a.Compute CBC-MAC for a message of 16 bits, “8642” (in Hexa). Assume a block size of 8 bits with an IV=F1 (in hexa). For simplicity, assume the encryption to be a simple XOR of the key with the plaintext. Let the encryption key be B4 (in Hexa). (Hint: Divide the message into blocks of 8 bits each; XOR each block with the previous cipher output; then encrypt this with the key. For the first block, XOR it with IV. Details in pages 325-326 Ch.12 of the textbook) b. Suppose Alice computes the Secret prefix MAC (page 322: secret prefix MAC(x) = h(key || x)) for the message ”AM” (in ASCII) with key “G” (in ASCII) that both Alice and Bob know. The hash function that is used is h(x1x2x3)= g(g(x1 XOR x2) XOR x3 ) where each xi is a character represented as 8 bits, and g(x) is a 8-bit string that is equal to the complement of bits in x. For example, g(10110011) = 01001100. The MAC is 8 bits. (8-bit ASCII representation of the characters is given below.)What is the Secret prefix MAC computed by Alice? Show the MAC as the single character.What information is sent by Alice to Bob?c. Suppose Alice computes the Secret suffix MAC (page 322: secret suffix MAC(x) = h(x || key)) for the message ”AM” with key “G” that both Alice and Bob know. The hash function that is used is h(x1x2x3)= g(g(x1 XOR x2) XOR x3 ) where each xi is a character represented as 8 bits, and g(x) is a 8-bit string that is equal to the complement of bits in x. For example, g(10110011) = 01001100. The MAC is 8 bits. (8-bit ASCII representation of the characters is given below.) What is the Secret suffix MAC computed by Alice? Show the MAC as the single character.What information is sent by Alice to Bob. Dec Hx Oct CharDec Hx Oct Html ChrDec Hx Oct Html Chr Dec Hx Oct Html Chr0 000 NUL (null)1 001 SOH (start of heading)2 002 STX (start of text)3 003 ETX (end of text)4 004 EOT (end of transmission)32 20 040 Space 64 40 100 @ @3321 041 ! !96 60 140 `65 41 101 A A97 61 141 a98 62 142 b b99 63 143 c100 64 144 d d69 45 105 E E 101 65 145 e e70 46 106 F F 102 66 146 G#102; f71 47 107 G G 103 67 147 G#103; g72 48 110 H H 104 68 150 h h105 69 151 i i106 6A 152 j j75 4B 113 K K 107 6B 153 k k108 6C 154 l 1109 6D 155 m marr2.34 22 042 "66 42 102 B B35 23 043 G#35; #3624044 $ $67 43 103 C C68 44 104 D D345 5 005 ENQ (enquiry)37 25 045 % *6 006 ACK (acknowledge)7 007 BEL (bell)8 010 BS9 011 TAB (horizontal tab)À 012 LFв 013 VTC 014 FFD 015 CRE 016 SOF 017 SI38 26 046 & &739 27 047 ' '40 28 050 G#40;41 29 051 ) )(NL line feed, new line) 42 2A 052 * *43 2B 053 G#43; +(NP form feed, new page) 44 2C 054 , ,45 2D 055 -46 2E 056 .47 2F 057 G#47; /48 30 060 0 0(backspace)73 49 111 I I74 4A 112 J J1011(vertical tab)1276 4C 114 L L77 4D 115 M M78 4E 116 N N79 4F 117 O 080 50 120 P P81 51 121 Q Q 113 71 161 q q82 52 122 R R 11472 162 r r13(carriage return)(shift out)(shift in)110 6E 156 n n1l1 6F 157 &#lll; o112 70 160 p p141516 10 020 DLE (data link escape)17 11 021 Dci (device control 1)18 12 022 DC2 (device control 2)19 13 023 DC3 (device contrd 3)20 14 024 DC4 (device controf 4)21 15 025 NAK (negative acknowledge)22 16 026 SYN (synchronous idle)23 17 027 ETB (end of trans. block)24 18 030 CAN (cancel)25 19 031 EM26 lA 032 SUB (substitute)27 1B 033 ESC (escape)28 10 034 FS29 1D 035 GS30 IE 036 RS31 1F 037 US49 31 061 1 150 32 062 2 251 33 063 3 352 34 064 4 453 35 065 5 583 53 123 S S115 73 163 s s84 54 124 T T 1l6 74 164 t t85 55 125 U U 117 75 165 u u86 56 126 V v 118 76 166 v v54 36 066 6 655 37 067 7 756 38 070 G#56; 887 57 127 W W119 77 167 w w88 58 130 X X 120 78 170 x x89 59 131 Y Y 121 79 171 y Y90 5A 132 Z Z91 5B 133 [ [92 5C 134 \ \(end of medium)57 39 071 9 958 3A 072 : :59 3B 073 ; ;60 3C 074 G#60; <61 3D 075 = =62 3E 076 > >63 3F 077 ? ?122 7A 172 z z(file separator)(group separator)(record separator)(unit separator)123 7B 173 { {124 7C 174 | |125 7D 175 } }126 7E 176 ~127 7F 177 DELSource: www.Lookup Tables.com93 5D 135 ] ]94 5E 136 ^ *95 5F 137 _ MAC{ (x) = h(k||x)mis called secret prefix MAC, and the second one:m= MAC&(x) =h(x||k)

b. Secret prefix MAC computed by Alice is "C" There is no encryption performed by Alice. Therefore…

Answered: Suppose Alice computes the Secret…

Computer Networking: A Top-Down Approach (7th Edition)

7th Edition

ISBN:9780133594140

Author:James Kurose, Keith Ross

Publisher:James Kurose, Keith Ross

Chapter1: Computer Networks And The Internet

Section: Chapter Questions

Problem R1RQ: What is the difference between a host and an end system? List several different types of end...

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Question

Compute CBC-MAC for a message of 16 bits, “8642” (in Hexa). Assume a block size of 8 bits with an IV=F1 (in hexa). For simplicity, assume the encryption to be a simple XOR of the key with the plaintext. Let the encryption key be B4 (in Hexa).

(Hint: Divide the message into blocks of 8 bits each; XOR each block with the previous cipher output; then encrypt this with the key. For the first block, XOR it with IV. Details in pages 325-326 Ch.12 of the textbook)

b. Suppose Alice computes the Secret prefix MAC (page 322: secret prefix MAC(x) = h(key || x)) for the message ”AM” (in ASCII) with key “G” (in ASCII) that both Alice and Bob know. The hash function that is used is h(x₁x₂x₃)= g(g(x₁ XOR x₂) XOR x₃ ) where each xi is a character represented as 8 bits, and g(x) is a 8-bit string that is equal to the complement of bits in x. For example, g(10110011) = 01001100. The MAC is 8 bits. (8-bit ASCII representation of the characters is given below.)

What is the Secret prefix MAC computed by Alice? Show the MAC as the single character.
What information is sent by Alice to Bob?

Suppose Alice computes the Secret suffix MAC (page 322: secret suffix MAC(x) = h(x || key)) for the message ”AM” with key “G” that both Alice and Bob know. The hash function that is used is h(x₁x₂x₃)= g(g(x₁

XOR x₂) XOR x₃ ) where each xi is a character represented as 8 bits, and g(x) is a 8-bit string that is equal to the complement of bits in x. For example, g(10110011) = 01001100. The MAC is 8 bits. (8-bit ASCII representation of the characters is given below.)