Mono-Alphabetic Substitution Cipher

A mono-alphabetic cipher (aka simple substitution cipher) is a substitution cipher where each letter of the plain text is replaced with another letter of the alphabet. It uses a fixed key which consist of the 26 letters of a “shuffled alphabet”.

Plain text alphabet: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Cipher text alphabet (key): M U A L V O Z K R N J X Q D F S H P E B C T I W Y G

With the above key, all “A” letters in the plain text will be encoded to an “M”.

This type of cipher is a form of symmetric encryption as the same key can be used to both encrypt and decrypt a message.

You can generate your own encryption keys and encrypt your own messages using our online mono-alphabetic substitution engine:

Frequency Analysis


One approach used to help decrypt a mono-alphabetic substitution cipher is to use a frequency analysis based on counting the number of occurrence of each letter to help identify the most recurrent letters. (e.g. In the English language, letters E, T and A).

Your Task:


Complete a frequency analysis to decrypt the following ciphers.
Cipher #1Cipher #2Cipher #3Cipher #4Cipher #5
“DJ DK C QLXDWI WF SDGDU PCX. XLRLU KQCSLKBDQK, KJXDHDET FXWZ C BDIILE RCKL, BCGL PWE JBLDX FDXKJ GDSJWXO CTCDEKJ JBL LGDU TCUCSJDS LZQDXL. IYXDET JBL RCJJUL, XLRLU KQDLK ZCECTLI JW KJLCU KLSXLJ QUCEK JW JBL LZQDXL’K YUJDZCJL PLCQWE, JBL ILCJB KJCX, CE CXZWXLI KQCSL KJCJDWE PDJB LEWYTB QWPLX JW ILKJXWO CE LEJDXL QUCELJ. QYXKYLI RO JBL LZQDXL’K KDEDKJLX CTLEJK, QXDESLKK ULDC XCSLK BWZL CRWCXI BLX KJCXKBDQ, SYKJWIDCE WF JBL KJWULE QUCEK JBCJ SCE KCGL BLX QLWQUL CEI XLKJWXL FXLLIWZ JW JBL TCUCVO…”

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“Q WNN JFNNW XP TFNNS, FNR FXWNW JXX
Q WNN JYNA GHXXA PXF AN DSR KXB
DSR Q JYQSE JX AKWNHP OYDJ D OXSRNFPBH OXFHR
Q WNN WEQNW XP GHBN DSR LHXBRW XP OYQJN
JYN GFQTYJ GHNWWNR RDK, JYN RDFE WDLFNR SQTYJ
DSR Q JYQSE JX AKWNHP OYDJ D OXSRNFPBH OXFHR
JYN LXHXFW XP JYN FDQSGXO WX ZFNJJK QS JYN WEK
DFN DHWX XS JYN PDLNW XP ZNXZHN TXQST GK
Q WNN PFQNSRW WYDEQST YDSRW WDKQST YXO RX KXB RX
JYNK’FN FNDHHK WDKQST Q HXUN KXB
Q YNDF GDGQNW LFKQST, Q ODJLY JYNA TFXO
JYNK’HH HNDFS ABLY AXFN JYDS Q’HH SNUNF ESXO
DSR Q JYQSE JX AKWNHP OYDJ D OXSRNFPBH OXFHR
KNW Q JYQSE JX AKWNHP OYDJ D OXSRNFPBH OXFHR”

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“IZRN P SPNA QWBRXS PN DPQRB ES DHEJVXR, QEDZRH QUHW GEQRB DE QR
BLRUOPNY IEHAB ES IPBAEQ, XRD PD VR
UNA PN QW ZEJH ES AUHONRBB BZR PB BDUNAPNY HPYZD PN SHEND ES QR
BLRUOPNY IEHAB ES IPBAEQ, XRD PD VR
XRD PD VR, XRD PD VR, XRD PD VR, XRD PD VR
IZPBLRH IEHAB ES IPBAEQ, XRD PD VR
UNA IZRN DZR VHEORN-ZRUHDRA LRELXR XPCPNY PN DZR IEHXA UYHRR
DZRHR IPXX VR UN UNBIRH, XRD PD VR
SEH DZEJYZ DZRW QUW VR LUHDRA, DZRHR PB BDPXX U GZUNGR DZUD DZRW IPXX BRR
DZRHR IPXX VR UN UNBIRH, XRD PD VR
XRD PD VR, XRD PD VR, XRD PD VR, XRD PD VR
WRUZ, DZRHR IPXX VR UN UNBIRH, XRD PD VR
XRD PD VR, XRD PD VR, XRD PD VR, XRD PD VR
IZPBLRH IEHAB ES IPBAEQ, XRD PD VR
XRD PD VR, XRD PD VR, XRD PD VR, WRUZ, XRD PD VR
IZPBLRH IEHAB ES IPBAEQ, XRD PD VR
UNA IZRN DZR NPYZD PB GXEJAW DZRHR PB BDPXX U XPYZD DZUD BZPNRB EN QR
BZPNR JNDPX DEQEHHEI, XRD PD VR
P IUOR JL DE DZR BEJNA ES QJBPG, QEDZRH QUHW GEQRB DE QR
BLRUOPNY IEHAB ES IPBAEQ, XRD PD VR
XRD PD VR, XRD PD VR, XRD PD VR, WRUZ, XRD PD VR
DZRHR IPXX VR UN UNBIRH, XRD PD VR
XRD PD VR, XRD PD VR, XRD PD VR, WRUZ, XRD PD VR
DZRHR IPXX VR UN UNBIRH, XRD PD VR
XRD PD VR, XRD PD VR, XRD PD VR, WRUZ, XRD PD VR
IZPBLRH IEHAB ES IPBAEQ, XRD PD VR”

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“ZRTFT IH PQFTHZ IQ ZRT XBGBOZIO HTQBZT. HTWTFBG ZRLPHBQV HLGBF HYHZTSH RBWT VTOGBFTV ZRTIF IQZTQZILQH ZL GTBWT ZRT FTEPKGIO.
ZRIH HTEBFBZIHZ SLWTSTQZ, PQVTF ZRT GTBVTFHRIE LD ZRT SYHZTFILPH OLPQZ VLLAP, RBH SBVT IZ VIDDIOPGZ DLF ZRT GISIZTV QPSKTF LD CTVI AQIXRZH ZL SBIQZBIQ ETBOT BQV LFVTF IQ ZRT XBGBJY.
HTQBZLF BSIVBGB, ZRT DLFSTF NPTTQ LD QBKLL, IH FTZPFQIQX ZL ZRT XBGBOZIO HTQBZT ZL WLZT LQ ZRT OFIZIOBG IHHPT LD OFTBZIQX BQ BFSY LD ZRT FTEPKGIO ZL BHHIHZ ZRT LWTFMRTGSTV CTVI…”

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“FX IWBBJX PB NB PB PWX GBBD. VSP FWO, JBGX JRO, PWX GBBD? FWO IWBBJX PWUJ RJ BSA NBRK? RDL PWXO GRO FXKK RJM FWO IKUGV PWX WUNWXJP GBSDPRUD? FWO, 35 OXRAJ RNB, EKO PWX RPKRDPUI? FWO LBXJ AUIX CKRO PXQRJ? FX IWBBJX PB NB PB PWX GBBD UD PWUJ LXIRLX RDL LB PWX BPWXA PWUDNJ, DBP VXIRSJX PWXO RAX XRJO, VSP VXIRSJX PWXO RAX WRAL, VXIRSJX PWRP NBRK FUKK JXATX PB BANRDUZX RDL GXRJSAX PWX VXJP BE BSA XDXANUXJ RDL JMUKKJ, VXIRSJX PWRP IWRKKXDNX UJ BDX PWRP FX RAX FUKKUDN PB RIIXCP, BDX FX RAX SDFUKKUDN PB CBJPCBDX, RDL BDX FWUIW FX UDPXDL PB FUD, RDL PWX BPWXAJ, PBB.”

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