1 00:00:00,900 --> 00:00:02,850 Previously, we spoke about the symmetric 2 00:00:02,850 --> 00:00:04,990 algorithms and how to use a share secret 3 00:00:04,990 --> 00:00:07,150 or private key to conduct the encryption 4 00:00:07,150 --> 00:00:08,770 and decryption functions. 5 00:00:08,770 --> 00:00:10,560 In this lesson, we're going to cover a little 6 00:00:10,560 --> 00:00:13,210 bit of detail about the common symmetric algorithms 7 00:00:13,210 --> 00:00:15,700 that you have to know for this security class exam. 8 00:00:15,700 --> 00:00:19,460 This includes DES, triple DES, IDEA, AES, 9 00:00:19,460 --> 00:00:22,391 Blowfish, Twofish, and the Rivest Ciphers, 10 00:00:22,391 --> 00:00:25,540 RC four, RC five, and RC six. 11 00:00:25,540 --> 00:00:27,700 The Data Encryption Standard or DES 12 00:00:27,700 --> 00:00:30,240 uses a 64-bit key with eight bits of that 13 00:00:30,240 --> 00:00:31,670 being used for parity. 14 00:00:31,670 --> 00:00:34,100 Therefore, DES only really has an effective 15 00:00:34,100 --> 00:00:35,980 key length of 56-bits, 16 00:00:35,980 --> 00:00:37,470 which is you probably guess by now, 17 00:00:37,470 --> 00:00:39,220 mean it's not very secured against 18 00:00:39,220 --> 00:00:40,790 modern computing power. 19 00:00:40,790 --> 00:00:43,670 DES was heavily used in the 1970s and used 20 00:00:43,670 --> 00:00:46,070 all the way up until the early 2000s. 21 00:00:46,070 --> 00:00:49,590 With DES, each messages broke it up in this 64-bit blocks 22 00:00:49,590 --> 00:00:52,050 and put through 16 rounds of transposition 23 00:00:52,050 --> 00:00:54,570 and substitution to create the cipher text. 24 00:00:54,570 --> 00:00:57,070 Due to DES weakness and its key, a modified 25 00:00:57,070 --> 00:00:58,820 version of it known as Tripe DES, 26 00:00:58,820 --> 00:01:02,000 written as three DES was also created. 27 00:01:02,000 --> 00:01:05,670 And in this version, there was three 56-bit keys used. 28 00:01:05,670 --> 00:01:07,750 The input data will subjected to encryption 29 00:01:07,750 --> 00:01:10,220 through the DES algorithm with the first key 30 00:01:10,220 --> 00:01:12,070 then decrypted through the algorithm 31 00:01:12,070 --> 00:01:13,420 using the second key. 32 00:01:13,420 --> 00:01:15,140 Again, this jumbles it up even more 33 00:01:15,140 --> 00:01:17,230 and then puts it through the DES algorithm 34 00:01:17,230 --> 00:01:19,380 again through another encryption function 35 00:01:19,380 --> 00:01:21,080 using that third key. 36 00:01:21,080 --> 00:01:22,870 This effectively created an algorithm 37 00:01:22,870 --> 00:01:24,770 that had a 112-bit key 38 00:01:24,770 --> 00:01:26,900 but it was three times slower than DES 39 00:01:26,900 --> 00:01:29,120 because of all those encrypting, decrypting 40 00:01:29,120 --> 00:01:30,750 and encrypting functions. 41 00:01:30,750 --> 00:01:33,630 Our next symmetric algorithm is called IDEA. 42 00:01:33,630 --> 00:01:35,620 IDEA stands for the International Data 43 00:01:35,620 --> 00:01:37,880 Encryption Algorithm and it's another symmetric 44 00:01:37,880 --> 00:01:40,610 block cipher which used a 64-bit block 45 00:01:40,610 --> 00:01:43,370 as its input and it uses that encrypt the data. 46 00:01:43,370 --> 00:01:46,890 The key size here is 128-bits and it's faster 47 00:01:46,890 --> 00:01:48,650 and harder to break than DES 48 00:01:48,650 --> 00:01:50,540 but it's not as widely used as the more 49 00:01:50,540 --> 00:01:52,770 common one AES which we're going to talk 50 00:01:52,770 --> 00:01:54,090 about in a moment. 51 00:01:54,090 --> 00:01:55,980 IDEA is commonly known only because 52 00:01:55,980 --> 00:01:57,700 it's really used inside a pretty good 53 00:01:57,700 --> 00:01:59,440 privacy suite which we'll talk about 54 00:01:59,440 --> 00:02:01,980 a little bit later on in the future lesson. 55 00:02:01,980 --> 00:02:04,390 Ultimately, DES and triple DES simply 56 00:02:04,390 --> 00:02:05,737 weren't strong enough though and there 57 00:02:05,737 --> 00:02:08,440 was this contest held to design a replacement. 58 00:02:08,440 --> 00:02:10,940 IDEA was one entrance to the contest but ultimately, 59 00:02:10,940 --> 00:02:11,970 it didn't win. 60 00:02:11,970 --> 00:02:14,030 The one that won is known as AES 61 00:02:14,030 --> 00:02:16,640 which is the Advanced Encryption Standard. 62 00:02:16,640 --> 00:02:18,720 AES was chosen as the replacement for DES 63 00:02:18,720 --> 00:02:20,931 and triple DES by the US government. 64 00:02:20,931 --> 00:02:24,040 AES can be used with a 128-bit, 65 00:02:24,040 --> 00:02:28,999 192-bit or 356-bit key and a matching block size. 66 00:02:28,999 --> 00:02:31,980 AES is known as the Rijndael algorithm as well 67 00:02:31,980 --> 00:02:33,410 which is named after its creator 68 00:02:33,410 --> 00:02:36,098 but most people simply called it AES. 69 00:02:36,098 --> 00:02:38,530 AES is widely used and it has become 70 00:02:38,530 --> 00:02:40,770 the de facto standard in encryption. 71 00:02:40,770 --> 00:02:42,630 In fact, it's still encryption standard 72 00:02:42,630 --> 00:02:44,210 that's used by the federal government 73 00:02:44,210 --> 00:02:45,870 for any encryption of sensitive 74 00:02:45,870 --> 00:02:47,690 but unclassified information. 75 00:02:47,690 --> 00:02:49,810 Next, we have Blowfish which is a block 76 00:02:49,810 --> 00:02:53,970 cipher that uses a 32-bit to 448-bit encryption key 77 00:02:53,970 --> 00:02:57,900 to encrypt 64-bit of data in blocks at a time. 78 00:02:57,900 --> 00:03:00,110 It was originally developed as replacement for DES 79 00:03:00,110 --> 00:03:02,050 but wasn't widely utilized. 80 00:03:02,050 --> 00:03:04,870 Another variant called Twofish was also developed 81 00:03:04,870 --> 00:03:06,470 and this one provides the ability to use 82 00:03:06,470 --> 00:03:09,350 128-bit blocks in its encryption algorithm 83 00:03:09,350 --> 00:03:14,350 and use 128-bit, 192-bit, or 256-bit encryption keys. 84 00:03:15,170 --> 00:03:17,680 Both Blowfish and Twofish were never patterned then 85 00:03:17,680 --> 00:03:20,580 and they were available for use as open source. 86 00:03:20,580 --> 00:03:22,760 Another set of symmetric algorithms was created 87 00:03:22,760 --> 00:03:25,450 by Ron Rivest, a cryptographer who's created 88 00:03:25,450 --> 00:03:27,850 six algorithms under the name RC 89 00:03:27,850 --> 00:03:29,930 which stands for the Rivest Cipher. 90 00:03:29,930 --> 00:03:31,940 RC one was never published. 91 00:03:31,940 --> 00:03:34,020 RC two was considered weak eventually 92 00:03:34,020 --> 00:03:35,150 and skipped over. 93 00:03:35,150 --> 00:03:36,900 And RC three was cracked before it was 94 00:03:36,900 --> 00:03:38,400 even released to the public. 95 00:03:38,400 --> 00:03:42,470 But RC four, RC five and RC six were released 96 00:03:42,470 --> 00:03:44,950 and can be found in common use today. 97 00:03:44,950 --> 00:03:47,020 RC four is a stream cipher 98 00:03:47,020 --> 00:03:49,760 and it uses a variable key size from 40-bits 99 00:03:49,760 --> 00:03:52,690 all the way up to 2048-bits. 100 00:03:52,690 --> 00:03:55,920 RC four is used in both Secure Sockets Layer, SSL 101 00:03:55,920 --> 00:03:58,490 and Wired Equivalent Privacy, WEP. 102 00:03:58,490 --> 00:04:00,770 Now, RC five is a block cipher, 103 00:04:00,770 --> 00:04:03,830 using key sizes up to 2048-bits. 104 00:04:03,830 --> 00:04:06,740 And RC six is based on the RC five cipher 105 00:04:06,740 --> 00:04:08,010 and it was really originally considered 106 00:04:08,010 --> 00:04:10,280 as the replacement for DES until Rijndael 107 00:04:10,280 --> 00:04:11,800 cipher was chosen as the winner 108 00:04:11,800 --> 00:04:15,290 and became the Advanced Encryption Standard or AES. 109 00:04:15,290 --> 00:04:17,420 Now, for the exam, if you're asked about 110 00:04:17,420 --> 00:04:19,520 these algorithms, you should be able to identify 111 00:04:19,520 --> 00:04:20,980 which of these are block ciphers 112 00:04:20,980 --> 00:04:22,690 and which are stream ciphers. 113 00:04:22,690 --> 00:04:23,670 Here's the hint, 114 00:04:23,670 --> 00:04:25,560 the only stream cipher we've talked about 115 00:04:25,560 --> 00:04:27,700 so far is RC four. 116 00:04:27,700 --> 00:04:30,020 All of the others are block ciphers. 117 00:04:30,020 --> 00:04:31,460 If you're not sure in the exam, 118 00:04:31,460 --> 00:04:33,110 choose block cipher because it is 119 00:04:33,110 --> 00:04:35,180 most commonly used and most commonly 120 00:04:35,180 --> 00:04:36,600 asked on the exam. 121 00:04:36,600 --> 00:04:38,360 Also, you should be able to identify 122 00:04:38,360 --> 00:04:40,640 the algorithm as either symmetric ciphers 123 00:04:40,640 --> 00:04:42,360 or asymmetric ciphers. 124 00:04:42,360 --> 00:04:44,400 Everything I've just covered in this lesson 125 00:04:44,400 --> 00:04:48,000 including DES, triple DES, IDEA, AES, 126 00:04:48,000 --> 00:04:50,900 Blowfish, Twofish, and the Rivest Ciphers 127 00:04:50,900 --> 00:04:53,490 are all considered symmetric ciphers. 128 00:04:53,490 --> 00:04:55,370 Keep this in mind when you take them exam 129 00:04:55,370 --> 00:04:57,432 and you're going to do great. 130 00:04:57,432 --> 00:04:59,441 (electronic music)