Name: Kerberosを弄る - コンピュータマニア (Taming Kerberos - Computerphile)
Uploaded: 2021-01-14T10:49:31.000Z
Duration: 16 min 6 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

過去形

All right, well, Steve did a great video on BP ends and how to have work remotely.

So I thought I'd talk also a little bit about networking or, you know, a cryptographic protocol, um, that we often use over networks.

In one of my previous videos, I talked about quantum computing and what kind of effect, if any, that would have on encryption.

And the answer, really is that it has quite a big effect on public key cryptography, but not that big an effect on on symmetric of geography.

You know, that's assuming we can build bigger quantum computers sometime.

Now, what I wanted to talk about today is a really cool protocol, but actually sees a lot of use particularly, I mean, everywhere, right on lots of different operating systems, but particularly on active directory is its main authentication mechanism.

Remember, curb off the three headed dog that guards ain't Haiti's, is it?

Curb loss is a really interesting protocol because away, off managing authentication and communication over a network like a giant enterprise level network.

But it does it without really requiring any kind of public key.

It'll eso it does it all with symmetric encryption.

So it is inherently very robust to any kind of quantum computer.

It's still maintained by a mighty, but obviously, in recent years, no barriers have appeared in things like Windows Active Directory.

I'm just gonna talk in general about her boss.

I'll try and draw attention to the differences between you know, the actor director of Asian.

But mostly it's naming differences, really, is what we're concerned with.

One of the issues, if we're going to use only symmetric encryption, is we have to work out how to share keys.

We can't do key exchange because that's public key.

We can't verify people using something like certificates, because that's our say, that's public key.

Well, one of the ways we can share Keith is using passwords so we could derive a key.

I could hash it in some known way, and then we could you could do the same thing.

If you were server but new my password or knew the hash on dhe, we could have a shared secret that way.

So okay, let's say we want to do this right.

Well, now let's think about the number of machines on a standard corporate network like maybe there's 2000 laptops on any given day kick to the network and 10,000 desktops on DDE 200 servers.

How many of these passwords are we using?

You were different passwords, different keys.

Let's imagine we have a network with 10 machines, so I'm just gonna draw 10 machines.

I can say five machines now if I wanna have a shared key.

But it's, let's say different for security reasons.

Between all of these machines, it's gonna look something like, I think that's all of them, right?

I mean, if I had another machine, a sick machine here, I've got to do this on 1/7 machine.

This is an absolute mess, but because we can't do key exchange so normally what you would do on the Internet is you would just talk to a machine to a quickie exchange, and then you've got yourself a session key for the rest of that conversation.

We can't do that because that's a public key protocol which is vulnerable to things like Quantum.

And also actually, at the time, I don't think if hell existed when this was first developed.

At least the protocols underpinning this so we're not gonna use public key is a solution.

We're gonna come up with something different.

What we're going to try and do is use the fact that we have this server, which I'm gonna draw Sort of nice and big here.

Server A big s on it, like the Superman, this server we all trust on because we will trust that server.

We can use that to give us temporary keys.

Let's imagine that these machines now have long term keys with this server.

So there's now 123457 keys There, seven permanent keys, Probably based off passwords.

Now let's imagine that this machine wants to talk to this machine.

What we do is we ask the server to send us a key that we can use for that conversation, and it just generates one at random on protects it using these encrypted channels on, then weaken temporarily use this green key for our session.

So the key exchange is now using this trusted third party.

So this is kind of what curb bosses about.

It has the benefit, but it doesn't rely on public key, but also there's an inherently, really elegant.

Waving it off indicates you because basically, you can't talk between these two machines and let's face it, giving you a key to do it, which is in some sense giving you permission to do it.

If it's too far, serve when you want access to far server.

It's only gonna work if you've got a key from here on dhe.

If it doesn't give you one because you're not allowed, good luck getting into the file server, right?

So it's quite a neat trick, but gets around just using symmetric and has this authentication built in that Kurt Boss is also a little bit more complicated than this.

So that's what we're gonna delve into now.

We're going to be on a fictitious network now, and this is me over here now.

You know, as you know, from my previous videos, I'm very good at drawing computers, and they always look realistic.

I'm gonna be a A for Alice saw, you know?

And here we have our authentication, our ticket granting service.

Boss, we're gonna have a big machine over here, and this is gonna have to servers in it or to Service is now in the original kerb lost.

This would be called a key distribution center or K.

Often this role is performed by something called a domain controller on active directory.

Now, in here we have two kinds of servers.

We have our authentication server, which I'm going to call s and our ticket granting server, which I'm going to call t on dhe.

Everything to do with authentication and connecting to, like an active directory or any other kind off herb or set up is going to be using these to service is so the authentication server is going to be responsible for checking your password essentially and making sure you actually do have an account on that directory or that network And the ticket granting service is going to be responsible for issuing tickets, which you can use to go on access things like file servers or printers or whatever else it is on the network.

The first thing to do is to approach the authentication server a shooting.

We've already had an account created and send him a message.

So we're gonna send him a message which says my name is a I would like to talk to the ticket granting server on here is a random number that I'm going to use to prevent replay attacks.

We're not gonna worry too much about them, which could've passing back and forth.

But the point is, I'm sending a message not really necessarily encrypted to this authentication server that I'm A and I'd like to talk to a ticket wanting server.

Now, the importing here is assuming that a has an account it has established key between A and S.

I have a key A s, which I can use to talk to about server for the long term because it's based on my past would maybe I only take them apart with every 12 months or whatever.

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Kerberosを弄る - コンピュータマニア (Taming Kerberos - Computerphile)

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