Secret Key Exchange (Diffie-Hellman) - Computerphile

How do we exchange a secret key in the clear? Spoiler: We don't - Dr Mike Pound shows us exactly what happens.
Mathematics bit: • Diffie Hellman -the Ma...
Computing Limit: • Computing Limit - Comp...
/ computerphile
/ computer_phile
This video was filmed and edited by Sean Riley.
Computer Science at the University of Nottingham: bit.ly/nottscomputer
Computerphile is a sister project to Brady Haran's Numberphile. More at www.bradyharan.com

[@OscarAlsing]

Poor Alice and Bob. Always exposed. Always out there. Never left alone. ❤️

[@kduhtdkzrt]

To answer the question about the aggressive tone in advance, I'm drunk, not austistic. No harm meant.

[@ragnkja]

Eve is always stalking them...

[@kduhtdkzrt]

Damnit. You're right.

[@malporveresto]

#Pray4AliceAndBob

[@TruthNerds]

Meh. What if Alice and Bob are just attention whores?

[@denisr5250]

The analogy with colors in this video is pure genius! Thank you guys, this was an amazing introduction to Diffie-Hellman!

[@aerodynamico6427]

Diffie-Hellman's original paper will drive you up the wall.

[@ScottPlude]

5 years later and this is still done a million times a minute out there. Very well explained, thank you!

[@nishantdalvi9470]

Hey can you please clear my doubt, Actually I am kind of bit confused about the ordering of the events which takes place while TLS handshake does the digital certificate part which server shoots to the client to tell the client it's integrity and provide client it's public key happens before Diffie Helman key exchange or after it or eventually during the key exchange

[@ScottPlude]

@@nishantdalvi9470 why are you responding to me after 5 months? FIVE MONTHS!?!?!?!

[@goshisanniichi]

Random squirting of fluids... exactly what I wanted to see this early in the morning...

[@therealquade]

the random squirting of fluids, by alice and bob, out in public.

[@troyjones9344]

ohhhhhh myyyyyyyy

[@TheWolfboy180]

Thomas Carrel It’s ok, no one minds if it’s done by Dr. Mike Pound

[@xxwaldi]

@@therealquade yeah they should rather put it in the privates

[@mrsmith1097]

Is that Super Sonico?

[@CGoody564]

Watched the defcon presentation from years ago given by the creator of the diffie-helman key exchange... It was absolutely fascinating. Dude is an innovator and pure genius. Seems like a nice guy as well

[@phoenix2464]

yessss him again

[@SuviTuuliAllan]

maxwell,cpp sexy, right?

[@kduhtdkzrt]

komma cpp ?!

[@treyquattro]

in for a penny, in for (Dr.) Mike Pound

[@Ozziepeck11]

wtf?!!

[@ABurntMuffin]

Mike is the best. Except for maybe Parker.

[@frenchify7506]

I really like this guy. Been watching and rewatching his lessons for like 3 hours.

[@RobertMilesAI]

Nice! This is a subject I should have covered immediately after the Public Key Cryptography video, since that one lays out the problem of exchanging keys that Diffie-Hellman solves. Great to see such a clear explanation, I doubt I'd have gone to the effort to get coloured liquids!

[@proloycodes]

robert miles with only 4 likes and no replies? also, first!

[@AyushMo]

Your public key crypto video was amazing! So was this one !

[@Democracy_Manifest]

Is it a 'clear' explanation though, or a coloured one?

[@dmatuzo]

How curious, PBS Infinite Series have been talking about encription in the last few days. Now I've got double the encryption bonanza! This has been a good week.

[@smob0]

I think the next video in the series will be about this key exchange.

[@remuladgryta]

Further, one of the Royal Institution's recent videos used the same color mixing analogy to demonstrate key exchange.

[@curtmack]

The color mixing analogy has been used to describe Diffie Hellman key exchange for a couple of decades at least.

[@heyraylux]

curious indeed.....

[@davidoconnor9167]

Excellent, clear explanation, and the colours really showed the process visually, thanks guys!

[@CristiNeagu]

1:04 First rule of cryptography: Unless your job is to create cryptographic algorithms, *never* implement your own cryptographic algorithms. You *will* screw it up.

[@paterfamiliasgeminusiv4623]

Nice advice because it is such a tempting prospect.

[@baatar]

Why would you even want to implement your own in the first place?

[@dapperking]

@@baatar for funnnnnn

[@paulzapodeanu9407]

In high school I thought I was being clever and did this. Took my deskmate about 1/2 an hour to crack it. Despite many evidence to the contrary, I still think I'm clever.

[@sir_slimestone3797]

@@paulzapodeanu9407 Let me guess, simple substitution

[@nO_d3N1AL]

What I like most about this channel is the ability of the presenters to explain things simply without mathematics. That is real teaching, not reciting formal proofs and equations

[@WofWca]

Reciting formal proofs is also teaching, just for more advanced.

[@kingbran923]

Sir, you have sincerely helped me with my homework far more than my textbook ever could. Thank you so much for making these videos! :D

[@Laurabeck329]

This demonstration was a classic Parker square.

[@CreamyRootBeer]

Matt Parker says "No."

[@benjohnson6251]

Such a good video! Really clever concept, and the colour analogy is great! Cheers! :D

[@ironman85000]

I'm a simple man. I see a computerphile video with Mike Pound, I click like

[@dasjucktmichnicht6727]

i love the style of the whole channel! proofs nobody really needs power point or laborious anmations.

[@wakomike29]

This helps soooo much with my university studies! Dr. Pound, your the best.

[@kigtod]

A very clear explanation as usual, but it would have been nice for Mike to briefly mention that a trio at GCHQ - Ellis, Cocks and Williamson - came up with the idea first.

[@waspstomper6250]

Shut up

[@1992Razvy]

Great video and execution. Always I need to know how something in practice works to know if I really need it in my project and then I need to know the math behind to reproduce myself. I just got here again after watching the math video, beause I have to go back to solidify the knowledge.

[@lukas.oppermann]

Great explanation. Makes this concept really easy and straight forward to understand. 👍Thank you

[@Dashrendar2507]

Hey, thanks! I was still having issues with this but your visual representation really helped :)

[@akshaykkapoor]

Best explanation of DH with such a simple example ..great work ..keep it up

[@wiltonlawrence882]

This is the best explanation of key exchange i came across, thanks for uploading this

[@ennis_w]

Everytime I feel confused by e2ee or key exchange, I will come back and see these videos. Really helps.

[@giorgibakradze8734]

Thank you. This video really made the concept of Diffie-Hellman key exchange clear for me.

[@RiGGeN83]

i always wanted to know how was the very first aproach! now i know! thank you! great video, keep up with your excelent work!

[@druidelf3]

Amazing video. I could not have found a better teacher. Thank you so much.

[@evarakovska3302]

Thanks for whole serie of videos! I found something useful for my students and it is great!

[@StuffOffYouStuff]

Fantasticly simple and easy to understand explanation, thank you for this. I'm studying for the Sec+, so basics atm. But i've been getting very confused by some of the terms around encryption. I'm going to ask a completely naive question. I understand to encrypt there are two components, 1) the algorithm, 2) the key. I've seen Diffie-Hellman described as a) a public key encryption algorithm, b) a key exchange protocol, c) a public-key encryption protocol. RSA is also described as an asymmetric public key encryption algorithm. Diffie-Hellman only generates keys, it does not provide an algorithm for use with those keys to then encrypt data RSA also generates keys, but can also encrypt/decrypt data So, my questions/assertions: 1) Is there general misuse of the term "encryption algorithm" or just "encrpytion" as to what that encompasses? What should it encompass? 2) My current feeling is, Encryption = 1) the algorithm, 2) the key (but not the key generation). Encryption algorithm = 1) literally just the algorithm, not the key. EErr, i don't know what term to use that would also encompass the key generation bit. So yeah confused still. 2) The process of Diffie-Hellman key generation/exchange is still considered an encryption algorithm because it outputs data (the shared public) that makes deciphering the input to create it practically impossible? 3) Diffie-Hellman is considered asymmetric because it generates a private/public key pair first? 4) Diffie-Hellman can also be used to generate asymmetric keys ONLY? 5) So the private symmetric keys Diffie-Hellman creates would form the symmetric keys for one of the symmetric encryption algorithms like RC4/AES? 4) Looking back at the above then, the term encryption looks like it should actually include the discrete phase of key generation/distribution?

[@tudoralexandruienulescu2214]

I am also studying Sec+ From what I (think I) know, here are my answers: 1 - There is no misuse. Encryption describes the goal of the action, the algorithm is what any algorithm is. A chain of operations for a specific goal. "Encryption algorithm" is fine. 2 - You are overthinking I guess. "Encryption" is a term used to describe the topic of the discussion (for example). The term "Encryption algorithm" is getting into details and explaining what is, why it's needed, how it works (each step of the process aka the algorithm), etc. 3 - Diffie-Hellman is assymetric because the Bob and Alice don't have all the same keys in their own pockets. Alice does not have the "b" key and Bob does not have the "a" key. 4 - From what I learned thus far, yes. DH is the general example for generating asymmetric keys. 5 - YES 6 (or maybe 4) - I don't think so. encrypting something using a cypher is one thing, using a handshake or other ways to communicate between parties is another (just like DH). The DH is the actual method used to sharing of a secret key between two people who have not contacted each other before. It does not refer to the cyphers at all.

[@chrisgsauce]

I've never seen a clearer explanation of DH. Thanks guy!

[@florianfanderl6674]

Recently discovered this channel and I love it ❤

[@rezaghochkhani]

This is the greatest video I have watched on encryption, ever! Thanks a lot.

[@999999GALLADE]

I was actually looking for a good Diffie Hellman video a couple of days ago - how convenient!

[@grrr1351]

I just love this guy! Keep him comin'.

[@kennyethwong5214]

your presentation is so clear and understandable, thanks a lot

[@MakerTim]

Thanx! I got NOW my college about EXACT this and your explanation is way more clear

[@DouroFusion]

amazing video, thanks Dr Mike Pound!

[@daviaquino3625]

I am writing Javascript decryption libraries for Apple Pay, Google Pay and Shopify and came across this video trying to learn more about the theory. Fantastic!

[@laurelineparis5407]

Nice, fun and accessible way to explain it :) Really enjoyed the analogical explanation Thanks for sharing 🙌

[@tapewormerbinkosti3141]

One of these mathematical functions is: Alice sends g to the power of a (modulo prime number p). Bob sends g to the power of b (modulo p). The shared key is then: g to the power of a (modulo p) to the power of b (modulo p) which is the same as g to the power of b (modulo p) to the power of a (modulo p).

[@syeduzairahmed]

Very simplified approach of teaching. Great video

[@jamie_ar]

Great video, but surely the simpler method with the colours would have been to have ramekins with clear water and then add X drops of food colouring for the stages?! 😂

[@AloisMahdal]

Apparently Mt.Dew vending machine was closer than a food coloring vending machine.

[@AlexRasengan1337]

But that wouldn't work, the private keys are different.

[@agentjeyjey9757]

@@AlexRasengan1337 Not for the private keys, for the public key (g)

[@pascalst5023]

this is so well explained. Thank you!

[@ChubBuddy69]

Excellent explanation. THANK YOU!

[@fridric2916]

Dr. Mike Pound is just a great great teacher

[@lenilsonsg]

You just got a new subscriber. Excellent content mate.

[@BackWithTheBoom]

Mathematical squirtings, LOVE THIS GUY XD, i follow this guy almost for a couple years, such a MVP

[@edmundderek]

so glad that your video made it in the bibliographie of my PFE

[@ramprasath219]

Superb video!!! Great job 👍👏

[@dubonbiton1706]

What an incredible video! Fantastic way to understand how VPN key exchange works!! Thumbs up

[@khawajaazfarasif4865]

Beautifully explained.

[@SirCutRy]

This is so simple yet so effective. Very interesting.

[@almiskea]

Great explanation, I have been searching and no one has explained it as well Thank you

[@user-qf6yt3id3w]

One thing I liked about Hellman was that not only did he invent a clever way to distribute private keys he also invented a decent tasting mayonnaise with an enormous shelf life. It has been forecast that a jar or mayonnaise will still be more or less OK even after being stored at refrigerator temperatures for five thousand years. If the Ancient Egyptians had known about Hellman's mayonnaise recipe and had stored a few sealed jars in the pyramids we'd still be able to open them and make a decent tuna mayo sandwich. Probably long after the nuclear apocalypse we'll be eating Hellman's Mayonnaise probably with roach meat. Or maybe the roaches will win and eat Human Mayo sandwiches.

[@lumanaughty1025]

This might be the quarantine talking, but I’m starting to get a crush on this dude

[@ruijiebai7531]

lol,i feel you ,i wish my lecturer could have his face then i wont skip any lecture

[@asherorourke6199]

what a terrific explanation. Terrific, and thank you!

[@AnimatedHooman]

Excellent explanation. Loved it

[@ekinseyjr]

A very clear explanation - many thanks!

[@unvergebeneid]

2:53 that sound though! =)

[@atulsharma4501]

Just love this guy !!!!! Great explanation!!

[@westa1979]

This video makes so much sense. And I get that it would be used to exchange, say, an AES key. But I thought symmetric keys were exchanged with asymmetric encryption, such as RSA. When would one chose DH instead? (Answer probably in another video)

[@jackboyle3688]

This is an excellent explanation, thanks a bunch!!

[@Deiwulf]

Finally explanation of the main part that's missing like literally everywhere else. Good lord.

[@DaMaZa1234]

I would like to Thank you Dr.Mike Pound for this information. it make me understand what is Diffie-Hellman is and i would like to take this video to be your reference in my work i have been put credit for u i really appreciate what u have done for us this video is just 8min it fun and i love this video Thank you

[@datag1199]

Great visual analogy. Thank you!

[@matteoagius-darrigo7632]

my favorite video on youtube!

[@afroeuropean5195]

FINALLY. Love your videos

[@Crypto_Wiz]

Brilliant. My professor could not even come close to such a great explanation.

[@ronaik]

Great explanation to understand DH key exchange. Also, as food for thought, wouldn't a highly skilled painter (hacker) know what colours add up to form that final colour? He does and that's where we add more complexities and algorithms to make DH what it is!

[@programmercouple]

Finally understood the Diffy-Hellman concept. Thanks

[@zeikjt]

The water with food coloring mixing is a subtraction (so it'll converge on a dark muddy color), but the computer generated mixing is an addition (it'll converge on white). Aka, paint vs light.

[@LHyoutube]

I would have understood a lot more mathematics had it been presented so intuitively!

[@ryantan5974]

Very well explained and elaboration are very clear.

[@Skaxarrat]

Stellar explanation.

[@GordonjSmith1]

What a wonderful demonstration!

[@fahansheikh]

thanks for the wonderful explanation 👍

[@tejasanvekar7367]

Huge fan of u sir....started encryption watching ur videos.....love ur accent

[@trollflix]

This guy is a genius. The explanation method is high level. You must be a teacher. 😍😋

[@pun15h3r.]

very nice video, plain and simple explanation ;D

[@sachinpandeyatd]

tomarrow I have new sec and cryptography exam, and this topic has high possibility of coming, this is the best explanation I found,

[@sargondinkha8492]

Fantastic content!

[@sebastianb2092]

This guy is absolutely awesome. Thanks a lot.

[@josemiranda6123]

Awesome explanation!!!

[@hashansachintha546]

Finally I have understand it with this simple example. Big thanks.

[@tomasxfranco]

I love Mike.

[@videogamemusicandfunstuff4873]

Dr. Mike is the best!

[@suhailidrees5782]

Great explanation! Thanks!

[@sunburststratocaster]

That's just straight up brilliant. How does someone even come up with this?

[@anshuman_eek]

Just cos

[@kanskejonasidag1]

Mike Pound?? Instant like! :D

[@moazelsawaf2000]

This is a pure intelligence ❤️ Great explanation sir ❤️

[@mercerkace2023]

Amazing explanation.

[@willk7184]

Neat, I finally understand the basics of something I was always curious about. But now I'm thirsty.

[@shivampokhriyal2782]

Awesome explanation. 👌👌

[@kauhanen44]

Hey, this could be used in actual paper messages as well. Just use some cipher that needs a key like Vigenere.

[@tuannguyen927]

Splendid video

[@bbittera1425]

Great explanation!

[@Flqmmable]

For the part where you mix the colors and you say that its hard to know what colours were put together to make the final color, I kind of think of it as if the color were in hex color code format; by itself, you have the hex value but theres not may you could definately know what two colors were 'put' together to make it.

[@TheDuckofDoom.]

Idea for video, the old rs-232 type serial cables, and maybe follow with USB and 1394. And seporate from that maybe some server side vids like various SAN setups.

[@mohamedhesham6008]

That is very very clear explanation. thank youuu