Quantum Cryptography Explained

With recent high-profile security decryption cases, encryption is more important than ever. Much of your browser usage and your smartphone data is encrypted. But what does that process actually entail? And when computers get smarter and faster due to advances in quantum physics, how will encryption keep up?

Creator/Editor: Dianna Cowern

Writer: Sophia Chen

Animator: Kyle Norby

Special thanks to Nathan Lysne

Source:

Music: APM and YouTube

[chillsahoy]

I heard of an analogy for encryption that went like this: Alice sends a suitcase to Bob, but it has been closed with a lock and only Alice has the key for that lock. When Bob receives the suitcase and checks that Alice's lock is on it, he adds his own lock, to which only he has the key, and sends the suitcase back to Alice. Once Alice has confirmed that Bob placed his own lock, she opens hers (now the suitcase only has Bob's lock) and sends it back to Bob. Bob can now undo his lock and open the suitcase.

The security there is that keys are never exchanged, Alice can only open her lock, and Bob can only open his, so even if someone intercepted the suitcase, they'd be unable to open it because the neither Alice nor Bob ever send the keys to each other.

[AntoshaPushkin]

Hey, what about "Happy physicsing"? I am watching 50% because of nice explanations of complicated physics and 50% because of that "happy physicsing" at the end

[zachheilman]

I know just enough about cryptography to say that I'm genuinely impressed by the research you did for this video. Nicely done!

[FirstRisingSouI]

For people who are confused: this video assumes you have a basic knowledge of quantum physics. Try searching for "Stern-Gerlach experiment" to learn about measuring particle spins.

[MalfunctonMke]

Ejboob spdlt is the name of the day for me now :D

[EugeneKhutoryansky]

We are just beginning to scratch the surface of the possible applications of quantum physics.

[NimNms]

Came here to understand quantum cryptography and ended up becoming a hacker. Thanks Ejboob.

[smileyball]

If quantum cryptography becomes state-of-the-practice encryption, is it possible that future attacks will focus primarily to destroying the message rather than eavesdropping it? Seems equally troublesome.

[betongitarre]

This video really helped me. When you are a physics student they expect you to be able to talk about this topic. I drew a recap on a sheet of paper to get it all right. Later I made out that it wasn't necessary. Sender and recipient don't have to take the former uncertainty of some 1 and 0 into consideration when they want to settle on a code. They just sort these cases out! ^^

BTW The part at 0:25 was a bit peculiar. But I might got you wrong.
The secrets he stole (he hadn't to solve a code because they granted him access) revealed that, in the first place, WE, not the american government, are in need to encrypt our messages. Especially when you are a foreigner and even when you are from a befriended country.

[ScienceAsylum]

The candy is back!

I think I'm going to have to watch this a few times for it to sink in. Quantum is weird.

[PhotonicEmission]

Damn girl. You just explained something that never made sense to me in a genuine lecture, with CANDY. Not only that, but I understood it at the end! Thank you!

[KazimirQG]

If just the fact of intercepting and measuring changes the key, which means that the original sender-receiver have to try again, you have just described the new Quantum DDoS Attack.

[rudresh]

I'll be honest, I did not understand anything beyond 4:00

[jr]

Now it makes sense to me.

Also, I admire you resisting the temptation to "sample" your props. :)

[XmdogmX]

Amazing. I love the way you have of explaining these advanced concepts in ways we can all understand. You rock!

[NovaCyn]

A lot of minute things I think you oversimplified too much in this video... Or in the first case made needlessly complex:

When you told us how you could use prime numbers to encrypt your message (you chose 11 and 13 as prime numbers, and multiplied everything with 11*13 = 143) you aren't actually showing the need for an asymmetric key. In fact you could have used any number, say 144 which is a composite of a lot of 2s and 3s, and the code would work the exact same way. As long as the sender and receiver agrees on the key the encryption works.

The only reason to use one way functions is the much more complex asymmetric algorithms as RSA which i agree very much you shouldn't go into detail on in this kind of video. But for those who are interested basically the product of the primes is PUBLICLY known so anyone can use it to encrypt, but the algorithm is made such that to de-crypt you need to know the prime factors (which you keep private).

The other one is you say that a random number can be used to encrypt a message if it is truly random. This is correct only if the number is as large as the message! There's a big difference between a random number and a random number at least sooo big.

[SamieVisual]

I watch this episode since it was posted. but i didn t undersand shit.
I just had a course of quantum cryptography and I realised I already watch an epidoe about what the teacher was talking about. It was an awsome feeling and thank you physics girl

[krisztianszirtes]

And just a thing I came across while thinking about this:
1) Generate a number from text
2) Multiply by a prime number
3) The original number itself in some way determines which part of the number is important, the rest will be deleted from before and after
We have prime multiplication and data loss as well. Could this be used at all?

[nayutaito]

The classic cipher system in the video does not require prime factoring. THe eavesdropper can take the greatest common divisor of all numbers, which can be done pretty fast, and it is likely to be the key itself.

[felixbade]

Very well explained! It was easy to understand even though I knew nothing about quantum cryptography. Thank you! :)