Placeholder Image

字幕列表 影片播放

  • 00:00:02,130 --> 00:00:05,420 Initialization vectors are a very common mechanism

  • used when dealing with encryption technologies.

  • Whenever you're sending information back and forth

  • between devices, whether it's over a wired network

  • or especially over a wireless network,

  • you want to make it as hard as possible for a bad guy who's

  • sneaking in and looking at that information

  • to be able to decipher that data that's going back and forth.

  • And if you're using the same key to encrypt this information

  • and send it across this network every time you're sending data,

  • you're making it very easy for the bad guy

  • to go through his algorithms rhythms

  • to decrypt that information.

  • And that's where initialization vectors come into play.

  • If you can change the key every time

  • and yet have the key exactly the same,

  • you make it very, very difficult for people

  • to be able to decrypt this.

  • So that's what the IV, the Initialization Vector, does.

  • It is added to the key to essentially

  • create a scrambled up or different key every time.

  • And it's done in a way that the station on the other end

  • is able to also know the initialization vector

  • and essentially undo what was done with that.

  • Makes it very, very easy to send information

  • over a network that's encrypted, but have it different

  • every time that data is sent.

  • Ideally, this now becomes very, very protected data.

  • But as we're about to find out, it

  • doesn't always work exactly the way we might have planned.

  • And if you're aware with 802.11 with WEP, encryption

  • even though it was using initialization vectors,

  • we created a bit of a problem.

  • It was not implemented in a way that

  • was protecting our data in the best possible form.

  • If you're trying to make sure that nobody's

  • able to get into this connection and see this encrypted data,

  • then you want to be sure you're using a mechanism that's

  • very, very strong.

  • Unfortunately, with 802.11, we found

  • that the cryptographic algorithms that

  • were used as they were associated

  • with these initialization vectors weren't strong enough.

  • There were a number of technological challenges

  • that really created this issue for us with 802.11 WEP.

  • One was that the federal government of the United States

  • said, you can't do heavy encryption

  • on these wireless networks.

  • We would not be able to look into that if you did.

  • And so it limited the key sizes you

  • would be able to use to encrypt this data.

  • The initial key sizes that you had were only 64 bits in size.

  • Later on, we got that increased to 128 bits, but at that point,

  • it became a little bit more of a problem.

  • We'll talk more about some of those issues in just a bit.

  • So what we ended up having was really a 40-bit key.

  • And because the initialization vector is also part of the key,

  • we had 24 bits that were set aside

  • for the initialization vector.

  • So that totaled 64 bits.

  • Let's look to see exactly how this process occurred.

  • What you would have whenever you're encrypting data

  • is you have some plain text.

  • You have what you would like to send to the other side.

  • And so we would take that data, and we also

  • created a cyclical redundancy check for that data-- a way

  • that we could check on the other side

  • that the data was not changed between point A and point B.

  • So those two things together are what

  • we would like to encrypt and send to the other station.

  • Now we also have this key that we're using to encrypt it with.

  • We have our WEP key here, and we have our initialization vector.

  • You can see these boxes are not to scale,

  • so don't think that the WEP key is

  • necessarily smaller than the IV.

  • But those two things are put together.

  • And a mechanism, a cypher, is used on those

  • to encrypt that data called RC4.

  • RC4 is also something you can use also

  • to decrypt the data very, very easily.

  • And we'll see why that's important in a moment.

  • But those two things combined together.

  • The RC4 created a key stream.

  • And the key stream and the combination

  • of the plain text and CRC put through x or mechanism the

  • finally creates the cypher text.

  • And on the other side, when we're ready to send it,

  • we take the initialization vector,

  • we connected to the cypher text, and we send it

  • across the network.

  • This is the mechanism that's used also on the other side.

  • It receives the IV in the cypher text

  • and knows what the IV is so they can then perform, or reverse,

  • the x or.

  • It gets a plain text in a key stream.

  • It reverses the RC4.

  • It knows what the initialization vector is, therefore

  • it knows what the WEP key is, and therefore it's

  • able now to decrypt what's going on.

  • This is also a challenge, of course,

  • because we're sending the initialization

  • vector in the clear.

  • And there are also some challenges now making

  • sure that this process of encrypting the data really

  • is strong as it really should be.

  • If you've ever worked with WEP or you

  • know how to implement this wireless encryption

  • on a wireless network, one of your first challenges

  • is that everybody has the same key.

  • There was no requirement in WEP that people's keys change

  • over time or that people could have different keys.

  • So everybody tends to have the same key.

  • That means if somebody leaves the organization,

  • they're taking the key with them.

  • So maybe you have to now change the key.

  • That now also means that you change the configuration

  • in every single person's wireless station.

  • And sometimes it's just not practical to be

  • able to do that.

  • Another problem we found-- this is

  • more in the details of the cryptography--

  • is that the initialization vector is only 24 bits long.

  • And in the big scheme of things, that's

  • a relatively small number.

  • That means that you only have just over 16,000,000

  • different possible iterations for an initialization

  • vector, which means it's very, very common once a lot of data

  • goes over the network, to see the same IV crop up again.

  • And if you can get two data streams

  • using the same initialization vector-- because I know what

  • that is, it's in the clear-- then I

  • can start comparing those two different pieces

  • of encrypted data to determine the key that

  • was used under the surface.

  • This is probably something that should have been avoided

  • to begin with, but because your key links were so small

  • there wasn't much of a choice there.

  • Another piece that was a challenge

  • is that there were certain initialization vectors that

  • would not properly encrypt the data.

  • It wasn't really giving you a very strong encryption.

  • So certain IVs were creating what

  • we call this weak type of initialization vector.

  • Later on, there were certain devices, certain access points,

  • and certain wireless cards that would not use those weak IVs.

  • But unfortunately, there were devices that absolutely was.

  • And if you could see some of those weak IVs coming

  • across the network, you could then

  • be able to discover what the key is, because things weren't

  • being encrypted very well.

  • The bad guys love this.

  • They thought, if I could then create a lot of initialization

  • vectors and really go through a lot of them,

  • I can create a lot of duplicates of those.

  • I'll churn through 16.7 million of those a couple of times,

  • and I'll start to see differences

  • in the encrypted data as it's coming through.

  • So they created software that would essentially just put

  • a ton of packets on the network so that they could

  • churn through all of those IVs and start

  • to get duplicates and start to examine the duplicates.

  • This made it very, very easy to find the key.

  • And if you see some of the modern types of software used

  • to do this, the WEP Crack software that you can download

  • for free on the internet, they're able in some cases

  • to identify the WEP key in just a few minutes.

  • And that's why whenever we talk about securing your wireless

  • network, one of the first things we always say is,

  • don't use WEP.

  • And that's why some of your new access points

  • don't even give you an option for WEP encryption,

  • because they know that there are so many attacks out there that

  • can very, very easily take advantage of these problems

  • within initialization vectors in the 802.11 WEP protocol.

00:00:02,130 --> 00:00:05,420 Initialization vectors are a very common mechanism

字幕與單字

影片操作 你可以在這邊進行「影片」的調整,以及「字幕」的顯示

A2 初級 美國腔

無線IV攻擊 - CompTIA Security+ SY0-401: 3.4 (Wireless IV Attacks - CompTIA Security+ SY0-401: 3.4)

  • 26 1
    Caurora 發佈於 2021 年 01 月 14 日
影片單字