Question

Below are six ciphertexts of the same message encrypted using the following four classical ciphers available in CrypTool: Caesar (shift), Substitution, Vigenere and Permutation.

Do your best to match ciphertexts with a cipher that could have been used to obtain the given ciphertext. If you are uncertain, you can list several ciphers per each ciphertext. Justify your answer. Find the plaintext, by breaking the Caesar (shift) cipher, and then find the keys for at least 3 ciphers used to encrypt the now known plaintext. All attacks must be documented. Brute-force attacks do not count.

Ciphertext 1

TFPEGO ZEKUUFJZ CZ NJNCSGZWV LWVJVH FWVL HDTD ISK QSRNYR BQJPJ

SZRPBV ML LVEIKLYVUBX WNLLQC SPJL SITU AAY EXIR TFPEGO ZEKUUFJZ

CZ NJNCSGZWR RACWHTQ HJCV CJRXSL JPIJAK NYR TG FXX CZRPBV ML

LVEIKLYVMFTIG PJCV XIPS KHQKG TS WKGWFUGKO NCQWZDTS TB TGTUAP

UBX YLRBPYSK HJCV XIPB LXQYAV WMCU NVL EFLPW VJNCSQ HB ZEKUUFJZ

CXS RVGSCGBQY HJCV AWIG UURJ AIEQ

Ciphertext 2

GSVGXK JOYOYMOJ LB NBJEOLLRO LRCTEK LRGL YGHO XBP KGHMPL TOQOJ

NBJEOL LB JOYOYMOJ LRO LRCTEK LRGL YGHO XBP ESGHGSVGXK JOYOYMOJ

LB NBJEOLLRO NJCOTHK LRGL FJBQOH PTLJPOMPL HB TBLNBJEOL LB

JOYOYMOJLRBKO LRGL RGQO KLPUA MX XBPGSVGXK JOYOYMOJ LB NBJEOL

LRO LJBPMSOK LRGL RGQO FGKKOH GVGXMPL TOQOJ NBJEOL LB JOYOYMOJ

LRO MSOKKCTEK LRGL UBYO OGUR HGX

Ciphertext 3

DOZDBVUHPHPEHU WR IRUJHWWKH WKLQJV WKDW PDGH BRX VDGEXW QHYHU

IRUJHW WR UHPHPEHUWKH WKLQJV WKDW PDGH BRX JODG DOZDBV UHPHPEHU

WR IRUJHWWKH IULHQGV WKDW SURYHG XQWUXHEXW GR QRW IRUJHW WR

UHPHPEHUWKRVH WKDW KDYH VWXFN EB BRXDOZDBV UHPHPEHU WR IRUJHW

WKH WURXEOHV WKDW KDYH SDVVHG DZDBEXW QHYHU IRUJHW WR UHPHPEHU

WKH EOHVVLQJV WKDW FRPH HDFK GDB

Ciphertext 4

AMESOV OHALEOIR EO ETUWETSAU GBSOWE THSR ETMD EGN VUGBAK YTEHS

NTRNEA RH AAFMHAAMEDE TEETBS OTAE ETTG EEG GYETTHGRFR PUFMETLB TE

PBRMSCYMR NENTRTU SOFT RTESSA MELEYOEET AL BTT UERETA MR

EOBRMHCARHTST EEIM SOTM BRMNE WE TTUOTTAYE OOHAERET CR FHAUGBGYA

RHHNNOHV OMRU AWRE BHHYTE TDOEIDL BTSDD TRHYRF RT DVOHSAEOIDT

EESOYTEAT OROE UEGB VAFM LAD

Ciphertext 5

ANWDCE ZEMGMEID BO FQRJIFBHE VHLRSA THCT PEPM YOW SDHNCT NGVHV

RWRGGT WS DMMEOBHVFPE TJIQKE BHAV MDHQ GOU ILDHMTWAAS UIYMMBGR WS

RWRGGTWLQ NRIGNGW FPAT RRRZQL UNVRXINCT DQ NRX RWRGGT WSDMMEOBHV

FPOSG TKEF PAVG SWYOS BY AOXEXEAYU RHQQUBET TR JAZGEVTKI FZOUDLHW

FPAT JAYI BISSGD DAMGBUV NHZQZ FOTGHX FW REOEPFQZTHG BOIEAINIS

WLMB COOE HEOP DAA

Ciphertext 6

VHIGCYI NKNBCNIVY DBICPKEKPIAPE FCHAPTVGVP FAYRYOHCQVE

NTNIDBICPKEKY FNKNKKFEYPIAPEF CHAPTVG VPFAYWCHVHO HZTAYS NKNKKFE

YBDYFKI KEAPNRIENFS HAPTVSEYOFPZR YEXRCQOPV FYVDBIC PKEK YFNK NKK

FEY DAPRAP TVAGTN PYRUMCTU AYWYHZTAY SNKNKKFEYB DYFKIKEAPP

KFYQCPNPY AGAPTOP TYHUPFPG ITACQVENT NIDBICPK EKYFNKNK KFEYPIMD

RPUPEFC HAPTVB YKNEPY GPSTA

Answer 1

From plaintext is encrypted using classic ciphers such as Caesar, Substitution, Vigenere and Permutation.

Decrypting Ciphertext-3 using CAESAR cipher technique with key K=3 we get the message as

"ALWAYS REMEMBER TO FORGET THE THINGS THAT MADE YOU SAD BUT NEVER FORGET TO REMEMBER THE THINGS THAT MADE YOU GLAD ALWAYS REMEMBER TO FORGET THE FRIENDS THAT PROVED UN TRUE BUT DO NOT FORGET TO REMEMBER THOSE THAT HAVE STUCK BY YOU ALWAYS REMEMBER TO FORGET THE TROUBLES THAT HAVE PASSED AWAY BUT NEVER FORGET TO REMEMBER THE BLESSINGS THAT COME EACH DAY"

Decrypting Ciphertext-2 using known plaintext cryptanalysis with the following key table

PLAIN TEXT

A

B

C

D

E

F

G

H

I

K

L

M

N

O

P

R

S

T

U

V

W

Y

CIPHER

G

M

U

H

O

N

E

R

C

A

S

Y

T

B

F

J

K

L

P

Q

V

X

we will get the original message

Upon analyzing the ciphertext-5 the characters 1, 3, 8, 9, 11, 16, 17, 19, 24, 25, 27, 32 and on are just reflecting the plaintext character from the message and there is no sign of permutation or substitution. So from this analysis we can conclude that the encryption technique used is VIGENERE!!!. Since the pattern is repeating as 1, 3, 8, 9, 11, 16... Length of the keyword is 8 and 'A' is the character in the key at position 1, 3 and 8.

Based on this preliminary analysis solving for the rest of the keyword characters using the VIGENERE technique formula

where

P - Plaintext Character

C - Ciphertext Character

K - Key

Example:

Plaintext character L is encrypted as N. Applying the values of L and N in the formula as,

If K = 2, then the result will be 13. Therefore, second character is C

Continuing in the same way, we get the key as "ACADEMIA"