1 1 00:00:00,480 --> 00:00:02,640 Email message security. 2 2 00:00:02,640 --> 00:00:04,440 Earlier we talked about MIME, 3 3 00:00:04,440 --> 00:00:06,330 but there's another extension that we can use 4 4 00:00:06,330 --> 00:00:07,980 known as S/MIME. 5 5 00:00:07,980 --> 00:00:11,790 S/MIME is the Secure/Multipurpose Internet Mail Extensions. 6 6 00:00:11,790 --> 00:00:12,690 And this is the ability 7 7 00:00:12,690 --> 00:00:14,760 for an email to have an encryption standard 8 8 00:00:14,760 --> 00:00:17,610 that adds digital signatures and public key cryptography 9 9 00:00:17,610 --> 00:00:19,980 to traditional MIME communications. 10 10 00:00:19,980 --> 00:00:21,090 Now for this to work, 11 11 00:00:21,090 --> 00:00:23,820 every user has to be issued a digital certificate 12 12 00:00:23,820 --> 00:00:25,740 containing his or her public key 13 13 00:00:25,740 --> 00:00:27,810 in order for them to use S/MIME. 14 14 00:00:27,810 --> 00:00:29,460 Now in addition to that public key, 15 15 00:00:29,460 --> 00:00:31,860 there's going to be a matching private key. 16 16 00:00:31,860 --> 00:00:35,250 Now, this private key has to be kept secret by the user. 17 17 00:00:35,250 --> 00:00:37,080 Nobody else in the world can ever know 18 18 00:00:37,080 --> 00:00:38,610 what their private key has, 19 19 00:00:38,610 --> 00:00:41,010 but that public key is one they should have 20 20 00:00:41,010 --> 00:00:42,930 and share with everybody else. 21 21 00:00:42,930 --> 00:00:44,820 Let's talk about how this works. 22 22 00:00:44,820 --> 00:00:47,970 Let's assume I want to send Mary some information. 23 23 00:00:47,970 --> 00:00:49,920 Well, if I wanted to do that using S/MIME, 24 24 00:00:49,920 --> 00:00:52,950 first, I would have to send Mary my digital certificate. 25 25 00:00:52,950 --> 00:00:56,550 That contains my public key and it validates my digital ID, 26 26 00:00:56,550 --> 00:00:59,040 my distinguished subject name and email address, 27 27 00:00:59,040 --> 00:01:02,850 and then I'm going to sign this message using my private key. 28 28 00:01:02,850 --> 00:01:05,400 After that, Mary is going to use the public key 29 29 00:01:05,400 --> 00:01:08,070 in the certificate to decode my signature 30 30 00:01:08,070 --> 00:01:10,170 and the signature of the CA, 31 31 00:01:10,170 --> 00:01:11,760 which is the authority who signs 32 32 00:01:11,760 --> 00:01:13,470 those public and private keys. 33 33 00:01:13,470 --> 00:01:15,930 And this is going to validate my digital certificate 34 34 00:01:15,930 --> 00:01:17,070 and the digital ID, 35 35 00:01:17,070 --> 00:01:20,190 and then she can decide if she's going to trust me or not. 36 36 00:01:20,190 --> 00:01:21,960 And in this case, she would because she saw 37 37 00:01:21,960 --> 00:01:24,390 that it was validated using the CA. 38 38 00:01:24,390 --> 00:01:25,980 Then we go into the third step, 39 39 00:01:25,980 --> 00:01:28,620 and Mary is going to respond with her digital certificate, 40 40 00:01:28,620 --> 00:01:30,120 which has her public key, 41 41 00:01:30,120 --> 00:01:33,000 and I am going to be able to follow the same process, 42 42 00:01:33,000 --> 00:01:35,460 and I'll be able to start deciding to trust Mary. 43 43 00:01:35,460 --> 00:01:36,480 So at this point, 44 44 00:01:36,480 --> 00:01:39,240 both Mary and I have each other's public key. 45 45 00:01:39,240 --> 00:01:42,390 Now, both Mary and I have each other's certificates 46 46 00:01:42,390 --> 00:01:44,310 in our trusted certificate stores, 47 47 00:01:44,310 --> 00:01:46,800 and this means we both have each other's public keys 48 48 00:01:46,800 --> 00:01:48,030 or a copy of them, 49 49 00:01:48,030 --> 00:01:50,790 so now we can start sending information securely. 50 50 00:01:50,790 --> 00:01:52,770 Let me show you how that's going to work. 51 51 00:01:52,770 --> 00:01:55,050 So now both Mary and I have 52 52 00:01:55,050 --> 00:01:56,940 each other's public key certificates 53 53 00:01:56,940 --> 00:01:59,400 inside of our trusted certificate stores. 54 54 00:01:59,400 --> 00:02:00,300 So at this point, 55 55 00:02:00,300 --> 00:02:03,240 if we start encrypting data with our private keys, 56 56 00:02:03,240 --> 00:02:06,330 the other one can decrypt it using our public keys 57 57 00:02:06,330 --> 00:02:08,250 because we've already done this trade. 58 58 00:02:08,250 --> 00:02:09,630 Let's take a look at how this looks 59 59 00:02:09,630 --> 00:02:11,970 when I want to send an email securely. 60 60 00:02:11,970 --> 00:02:14,250 Now, there's two different ways I can talk about security 61 61 00:02:14,250 --> 00:02:15,480 when I'm sending an email. 62 62 00:02:15,480 --> 00:02:17,880 One is integrity and non-repudiation 63 63 00:02:17,880 --> 00:02:19,770 and the other is confidentiality. 64 64 00:02:19,770 --> 00:02:21,660 Let's take them one at a time. 65 65 00:02:21,660 --> 00:02:24,840 First, we're going to talk about integrity and non-repudiation. 66 66 00:02:24,840 --> 00:02:27,180 Let's say I wanted to send a message to Mary, 67 67 00:02:27,180 --> 00:02:28,530 but Mary wants to make sure 68 68 00:02:28,530 --> 00:02:31,530 that only Jason could have sent this information. 69 69 00:02:31,530 --> 00:02:33,480 Well, to make sure that happens, 70 70 00:02:33,480 --> 00:02:36,300 what we are going to do is I'm going to take my message, 71 71 00:02:36,300 --> 00:02:38,820 and I am going to do a digital hash of it. 72 72 00:02:38,820 --> 00:02:40,080 I'm going to take that hash, 73 73 00:02:40,080 --> 00:02:42,570 and I'm going to encrypt it using my private key. 74 74 00:02:42,570 --> 00:02:44,190 And then I have this plaintext message 75 75 00:02:44,190 --> 00:02:46,560 and this encrypted ciphertext hash, 76 76 00:02:46,560 --> 00:02:49,080 and I send them both over to Mary. 77 77 00:02:49,080 --> 00:02:51,360 When Mary gets it, she's going to use that public key 78 78 00:02:51,360 --> 00:02:53,700 that she just got from me in our earlier exchange 79 79 00:02:53,700 --> 00:02:57,000 from her trusted key store to unlock my private key. 80 80 00:02:57,000 --> 00:02:59,040 Because remember, if you encrypt with private, 81 81 00:02:59,040 --> 00:03:00,750 you have to decrypt with public. 82 82 00:03:00,750 --> 00:03:03,150 You learned this back in your Security+ classes. 83 83 00:03:03,150 --> 00:03:06,120 At this point, we now have a plaintext of the message, 84 84 00:03:06,120 --> 00:03:07,590 which has always been plaintext, 85 85 00:03:07,590 --> 00:03:10,320 and we now have a plaintext of the hash. 86 86 00:03:10,320 --> 00:03:12,060 Mary's computer is going to run a hash 87 87 00:03:12,060 --> 00:03:14,160 against the message itself. 88 88 00:03:14,160 --> 00:03:17,070 She's then going to compare that hash to the one I sent. 89 89 00:03:17,070 --> 00:03:19,890 If those two match, that means this message 90 90 00:03:19,890 --> 00:03:23,250 has not changed during transit, and we have integrity 91 91 00:03:23,250 --> 00:03:25,410 because the hash that I sent her 92 92 00:03:25,410 --> 00:03:28,860 matches the hash that she calculated based on that message. 93 93 00:03:28,860 --> 00:03:31,140 Now, how do we get non-repudiation? 94 94 00:03:31,140 --> 00:03:34,320 Well, what did I use to sign that hash? 95 95 00:03:34,320 --> 00:03:35,940 I used my private key. 96 96 00:03:35,940 --> 00:03:37,440 Who is the only person in the world 97 97 00:03:37,440 --> 00:03:39,030 who has that private key? 98 98 00:03:39,030 --> 00:03:41,730 Me, and therefore, you have non-repudiation 99 99 00:03:41,730 --> 00:03:44,010 because only Jason could have sent this message. 100 100 00:03:44,010 --> 00:03:47,070 Because Jason, me, used his private key 101 101 00:03:47,070 --> 00:03:48,450 to encrypt that hash. 102 102 00:03:48,450 --> 00:03:50,580 That's why using a digital signature, 103 103 00:03:50,580 --> 00:03:53,910 which is an encrypted hash of the digital message 104 104 00:03:53,910 --> 00:03:55,890 and being sent over to the other person, 105 105 00:03:55,890 --> 00:03:58,710 gives you integrity and non-repudiation. 106 106 00:03:58,710 --> 00:04:00,150 But that doesn't stop anyone 107 107 00:04:00,150 --> 00:04:01,530 from actually reading this message, 108 108 00:04:01,530 --> 00:04:03,060 so there's no confidentiality 109 109 00:04:03,060 --> 00:04:06,840 because that email I sent was unencrypted or decrypted 110 110 00:04:06,840 --> 00:04:09,330 the entire time and sent in plaintext. 111 111 00:04:09,330 --> 00:04:12,600 So we need to do something else to give you confidentiality. 112 112 00:04:12,600 --> 00:04:14,970 And that brings us to our second part of this. 113 113 00:04:14,970 --> 00:04:16,740 When we're dealing with confidentiality, 114 114 00:04:16,740 --> 00:04:19,020 let's say I want to send that same message, 115 115 00:04:19,020 --> 00:04:20,580 I'm going to do both of these at the same time, 116 116 00:04:20,580 --> 00:04:22,530 but we're taking the confidentiality part. 117 117 00:04:22,530 --> 00:04:25,410 Now, I'm going to use Mary's public key. 118 118 00:04:25,410 --> 00:04:28,470 I'm going to take my message at the top, my email, 119 119 00:04:28,470 --> 00:04:29,730 and I'm going to encrypt it. 120 120 00:04:29,730 --> 00:04:31,470 Now, I take that encrypted email 121 121 00:04:31,470 --> 00:04:33,150 that's encrypted with Mary's public key, 122 122 00:04:33,150 --> 00:04:35,640 which means even I can't read it at this point, 123 123 00:04:35,640 --> 00:04:37,410 and I'm going to send it over to Mary. 124 124 00:04:37,410 --> 00:04:38,310 When she gets it, 125 125 00:04:38,310 --> 00:04:41,130 she's going to unlock that using her private key. 126 126 00:04:41,130 --> 00:04:43,170 Now, the great thing about this is the only person 127 127 00:04:43,170 --> 00:04:46,200 in the whole world who has that private key is Mary, 128 128 00:04:46,200 --> 00:04:49,170 so she's going to be the one who's able to read that message. 129 129 00:04:49,170 --> 00:04:51,210 Even if they could grab it in transmission, 130 130 00:04:51,210 --> 00:04:53,670 it's going to be encrypted and they won't be able to read it. 131 131 00:04:53,670 --> 00:04:56,220 Now, could they read some part of this message? 132 132 00:04:56,220 --> 00:04:58,470 Yes, they could read the digital hash 133 133 00:04:58,470 --> 00:04:59,910 that I digitally signed. 134 134 00:04:59,910 --> 00:05:00,743 Why? 135 135 00:05:00,743 --> 00:05:02,610 Because I encrypted it with my private key, 136 136 00:05:02,610 --> 00:05:04,470 going back to our last section here. 137 137 00:05:04,470 --> 00:05:06,360 And when I encrypted something with my private key, 138 138 00:05:06,360 --> 00:05:09,270 like that digital hash, anyone in the world can read it. 139 139 00:05:09,270 --> 00:05:11,790 But they can't read the message associated, 140 140 00:05:11,790 --> 00:05:13,410 only the hash value. 141 141 00:05:13,410 --> 00:05:15,120 And that's why we put these two things together 142 142 00:05:15,120 --> 00:05:18,750 by using the integrity and non-repudiation of the hash 143 143 00:05:18,750 --> 00:05:21,990 with the confidentiality of using Mary's public key 144 144 00:05:21,990 --> 00:05:23,160 for the message. 145 145 00:05:23,160 --> 00:05:24,750 By using both of these together, 146 146 00:05:24,750 --> 00:05:26,700 this is going to give you the digital signature of the email 147 147 00:05:26,700 --> 00:05:28,380 for encryption and non-repudiation 148 148 00:05:28,380 --> 00:05:30,450 and the digital encryption of the message 149 149 00:05:30,450 --> 00:05:31,890 using Mary's public key. 150 150 00:05:31,890 --> 00:05:34,860 Now, the email client is going to be able to determine for you 151 151 00:05:34,860 --> 00:05:37,050 if your digital signature is valid, 152 152 00:05:37,050 --> 00:05:39,600 and it will display an icon for you when it does that. 153 153 00:05:39,600 --> 00:05:40,980 As I said in my explanation, 154 154 00:05:40,980 --> 00:05:43,230 when Mary got that first message from me, 155 155 00:05:43,230 --> 00:05:46,590 her machine takes that message, it runs it through the hash, 156 156 00:05:46,590 --> 00:05:48,450 and compares it against the hash that I sent, 157 157 00:05:48,450 --> 00:05:49,800 digitally signed. 158 158 00:05:49,800 --> 00:05:51,930 When it does that, if they match, 159 159 00:05:51,930 --> 00:05:53,940 you're going to see something that looks like this. 160 160 00:05:53,940 --> 00:05:54,773 In this case, 161 161 00:05:54,773 --> 00:05:57,480 you could see it says "Signed by" the person who signed it 162 162 00:05:57,480 --> 00:05:59,820 and it has that little ribbon off to the right side. 163 163 00:05:59,820 --> 00:06:01,920 This means that was a valid signature 164 164 00:06:01,920 --> 00:06:03,360 and everything was good. 165 165 00:06:03,360 --> 00:06:06,210 Now, if Mary's machine went through and checked that 166 166 00:06:06,210 --> 00:06:07,890 and it didn't have a hash that matched 167 167 00:06:07,890 --> 00:06:08,940 the one that was sent, 168 168 00:06:08,940 --> 00:06:10,890 then she's going to see something like this. 169 169 00:06:10,890 --> 00:06:12,840 It's going to be an email with a red X. 170 170 00:06:12,840 --> 00:06:15,210 This is going to tell you that that message was not sent 171 171 00:06:15,210 --> 00:06:16,830 with a digital certificate. 172 172 00:06:16,830 --> 00:06:18,090 And that's the difference here. 173 173 00:06:18,090 --> 00:06:20,370 When you see that little ribbon, you know that that message 174 174 00:06:20,370 --> 00:06:22,170 was digitally signed by that person. 175 175 00:06:22,170 --> 00:06:25,103 When you see something looks like this, it means you don't.