WEBVTT 00:00.620 --> 00:07.430 Asymmetric encryptions are incredibly powerful tools things like Orris a are just absolutely amazing 00:07.430 --> 00:08.740 in terms of their power. 00:08.870 --> 00:16.050 However asymmetric encryption generally requires a lot of overhead with RSA. 00:16.160 --> 00:22.400 We have all kinds of other tools to provide authentication and we cover this in other episodes. 00:22.400 --> 00:27.650 What it boils down to is that there's a lot of situations where you don't need a lot of authentication 00:27.650 --> 00:34.100 or anything like that you just want to exchange a session key so you can kick a symmetric encryption 00:34.190 --> 00:35.230 into gear. 00:35.570 --> 00:43.670 And that's where something called Diffie Helman comes into play Diffie Helman is an asymmetric algorithm. 00:43.670 --> 00:45.880 That's the first thing you need to understand. 00:46.310 --> 00:52.070 But the only thing Diffie Hellman does is it doesn't really provide encryption per se it only provides 00:52.070 --> 00:57.260 a methodology for two parties to come up with the same session key. 00:57.260 --> 00:58.920 It's absolutely fascinating. 00:59.000 --> 01:03.890 Diffie Helman is an incredibly powerful tool but you got to be careful. 01:03.890 --> 01:11.480 It does use an asymmetric methodology but it doesn't have a classic public private pre-generated key 01:11.480 --> 01:13.430 that you'd see with like RSA. 01:13.490 --> 01:19.640 This is all kind of done on the fly using some fascinating integer mathematics in fact the mathematics 01:19.640 --> 01:22.990 is so fascinating that it actually started to put me to sleep. 01:23.030 --> 01:29.990 And unless you're really into discrete logarithms and modulo arithmetic you may not want to go through 01:29.990 --> 01:30.650 all the details. 01:30.650 --> 01:36.770 The beautiful part is is that when it comes to Diffie Hellman there's a wonderful analogy using your 01:36.770 --> 01:44.620 Edhi color Alice and Bob want to send encrypted data to each other using some form of symmetric encryption. 01:44.740 --> 01:47.350 So to do this they need the same key. 01:47.350 --> 01:53.130 But the problem here is that we have Ebe a potential third party listening in and we don't want either 01:53.230 --> 01:56.680 to be able to determine what our symmetric key is going to be. 01:56.860 --> 02:02.980 So somehow we've got to come up with a magic way that both Bob and Alice can have the same symmetric 02:02.980 --> 02:08.940 key without that key actually ever being moved across the wire so that IID could see it. 02:09.130 --> 02:16.840 Now to do this we're going to use Diffie Hellman Diffie Helman is a key agreement protocol Sometimes 02:16.840 --> 02:23.770 it's called a key exchange protocol and the whole goal of Diffie Helman is to take advantage of what 02:23.770 --> 02:25.240 we called modular arithmetic. 02:25.250 --> 02:28.520 So here's an example of modulo arithmetic. 02:28.750 --> 02:34.960 This particular formula it's really really hard to figure out what three you'll see three to this question 02:34.960 --> 02:36.010 mark power there. 02:36.190 --> 02:42.010 Given this type of value it's very hard to figure out what we call the discrete logarithm of this particular 02:42.010 --> 02:43.570 type of equation now. 02:43.870 --> 02:50.620 So without going into any more detail than that well it makes it a lot more sense if instead of using 02:50.680 --> 03:01.480 numbers like this let's pretend that we want both Alice and Bob to have a unique color. 03:01.690 --> 03:10.730 So to do this we actually do use asymmetric encryption here in that first of all either Bob or Alice. 03:10.750 --> 03:13.350 Define a particular public key. 03:13.360 --> 03:15.590 Now this public key is a big long number. 03:15.670 --> 03:18.850 But in this case let's just make it the color yellow because it's a little bit easier. 03:18.850 --> 03:21.260 This is a unique color. 03:21.250 --> 03:29.410 Now what we're going to do here is just as if we mix two different colors together to get a unique color 03:30.220 --> 03:33.230 it is very easy to mix these two colors together. 03:33.400 --> 03:40.180 But it's extremely difficult to get the exact to original colors out of that just by mixing them. 03:40.240 --> 03:42.790 It's there's a million different potential colors. 03:42.850 --> 03:44.510 So with that I did mind. 03:44.560 --> 03:46.810 Let's go through a Diffee home in exchange. 03:46.930 --> 03:47.470 OK. 03:47.510 --> 03:53.100 So right now Allison Bob each have a public key and we're going to call this public key. 03:53.140 --> 03:55.710 That will be the color yellow in this particular case. 03:55.720 --> 03:58.290 Now Yves could see this public key too and you know what. 03:58.330 --> 03:59.860 We don't care. 03:59.860 --> 04:02.760 Now both Alice and Bob on their own. 04:02.860 --> 04:06.600 Generate a random private value in this case. 04:06.640 --> 04:10.680 We're going to say Alice is the color red and Bob is the color blue. 04:11.110 --> 04:15.140 So what they're going to do is using this groovy mathematics. 04:15.250 --> 04:20.420 In essence they're going to mix these colors together creating this third color. 04:20.420 --> 04:25.420 Now Yves could see these colors but it's not going to do her any good because she doesn't know the private 04:25.420 --> 04:27.520 color by which they derive that value. 04:27.520 --> 04:34.190 So she she can't do anything with that so they go ahead and Alice and Bob exchange this mix. 04:34.350 --> 04:36.010 And now here's the cool part. 04:36.060 --> 04:41.960 Allison Bob then add their own private colors to this mix. 04:42.770 --> 04:46.820 And it creates the exact same value. 04:47.000 --> 04:53.930 So this funny looking kind of brownish color is actually a unique number and this is the number that 04:53.930 --> 04:58.600 we can go ahead and do symmetric encryption with an e. 04:58.640 --> 05:04.060 We'll never know what that number is Diffie Hellmann's been around for a long time. 05:04.090 --> 05:10.780 And one of the challenges we run into with the Hellman is that because it uses big Energizers as the 05:10.780 --> 05:17.380 initial seed to generate the key exchange some of these have shown themselves to be potentially crackable. 05:17.560 --> 05:24.610 So what we do over the years is that the Diffie Helman people generate what we call the Hellmann groups. 05:24.820 --> 05:28.750 So here's an example of some of these Diffie Hellman groups and you'll see that they have a numerical 05:28.750 --> 05:30.630 value associated with them. 05:30.640 --> 05:36.940 These numbers are simply used by the allicin Bobs who want to do DIFI home and to negotiate how big 05:36.940 --> 05:38.770 of a number that they might want to use. 05:38.770 --> 05:42.630 Now if you look at the bottom of this list you'll see it says elliptical curve. 05:42.640 --> 05:44.290 Let me explain what that is. 05:45.700 --> 05:52.660 Diffie Hellman because it uses large integers is subject potentially to cracking. 05:52.660 --> 06:00.040 So just as we've seen with other types of asymmetric encryption the idea of using elliptic curve has 06:00.040 --> 06:01.820 become very very popular. 06:01.870 --> 06:09.040 So there are now ways to use elliptic curve Diffie Hellman in order to do the key exchange. 06:09.040 --> 06:11.780 The nice part for us is we don't have to worry about that. 06:11.890 --> 06:17.680 We just generate applications where that Alice and bobs that are doing to the Hellmann can negotiate 06:17.710 --> 06:21.550 and they can ask for whatever group they want including elliptic curve 06:31.000 --> 06:35.130 and.