What if we just go 1 level deeper?

408
00:29:55,100 --> 00:29:59,450
It could even be your processor.

409
00:29:59,450 --> 00:30:01,250
As ridiculous as it could possibly be,

410
00:30:01,250 --> 00:30:06,690
maybe there's some rogue employee at Intel who creates these processors

411
00:30:06,690 --> 00:30:12,400
that whenever that processor notices that you're running some command

412
00:30:12,400 --> 00:30:14,570
that's meant to login to the computer,

413
00:30:14,570 --> 00:30:19,230
the processor will accept some specific username and password combination.

414
00:30:19,230 --> 00:30:21,530
It would be wildly complicated,

415
00:30:21,530 --> 00:30:24,790
but someone could do it.

416
00:30:24,790 --> 00:30:29,350
At that point, are you really going to open up your computer to look at the processor

417
00:30:29,350 --> 00:30:35,970
and use a microscope to recognize that these circuits are not lined up as they should be?

418
00:30:35,970 --> 00:30:39,730
No one is ever going to catch that error.

419
00:30:39,730 --> 00:30:45,570
At some point, you just have to give up and trust something.

420
00:30:45,570 --> 00:30:48,390
Most people do trust the compiler at this point.

421
00:30:48,390 --> 00:30:55,760
That is to say not necessarily that you should.

422
00:30:55,760 --> 00:30:59,350
Looking at a somewhat infamous video--

423
00:30:59,350 --> 00:31:09,280
[dramatic music playing]

424
00:31:09,280 --> 00:31:13,270
[It's a UNIX system.  I know this.]

425
00:31:13,270 --> 00:31:14,470
[It's all the files--]

426
00:31:14,470 --> 00:31:18,950
She said, "It's a UNIX system. I know this."

427
00:31:18,950 --> 00:31:21,760
Replace UNIX with whatever your favorite operating system is--

428
00:31:21,760 --> 00:31:25,230
she could have said, "It's a Windows system. I know this."

429
00:31:25,230 --> 00:31:29,710
It's a completely meaningless statement, 

430
00:31:29,710 --> 00:31:34,450
but for all we know, she happens to know a back door into the UNIX system.

431
00:31:34,450 --> 00:31:38,840
She knows some username/password combination that will actually let her

432
00:31:38,840 --> 00:31:41,540
do whatever she wants.

433
00:31:41,540 --> 00:31:49,000
>> All right. The moral of today is basically you can't trust anything.

434
00:31:49,000 --> 00:31:52,620
Even things you write--you didn't write the compiler.

435
00:31:52,620 --> 00:31:53,870
The compiler could be bad.

436
00:31:53,870 --> 00:31:59,140
Even if you did write the compiler, the thing that's running the compiler could be bad.

437
00:31:59,140 --> 00:32:05,210
(laughing) There's not much you can do.

438
00:32:05,210 --> 00:32:09,050
The world is doomed.

439
00:32:09,050 --> 00:32:11,570
Back to David!

440
00:32:11,570 --> 00:32:19,540
[applause]

441
00:32:19,540 --> 00:32:21,340
>> [David] Thanks. That was really depressing.

442
00:32:21,340 --> 00:32:23,910
But indeed, Rob is correct. 

443
00:32:23,910 --> 00:32:27,150
We don't really have a solution to that, but you're about to get some solutions

444
00:32:27,150 --> 00:32:29,150
to some more common defenses.

445
00:32:29,150 --> 00:32:31,170
In anticipation of this, what Nate and I have been doing offstage there

446
00:32:31,170 --> 00:32:33,950
is knowing that there are so many laptops in this room,

447
00:32:33,950 --> 00:32:37,020
we've been sniffing all of the wireless traffic going through this room for the past 20 minutes

448
00:32:37,020 --> 00:32:39,260
during Rob's talk, so we're going to take a 2 minute break here.

449
00:32:39,260 --> 00:32:41,740
Nate's going to set up, and then we're going to talk about all of the stuff

450
00:32:41,740 --> 00:32:46,380
we could have found. (laughter)

451
00:32:46,380 --> 00:32:51,990
>> So, I may have exaggerated a little bit just for the sake of drama,

452
00:32:51,990 --> 00:32:55,990
but we could have been sniffing all of your wireless traffic because indeed,

453
00:32:55,990 --> 00:32:57,240
it is that easy.

454
00:32:57,240 --> 00:32:59,790
But there are also ways that you can defend against this, and so with that,

455
00:32:59,790 --> 00:33:03,160
I give you Nate Hardison. >>[Nate] Sweet.

456
00:33:03,160 --> 00:33:06,300
(applause)

457
00:33:06,300 --> 00:33:08,650
>> [Nate] Thanks, man. I appreciate the shout out.

458
00:33:08,650 --> 00:33:12,790
All right! It's game week. Are you guys excited? 

459
00:33:12,790 --> 00:33:16,670
Hopefully it's going to be a big game on Saturday.

460
00:33:16,670 --> 00:33:20,220
I imagine you guys at this point--given that you have a quiz on Wednesday

461
00:33:20,220 --> 00:33:24,430
all about code, and we just sat through a wonderful lecture by Rob 

462
00:33:24,430 --> 00:33:25,850
with a whole bunch of C code in it--

463
00:33:25,850 --> 00:33:28,330
are maybe a little bit tired of code.

464
00:33:28,330 --> 00:33:32,180
In this part, we're actually not going to touch any code whatsoever.

465
00:33:32,180 --> 00:33:36,960
We're just going to talk about a technology that you use every day,

466
00:33:36,960 --> 00:33:39,790
often for many, many hours a day,

467
00:33:39,790 --> 00:33:46,220
and we'll talk about the implications with security that there are.

468
00:33:46,220 --> 00:33:48,960
>> We've talked a lot about security over the course of the semester,

469
00:33:48,960 --> 00:33:53,030
and we started off with a little bit of crypto.

470
00:33:53,030 --> 00:33:55,030
[Bdoh lv vwlqng!]

471
00:33:55,030 --> 00:33:57,890
And while you guys are probably super-excited to be passing notes to each other

472
00:33:57,890 --> 00:33:59,890
in class using a Caesar cipher like this one,

473
00:33:59,890 --> 00:34:03,870
in reality, there's some more fun to be had when you're actually talking about security

474
00:34:03,870 --> 00:34:05,870
and  that kind of stuff.

475
00:34:05,870 --> 00:34:09,090
Today, we're going to cover a few technologies

476
00:34:09,090 --> 00:34:13,650
that people actually use in the real world to do all sorts of things

477
00:34:13,650 --> 00:34:18,360
from sniffing people's packets to actually going in and

478
00:34:18,360 --> 00:34:20,409
breaking into people's bank accounts and all of that.

479
00:34:20,409 --> 00:34:23,460
These are legitimate tools that we're talking about

480
00:34:23,460 --> 00:34:26,320
with the exception of possibly one tool.

481
00:34:26,320 --> 00:34:28,889
>> And I just want to make a quick disclaimer.

482
00:34:28,889 --> 00:34:34,909
When we talk about these things, we're talking about them so you know what's out there,

483
00:34:34,909 --> 00:34:39,389
and you're aware of how to be safe when you're out using your computer.

484
00:34:39,389 --> 00:34:44,000
But we definitely don't want to imply that you should use these tools

485
00:34:44,000 --> 00:34:48,090
in your dorm or your house because you can run into lots of big issues.

486
00:34:48,090 --> 00:34:52,760
That's one reason today that we actually weren't sniffing your packets.

487
00:34:52,760 --> 00:35:01,300
>> All right. Last Monday, we talked about cookies, and HTTP, and authentication,

488
00:35:01,300 --> 00:35:05,920
and how Firesheep opens this big door into your Facebook account,

489
00:35:05,920 --> 00:35:08,670
to your Hotmail account--if anybody's still using Hotmail--

490
00:35:08,670 --> 00:35:12,360
and many other accounts.

491
00:35:12,360 --> 00:35:16,980
A lot of this stuff is going to build off of that,

492
00:35:16,980 --> 00:35:22,070
but first, I want to take a quick tour of how the Internet has evolved over time.

493
00:35:22,070 --> 00:35:27,490
Back in the '90s, you guys might have remembered actually plugging in

494
00:35:27,490 --> 00:35:29,880
your computers with one of these.

495
00:35:29,880 --> 00:35:32,640
Now we don't do that so much anymore.

496
00:35:32,640 --> 00:35:37,230
It actually turns out that in order to plug an Ethernet cable into my laptop,

497
00:35:37,230 --> 00:35:41,710
I now have to use one of these adapters which is kind of crazy.

498
00:35:41,710 --> 00:35:47,580
>> Instead, in 1997 we had this new, fun technology

499
00:35:47,580 --> 00:35:54,960
came out that is known as IEEE 802.11, so this is the wireless internet standard

500
00:35:54,960 --> 00:36:00,430
The IEEE is this governing body that gives out all sorts of--

501
00:36:00,430 --> 00:36:04,770
publishes all sorts of standards with relation to computers.

502
00:36:04,770 --> 00:36:08,780
The 802 standards are all about Internet technologies.

503
00:36:08,780 --> 00:36:12,690
So 802.3, for example, is the Ethernet standard,

504
00:36:12,690 --> 00:36:17,120
802.15.1 I believe is the Bluetooth standard,

505
00:36:17,120 --> 00:36:19,540
and 802.11 is all about wireless Internet.

506
00:36:19,540 --> 00:36:24,150
In 1997 this came out. It didn't quite catch on right away.

507
00:36:24,150 --> 00:36:30,200
It wasn't until 1999 and the 802.11b standard came out that just got really popular.

508
00:36:30,200 --> 00:36:36,330
>> How many of you remember when computers started coming out and getting wi-fi on them?

509
00:36:36,330 --> 00:36:38,330
That was kind of cool, huh?

510
00:36:38,330 --> 00:36:41,260
I remember getting my first laptop in high school,

511
00:36:41,260 --> 00:36:44,250
and it had a wireless card in it.

512
00:36:44,250 --> 00:36:49,580
My dad gave it to me and was saying that I should use it for my college apps and all of that,

513
00:36:49,580 --> 00:36:53,030
and I had no idea how I was going to look up this stuff online.

514
00:36:53,030 --> 00:36:54,640
But fortunately, I had a wireless card, so that was pretty cool.

515
00:36:54,640 --> 00:37:04,090
Nowadays, you'll also see 802.11g which is one of the other really popular

516
00:37:04,090 --> 00:37:06,090
wireless standards that's out there.

517
00:37:06,090 --> 00:37:08,660
Both b and g are pretty outdated at this point.

518
00:37:08,660 --> 00:37:12,580
Anybody know what version most people are on right now

519
00:37:12,580 --> 00:37:15,110
if they're buying new wireless routers and that kind of stuff?

520
00:37:15,110 --> 00:37:24,290
N. Exactly. Bingo. And it turns out that the ac standard is just coming out in a draft form,

521
00:37:24,290 --> 00:37:28,050
and there are other versions on the way.

522
00:37:28,050 --> 00:37:31,190
With each of these standards what we're gaining is more bandwidth,

523
00:37:31,190 --> 00:37:33,900
more data at a faster rate.

524
00:37:33,900 --> 00:37:36,260
These things keep changing pretty quickly.

525
00:37:36,260 --> 00:37:39,880
It also makes it so that we have to buy more routers and all that fun stuff.

526
00:37:39,880 --> 00:37:48,160
>> Let's talk about what wireless communication actually is at its core.

527
00:37:48,160 --> 00:37:51,790
With Ethernet and those old dial-up modems,

528
00:37:51,790 --> 00:37:55,780
you actually had this stuff that you plugged into your computer,

529
00:37:55,780 --> 00:37:59,820
and then you plugged into a modem of sorts, and then you plugged it into a jack in your wall.

530
00:37:59,820 --> 00:38:01,820
You had this wired connection, right?

531
00:38:01,820 --> 00:38:06,030
The whole point of wireless is getting rid of this stuff.

532
00:38:06,030 --> 00:38:10,300
In order to do that, what we have is essentially

533
00:38:10,300 --> 00:38:13,960
a radio communication where our wireless router--

534
00:38:13,960 --> 00:38:16,230
designated by our little wireless icon--

535
00:38:16,230 --> 00:38:21,730
is connected to the Internet with this solid arrow indicating some sort of wired connection,

536
00:38:21,730 --> 00:38:24,640
but when you connect to your wireless router

537
00:38:24,640 --> 00:38:29,190
you're actually using almost like a walkie-talkie between 

538
00:38:29,190 --> 00:38:31,960
your computer and your wireless router.

539
00:38:31,960 --> 00:38:35,150
What's really cool about this is you can move around.

540
00:38:35,150 --> 00:38:40,900
You can carry your computer all over Sanders, go surf the web, whatever you want,

541
00:38:40,900 --> 00:38:43,240
just like you all know and love,

542
00:38:43,240 --> 00:38:46,030
and you don't ever have to be plugged in to anything.

543
00:38:46,030 --> 00:38:53,880
For this to work, we have both this reception and transmission.

544
00:38:53,880 --> 00:38:56,060
It really is like that walkie-talkie.

545
00:38:56,060 --> 00:39:03,800
>> This wireless router--which in Sanders is sitting underneath this stage, right here--

546
00:39:03,800 --> 00:39:06,590
is always broadcasting and receiving, broadcasting and receiving,

547
00:39:06,590 --> 00:39:09,330
and likewise, your computers are all doing that same sort of thing, too.

548
00:39:09,330 --> 00:39:12,840
We just can't hear it.

549
00:39:12,840 --> 00:39:17,900
The other thing that you can do is you can have multiple computers

550
00:39:17,900 --> 00:39:22,200
talking to the same wireless router.

551
00:39:22,200 --> 00:39:25,680
The closer you are to a router--and again, this is a radio communication--

552
00:39:25,680 --> 00:39:30,320
the closer you are, the better your signal is, the better your computer 'hears' the router

553
00:39:30,320 --> 00:39:32,460
and can communicate with the Internet.

554
00:39:32,460 --> 00:39:39,520
If you guys are ever at your dorm, at your house and you're wondering why your signal's bad,

555
00:39:39,520 --> 00:39:42,230
it's probably because a). you're not very close to your router, or

556
00:39:42,230 --> 00:39:46,930
b). there's something in between you and your router like a cement wall or something

557
00:39:46,930 --> 00:39:50,720
that doesn't let those radio waves go through.

558
00:39:50,720 --> 00:39:57,850
>> Let's talk a little bit about why bad guys like wi-fi.

559
00:39:57,850 --> 00:40:02,980
Bad guys love wi-fi for a few reasons.

560
00:40:02,980 --> 00:40:06,670
Here's our nasty bad guy right there.

561
00:40:06,670 --> 00:40:10,660
One reason why this bad guy loves wi-fi

562
00:40:10,660 --> 00:40:18,770
is because, by default, a lot of wireless routers come and when you set them up,

563
00:40:18,770 --> 00:40:20,950
they're unencrypted.

564
00:40:20,950 --> 00:40:23,970
This has been a problem, and there have been instances--

565
00:40:23,970 --> 00:40:28,210
multiple instances, now--where bad guy shows up to somebody's house,

566
00:40:28,210 --> 00:40:32,630
notices that there's an unencrypted wi-fi to which they can connect.

567
00:40:32,630 --> 00:40:37,350
They connect to the wi-fi, and then they start downloading all sorts of fun stuff.

568
00:40:37,350 --> 00:40:40,890
And they're not downloading kittens, they're not downloading puppies.

569
00:40:40,890 --> 00:40:44,610
This is like BitTorrent. This is the nasty of the nastiest.

570
00:40:44,610 --> 00:40:48,740
There have been cases where the FBI has even gotten involved

571
00:40:48,740 --> 00:40:52,390
thinking that the person who owns the house is actually the one

572
00:40:52,390 --> 00:40:56,090
going out there and downloading stuff that they really shouldn't be.

573
00:40:56,090 --> 00:41:00,730
Having unencrypted wi-fi is definitely not something you want to do,

574
00:41:00,730 --> 00:41:06,340
if only to not have the FBI come knock at your door.

575
00:41:06,340 --> 00:41:09,910
>> Another reason why bad guys love wi-fi

576
00:41:09,910 --> 00:41:13,870
is the reason that David talked about earlier during the break.

577
00:41:13,870 --> 00:41:17,240
Because it's a radio communication at its core,

578
00:41:17,240 --> 00:41:22,460
if you know the channel, you can listen to that radio station.

579
00:41:22,460 --> 00:41:31,870
For example, if there's a bad right there sitting in the middle right next to the access point,

580
00:41:31,870 --> 00:41:36,830
right next to that wireless router, the bad guy can listen in on all of the wireless traffic

581
00:41:36,830 --> 00:41:40,240
that's coming from all of those computers.

582
00:41:40,240 --> 00:41:44,590
In fact, these guys--these lucky few who are here in the front row--

583
00:41:44,590 --> 00:41:47,610
because they are super-close to all of these wireless routers 

584
00:41:47,610 --> 00:41:49,950
that sit just underneath the stage, 

585
00:41:49,950 --> 00:41:53,780
they would be able to hear everybody's traffic in this entire room

586
00:41:53,780 --> 00:41:59,480
if you're connected to wi-fi and start browsing through these access points.

587
00:41:59,480 --> 00:42:03,740
It's not very hard to sit yourself in a good position to sniff and figure out

588
00:42:03,740 --> 00:42:07,030
what other people are doing.

589
00:42:07,030 --> 00:42:10,830
It's something to keep in mind, especially if you're not sure where the access point is,

590
00:42:10,830 --> 00:42:15,010
and you're browsing say, at a Starbucks.

591
00:42:15,010 --> 00:42:17,360
>> It turns out that sniffing and all of that

592
00:42:17,360 --> 00:42:19,440
isn't really all that hard to do.

593
00:42:19,440 --> 00:42:25,430
There's a program called tcpdump which dumps all sorts of TCP traffic

594
00:42:25,430 --> 00:42:29,910
and you can run it pretty simply--just like I did this morning.

595
00:42:29,910 --> 00:42:32,810
Here's a little bit of a dump, and here's some of the traffic that was coming over

596
00:42:32,810 --> 00:42:34,960
my network at the time.

597
00:42:34,960 --> 00:42:41,500
You can see--if you squint really hard--there's a little bit of Spotify in there.

598
00:42:41,500 --> 00:42:44,050
On top of tcpdump--because this is kind of a pain to use--

599
00:42:44,050 --> 00:42:48,860
there's a program called Wireshark which bundles this all up in a nice GUI.

600
00:42:48,860 --> 00:42:51,970
Wireshark is super-handy so if you go on to take networking classes,

601
00:42:51,970 --> 00:42:56,780
this is a tool that you'll come to love since it helps you dissect all of the packets

602
00:42:56,780 --> 00:42:59,400
that are floating around out there.

603
00:42:59,400 --> 00:43:01,810
But it can also be used for bad.

604
00:43:01,810 --> 00:43:05,810
It's very simple to just download this program, boot it up,

605
00:43:05,810 --> 00:43:09,300
start a network capture, and see everything that's going on--

606
00:43:09,300 --> 00:43:14,130
and filter and do all sorts of fun stuff with it.

607
00:43:14,130 --> 00:43:17,930
>> The other thing that you can do with wireless communication

608
00:43:17,930 --> 00:43:25,380
is not only can you eavesdrop but you can also learn how to screw with the network

609
00:43:25,380 --> 00:43:31,020
and inject your own information to control the experience that other people 

610
00:43:31,020 --> 00:43:35,140
on the same wireless network are getting.

611
00:43:35,140 --> 00:43:37,140
Let's take a look at that.

612
00:43:37,140 --> 00:43:40,700
Here's Firesheep--which we know and love from last week--

613
00:43:40,700 --> 00:43:43,590
which is that eavesdropping technology.

614
00:43:43,590 --> 00:43:50,360
If, for example, we wanted to actively have our bad guy go and mess around with

615
00:43:50,360 --> 00:43:52,690
one of these computers,

616
00:43:52,690 --> 00:43:58,380
in this scenario we've got a computer trying to go surf to harvard.edu.

617
00:43:58,380 --> 00:44:04,690
What happens is, the computer first sends a message to the wireless router and says,

618
00:44:04,690 --> 00:44:07,920
hey, I want to go visit www.harvard.edu.

619
00:44:07,920 --> 00:44:10,610
Say for some reason they're trying to get information about the game this weekend.

620
00:44:10,610 --> 00:44:14,940
Bad guy, since he's sitting right in the middle,

621
00:44:14,940 --> 00:44:18,730
right next to that access point, can see that communication coming from the computer

622
00:44:18,730 --> 00:44:26,170
into the router, and he knows, "Aha! Somebody's going to harvard.edu." (evilly laughs)

623
00:44:26,170 --> 00:44:33,870
There's going to be this latency while the communication goes from the router

624
00:44:33,870 --> 00:44:37,780
out to the Internet to go find the webpage at harvard.edu--

625
00:44:37,780 --> 00:44:42,020
just like you guys all know after doing your PHP psets--

626
00:44:42,020 --> 00:44:45,680
and so the bad guy has a little bit of time, a little bit of window,

627
00:44:45,680 --> 00:44:49,410
in which he can respond with some stuff.

628
00:44:49,410 --> 00:44:53,660
>> Let's say this bad guy, of course, is a Yaley.

629
00:44:53,660 --> 00:44:59,990
He responds with harvardsucks.org. Boo!

630
00:44:59,990 --> 00:45:02,300
Bad, bad guy! Bad Yaley!

631
00:45:02,300 --> 00:45:06,020
Or even worse, he might respond with that. [http://youtu.be/ZSBq8geuJk0].

632
00:45:06,020 --> 00:45:09,530
I'll let you guys figure out what that is.

633
00:45:09,530 --> 00:45:14,840
This is actually a technology called Airpwn! which was debuted at 

634
00:45:14,840 --> 00:45:18,950
one of the security conferences a few years back.

635
00:45:18,950 --> 00:45:25,190
With Airpwn! you're able to actually inject traffic back into the network.

636
00:45:25,190 --> 00:45:30,060
The computers that were trying to go out to the Internet and trying to get to

637
00:45:30,060 --> 00:45:33,090
Google.com, to Facebook.com, to harvard.edu

638
00:45:33,090 --> 00:45:39,190
see the malicious response come in and immediately assume, okay,

639
00:45:39,190 --> 00:45:43,550
that's the response that I was waiting for and end up getting content from

640
00:45:43,550 --> 00:45:48,860
harvardsucks.org or nameyourfavoriteshocksite.com,

641
00:45:48,860 --> 00:45:55,270
and you can see how quickly things will deteriorate.

642
00:45:55,270 --> 00:46:00,190
>> All of these sorts of things can't be done

643
00:46:00,190 --> 00:46:05,870
with these wired connections because with a wired connection

644
00:46:05,870 --> 00:46:08,710
it's hard to snoop on to traffic.

645
00:46:08,710 --> 00:46:13,020
If I'm a bad guy and on one end is your computer

646
00:46:13,020 --> 00:46:14,460
and on the other end is your router--your modem--

647
00:46:14,460 --> 00:46:20,180
the only way I can get in between that connection is to actually splice my computer

648
00:46:20,180 --> 00:46:22,180
in somewhere in the middle

649
00:46:22,180 --> 00:46:26,820
or do something else with the router, something downstream.

650
00:46:26,820 --> 00:46:33,360
But with wireless, it can be as easy as sitting in the front row of a classroom,

651
00:46:33,360 --> 00:46:38,200
and you can do all sorts of nasty stuff to the people in the back.

652
00:46:38,200 --> 00:46:41,570
>> Let's talk about how you might defend against some of these things.

653
00:46:41,570 --> 00:46:46,860
The people who developed the wireless standards--the 802.11--

654
00:46:46,860 --> 00:46:50,820
they are not dumb people by any stretch of the imagination.

655
00:46:50,820 --> 00:46:56,110
This is cool technology and when it debuted in 1999,

656
00:46:56,110 --> 00:47:00,780
they came out with this standard called WEP.

657
00:47:00,780 --> 00:47:03,360
You can see here when you try and join a wireless network,

658
00:47:03,360 --> 00:47:07,450
you have all sorts of different security options.

659
00:47:07,450 --> 00:47:11,800
That's kind of a pain because there are 6 all together

660
00:47:11,800 --> 00:47:14,790
and it never really makes sense which 1 to join.

661
00:47:14,790 --> 00:47:19,190
This 1 at the top is the first one that they came up with called WEP.

662
00:47:19,190 --> 00:47:27,960
WEP stands for Wired Equivalent Privacy, I believe,

663
00:47:27,960 --> 00:47:31,730
not Wireless Encryption Protocol which is a common misnomer.

664
00:47:31,730 --> 00:47:36,170
Because it tries to give you privacy equivalent and security protection 

665
00:47:36,170 --> 00:47:40,590
equivalent to that of a wired network

666
00:47:40,590 --> 00:47:46,710
With WEP what ends up happening is,

667
00:47:46,710 --> 00:47:52,300
you have a simple, little password that you type in and that serves to encrypt

668
00:47:52,300 --> 00:47:56,210
all of your communications between your computer and your router.

669
00:47:56,210 --> 00:47:58,210
>> What's the problem with WEP though?

670
00:47:58,210 --> 00:48:01,470
The password with WEP is really short, 

671
00:48:01,470 --> 00:48:04,900
and also everybody uses that same exact password,

672
00:48:04,900 --> 00:48:07,610
 and so it's really easy to decrypt.

673
00:48:07,610 --> 00:48:10,580
So very quickly people figured out that WEP was a problem,

674
00:48:10,580 --> 00:48:16,100
and the only reason you see it show up still on this little guy is--

675
00:48:16,100 --> 00:48:18,890
there are some older systems that do use WEP--

676
00:48:18,890 --> 00:48:25,710
what you should instead be looking for are the WPA and even WPA2 standards

677
00:48:25,710 --> 00:48:29,130
that were released later on.

678
00:48:29,130 --> 00:48:35,040
These systems are a much better go at protection on wireless Internet.

679
00:48:35,040 --> 00:48:41,090
That said, they still do have some hackability.

680
00:48:41,090 --> 00:48:44,010
There are tools out there that can go do this.

681
00:48:44,010 --> 00:48:47,490
One thing in particular that can be nasty is that

682
00:48:47,490 --> 00:48:55,370
if you connect and authenticated to a wireless router and are using some sort of

683
00:48:55,370 --> 00:49:00,940
encrypted communication, it turns out that a hacker can easily send a single packet

684
00:49:00,940 --> 00:49:03,990
to disconnect you from the router,

685
00:49:03,990 --> 00:49:07,220
and once they've disconnected you they can then listen in--

686
00:49:07,220 --> 00:49:11,800
they can sniff those packets as you try to re-establish the connection with your router.

687
00:49:11,800 --> 00:49:16,800
And with that information they can then go in and decrypt the rest of your communication.

688
00:49:16,800 --> 00:49:24,580
This isn't by any means any sort of secure beyond all imagination.

689
00:49:24,580 --> 00:49:30,060
>> The other thing you can do when you're setting up wireless networks

690
00:49:30,060 --> 00:49:35,460
or you're joining them is--you notice that here when I'm joining this network, 

691
00:49:35,460 --> 00:49:37,640
it asks for the name of my network.

692
00:49:37,640 --> 00:49:41,060
This is also known as the SSID.

693
00:49:41,060 --> 00:49:48,610
And you see here that on the right I have a box that shows me the available SSIDs.

694
00:49:48,610 --> 00:49:52,690
There's a Harvard University, a CS50, and a CS50 Staff network.

695
00:49:52,690 --> 00:49:59,180
Now, how many of you knew there was a CS50 Staff network around?

696
00:49:59,180 --> 00:50:01,910
Some of you. Not all of you.

697
00:50:01,910 --> 00:50:08,800
The problem with this, of course, is that had we not put this up on our list of SSIDs,

698
00:50:08,800 --> 00:50:10,930
nobody would have known about it most likely.

699
00:50:10,930 --> 00:50:16,090
I hope. Unless you guys are all trying to crack into our wireless.

700
00:50:16,090 --> 00:50:18,700
But this is something you can do that's really important when you're setting up

701
00:50:18,700 --> 00:50:20,280
a router at home.

702
00:50:20,280 --> 00:50:22,820
This probably won't happen for a few years for a lot of you,

703
00:50:22,820 --> 00:50:29,010
but do keep in mind that keeping that SSID out of there and not also naming it

704
00:50:29,010 --> 00:50:34,630
something super-common will help keep you more secure in the long run.

705
00:50:34,630 --> 00:50:38,070
>> A final couple of things you can do. One is HTTPS.

706
00:50:38,070 --> 00:50:44,760
If you are at a Starbucks, if you are in a public wi-fi area

707
00:50:44,760 --> 00:50:52,620
and you do decide to access your bank account, access your Gmail, your Facebook,

708
00:50:52,620 --> 00:50:56,140
make sure that those connections are going over HTTPS.

709
00:50:56,140 --> 00:50:59,800
It's an added layer of security, an added layer of encryption.

710
00:50:59,800 --> 00:51:01,520
The one thing to keep in mind here is,

711
00:51:01,520 --> 00:51:04,740
how many of you have ever clicked through that big, red screen that says,

712
00:51:04,740 --> 00:51:07,480
"This website might be bad."

713
00:51:07,480 --> 00:51:09,710
I know I have.

714
00:51:09,710 --> 00:51:13,090
It's probably when you're all browsing to go see Homeland or something like that, right?

715
00:51:13,090 --> 00:51:19,900
Yeah. (audience laughter) Yeah. There you go. We know who's watching Homeland.

716
00:51:19,900 --> 00:51:24,540
That big, red screen right there

717
00:51:24,540 --> 00:51:28,600
often indicates that something funky is going on.

718
00:51:28,600 --> 00:51:32,530
Sometimes it's just the website itself is insecure,

719
00:51:32,530 --> 00:51:35,520
but that same big, red screen comes up when people are trying to

720
00:51:35,520 --> 00:51:37,520
mount network attacks on you.

721
00:51:37,520 --> 00:51:40,220
So if you see that big, red screen come up at a Starbucks,

722
00:51:40,220 --> 00:51:42,440
don't click through it.

723
00:51:42,440 --> 00:51:45,350
Bad news. Bad news bears.

724
00:51:45,350 --> 00:51:51,490
>> The final thing that you can look at 

725
00:51:51,490 --> 00:51:54,120
is some sort of VPN.

726
00:51:54,120 --> 00:52:00,280
This VPN is available through Harvard--vpn.fas.harvard.edu--

727
00:52:00,280 --> 00:52:03,260
and what this does is it actually establishes a secure connection

728
00:52:03,260 --> 00:52:06,460
between you and Harvard, funnels your traffic through it,

729
00:52:06,460 --> 00:52:12,160
and that way if you're sitting at a place like a Starbucks

730
00:52:12,160 --> 00:52:19,030
you can connect to Harvard, get that safe traffic, and then browse from Harvard.

731
00:52:19,030 --> 00:52:21,950
Again, not foolproof. People can get in the middle.

732
00:52:21,950 --> 00:52:25,850
They can start to break it, but this is far more secure than relying on the security

733
00:52:25,850 --> 00:52:28,620
of the wi-fi alone.

734
00:52:28,620 --> 00:52:32,570
>> All right. In sum,

735
00:52:32,570 --> 00:52:34,580
when you are setting up wireless networks,

736
00:52:34,580 --> 00:52:37,250
when you are going out to use wireless in public--

737
00:52:37,250 --> 00:52:43,430
whether it's a Starbucks, whether it's Five Guys, whether it's B.Good,

738
00:52:43,430 --> 00:52:46,440
something like that--wherever they have wi-fi--

739
00:52:46,440 --> 00:52:48,440
be aware of your surroundings.

740
00:52:48,440 --> 00:52:50,440
Be aware of what people can do.

741
00:52:50,440 --> 00:52:53,890
And be safe. Don't access your bank account.

742
00:52:53,890 --> 00:52:58,740
It could be a rude awakening if somebody shows up with your password later on.

743
00:52:58,740 --> 00:53:05,480
With that, go crimson! And I'm going to turn things back over to David for a final word.

744
00:53:05,480 --> 00:53:11,270
(applause)

745
00:53:11,270 --> 00:53:14,360
>> [David] I thought I'd share one thing from personal experience.

746
00:53:14,360 --> 00:53:19,940
A tool you might like to play with--though Apple has largely eradicated this issue

747
00:53:19,940 --> 00:53:22,710
if you've updated your software since--

748
00:53:22,710 --> 00:53:26,670
but toward this end of not really being able to trust software that we use,

749
00:53:26,670 --> 00:53:33,270
and to Nate's points, being able to sniff quite a bit of what other people are doing

750
00:53:33,270 --> 00:53:37,010
out there--this was a piece of software that came out about a year-and-a-half ago now.

751
00:53:37,010 --> 00:53:39,010
[iPhoneTracker] [http://petewarden.github.com/iPhoneTracker/]

752
00:53:39,010 --> 00:53:41,010
For some time, iTunes--before iCloud, when you were syncing your iPods or your iPhones or

753
00:53:41,010 --> 00:53:45,570
or your iPads with iTunes--in the interest of backups,

754
00:53:45,570 --> 00:53:48,340
what your iPhone and these other devices have been doing for some time is

755
00:53:48,340 --> 00:53:50,340
making use of GPS data.

756
00:53:50,340 --> 00:53:52,710
>> You all know perhaps that your iPhones and Androids and Windows mobile phones

757
00:53:52,710 --> 00:53:55,410
and the like these days can track where you are in the interest of showing you maps

758
00:53:55,410 --> 00:53:59,440
and similar--well what Apple and these other companies do is

759
00:53:59,440 --> 00:54:02,650
they typically track almost everywhere you've actually been in the interest of 

760
00:54:02,650 --> 00:54:05,380
improving quality of service.

761
00:54:05,380 --> 00:54:07,170
One, you can get more targeted advertising and the like,

762
00:54:07,170 --> 00:54:10,740
but two, they can also figure out where are there wireless hotspots in the world,

763
00:54:10,740 --> 00:54:14,780
and this can help with geo-location--sort of triangulation of people's position.

764
00:54:14,780 --> 00:54:18,520
>> Long story short, all of us had been walking antennae for some amount of time.

765
00:54:18,520 --> 00:54:22,180
Unfortunately, Apple had made the design decision--or lack thereof--

766
00:54:22,180 --> 00:54:26,590
to not encrypt this information when it was being backed-up to iTunes.

767
00:54:26,590 --> 00:54:30,330
And what the security researcher found was that this was just a huge XML file--

768
00:54:30,330 --> 00:54:33,810
a huge text file--sitting in people's iTunes software,

769
00:54:33,810 --> 00:54:35,400
and if you were just a little bit curious,

770
00:54:35,400 --> 00:54:38,990
you could go poking around your spouse's history, your roommate's history,

771
00:54:38,990 --> 00:54:41,050
your sibling's history and the like,

772
00:54:41,050 --> 00:54:44,590
and thanks to some free software, you could plot all of these GPS coordinates--

773
00:54:44,590 --> 00:54:46,590
latitude and longitude.

774
00:54:46,590 --> 00:54:48,590
>> So, I actually did this with my own phone.

775
00:54:48,590 --> 00:54:51,210
I plugged in my phone, and sure enough, my version of iTunes was not encrypted at the time,

776
00:54:51,210 --> 00:54:53,900
and what I was able to see were my own patterns.

777
00:54:53,900 --> 00:54:56,970
Here's the United States and each of these blue circles represents

778
00:54:56,970 --> 00:55:01,670
where I happened to have been over those previous months of owning this particular phone.

779
00:55:01,670 --> 00:55:04,940
 I spend a lot of time, of course, up in the Northeast, a little time in California,

780
00:55:04,940 --> 00:55:08,690
a short-lived trip to Texas, and if you then zoom in on this--

781
00:55:08,690 --> 00:55:11,120
this is all sort of fine and interesting, but I knew this.

782
00:55:11,120 --> 00:55:13,890
Most of my friends knew this, but if you dive in deeper,

783
00:55:13,890 --> 00:55:17,090
you see where I spend most of my time in the Northeast.

784
00:55:17,090 --> 00:55:20,330
If you latch onto some familiar-looking towns--

785
00:55:20,330 --> 00:55:24,670
this big, blue ink splotch is essentially centered over Boston,

786
00:55:24,670 --> 00:55:29,510
and then I spend a little bit of time out in the suburbs radiating out from Boston.

787
00:55:29,510 --> 00:55:32,780
But I was also doing quite a bit of consulting that year.

788
00:55:32,780 --> 00:55:36,090
And this year is the eastern seaboard, and you can actually see me

789
00:55:36,090 --> 00:55:41,920
and my iPhone in my pocket traveling back and forth between Boston and New York

790
00:55:41,920 --> 00:55:47,510
and Philadelphia further down, as well as spending a little bit of vacation time

791
00:55:47,510 --> 00:55:50,340
on the Cape, which is the little arm out there.

792
00:55:50,340 --> 00:55:53,030
So, each one of these dots represents some place I had been,

793
00:55:53,030 --> 00:55:56,970
and completely unbeknownst to me, this entire history was just sitting there

794
00:55:56,970 --> 00:55:58,410
on my desktop computer.

795
00:55:58,410 --> 00:56:00,470
If you zoom out--this actually was a little troubling.

796
00:56:00,470 --> 00:56:04,190
I had no recollection of ever having been in Pennsylvania that particular year.

797
00:56:04,190 --> 00:56:07,840
But I though a little harder about it and I figured out, oh, it was in fact that trip

798
00:56:07,840 --> 00:56:11,160
and sure enough, my phone had caught me.

799
00:56:11,160 --> 00:56:14,180
>> Apple has since encrypted this information, 

800
00:56:14,180 --> 00:56:17,380
but this too is just testament to how much information is being collected about us,

801
00:56:17,380 --> 00:56:20,850
and how easily--for better or for worse--it's acceptable.

802
00:56:20,850 --> 00:56:23,340
One of the take-aways hopefully from Rob's talk, from Nate's talk

803
00:56:23,340 --> 00:56:27,370
and little visuals like this today is just to be all the more cognizant of this

804
00:56:27,370 --> 00:56:31,160
so that even though--as to Rob's point--we're sort of screwed, right?

805
00:56:31,160 --> 00:56:33,920
There's not much we can do when it comes to some of these threats,

806
00:56:33,920 --> 00:56:37,130
but at the end of the day we have to trust something or someone

807
00:56:37,130 --> 00:56:38,510
if we want to actually use these technologies.

808
00:56:38,510 --> 00:56:43,150
At least we can be making informed decisions and calculated decisions whether or not

809
00:56:43,150 --> 00:56:46,390
we should actually be checking this particularly sensitive account 

810
00:56:46,390 --> 00:56:49,330
or we should actually be sending that slightly suspect instant message

811
00:56:49,330 --> 00:56:52,180
 in a wi-fi environment like this.

812
00:56:52,180 --> 00:56:54,990
>> So, with that said, just one quiz remains, one lecture remains.

813
00:56:54,990 --> 00:56:57,740
We'll see you on Wednesday then Monday.

814
00:56:57,740 --> 00:57:02,100
(applause and cheers)

815
00:57:02,100 --> 00:57:06,100
[CS50TV]