TLS Handshake Explained - Computerphile

How does your computer arrange with a server to start talking in code? Dr Mike Pound explains the TLS handshake where the server and client organise everything.
/ 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

[@gram.]

I like the way this guy talks and explains things, duno what it is. He obviously really knows his stuff to be able to explain it so well and simplify it enough for me to understand!😊 Thanks

[@mo99]

Didn't study Computer Science but I really wish I had someone like Sir Dr Mike Pound at my university. Those folk at Nottingham are lucky

[@Hasi29347]

He seems like he enjoy what he is doing and that is reflected on his presentations.

[@markstevens7699]

Some days I spend 8 hours listening to the playlist of only him. He makes everything he says make sense, even if you don't get it the first timr

[@toast_on_toast1270]

To me it seems like he's explaining from a design perspective, that is "how the protocol addresses the problem", and has the knowledge to back it up. I think it's the correct level of abstraction to explain the problem clearly with only the important details.

[@larsrosenkilde7872]

He's got passion for computer science...

[@belledelphine4313]

I am in rabbit hole, he said in every video "that's what we talk about last time" so I am looking for last video and again and again and again... HELP :D

[@MrMarkgyuro]

if you search for numberphile cryptography you ll find the whole playlist in this topic

[@WilliamAndrea]

I believe these are all of them, chronologically. LMK if I missed any. Apr 18, 2014 | Heartbleed, Running the Code Jul 22, 2014 | Public Key Cryptography Oct 23, 2015 | Man in the Middle Attacks & Superfish Mar 22, 2016 | Secure Web Browsing Mar 30, 2017 | End to End Encryption (E2EE) Apr 11, 2017 | SHA: Secure Hashing Algorithm Dec 15, 2017 | Secret Key Exchange (Diffie-Hellman) Dec 29, 2017 | Key Exchange Problems Jan 16, 2018 | Elliptic Curves Aug 14, 2019 | Almost All Web Encryption Works Like This (SP Networks) Nov 20, 2019 | One Encryption Standard to Rule Them All! Nov 22, 2019 | AES Explained (Advanced Encryption Standard) Oct 23, 2020 | Transport Layer Security (TLS)

[@WujuStyler]

@@WilliamAndrea best comment ever, thanks

[@fanllawf]

@@WilliamAndrea Thank you so much. If a blank sheet of paper wants to learn this, would watching the series in release chronological order be appropriate?

[@WilliamAndrea]

@@fanllawf I guess so, yeah. You could probably skip the first one.

[@rafaelbianco252]

This video is pure gold. I work in the IT industry and it's hard to find a better explanation than this about TLS.

[@joseguillermo1790]

I agree. Insane domain of the topic.

[@slashingbison2503]

Yeah its excellent, its a guy who knows what he is talking about in a simple way to an IT tech who always gets overwhelmed by encryption

[@MathewCrane]

I would be interested in a separate video about TLS 1.3 versus 1.2, especially related to Encrypted SNI (ESNI) and how if affects transparent proxies and other security tools

[@maverickmaverick5]

@Dr Mike - same request.

[@yes-ni1od]

ESNI is being replaced with ECH, both still very young protocols

[@yasyasmarangoz3577]

I like how he screams at the start.

[@swine13]

I THOUGHT EVERYONE STARTed conversations that way?

[@yasyasmarangoz3577]

@@swine13 lol 😂

[@danieljaszczyszczykoeczews2616]

yeah such a sudden portion of british accent :D

[@yasyasmarangoz3577]

@@danieljaszczyszczykoeczews2616 Yup ^^

[@SkytraxX1]

Class clown are we? 🤡

[@jackc3727]

Nothing better than a Friday Pounding.

[@coldblaze100]

I-

[@WmSrite-pi8ck]

That sounds so homosexual. (Not that there's anything wrong with that.)

[@zaaap0]

giggity

[@jackc3727]

@@WmSrite-pi8ck What do you mean? Getting Pounded isn't sexual.

[@WmSrite-pi8ck]

@@jackc3727 Maybe not where you're from.

[@sghost128]

11:28 this is an underrated piece of editing right here.

[@rickelmonoggin]

It's very convenient that you created these videos just when I decided to start learning TLS. Very clear and easy to understand. Only bad thing is that the adverts come at rather annoying times.

[@romel304]

Thank you for explaining with context and really breaking it down. It’s the context and bit of history on how something came to being is what makes things interesting. Thousand kudos.

[@ramuthra1]

Cryptography is such a cool subject. Absolutely love it when Mike is on!

[@almightyhydra]

New record for advert: 2:15. Two of them, of course, after two at the start. 2030: videos are now entirely adverts, no content. 2040: content is back, but only videos containing nothing but adverts are accepted

[@Twisted_Code]

not even just product placement. It has to be full on "paid programming" level of advertisement. But wait, there's more! Comment today and we'll throw in this free sub to a channel you'll never watch again!

[@lawrencedoliveiro9104]

youtube-dl is still available.

[@vicentelouvet7160]

KZbin-dl

[@LayMyBurdenDown]

you just reinvented the "info-mercial" :)

[@ream88]

KZbin Premium

[@F1ghteR41]

I think this video can serve as a sort of hub or strarting point for many Dr. Pound's videos, both existing and upcoming. Basically it lists in one string a lot of topics he covered, which is quite convenient.

[@kristoffseisler2163]

I forgive the camera man for hollering in to the mic so that it distorted like that cause he got Mike Pound on

[@MelroyvandenBerg]

He really should wear a microphone

[@giosuecarducci5318]

This guy explaining is awesome and inspired me to do my thesis on ROCA attack. you rock

[@azizlol1907]

what a energetic man, wish had a teacher like him. I could learn from him till I die

[@hafidmrhailaf8084]

The best explanation, that someone could find on the Internet. Thank you Michael

[@wedusk]

Love the videos with Dr. Pound. Hope you guys make one on IPSec.

[@ashwanipundir535]

Wow ! I wish he was my teacher in college! I am glad that I found this channel. Thank you 🙏🏻

[@SuperAvenger96]

Hey Guys! It would be great to see you guys doing the promised difference between TLS1.2 and 1.3. I really like your videos! They are great to understand the basics of computer science and I like to watch videos related to the toppics i have in my master course. Greetings from Germany!

[@sreeramrm7997]

This video is pure fantastic.Hey after the handshake the client and server uses symmetric key encryption.

[@SamiCSc]

WOW! I love this channel and he explains everything well. Keep up the good work 🙏

[@marioh9926]

Very much thanks for your excellent explanation, Mike. I appreciate a lot your work.

[@yawarjamal909]

Dr. Pound + CS + Accent = Complete Package Thanks Computerphile as always

[@waynesrealworld5801]

Thank-you for these post they are helpful, informative, and just plain entertaining

[@bloodd11]

Thank you to share this knowledge. Dr Pound explain so clear this matters. Thank you for this channels and this videos. Greetings from Argentina.

[@TheRealLughnatic]

That was the most concise explanation of TLS 1.3 I have ever heard.

[@credence7777777]

it was for TLS 1.2

[@TheRealLughnatic]

@@credence7777777 He discusses TLS 1.3 towards the end of the video.

[@__mk_km__]

I dunno why but this video reminded me of something I read an article about long time ago - encrypted calculations. Essentially these allow you to perform various operations on ciphertext(like addition and multiplication) as if it was plaintext, but without actually knowing the values. The formal name for these is homomorphic encryption systems. It would be cool if you did a video on them

[@juliadow5400]

I love how he can talk about something boring with such enthusiasm. He makes it interesting.

[@jmontign1]

Amazingly useful details and explanations. Thank you.

[@vjself]

Your videos are absolutely fantastic.

[@damonhage7451]

Man I could have really used this when working on a project a year ago.

[@akshay-kumar-007]

Hey @Computerphile great video and I always come back here to refresh my memory about how TLS works. Can you also do an extension video of this with mTLS? Thanks

[@YannStoneman]

It would be awesome if you created a playlist of all these TLS-handshake related videos mentioned and linked to it in the description of this video.

[@Jesseeeeee]

I wanna hear Dr Mike say "My name is Pound, Mike Pound"

[@pjsixhundred]

Perfect candidate for a TV Tech Show which goes into more depth on how things work.

[@warlockpaladin2261]

I miss TechTV. 😭

[@klightspeed]

As an aside, 2:22 the example cipher suite just happens to be one of the ones that Windows 7 and Windows 8 do not support - it only supports those parameters if an ECDSA certificate is used - so 6:20 the server will respond with a failure message when using e.g. the Windows TLS libraries to communicate with such a server.

[@MAli-wu4rx]

Excellent instructor, excellent KZbin channel ! As a medical doctor I find this stuff amusing.

[@Shadowwand]

MQTT is a service that provides detailed connection session storage. Since the same device connecting to the server can use the same connection states, so it can immediate resume receiving topics with retained information.

[@maksymmryhlod3093]

Very simple and clear explanation.

[@timgeldof7720]

Thank you very much for your clear explanation! Interesting stuff!

[@anonymousvevo8697]

the only voice i like to hear, amazing explanations =)

[@shehyaazkhannayazi2726]

Thank you for this amazing video !! Could you please do a video on Certificate Transparency and IKP in the future ?

[@LincolnChamberlin]

This dude is one of my faves

[@miked2560]

Awesome video! What is the best way to see the full exchange--Wireshark?

[@Ruhigengeist]

I'd love to see a video on ACME considering it's largely replaced most of how servers set up trust now. I understand pretty solidly how it all works (I help maintain the Caddy project) but I'm sure it would help for more of the public to understand how this all works. i.e. how the ACME challenges replace the legacy method of paying for certificates, etc.

[@CubeApril]

Say hi to Matt for me. :)

[@mcnamaraky]

Thank you sirs. We all appreciate ya.

[@calistan5431]

Incredibly helpful for my Sec+ studies thank you!

[@danielgrace7887]

It sounds like you could use a different suite of ciphers in the future, and this system would be all that's ever needed for these communications.

[@gasparem16]

keep up the good work! awesome learning videos!

[@rashidxd]

Everyone: We can't do handshakes TCP: SYN

[@Twisted_Code]

ACK (dammit you beat me to it by 1 hour)

[@BenjaminCronce]

The internet is full of syn.

[@Acorn_Anomaly]

@@Twisted_Code You missed the SYN/ACK. :P

[@Twisted_Code]

@@Acorn_Anomaly dammit well what do I know. I have no practical experience with handshakes (yet). I only know how to reply at all because college courses LOL TBH, said inexperience is part of the reason I clicked this video... That and of course I was going to make the handshake joke if nobody had already

[@kebman]

ACK ACK ACK, said the Martian.

[@msscash729]

I love your channel, the content is just incredible. English subtitles are missing ... this needs to be easily accessible.

[@philivey4300]

I love there videos, please keep them coming

[@Flankymanga]

Excellent explanation Dr.Pound. :) i mean i thought i know TLS 1.3 but it seems i was wrong. I did not know about the Finish message.

[@Maxmekker42]

these videos are gold a couple weeks before exams

[@deepbluedrone]

Awesome 👏 Thanks for these videos

[@evang8259]

This helps me understand something in my job as tech support. Thanks!

[@rikschaaf]

Can you do a video on the single round-trip next?

[@psidianculpa5929]

This is the KZbin I we need to be watching.

[@clebfelm4170]

Great work

[@darraghfoley831]

Would you do a video on trying to detect tor over tlsv1.3 as the subject and issuer are now not known in the handshake. And to build on this in future iterations of tls1.3, if the server name is also not known.

[@honpaul2203]

Great, again and again! 👌

[@Ribby00]

Mike Pound for president. Mike Pound 2020.

[@kallikantzaros]

just when I needed it.

[@nkershaw]

I'm a fan. well explained. not rigid. and you guys come across as human. which is hard to do when teaching anything, especially computers.

[@randName]

2:27 would be the perfect place to add an info card to the Kindle Text Problem video

[@AterNyctos]

5:26 Basically my reaction everytime haha Great video!

[@freedomfeind]

Can you do a video on the mathematical algorithms used in encryption? Euler, Extended Euclidean, matrices, multiplicative inverses, etc. There are a lot of college students who are looking for these videos and there are not that many and the videos available are not very well explained. I'm sure you will gain a lot of traffic if you do this.

[@techwithmohitkr]

Pretty well explained

[@Twisted_Code]

anyone else notice that the clip from at 8:40 says "obi one" rather than Obi Wan? surely someone had at least noticed it and commented on the previous video, even if no one (besides me) noticed today.

[@ColinRichardson]

Will there be episode on TLS vs QUIC ? As these have solidified and filled in a few gaps I had about TLS.. I know nothing about QUIC except it's UDP..

[@Kivencito]

This is gold....

[@MidKnight_Reign]

Client and Server: [does handshake things] Client and Server: "We done? Here's a transcript of what we just said, encrypted. We'll talk again under this encryption kthxbye. [they both check what they sent against what they received. They don't match] Client and Server: "..." (uhh I'm just gonna NOPE RIGHT TF OUT OF THIS ONE!) Attacker: "Aw shucks."

[@YourMJK]

But it's still susceptible to MitM attacks that simply communicate with both in TLS, if you can't verify that the public key you get actually belongs to the party you thing you're speaking to. Which you can't for sure, unless you trust a CA or meet in person and compare keys.

[@benjamin11235]

You mentioned TLS 1.3, now you have to do a video about it!

[@TheTheThewillow]

Frodo explaining TLS, who would of knew. Thank you very informative

[@bobbyboygaming2157]

amazing videos

[@Elias-wz3sp]

The thumbnail is just a classic x)

[@chinmay9402]

like the vids by dr Mike. Please do a video on honeypot, seems like an interesting thing. Thanks :)

[@jlxip]

Great video! I do have a question that has been bothering me for a while, though. Why are both RSA and ECDH used? The server sends the certificate, couldn't the client just encrypt a randomly generated AES key with the server's RSA public key, send it, and skip Diffie-Hellman?

[@leogama3422]

RSA encryption is too slow for on-the-fly encryption (and in massive amounts for the server) like web traffic...

[@jlxip]

@@leogama3422 True, however: - Both the client and the server only have to use it once per connection. - They are already using it anyway since the server signs stuff, and as far as I know, encrypting and signing are equivalent operations in RSA. The server currently signs doing PKCS#1, powering to 'd'. The client checks the signature powering to 'e'. This is equivalent to encryption, but in reverse order, isn't it?

[@jlxip]

To anyone that might read this, I just got it. The handshake I proposed is called "RSA key-exchange". Its problem is that it does not offer forward secrecy, so all previous traffic, if recorded, could be decrypted if the server's RSA key is compromised. ECDHE prevents this: previous communications will never be decrypted, even though future ones could.

[@soulclean1983]

What does the last byte usually mean if it is repeated by a few instance but in no specific order?

[@martin1b]

Love the greenbar 'paper'

[@M1stersupersonic8]

Huh. The new TLS session after inactivity would definitely explain why tabs reload after I've been tabbed away from them for a while. Learn something new everyday!

[@silkwesir1444]

that should not explain it. there's something else going on which triggers the reload. otherwise you would just look at the page as you loaded it last.

[@heidiemiliaholappa]

Funny and educational stuff. Thanks!

[@IAMSolaara]

I'd love to see something on LVM, ZFS or btrfs from you

[@IboKnowsBest]

WTF I was just studying that thingy and boom! Couldn't timed better ^^

[@qzbnyv]

+1 to that. I was looking for videos on it about a month back and wasn’t happy with any of them really. Happy to have Dr. Mike Pounder showing us how it’s done

[@lakshminarasimmanv]

Google also tracks and read minds.

[@BlueyMcPhluey]

@@qzbnyv I could have really used this at the end of August when I was writing a paper on this 😂

[@qzbnyv]

@@lakshminarasimmanv Well, I know KZbin creators often make their videos based around general internet search terms frequency as a way of being timely and catching wind from trends. I haven’t looked into what the KZbin creator dashboard looks like these days, but I wonder if Google has an API that could easily display “People who watch Computerphile regularly have been searching for” stats.

[@ezekielgrave]

Would you do a video, or set of videos on ACME ( RFC 8555 )?

[@hundehausen]

Is see Dr Mike Pound, I hit like.

[@NeunEinser]

Finding a website that supports 1.3 was easy. I am on it right now.

[@TotalImmort7l]

KZbin use QUIC, not TLS.

[@NeunEinser]

@@TotalImmort7l It says TLS 1.3 on the padlock tho

[@TotalImmort7l]

@@NeunEinser which device are you using? On a phone, it shows QUIC.

[@NeunEinser]

@@TotalImmort7l Desktop, Win 10, Firefox

[@adedejiemmanuel1]

In what sequence will TCP handshake and TLS handshake happen? Which one happens first in a connection?

[@distrologic2925]

this is GOLD

[@alsorew]

Wash your TLS Hands after TLS Handshake with TLS Soap.

[@rusiraliyanage6643]

very imformative and very clear :)

[@bubblesgrappling736]

Which of these steps use the mac for authentification?

[@kramer3d]

so awesome that Jared from Silicon Valley is on the channel

[@SaiKrishnanSathiarthi]

🤣🤣🤣

[@petersonjr8015]

Thanks for your explanation of TLS. My question: Why do the client and server not just use the opposite public keys to encrypt and their private keys to decrypt all the communication. Why the need for more keys e.g session keys etc ?

[@lisasun8596]

They are using Elliptic-curve Diffie-Hellman when they use their public/private key pairs. ECDH is fairly fast, but session keys use even faster cryptography like AES. If the cryptography is faster, loading the website would also be faster.

[@gandelgerlant565]

Another problem with using it is that if someone takes over the private key, they can decipher all previous communication, but with Diffie Helmand a new key is generated each session

[@liuqingwang4408]

Perfect Forward Secrecy is the keyword here

[@maxinator80ify]

Asymmetric cryptography is great, but slow and demanding. One operation or RSA is much more complicated than one AES operation for example. Symmetric crypto is MUCH more efficient and also has some bonus features, like automatically included integrity checking. Therefore it makes sense to use public key crypto for exchanging a key, which is then used in symmetric crypto shenaningans. This way, we make use of the best of both worlds and get great security as well as great performance.

[@charleslondon9900]

I love your videos, your doodles could be better, but it is great to have a British expert on KZbin. I have one picky comment on this video , and that is that you have not mentioned "Transport Layer Security". I just wonder if sometimes just explaining the acronym might help some people. I am in IT security and I know we use abbreviations and in-terms like words, it's only natural, but I think saying the whole word might help us sometimes. Thank you for your great work on this channel, your a fantastic team.

[@AI7KTD]

13:55 two roundtrips (assuming you're 200ms away from a server) would be 800ms

[@WujuStyler]

I came to the comments looking for this hahah

[@bourbonwarrior1618]

Mike may have not described it clearly but network latency is measured by Round Trip Time. So his 400ms is correct.

[@drugndrop924]

I'be been waiting some wireshark capturing till the end

[@nicolaiveliki1409]

I did have to allow TLS1.2 explicitly on nodejs wss connection for Iphone because apparently it assumes that every browser in use can do 1.3 which is not the case for Iphones version 7 and lower

[@balamuralidhanushkodi7598]

In Key exchange part, server sends the hash function of previous messages in digital signature which signed using private key and you say client verifies it using public key how this is shared to client?

[@tepidrachet95]

Still waiting for the TLS 1.3 video!!