Assume a message m is encrypted using the Shift cipher and the resulting ciphert

ID: 3755345 • Letter: A

Question

Assume a message m is encrypted using the Shift cipher and the resulting ciphertext is as follows:

TEBKFKQEBZLROPBLCERJXKBSBKQP

What would be the values of m and key k in this case? Assume that encryption and decryption in the shift cipher are dened as ci = (mi k) mod 26 and mi = (ci + k) mod 26, respectively. Here mi and ci denote the ith character in message m and ciphertext c, respectively. Please justify your answer. (Hint: you need to do an exhaustive search or brute force attack over 26 possible keys.)

*****DO NOT USE ANY PROGRAMMING TO GET THE ANSWER. THIS QUESTION IS TO BE ANSWERED USING PEN AND PAPER ONLY AND SHOULD CONTAIN NO CODE*****

Explanation / Answer

Given Ciphertext: TEBKFKQEBZLROPBLCERJXKBSBKQP

The possible message is: WHENINTHECOURSEOFHUMANEVENTS

Key: 23

Possible Key and Messages using brute force attack

Key

Message

SDAJEJPDAYKQNOAKBDQIWJARAJPO

RCZIDIOCZXJPMNZJACPHVIZQZION

QBYHCHNBYWIOLMYIZBOGUHYPYHNM

PAXGBGMAXVHNKLXHYANFTGXOXGML

OZWFAFLZWUGMJKWGXZMESFWNWFLK

NYVEZEKYVTFLIJVFWYLDREVMVEKJ

MXUDYDJXUSEKHIUEVXKCQDULUDJI

LWTCXCIWTRDJGHTDUWJBPCTKTCIH

KVSBWBHVSQCIFGSCTVIAOBSJSBHG

+10

JURAVAGURPBHEFRBSUHZNARIRAGF

+11

ITQZUZFTQOAGDEQARTGYMZQHQZFE

+12

HSPYTYESPNZFCDPZQSFXLYPGPYED

+13

GROXSXDROMYEBCOYPREWKXOFOXDC

+14

FQNWRWCQNLXDABNXOQDVJWNENWCB

+15

EPMVQVBPMKWCZAMWNPCUIVMDMVBA

+16

DOLUPUAOLJVBYZLVMOBTHULCLUAZ

+17

CNKTOTZNKIUAXYKULNASGTKBKTZY

+18

BMJSNSYMJHTZWXJTKMZRFSJAJSYX

+19

ALIRMRXLIGSYVWISJLYQERIZIRXW

+20

ZKHQLQWKHFRXUVHRIKXPDQHYHQWV

+21

YJGPKPVJGEQWTUGQHJWOCPGXGPVU

+22

XIFOJOUIFDPVSTFPGIVNBOFWFOUT

+23

WHENINTHECOURSEOFHUMANEVENTS

+24

VGDMHMSGDBNTQRDNEGTLZMDUDMSR

+25

UFCLGLRFCAMSPQCMDFSKYLCTCLRQ

Key