1 00:00:01,600 --> 00:00:11,220 It's now onto digital signatures now I did you tell signature is a hash value which is here which we 2 00:00:11,220 --> 00:00:12,380 just discussed. 3 00:00:12,390 --> 00:00:20,520 So it's the fixed lenth result of a hash function that is encrypted with the sender's private key to 4 00:00:20,520 --> 00:00:24,730 produce the digital signature or the signed message. 5 00:00:24,930 --> 00:00:32,010 So the digital signature is technically a stamp of approval for the sign. 6 00:00:32,010 --> 00:00:37,740 It is a provider of guarantee over whatever it is that's being signed. 7 00:00:37,830 --> 00:00:44,880 When something is digitally signed it provides authentication because it's been encrypted with the private 8 00:00:44,880 --> 00:00:49,690 key which only the person who has the private key can encrypt with. 9 00:00:49,710 --> 00:00:51,520 So that is the authentication. 10 00:00:51,570 --> 00:00:58,020 It provides non repudiation because again the sender's private key is used and it provides integrity 11 00:00:58,110 --> 00:01:03,900 because we are hashing a digital signature could be used for example with software. 12 00:01:03,990 --> 00:01:08,310 It could be used for drivers within your operating system. 13 00:01:08,400 --> 00:01:15,150 It could be used for certificates to validate that all of those things are genuinely from the person 14 00:01:15,150 --> 00:01:21,980 that they claim to be from and that the integrity of them has been maintained or there's been no changes. 15 00:01:21,990 --> 00:01:30,130 So if we go and have a look here at the chrome install file properties and you'll be able to do this 16 00:01:30,730 --> 00:01:33,220 in any operating system or the equivalent of. 17 00:01:33,400 --> 00:01:45,970 And we look here the digital signatures we click here you can see already some details me view the certificate. 18 00:01:46,270 --> 00:01:52,990 What we can see is this is an issue to Google by Verizon. 19 00:01:52,990 --> 00:02:01,240 So is there a sign the private key has been used to digitally sign this software code is saying this 20 00:02:01,240 --> 00:02:05,410 software is legitimate and it hasn't been changed. 21 00:02:05,470 --> 00:02:13,780 So as it says here in schul software came from software publisher pre-text software from alteration 22 00:02:13,840 --> 00:02:17,610 after publication to know this digital signature is valid. 23 00:02:17,830 --> 00:02:24,460 We have to reverse the original process so we have the digital signature here or the signed message 24 00:02:24,460 --> 00:02:25,940 or the sign software. 25 00:02:26,010 --> 00:02:28,200 We then use the sender's public key. 26 00:02:28,240 --> 00:02:35,800 In that case it would be there a sign to decrypt to reveal the hash which you can then verify yourself. 27 00:02:36,020 --> 00:02:37,680 You'll have a hash value for it. 28 00:02:37,690 --> 00:02:40,810 It will have been taken from the digital signature. 29 00:02:40,810 --> 00:02:46,960 You can then take the file many through the same hashing algorithm and you compare hashes and you can 30 00:02:46,960 --> 00:02:51,150 see that this software has maintained its integrity but when it comes to software. 31 00:02:51,160 --> 00:02:56,770 This is all happening behind the scenes and it's been verified without even knowing if verification 32 00:02:56,770 --> 00:02:57,890 doesn't happen. 33 00:02:57,970 --> 00:03:01,710 You get warning messages and you've seen these before. 34 00:03:02,080 --> 00:03:03,410 Here's an example of them. 35 00:03:03,430 --> 00:03:06,030 Windows cannot verify the publisher. 36 00:03:06,110 --> 00:03:12,220 This driver software that means that it either does not have a digital signature or you see how the 37 00:03:12,520 --> 00:03:19,410 code was the person that verified that digital signature that your operating system doesn't trust very 38 00:03:19,430 --> 00:03:26,630 code and will go in later as to why you might trust very code or not transfer code when we get to certificates. 39 00:03:26,710 --> 00:03:34,900 Windows 10 has introduced new technology called device code which is a way of using digital signatures 40 00:03:35,320 --> 00:03:40,360 to lock down what your operating system will and will not run. 41 00:03:40,360 --> 00:03:47,570 So device God will only allow certain types of signed files to be wrong. 42 00:03:47,590 --> 00:03:54,450 Theory being that then malware cannot be run or rats or trojans because they won't be signed. 43 00:03:54,530 --> 00:03:57,710 Or of course ways around this which we'll discuss later. 44 00:03:57,760 --> 00:04:01,420 That device God is another layer of defense. 45 00:04:01,450 --> 00:04:06,480 So let's get through this just one more time because I think it can be sometimes a little bit tricky. 46 00:04:06,520 --> 00:04:12,790 So a hash value that has been encrypted with the sender or issue is private key. 47 00:04:12,790 --> 00:04:14,870 That is a digital signature. 48 00:04:14,890 --> 00:04:18,870 It provides authentication no repudiation and integrity. 49 00:04:18,880 --> 00:04:26,590 And if you encrypt something and also provide a digital signature then you're also going to get confidentiality 50 00:04:26,680 --> 00:04:30,590 along with authentication repudiation and integrity. 51 00:04:30,610 --> 00:04:37,060 Digital signatures ensure that the software or whatever it is that you've got came from that person 52 00:04:37,060 --> 00:04:44,260 or that publisher and it protects that software or that message from alteration after it has been published 53 00:04:44,290 --> 00:04:45,090 or sent.