text stringlengths 1 81 | start float64 0 10.1k | duration float64 0 24.9 |
|---|---|---|
this is probably a net positive to
switch to a password manager instead. | 4,270.05 | 5.1 |
If, however, though, you've actually
been a very good internet citizen, | 4,275.15 | 3.9 |
and you've been choosing
hard-to-guess, unique passwords | 4,279.05 | 3.135 |
for all different sites-- they're
not written down on a post-it | 4,282.185 | 2.625 |
or easily accessible-- then
this might be a net negative | 4,284.81 | 2.85 |
for you to put all of those
eggs, so to speak, in one basket, | 4,287.66 | 2.7 |
thereby making them more vulnerable. | 4,290.36 | 3.12 |
From experience and from
the head nods and admissions | 4,293.48 | 3.06 |
that we get from
students over the years, | 4,296.54 | 1.78 |
I guess that most of
us in this room would | 4,298.32 | 2.81 |
benefit as a net positive
from a password manager. | 4,301.13 | 2.85 |
But there, too, you should
decide for yourself. | 4,303.98 | 2.322 |
And again, one of our lessons
for today is don't just | 4,306.302 | 2.208 |
believe something some guy
on the internet told you. | 4,308.51 | 2.64 |
Decide for yourself based on these trade
offs, these upsides and. downsides. | 4,311.15 | 4.74 |
Now, password managers
are not all upside. | 4,315.89 | 2.94 |
Indeed, if you lose or
forget that primary password, | 4,318.83 | 3.9 |
you might lose access to
all of your other accounts. | 4,322.73 | 3.15 |
Fortunately, there is
an alternative that's | 4,325.88 | 2.13 |
increasingly available on websites
and apps known as passkeys. | 4,328.01 | 3.63 |
And what's nice about passkeys
is that moving forward, | 4,331.64 | 2.87 |
it will be your Mac,
your PC, or your phone | 4,334.51 | 2.45 |
that generates a passkey
for a new website | 4,336.96 | 2.79 |
or app for which you're registering. | 4,339.75 | 1.62 |
You yourself don't have to
remember what that passkey is, | 4,341.37 | 2.91 |
and indeed it isn't even just one value. | 4,344.28 | 2.01 |
Rather it's a pair of values, a
private value and a public value, | 4,346.29 | 3.93 |
that have a mathematical
relationship between the two. | 4,350.22 | 3 |
And those two values are used. | 4,353.22 | 2.2 |
The next time you try to access that
website or application, your Mac, | 4,355.42 | 3.75 |
your PC, or your phone will use those
values to automatically authenticate | 4,359.17 | 3.89 |
you thereafter. | 4,363.06 | 0.81 |
And better yet those
values are synchronized | 4,363.87 | 2.07 |
as needed across your devices so
that you can use your Mac and your PC | 4,365.94 | 3.96 |
and your phone or any other
such devices to authenticate. | 4,369.9 | 3.06 |
But to better understand
these passkeys, we'll | 4,372.96 | 2.22 |
need to know a little something
about the world of cryptography. | 4,375.18 | 3.52 |
And so for that, we'll wait for our
discussion of securing your data. | 4,378.7 | 3.72 |
So more on that next time. | 4,382.42 | 3.19 |
0 | 17.255 | |
SPEAKER 1: All right, this is
CS50 and this is week five. | 17.255 | 3.685 |
And let's take a look at
where we left off last time. | 20.94 | 2.62 |
You may recall this guy here,
Binky from our friends at Stanford. | 23.56 | 4.14 |
And we used Binky to start
talking about pointers. | 27.7 | 3.25 |
What is a pointer? | 30.95 | 1.209 |
So, a pointer is just
an address, the location | 32.159 | 2.336 |
of some piece of data in memory,
because recall at the end of the day | 34.495 | 2.875 |
your computer just has a few pieces
of hardware inside of it, one of which | 37.37 | 4.36 |
is RAM or Random Access Memory. | 41.73 | 2.18 |
And in RAM you have the ability to
store bunches and bunches of bytes, | 43.91 | 4.04 |
or kilobytes, or
megabytes, or gigabytes, | 47.95 | 2.117 |
depending on how much memory you have. | 50.067 | 1.583 |
And if you assume that no
matter how much RAM you have you | 51.65 | 3.41 |
can enumerate the bytes-- this is byte
0, this is byte 1, this is byte 2, | 55.06 | 4.06 |
and so forth-- you can give each of
the bytes of your computer's memory | 59.12 | 3.19 |
an address and those addresses
are simply called pointers. | 62.31 | 3.149 |
And now in C we have the
ability to use pointers | 65.459 | 3.471 |
both to go to any location
in memory that we want | 68.93 | 3.5 |
and even to dynamically allocate
memory in case we don't necessarily | 72.43 | 3.43 |
know a priori how much memory
we might need for a program. | 75.86 | 4.177 |
Now, in terms of your
computer's RAM, recall | 80.037 | 1.833 |
that we divided the
world into this picture | 81.87 | 2 |
here whereby if this rectangular region,
arbitrarily, represents your computer's | 83.87 | 5.01 |
memory, here is how the
computer divvies it up | 88.88 | 2.02 |
when you're actually using a program. | 90.9 | 2.37 |
At the bottom of your computer's area
of memory, you have the so-called stack. | 93.27 | 4.31 |
And recall that the stack is where
any time you call a function, | 97.58 | 3.17 |
it gets a slice of
memory-- a frame of memory, | 100.75 | 2.51 |
if you will-- for all of its local
variables, all of its arguments | 103.26 | 2.84 |
and anything else that it might need. | 106.1 | 1.69 |
On top of that might go another
slice or frame of memory | 107.79 | 3.14 |
if that first function calls another. | 110.93 | 1.93 |
And if that second function in
turn calls another function, | 112.86 | 2.56 |
you might have a third
frame on the stack. | 115.42 | 2.064 |
Of course, this doesn't end well if you
keep calling function after function | 117.484 | 3.166 |
after function after function. | 120.65 | 1.2 |
And so, hopefully you don't accidentally
induce some kind of infinite loop | 121.85 | 3.13 |
such that these frames pile on
top of each other infinitely | 124.98 | 3.08 |
many times, because eventually they'll
run the risk of hitting the heap. | 128.06 | 3.39 |
Now, the heap is the same
type of physical memory. | 131.45 | 2.1 |
You're just using it in
a slightly different way. | 133.55 | 2.59 |
The heap is used any time you want
to dynamically allocate memory, | 136.14 | 3.95 |
when you don't know in
advance how many bytes | 140.09 | 2.23 |
you need but you do know once the
program is running how many you now | 142.32 | 2.95 |
want. | 145.27 | 0.57 |
You can ask via functions
like malloc the operating | 145.84 | 3.13 |
system for some number
of bytes, and those bytes | 148.97 | 2.26 |
are allocated from the heap. | 151.23 | 1.78 |
So, those two have addresses or numbers. | 153.01 | 1.862 |
And so, the operating
system, by way of malloc, | 154.872 | 1.958 |
just figures out which of
those bytes are not yet | 156.83 | 2.041 |
being used so that you can
now put whatever piece of data | 158.871 | 3.229 |
you have in that particular place. | 162.1 | 1.972 |
Now, beyond that [? appear ?]
things like initialized data, | 164.072 | 2.458 |
uninitialized data. | 166.53 | 0.91 |
That's where things like global
variables that are initialized or not | 167.44 | 3.26 |
end up that might be outside
of your main function. | 170.7 | 2.36 |
And then above that is the
so-called text segment, | 173.06 | 2.12 |
which are these zeros and ones
that actually compose your program. | 175.18 | 3.75 |
So when you double click an
icon on Windows or Mac OS | 178.93 | 3.33 |
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