text stringlengths 1 81 | start float64 0 10.1k | duration float64 0 24.9 |
|---|---|---|
mean something analogously, whereby
you're using software to digitally try | 268 | 4.83 |
all possible passwords. | 272.83 | 2.01 |
And so here, too, are you vulnerable
because if your password is too short, | 274.84 | 3.87 |
even if it's random with
letters, numbers, and symbols, | 278.71 | 3.03 |
odds are an adversary or a
hacker that has enough time | 281.74 | 2.79 |
and enough technical
savvy, they can just try | 284.53 | 2.19 |
every possible password in the world. | 286.72 | 2.67 |
And eventually, they might
very well get into your system. | 289.39 | 3.01 |
So how do we go about defending
against these kinds of attacks? | 292.4 | 4.222 |
Well, we use these passwords,
but these passwords of course | 296.622 | 2.458 |
come in different forms. | 299.08 | 1 |
And it's kind of a low bar that is
set by default on a lot of devices | 300.08 | 4.7 |
still nowadays. | 304.78 | 0.75 |
For instance, on your
phone if you'd like | 305.53 | 2.04 |
to chime in here in the chat, how many
characters or digits, in particular, | 307.57 | 5.49 |
are typically required of systems? | 313.06 | 1.815 |
Well, I would conjecture that
very often when I set up a phone, | 314.875 | 2.625 |
I'm only asked for a passcode, a
numeric password, of four digits alone. | 317.5 | 5.4 |
Now, if you have a four-digit passcode
or password more generally, how secure | 322.9 | 6.99 |
is that? | 329.89 | 0.66 |
And how do we even go about thinking
about how secure that password is? | 330.55 | 4.23 |
Well, I would propose that we could
start to measure not even using | 334.78 | 3.45 |
fancy math, but just some basic
heuristics, we could measure | 338.23 | 2.76 |
the security of a password that has
just four digits by considering well, | 340.99 | 4.38 |
how many possible four-digit
passcodes are there? | 345.37 | 3.06 |
So perhaps if you'd like to
chime in here in the chat, | 348.43 | 2.25 |
how many possible passwords
are there if they're | 350.68 | 3.36 |
all digits 0 through 9, decimal digits,
and if you only have four of them? | 354.04 | 4.95 |
How many possibilities are there? | 358.99 | 1.87 |
I'm seeing 1,000. | 360.86 | 0.92 |
I'm seeing 10,000. | 361.78 | 1.02 |
I'm seeing 9,999. | 362.8 | 2.55 |
And I'm seeing a whole range. | 365.35 | 1.283 |
And I think a lot of you
have the answer is spot on. | 366.633 | 2.167 |
It's 10,000. | 368.8 | 1.71 |
It's 10,000. | 370.51 | 0.82 |
Why? | 371.33 | 0.5 |
Well if we just think
about this numerically, | 371.83 | 2.04 |
if I've got four decimal
digits, 0 through 9, well, | 373.87 | 3.24 |
the smallest password I could come
up with, so to speak, would be 0000. | 377.11 | 4.02 |
And the largest password I could
come up with would be 99999. | 381.13 | 4.35 |
Now, you might think OK, well,
that's, obviously 9,999 possibilities. | 385.48 | 4.32 |
But not quite because if you include
0000, that's the 10,000th possibility. | 389.8 | 5.97 |
So indeed there's 10,000
possible passwords | 395.77 | 3.69 |
if we're using four digits specifically. | 399.46 | 2.98 |
So how do we actually think
about that more generally, | 402.44 | 2.45 |
especially so that we can now figure out
the math for larger passwords as well? | 404.89 | 4.36 |
Well, if you've got 0 through
9 as the first possible digit, | 409.25 | 3.26 |
and 0 through 9 as the
next, and 0 through 9 | 412.51 | 2.13 |
is the third, and 0
through 9 as the fourth, | 414.64 | 2.49 |
you have 10 possibilities times 10
possibilities times 10 times 10. | 417.13 | 3.833 |
This, of course, if we do
it out more mathematically | 420.963 | 2.167 |
is 10 to the fourth power,
the exponent being 4. | 423.13 | 3.42 |
And that, of course,
gives us 10,000 as well. | 426.55 | 2.53 |
So that might be the more
mathematical way of approaching it, | 429.08 | 2.81 |
versus just the more intuitive, that
0000 can go all the way up to 9999. | 431.89 | 5.28 |
Now, again, a question
for the group, how long | 437.17 | 2.79 |
do you think it might take
for an adversary or a hacker | 439.96 | 4.17 |
to get into my device, for
instance, my phone, if I do | 444.13 | 4.41 |
have a four-digit password? | 448.54 | 3.06 |
If I've got a four-digit password, this
means there might have to try as many | 451.6 | 3.42 |
as 10,000 possibilities because in the
easiest case, sure, they get lucky, | 455.02 | 5.49 |
and my password is
still the default 0000. | 460.51 | 2.73 |
But in the worst case, I chose
9999, and they don't get to that | 463.24 | 3.57 |
until the very end of their attempts. | 466.81 | 1.74 |
Or maybe I choose
something there in between. | 468.55 | 2.22 |
I'm seeing 10 seconds, less than a
second, milliseconds, 10 seconds a day, | 470.77 | 3.99 |
4 hours. | 474.76 | 1.02 |
So the responses are all over the place. | 475.78 | 2.59 |
So how can we go about actually
measuring this or estimating this? | 478.37 | 3.72 |
Well, let me propose this. | 482.09 | 1.13 |
I'm going to go over
to my computer here. | 483.22 | 1.708 |
And even if you've never
written any code before, | 484.928 | 2.942 |
let's go ahead and write
some code together here. | 487.87 | 2.4 |
I'm going to go ahead and open a
program called VS Code, Visual Studio | 490.27 | 3.63 |
Code, which is a free program
that we use in CS50 more generally | 493.9 | 3.57 |
that allows me to write code
on my Mac or PC or really | 497.47 | 3.42 |
any internet-based device. | 500.89 | 1.38 |
And I can actually write code,
and not only write it, but run it. | 502.27 | 3.22 |
And I'm going to write code, in this
case, in a language called Python. | 505.49 | 2.99 |
And this is just a
very popular language, | 508.48 | 1.83 |
but I could use any of a dozen or
more different programming languages. | 510.31 | 4.02 |
And the goal here is
not to learn Python-- | 514.33 | 2.01 |
for that, we have whole other classes-- | 516.34 | 2.01 |
but to just demonstrate what
an adversary, what a hacker | 518.35 | 3.959 |
need to do if they want to get into, for
instance, your iPhone or Android device | 522.309 | 4.411 |
or anything that has just
a four-digit password. | 526.72 | 3.48 |
Now, my presumption here
for demonstration sake | 530.2 | 2.4 |
is that I'm going to go ahead
and write code that just prints | 532.6 | 2.79 |
all possible passwords on the screen. | 535.39 | 2.29 |
But you could imagine if I had a USB
cable or maybe a lightning cable, | 537.68 | 3.83 |
I could connect this
phone to this laptop, | 541.51 | 2.76 |
especially if it's your phone
that I just swiped from a table, | 544.27 | 3.03 |
could quickly plug it
into my computer here, | 547.3 | 1.95 |
run the code that I'm about to
write, and maybe automatically send | 549.25 | 3.54 |
all 10,000 possibilities to
your device before you even | 552.79 | 3.72 |
realize the phone is gone. | 556.51 | 1.5 |
Now, here's how I'm going to do this. | 558.01 | 1.72 |
I'm going to go ahead, and in
a text file called crack.py, | 559.73 | 3.35 |
where crack is actually a term of art. | 563.08 | 1.78 |
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