1
00:00:00,150 --> 00:00:02,670
The Fidelman comes in different forms.

2
00:00:03,300 --> 00:00:06,689
Duffy Holman One is 768 bits in length.

3
00:00:07,200 --> 00:00:10,470
Duffy Holman two is 1024 bits in length.

4
00:00:10,920 --> 00:00:14,730
Duffy Holman five is 1536 bits in length.

5
00:00:15,180 --> 00:00:19,200
Once again, the longer the key length, the more secure.

6
00:00:19,770 --> 00:00:23,850
But the downside is more processing power would be required.

7
00:00:24,770 --> 00:00:32,450
Now, just to reiterate, asymmetric key algorithms are used in VPNs today, not for bulk encryption

8
00:00:32,450 --> 00:00:36,770
of data, but they help with the establishment of a shared secret.

9
00:00:37,340 --> 00:00:42,380
Are also used for other things like authentication, which I'm going to talk about in a moment.

10
00:00:42,890 --> 00:00:49,070
Symmetric key algorithms such as these are used for bulk encryption of data.

11
00:00:49,790 --> 00:00:52,550
So we've covered confidentiality or encryption.

12
00:00:52,760 --> 00:00:56,150
Let's look at the second goal, which is integrity.

13
00:00:56,510 --> 00:00:59,510
We want to ensure that data has not been tampered with.

14
00:00:59,870 --> 00:01:05,480
In other words, we want to know that the data has traversed the Internet or other network unchanged

15
00:01:05,480 --> 00:01:06,890
between the two parties.

16
00:01:07,580 --> 00:01:14,630
Data Integrity uses algorithms known as hashing algorithms, also known as trapdoor or message digests.

17
00:01:15,290 --> 00:01:20,420
These are one way algorithms, unlike encryption algorithms, which can be reversed.

18
00:01:21,360 --> 00:01:26,430
Hashing algorithms convert arbitrary data into a fixed length hash.

19
00:01:27,060 --> 00:01:35,430
An example would be MD5 or Message Digest Algorithm five, which has a fixed length of 128 bits.

20
00:01:36,870 --> 00:01:38,280
Now to demonstrate hedging.

21
00:01:38,880 --> 00:01:41,820
Notice I can take a piece of arbitrary information.

22
00:01:41,820 --> 00:01:42,900
Let's say my name.

23
00:01:43,580 --> 00:01:45,050
And I can hash it.

24
00:01:45,680 --> 00:01:47,540
In this case using Sha.

25
00:01:49,150 --> 00:01:51,500
Shore or secure.

26
00:01:51,520 --> 00:01:54,670
Hash algorithm is more secure than MD5.

27
00:01:55,180 --> 00:02:01,390
This is the hexadecimal value or sha and the binary value for sha.

28
00:02:02,210 --> 00:02:09,410
Notice if I change one value, for instance, making that David one and hash it again, notice the entire

29
00:02:09,410 --> 00:02:10,639
hash changes.

30
00:02:11,030 --> 00:02:13,010
But notice it's of a fixed length.

31
00:02:14,480 --> 00:02:17,300
I could put a bunch of people's names in there.

32
00:02:25,600 --> 00:02:26,770
And hash it again.

33
00:02:27,520 --> 00:02:30,970
Notice the entire hash changes but is of a fixed length.

34
00:02:31,830 --> 00:02:33,660
I could go and copy some text.

35
00:02:35,370 --> 00:02:37,260
From, let's say, USA Today.

36
00:02:41,720 --> 00:02:42,730
Arbitrary length.

37
00:02:46,020 --> 00:02:46,950
Pasted it in.

38
00:02:50,710 --> 00:02:50,890
Tree.

39
00:02:51,280 --> 00:02:53,830
I could take the Encyclopedia Britannica.

40
00:02:54,950 --> 00:02:58,910
Put it through an MD5 hash and come up with 128 bits.

41
00:03:01,150 --> 00:03:08,920
So for example, I could take that us today article, put it into an MD5 hash generator and notice it

42
00:03:08,920 --> 00:03:11,740
will come up with 128 bit hash value.

43
00:03:12,400 --> 00:03:16,330
Or I could replace that with let's just say my name.

44
00:03:18,380 --> 00:03:21,230
And will come up with 128 bit hash value.

45
00:03:22,990 --> 00:03:26,950
Hashing is not reversible because data is lost.

46
00:03:27,220 --> 00:03:35,010
You cannot take 128 bit MD5 hash, reverse it and come up with the Encyclopedia Britannica.

47
00:03:35,020 --> 00:03:41,020
But you can take the Encyclopedia Britannica, hash it and come up with 128 bit value.

48
00:03:41,710 --> 00:03:47,770
Please note that the hash will change, as I've demonstrated if any part of the input value changes.

49
00:03:48,550 --> 00:03:52,090
So with hashing we can take data of arbitrary length.

50
00:03:52,940 --> 00:03:55,430
Put it through an MD5 or sha hash.

51
00:03:55,730 --> 00:04:01,850
In this case it's md5 and come up with a fixed 128 bit hash value.

52
00:04:02,450 --> 00:04:09,380
You cannot take the 128 bit hash value and reverse the process and come up with the original data.

53
00:04:10,200 --> 00:04:14,400
It is a one way function or trapdoor function.

54
00:04:16,279 --> 00:04:18,769
There are various hashing algorithms that can be used.

55
00:04:18,769 --> 00:04:21,350
MD5 once again is 128 bits.

56
00:04:21,920 --> 00:04:25,790
MD5 is not recommended today in networking environments.

57
00:04:26,480 --> 00:04:28,790
SHA one is 160 bits and length.

58
00:04:28,970 --> 00:04:32,450
SHA two is 256 or 512 bits in length.

59
00:04:33,050 --> 00:04:36,890
And SHA three is scheduled for release in 2012.

60
00:04:37,340 --> 00:04:40,880
Just be aware that there are various hashing algorithms once again.

61
00:04:41,030 --> 00:04:44,870
SHA two is what's recommended in today's networking environments.

62
00:04:46,220 --> 00:04:56,090
So as an example, if Peter wanted to send data to Sarah ensuring confidentiality and integrity, the

63
00:04:56,090 --> 00:04:57,320
following would happen.

64
00:04:58,910 --> 00:05:06,380
Is private information that no one else except Sarah should read is encrypted, firstly, with an encryption

65
00:05:06,380 --> 00:05:08,120
algorithm like these.

66
00:05:08,630 --> 00:05:14,000
Now, in this case, we're assuming that a shared secret or shared key has been derived.

67
00:05:14,270 --> 00:05:21,260
So assuming that that's happened, Peter can encrypt the data using a symmetric key algorithm like Amy's.

68
00:05:21,680 --> 00:05:25,910
So the clear text information is encrypted into ciphertext.

69
00:05:26,150 --> 00:05:28,400
This provides confidentiality.

70
00:05:29,540 --> 00:05:38,840
Peter then takes the encrypted text or ciphertext and hashes it with a hashing algorithm like SHA or

71
00:05:38,840 --> 00:05:43,370
MD5, which comes up with a fixed length hash.

72
00:05:44,200 --> 00:05:51,880
This will ensure data integrity because if any part of the data is changed, remember the hash will

73
00:05:51,880 --> 00:05:52,930
also change.

74
00:05:54,240 --> 00:06:01,500
So Peter takes the clear text encrypted with an algorithm like ease to come up with ciphertext.

75
00:06:02,010 --> 00:06:06,180
He hashes that encrypted text and comes up with a hash.

76
00:06:06,870 --> 00:06:14,670
He then append the hash to the encrypted ciphertext and sends it to Sarah.

77
00:06:15,630 --> 00:06:22,050
Sarah upon receipt of the data in this case, the encrypted ciphertext wants to make sure that the data

78
00:06:22,050 --> 00:06:27,480
hasn't been tampered with before, going through all the effort of decrypting the text.

79
00:06:27,780 --> 00:06:35,640
So Sarah will take the encrypted text and hash it herself to come up with a MD5 or sha hash.

80
00:06:36,940 --> 00:06:46,240
She will then compare the hash that she derived with the hash appended to the encrypted data only if

81
00:06:46,240 --> 00:06:48,220
the hashes are the same.

82
00:06:49,110 --> 00:06:52,740
Does she bother decrypting the text now?

83
00:06:52,740 --> 00:06:57,180
If the hashes are the same, it means that the data hasn't changed in transit.

84
00:06:57,930 --> 00:07:05,490
If the hashes are the same, Sara can decrypt the data by reversing the A's encryption, knowing that

85
00:07:05,490 --> 00:07:07,680
the data hasn't been tampered with.

86
00:07:08,520 --> 00:07:10,140
However, that being said.

87
00:07:11,110 --> 00:07:15,760
What stops Joe Hacker receiving the data?

88
00:07:15,790 --> 00:07:16,960
Changing it.

89
00:07:16,960 --> 00:07:20,170
So manipulating the data before it reaches error.

90
00:07:20,980 --> 00:07:22,690
Encrypting it with ease.

91
00:07:22,720 --> 00:07:31,510
Hashing that fake data with, let's say SHA and appending a new hash to the data and then transmitting

92
00:07:31,510 --> 00:07:32,650
it to Sara.

93
00:07:33,790 --> 00:07:40,450
Sarah has no way of knowing that the data has been manipulated because when she reverses the process

94
00:07:40,450 --> 00:07:47,650
by hashing this new data, her hash will be the same as Joe Hacker's hash that he appended to the new

95
00:07:47,650 --> 00:07:48,250
data.

96
00:07:48,760 --> 00:07:56,290
So to combat that, what Peter needs to do is use something called hash message authentication code

97
00:07:56,290 --> 00:07:57,460
or Mac.

98
00:07:57,730 --> 00:07:59,200
And there are two variants of this.

99
00:07:59,200 --> 00:08:03,370
You have Mac MD5 and Mac Sha.

100
00:08:03,730 --> 00:08:08,080
And what Peter needs to do is take the data of arbitrary lengths.

101
00:08:08,080 --> 00:08:10,360
So in other words, the data that he wants to send to Sarah.

102
00:08:11,440 --> 00:08:15,910
Plus a secret key that only Sarah and he knows.

103
00:08:16,420 --> 00:08:22,450
And now hash those two values with MD5 or SHA to get the hash.

104
00:08:23,600 --> 00:08:32,120
That will combat Joe Hacker from manipulating the data because Joe Hacker won't know what the secret

105
00:08:32,120 --> 00:08:38,870
key is that Peter and Sarah are using in combination with the hashing algorithm.

106
00:08:40,230 --> 00:08:43,320
Joe Hacker will not know what the secret key is.

107
00:08:43,740 --> 00:08:45,840
So when he hashes the data.

108
00:08:46,550 --> 00:08:53,090
Sarah will know that the data has been manipulated because the hash that she derives will not be the

109
00:08:53,090 --> 00:08:54,140
same hash.

110
00:08:55,040 --> 00:08:57,620
Sarah will be taking the encrypted data.

111
00:08:58,420 --> 00:09:04,840
In combination with the secret key and hashing those two together to come up with her hash.

112
00:09:05,500 --> 00:09:08,500
Joe Hacker will not know what the secret key is.

113
00:09:08,620 --> 00:09:17,470
So when Joe Hacker hashes the data, he's hash will not be the same as the new hash that Sarah derives.

114
00:09:17,890 --> 00:09:21,460
And she will therefore know that the data has been tampered with.

115
00:09:22,220 --> 00:09:30,470
Only Peter and Sarah know what that secret key is, not Joe Hacker, so he cannot successfully manipulate

116
00:09:30,470 --> 00:09:33,320
the data and derive the same hash value.

117
00:09:33,980 --> 00:09:40,130
Thus, data integrity is provided with HMC in combination with MD5 and SHA.

118
00:09:40,980 --> 00:09:43,650
The third goal to accomplish is authentication.

119
00:09:44,470 --> 00:09:51,490
Now authentication is knowing that data received is the same data that was sent and that the claim sender

120
00:09:51,490 --> 00:09:53,530
is in fact the actual sender.

121
00:09:54,250 --> 00:09:56,200
Now, we've already spoken about integrity.

122
00:09:56,380 --> 00:10:02,410
Now we're looking at authenticating a peer to make sure that they are actually who they say they are.

123
00:10:03,320 --> 00:10:08,300
This goes beyond validating the source attempting to access a service during initial login.

124
00:10:08,810 --> 00:10:14,330
You should also validate that the source has not been replaced by an attacking host in the course of

125
00:10:14,330 --> 00:10:17,570
the conversation, which is known as session hijacking.

126
00:10:17,990 --> 00:10:23,510
You want to make sure that the person that you're talking to is the person that they say they are and

127
00:10:23,510 --> 00:10:26,030
that they haven't been replaced by a hacker.

128
00:10:26,760 --> 00:10:28,770
They are two types of authentication.

129
00:10:29,130 --> 00:10:36,060
So we could authenticate rather one to write a two using either a preset key, which is a secret key

130
00:10:36,060 --> 00:10:40,800
value entered into each pair manually and is used to authenticate the pair.

131
00:10:41,340 --> 00:10:46,830
Or we could use RSA signatures which encrypt the hash with a private key.

132
00:10:47,520 --> 00:10:49,320
So firstly, appreciate key.

133
00:10:49,800 --> 00:10:53,460
In this example, Peter needs to be authenticated by Sarah.

134
00:10:54,620 --> 00:10:59,270
In this case, PITA takes the Doofy helm and shade key that they derived.

135
00:11:00,300 --> 00:11:07,140
The pre sched key that was agreed upon with Sarah, which should have been done out of band and other

136
00:11:07,140 --> 00:11:09,240
information relating to IP sick.

137
00:11:09,330 --> 00:11:17,790
And he hashes that with either MD5 or SHA and he attaches the hash to a packet with his ID information,

138
00:11:17,910 --> 00:11:22,740
which may be the IP address or hostname that is used for the VPN.

139
00:11:23,400 --> 00:11:32,100
Sarah can then hash her local copy of the information, which includes the agreed upon preset key and

140
00:11:32,100 --> 00:11:34,800
derive an MD5 or SHA hash.

141
00:11:35,940 --> 00:11:43,230
She can then compare her locally derived hash with the hash that she received from PETA.

142
00:11:44,680 --> 00:11:46,060
If they the same.

143
00:11:46,060 --> 00:11:52,450
She knows that Peter has the same pre shaved key as she does and she can thus authenticate Peter.

144
00:11:52,870 --> 00:11:58,870
If the hashes are different, she knows Peter does not have the correct preset key and therefore the

145
00:11:58,870 --> 00:12:00,310
VPN is not set up.

146
00:12:01,160 --> 00:12:03,560
The second option is to use digital signatures.

147
00:12:04,010 --> 00:12:11,270
Digital signatures have multiple advantages, including the automatic exchange of keys without the need

148
00:12:11,270 --> 00:12:16,130
of programming static authentication keys on multiple devices.

149
00:12:16,550 --> 00:12:18,350
This allows for scalability.

150
00:12:19,530 --> 00:12:21,630
The key lengths are also a lot greater.

151
00:12:22,140 --> 00:12:27,450
Pre shared keys should be changed on a regular basis, and in reality that often doesn't happen.

152
00:12:28,360 --> 00:12:35,380
Another advantage of digital signatures is non repudiation, which means you cannot deny being involved

153
00:12:35,380 --> 00:12:40,990
in a conversation because you're the only person that has your private key.

154
00:12:41,780 --> 00:12:50,000
So the way it works is PETA in this example takes the diffi hellman shade key and other information

155
00:12:50,000 --> 00:12:54,260
and hashes it in a very similar way to appreciate keys.

156
00:12:54,260 --> 00:12:56,840
But notice the pre shade key is not in this list.

157
00:12:57,590 --> 00:13:03,140
That hash is now signed with Peter's private key.

158
00:13:03,740 --> 00:13:07,700
And remember that Peter is the only person that has that private key.

159
00:13:08,460 --> 00:13:11,100
That creates what's called a digital signature.

160
00:13:11,460 --> 00:13:17,910
So a digital signature is created when information is encrypted with a private key.

161
00:13:18,450 --> 00:13:24,480
Please remember that if something is encrypted with someone's private key, only that person's public

162
00:13:24,480 --> 00:13:26,100
key can decrypt it.

163
00:13:27,040 --> 00:13:29,740
Peter now sends that information to Sarah.

164
00:13:31,180 --> 00:13:38,230
Sarah takes the received signature from Peter and decrypts it with Peter's public key, which she had

165
00:13:38,230 --> 00:13:44,500
previously received from Peter that will result in the original hash that Peter created.

166
00:13:45,100 --> 00:13:53,560
Sarah now takes the same information that she has locally and hashes it herself to derive her own hash

167
00:13:53,770 --> 00:13:55,390
of the various parameters.

168
00:13:56,020 --> 00:14:00,040
She then compares the two hashes if they the same.

169
00:14:00,040 --> 00:14:03,640
She knows firstly that Peter has all the correct information.

170
00:14:04,120 --> 00:14:12,130
She also knows that this information could only have come from Peter because only Peter's public key

171
00:14:12,520 --> 00:14:16,360
can decrypt something encrypted with Peter's private key.

172
00:14:16,960 --> 00:14:23,290
So the digital signature proves that the information came from Peter and that all of this information

173
00:14:23,290 --> 00:14:24,190
is correct.

174
00:14:25,010 --> 00:14:27,410
She has thus been able to authenticate Peter.

175
00:14:28,600 --> 00:14:32,860
Now the reverse will happen for both preset keys and digital signatures.

176
00:14:32,890 --> 00:14:34,180
Peter will authenticate.

177
00:14:34,180 --> 00:14:42,010
Sarah So there's mutual two way authentication either by using preset keys or by using digital signatures.