dear fellow Scholars this is 2 minute
papers with car cryptography helps us
communicate securely with someone in the
presence of third parties we use this
when we do for instance online banking
or even as mundane tasks as reading our
Gmail one of the simplest ways of doing
cryptography is using the Caesar Cipher
we have a message and each letter we
shift with the same amount okay wait
what does shifting mean Shifting The
Letter A by one becomes B e and shifting
e by one becomes F and so on the amount
of Shifting doesn't have to be exactly
one it can be anything as long as we
shift all letters in the message with
the same amount if we would run out of
the alphabet for instance by Shifting
the last letter Z by one we get a the
first letter back there's a special case
of Caesar ciphers that we call rth 13
that has an interesting property it
means that we shift the entirety of the
message by 13 letters let's encrypt a
message with Rod 13 we obtained some
gibberish okay now let's pretend that
this gibberish is again a message that
we would like to encrypt we get the
original message back why is that since
there is 26 letters in the basic Latin
alphabet we first shift by 13 then doing
it again we shift by 13 letters which is
a total of 26 therefore we went around
the clock and ended up where we start
started mathematicians like to describe
this concisely by saying that the
inverse of the rod 13 function is itself
if you call it again you end up with the
same message we know the statistical
probabilities of different letters in
the English language for instance we
know that the letter e is relatively
common and Z is pretty rare if we shift
our Alphabet by a fixed amount the
probabilities will remain the same only
for different letters therefore this
Cipher is quite easy to break even
automatically with a computer this is
anything but secure communication the
onetime pad encryption is One Step
Beyond this where we don't shift each
letter with the same amount but with
different amounts this list of numbers
to use for shifting is called a pad
because it can be written on a pad of
paper and it has to be as long as the
message itself why one time why paper no
worries we're going to find out soon
enough if we use this technique we'll
enjoy a number of benef beneficial
properties for instance take a look at
this example with a onetime
pad we have two v's in the encrypted
output but the first V corresponds to an
h and the second V corresponds to a p
therefore if I see a v in the encrypted
output I have no idea which letter it
was in the input Computing statistical
probabilities doesn't make any sense
here and we're powerless in Breaking
this so even even if you can intercept
this message as a third party you have
no idea what it is about it's very easy
to prove mathematically that the
probability of the message being happy
is the very same probability as hello or
ABCDE e or actually any
gibberish the onetime pad is the only
known technique that has optimal perfect
secrecy meaning that it is impossible to
crack as long as it is used correctly
this is mathematically proven it is not
a surprise that it had seen plenty of
use during the second world war so what
does it mean to use it correctly several
things pads need to be delivered
separately from the message itself for
instance you walk up to the recipient
and give them the pad in person the
exchange of the pads is a huge problem
if you're on the Internet or at War now
you must also be worried that the pad
must not be damaged if you lose just one
number the remainder of your message is
going to be completely gone are build up
you're done the key in the pad needs
perfectly random numbers no shortcuts
generating perfectly random numbers is
anything but a trivial task and is
subject to lots of discussion one time
pads have actually been broken because
of this there's an excellent episode on
a well-known Channel called Vsauce on
what random really means make sure to
check it out the pad has to be destroyed
upon use and should never be reused so
if you do all this you're using it
correctly corly in the age of the
internet it is not really practical
because you cannot send a delivery guy
with the secret pad next to every
message you send on the internet so in a
nutshell onetime pad is great but it is
not practical for large scale real-time
communication from AAR and as crazy as
it sounds if a civilization can find a
method to do practical communication
with perfect cryptography their
communication will look
indistinguishable from noise this is
amazing there's tons of ongoing debates
on the fact that we're being exposed to
tons of radio signals around the earth
why can we still not find any signs of
extraterrestrial communication well
there you have the answer and this is
going to blow your mind if practical
perfect cryptography is mathematically
possible the communication of any
sufficiently advanced civilization is
indistinguishable from noise they may be
transmitting their diabolical plans
through us this very moment and all we
would here is White
Noise crazy isn't it thanks for watching
and for your generous support and I'll
see you next time