alg2 cryptography hw

8/13/2019 Alg2 Cryptography HW

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Cryptography.doc 1 CSCI 1321

You must do at least 90% of this homework without the assistance of anyone else. Once you have 90% ormore of the homework completed, you may double check your answers with a team-mate or study-partner.

I have completed at least 90% this homework assinment on my own. I!"e reali#e that it is a violation ofacademic interity to share this work with others, either this semester, or after the class is over.

I!"e reali#e that the penalty for turnin in work that is not my own, or assistin others in doin so, can ranefrom an $$ in the class to dismissal from &rinity 'niversity

(rint )ame ***************************************** &ime +euired ******.**** rs.

/inature ***************************************************************

&eam-ate )ame **********************************************************

Cryptographyomework12 (oints

1. ******* In the public-key method of cryptoraphy, which key is publicly known345 6ncryption key only75 8ecryption key only5 7oth85 )one of the above

:. ******* . 4 cipher is *3*

45 4n encryption alorithm75 4 decryption alorithm5 4 private key85 ;a5 or ;b5


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75 ipherte=t5 ryptonite85 (lainte=t

1D. /****************************** "************************* ryptoraphy meant *3* inBreek

12. ****************************** *3* is the art and science of transformin messaes to makethem secure and immune to attacks

1?. ****************************** *3* *3* renders a messae unintelliible to unauthori#edpersonnel.

1@. ****************************** *3* transforms an intentionally unintelliible messae intomeaninful information.

1C. ********************** ********************** In cryptoraphy, the encryption!decryptionalorithms are *3* Epublic!secretFG the keys are *3* Epublic!secretF.

19. ******* E&!F 6very sender!receiver pair needs its own cipher for secure communication.

:0. ********************** One cipher can serve millions of communicatin pairs throuh the use of *3* Epublic!secretF keys and *3* Epublic!secretF ciphers.

:1. **********************-key **********************-key 4ll cryptoraphy alorithms can bedivided into two roupsH *3* ;also called secret key5 and *3* ;also called public key5

::. **********************-key **********************-key 4ll cryptoraphy alorithms can bedivided into two roupsH *3* ;also called asymmetric key5 and *3* ;also called symmetric key5

:


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45 &ranslation75 6ncryption!8ecryption5 4uthentication85 ompression

client.


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D0. ******************************************************** 'sin the more advancedmonoalphabetic cipher key above, encrypt the plainte=t messae L4&&4N )O"M. Jist the cipherte=t.

D1. ******************************************************** 'sin the more advancedmonoalphabetic cipher key above, decrypt the cipherte=t messae L+ + 8IM. Jist the cipherte=t.

D:. ******** In monoalphabetic substitution, the relationship between a character in the plainte=t and acharacter in the cipherte=t is *3*.

45 one-to-one

75 one-to-many5 many-to-one85 one-to-many

Dienere cipherrid above, decrypt the cipherte=t L (" S6I&S > O674 &7S 6+S(/N+6&M usin the keyL6&6+)6&M. "rite the plainte=t messae.

D?. ******* E&!F &here are many collections of letters, and or diits, that can be used for the >ieneresuare!rid.


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D@. ******** In polyalphabetic substitution, the relationship between a character in the plainte=t and acharacter in the cipherte=t is *3*.

45 one-to-one75 one-to-many5 many-to-one85 one-to-many

Plaintext Ciphertext

DC. 'sin the eleven character transpositional cipher key above, encrypt the cipherte=t messaeL+Y(&OB+4(Y I/ &6 4+& 4)8 /I6)6 O &+4)/O+I)B 6//4B6/ &O 4N6 &6/6'+6 4)8 I')6 &O 4&&4N/M. (lace the continuous flow plainte=t on the left and transform it toappropriate cipherte=t on the riht.

Ciphertext Plaintext

D9. 'sin the eleven character transpositional cipher key above, decrypt the cipherte=t messae


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LOGYRTCPARPHORAIGYHT LM PAUESLB_RI TAHDC_ENKRES_AERPY_I__T__V__AE M.(lace the continuous flow cipherte=t on the left and transform it to appropriate plainte=t on the riht.

20. ******* E&!F In symmetric-key cryptoraphy, the same key is used by the sender ;for encryption5 andthe receiver ;for decryption5.

21. ******************************************************************************* Oneof the maKor advantaes of symmetric-key cryptoraphy is efficiency. "hy are these small keys moreefficient3

2:. ******************************** One of the maKor disadvantaes of symmetric-keycryptoraphy is that each pair must have a uniue symmetric key. If ) people want to use this method, thereneeds to be *3* symmetric keys. Jist the formula.

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00100010 00011000 = *** *** *** *** *** *** *** *** */*

00100010 00101000 = *** *** *** *** *** *** *** *** ***

00100001 01000010 = *** *** *** *** *** *** *** *** ***

00100010 00100001 = *** *** *** *** *** *** *** *** ***

00100001 00011000 = *** *** *** *** *** *** *** *** ***

00100001 01000001 =*** *** *** *** *** *** *** *** ***

'se the bit-level decoder above, and the 4/II table at the beinnin of this assinment sheet, to decrypt

the cipherte=t L00100010 00011000 00100010 00101000 00100001 01000010

00100010 00100001 00100001 00011000 00100001 01000001

2@. **** &he *3* (-7o= above is used for bit-level encryption and decryption. 45 ompressed 75 6=panded 5 /traiht

2C. **** &he *3* (-7o= above is used for bit-level encryption and decryption. 45 ompressed 75 6=panded 5 /traiht

29. **** &he *3* (-7o= above is used for bit-level encryption and decryption. 45 ompressed 75 6=panded 5 /traiht


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?0. ************************ "hich of the three (-7o=es above would be of little use encryptin te=tand raphic information because of the data loss.

?1. *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***

*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***'se the e=panded p-bo= encoder above, and the 4/II table at the beinnin of this assinment sheet, toencrypt the plainte=t L)'&M. +emember to complete the last byte by fillin in 0Qs.

?:. *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ****

*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ****

*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ****'se the e=panded p-bo= encoder above, and the 4/II table at the beinnin of this assinment sheet, to

decrypt the cipherte=t L00010111 10010100 00010101 01010100M. +emember tocomplete the last byte by fillin in 0Qs.

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?D. *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ****

*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ****

*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ****'se the straiht p-bo= encoder above, and the 4/II table at the beinnin of this assinment sheet, to

decrypt the cipherte=t L00101111 10100001 10100111M. +emember to complete the lastbyte by fillin in 0Qs.

?2. B *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***

O *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***'se the /-bo= encoder above, and the 4/II table at the beinnin of this assinment sheet, to encrypt

the plainte=t LGOM.


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??. *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ****

*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ****'se the /-bo= encoder above, and the 4/II table at the beinnin of this assinment sheet, to decrypt

the cipherte=t L10110001 10110000M.

?@. ********************************** &he bit-level encryption diaram above illustrates a;n5 *3*.

?C. In the table for an 6=clusive O+, the followin hold trueH

6=clusive O+ ;0,05 ***** E0!1F 6=clusive O+ ;0,15 *****E0!1F

6=clusive O+ ;1,05 *****E0!1F 6=clusive O+ ;1,15 *****E0!1F

?9. In the table for an O+, the followin hold trueH

O+ ;0,05 ***** E0!1F O+ ;0,15 *****E0!1F

O+ ;1,05 *****E0!1F O+ ;1,15 *****E0!1F


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) *** *** *** *** *** *** *** *** Y *** *** *** *** *** *** *** ***

Ney *** *** *** *** *** *** *** *** Ney *** *** *** *** *** *** *** ***

ipherhar *** *** *** *** *** *** *** *** ipherhar *** *** *** *** *** *** *** ***

6 *** *** *** *** *** *** *** *** & *** *** *** *** *** *** *** ***

Ney *** *** *** *** *** *** *** *** Ney *** *** *** *** *** *** *** ***


@0. *********************************************************************** 'se the6=clusive O+ bit-level encryption to encrypt plainte=t L)Y6&M with the Ney L1 1 1 0 0 1 1 1M Jist the completypherte=t messae in the space provided.


Ney *** *** *** *** *** *** *** *** Ney *** *** *** *** *** *** *** ***

har1 *** *** *** *** *** *** *** *** har: *** *** *** *** *** *** *** ***

@1. *********************************************************************** 'se the6=clusive O+ bit-level encryption to encrypt plainte=t L10101001 10101000M with the Ney L1 1 1 0 0 1 1 1MJist the complete ipherte=t messae in the space provided.

*** *** *** *** *** *** *** ***

T+1U *** *** *** *** *** *** *** ***

T+:U *** *** *** *** *** *** *** ***

T+


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/ *** *** *** *** *** *** *** ***

T+1U *** *** *** *** *** *** *** ***

T+:U *** *** *** *** *** *** *** ***

T+


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C:. *********************************************************************** &he illustrationabove describes one possible combination of subkeys for the *3* encryption alorithm .

C


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C9. ******* E&!F In public-key encryption, knowin the encryption alorithm and the key makes it uite easyto crack the decryption alorithm.

90. **************************************** /uppose the +/4 public key encryptionQs primenumbers were 2 and 1@. "hat is )3

91. **************************************** /uppose the +/4 public key encryptionQs primenumbers were @ and 1@. "hat is )3

9:. **************************************** /uppose the +/4 public key encryptionQs primenumbers were 2 and 1@. "hat is A3

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