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Caesar cipher

Caesar cipher, is one of the simplest and most widely known encryption techniques. The transformation can be represented by aligning two alphabets, the cipher alphabet is the plain alphabet rotated left or right by some number of positions.

When encrypting, a person looks up each letter of the message in the 'plain' line and writes down the corresponding letter in the 'cipher' line. Deciphering is done in reverse.
The encryption can also be represented using modular arithmetic by first transforming the letters into numbers, according to the scheme, A = 0, B = 1,..., Z = 25. Encryption of a letter x by a shift n can be described mathematically as

Plaintext: skybal
cipher variations:
tlzcbm umadcn vnbedo wocfep xpdgfq
yqehgr zrfihs asgjit bthkju cuilkv
dvjmlw ewknmx fxlony gympoz hznqpa
iaorqb jbpsrc kcqtsd ldrute mesvuf
nftwvg oguxwh phvyxi qiwzyj rjxazk

Decryption is performed similarly,

(There are different definitions for the modulo operation. In the above, the result is in the range 0...25. I.e., if x+n or x-n are not in the range 0...25, we have to subtract or add 26.)
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Atbash Cipher

Atbash is an ancient encryption system created in the Middle East. It was originally used in the Hebrew language.
The Atbash cipher is a simple substitution cipher that relies on transposing all the letters in the alphabet such that the resulting alphabet is backwards.
The first letter is replaced with the last letter, the second with the second-last, and so on.
An example plaintext to ciphertext using Atbash:
Plain: skybal
Cipher: hpbyzo

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Baconian Cipher

To encode a message, each letter of the plaintext is replaced by a group of five of the letters 'A' or 'B'. This replacement is done according to the alphabet of the Baconian cipher, shown below.
a   AAAAA   g    AABBA     m    ABABB   s    BAAAB     y    BABBA
b   AAAAB   h    AABBB     n    ABBAA   t    BAABA     z    BABBB
c   AAABA   i    ABAAA     o    ABBAB   u    BAABB 
d   AAABB   j    BBBAA     p    ABBBA   v    BBBAB
e   AABAA   k    ABAAB     q    ABBBB   w    BABAA
f   AABAB   l    ABABA     r    BAAAA   x    BABAB

Plain: skybal

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Affine Cipher
In the affine cipher the letters of an alphabet of size m are first mapped to the integers in the range 0..m - 1. It then uses modular arithmetic to transform the integer that each plaintext letter corresponds to into another integer that correspond to a ciphertext letter. The encryption function for a single letter is

where modulus m is the size of the alphabet and a and b are the key of the cipher. The value a must be chosen such that a and m are coprime.
Considering the specific case of encrypting messages in English (i.e. m = 26), there are a total of 286 non-trivial affine ciphers, not counting the 26 trivial Caesar ciphers. This number comes from the fact there are 12 numbers that are coprime with 26 that are less than 26 (these are the possible values of a). Each value of a can have 26 different addition shifts (the b value) ; therefore, there are 12*26 or 312 possible keys.
Plaintext: skybal
cipher variations:

The decryption function is

where a - 1 is the modular multiplicative inverse of a modulo m. I.e., it satisfies the equation

The multiplicative inverse of a only exists if a and m are coprime. Hence without the restriction on a decryption might not be possible. It can be shown as follows that decryption function is the inverse of the encryption function,

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ROT13 Cipher
Applying ROT13 to a piece of text merely requires examining its alphabetic characters and replacing each one by the letter 13 places further along in the alphabet, wrapping back to the beginning if necessary. A becomes N, B becomes O, and so on up to M, which becomes Z, then the sequence continues at the beginning of the alphabet: N becomes A, O becomes B, and so on to Z, which becomes M. Only those letters which occur in the English alphabet are affected; numbers, symbols, whitespace, and all other characters are left unchanged. Because there are 26 letters in the English alphabet and 26 = 2 * 13, the ROT13 function is its own inverse:

ROT13(ROT13(x)) = x for any basic Latin-alphabet text x

An example plaintext to ciphertext using ROT13:

Plain: skybal
Cipher: fxlony

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Polybius Square

A Polybius Square is a table that allows someone to translate letters into numbers. To give a small level of encryption, this table can be randomized and shared with the recipient. In order to fit the 26 letters of the alphabet into the 25 spots created by the table, the letters i and j are usually combined.
1 2 3 4 5
1 A B C D E
2 F G H I/J K
3 L M N O P
4 Q R S T U
5 V W X Y Z

Basic Form:
Plain: skybal
Cipher: 345245211113

Extended Methods:
Method #1

Plaintext: skybal
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
s k y b a l 
3 5 4 2 1 1 
4 2 5 1 1 3 
They are then read out in rows:
Then divided up into pairs again, and the pairs turned back into letters using the square:
Plain: skybal
Cipher: xiaiel

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Method #3

Plaintext: skybal
method variations:
yrkaan rkaany kaanyr
aanyrk anyrka nyrkaa

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Permutation Cipher
In classical cryptography, a permutation cipher is a transposition cipher in which the key is a permutation. To apply a cipher, a random permutation of size E is generated (the larger the value of E the more secure the cipher). The plaintext is then broken into segments of size E and the letters within that segment are permuted according to this key.
In theory, any transposition cipher can be viewed as a permutation cipher where E is equal to the length of the plaintext; this is too cumbersome a generalisation to use in actual practice, however.
The idea behind a permutation cipher is to keep the plaintext characters unchanged, butalter their positions by rearrangement using a permutation
This cipher is defined as:
Let m be a positive integer, and K consist of all permutations of {1,...,m}
For a key (permutation) , define:
The encryption function
The decryption function
A small example, assuming m = 6, and the key is the permutation :

The first row is the value of i, and the second row is the corresponding value of (i)
The inverse permutation, is constructed by interchanging the two rows, andrearranging the columns so that the first row is in increasing order, Therefore, is:

Total variation formula:

e = 2,718281828 , n - plaintext length

Plaintext: skybal

all 720 cipher variations:
skybal skybla skyabl skyalb skylab skylba skbyal skbyla skbayl skbaly skblay
skblya skabyl skably skaybl skaylb skalyb skalby sklbay sklbya sklaby sklayb
sklyab sklyba sykbal sykbla sykabl sykalb syklab syklba sybkal sybkla sybakl
sybalk syblak syblka syabkl syablk syakbl syaklb syalkb syalbk sylbak sylbka
sylabk sylakb sylkab sylkba sbykal sbykla sbyakl sbyalk sbylak sbylka sbkyal
sbkyla sbkayl sbkaly sbklay sbklya sbakyl sbakly sbaykl sbaylk sbalyk sbalky
sblkay sblkya sblaky sblayk sblyak sblyka saybkl sayblk saykbl sayklb saylkb
saylbk sabykl sabylk sabkyl sabkly sablky sablyk sakbyl sakbly sakybl sakylb
saklyb saklby salbky salbyk salkby salkyb salykb salybk slybak slybka slyabk
slyakb slykab slykba slbyak slbyka slbayk slbaky slbkay slbkya slabyk slabky
slaybk slaykb slakyb slakby slkbay slkbya slkaby slkayb slkyab slkyba ksybal
ksybla ksyabl ksyalb ksylab ksylba ksbyal ksbyla ksbayl ksbaly ksblay ksblya
ksabyl ksably ksaybl ksaylb ksalyb ksalby kslbay kslbya kslaby kslayb kslyab
kslyba kysbal kysbla kysabl kysalb kyslab kyslba kybsal kybsla kybasl kybals
kyblas kyblsa kyabsl kyabls kyasbl kyaslb kyalsb kyalbs kylbas kylbsa kylabs
kylasb kylsab kylsba kbysal kbysla kbyasl kbyals kbylas kbylsa kbsyal kbsyla
kbsayl kbsaly kbslay kbslya kbasyl kbasly kbaysl kbayls kbalys kbalsy kblsay
kblsya kblasy kblays kblyas kblysa kaybsl kaybls kaysbl kayslb kaylsb kaylbs
kabysl kabyls kabsyl kabsly kablsy kablys kasbyl kasbly kasybl kasylb kaslyb
kaslby kalbsy kalbys kalsby kalsyb kalysb kalybs klybas klybsa klyabs klyasb
klysab klysba klbyas klbysa klbays klbasy klbsay klbsya klabys klabsy klaybs
klaysb klasyb klasby klsbay klsbya klsaby klsayb klsyab klsyba yksbal yksbla
yksabl yksalb ykslab ykslba ykbsal ykbsla ykbasl ykbals ykblas ykblsa ykabsl
ykabls ykasbl ykaslb ykalsb ykalbs yklbas yklbsa yklabs yklasb yklsab yklsba
yskbal yskbla yskabl yskalb ysklab ysklba ysbkal ysbkla ysbakl ysbalk ysblak
ysblka ysabkl ysablk ysakbl ysaklb ysalkb ysalbk yslbak yslbka yslabk yslakb
yslkab yslkba ybskal ybskla ybsakl ybsalk ybslak ybslka ybksal ybksla ybkasl
ybkals ybklas ybklsa ybaksl ybakls ybaskl ybaslk ybalsk ybalks yblkas yblksa
yblaks yblask yblsak yblska yasbkl yasblk yaskbl yasklb yaslkb yaslbk yabskl
yabslk yabksl yabkls yablks yablsk yakbsl yakbls yaksbl yakslb yaklsb yaklbs
yalbks yalbsk yalkbs yalksb yalskb yalsbk ylsbak ylsbka ylsabk ylsakb ylskab
ylskba ylbsak ylbska ylbask ylbaks ylbkas ylbksa ylabsk ylabks ylasbk ylaskb
ylaksb ylakbs ylkbas ylkbsa ylkabs ylkasb ylksab ylksba bkysal bkysla bkyasl
bkyals bkylas bkylsa bksyal bksyla bksayl bksaly bkslay bkslya bkasyl bkasly
bkaysl bkayls bkalys bkalsy bklsay bklsya bklasy bklays bklyas bklysa byksal
byksla bykasl bykals byklas byklsa byskal byskla bysakl bysalk byslak byslka
byaskl byaslk byaksl byakls byalks byalsk bylsak bylska bylask bylaks bylkas
bylksa bsykal bsykla bsyakl bsyalk bsylak bsylka bskyal bskyla bskayl bskaly
bsklay bsklya bsakyl bsakly bsaykl bsaylk bsalyk bsalky bslkay bslkya bslaky
bslayk bslyak bslyka bayskl bayslk bayksl baykls baylks baylsk basykl basylk
baskyl baskly baslky baslyk baksyl baksly bakysl bakyls baklys baklsy balsky
balsyk balksy balkys balyks balysk blysak blyska blyask blyaks blykas blyksa
blsyak blsyka blsayk blsaky blskay blskya blasyk blasky blaysk blayks blakys
blaksy blksay blksya blkasy blkays blkyas blkysa akybsl akybls akysbl akyslb
akylsb akylbs akbysl akbyls akbsyl akbsly akblsy akblys aksbyl aksbly aksybl
aksylb akslyb akslby aklbsy aklbys aklsby aklsyb aklysb aklybs aykbsl aykbls
ayksbl aykslb ayklsb ayklbs aybksl aybkls aybskl aybslk ayblsk ayblks aysbkl
aysblk ayskbl aysklb ayslkb ayslbk aylbsk aylbks aylsbk aylskb aylksb aylkbs
abyksl abykls abyskl abyslk abylsk abylks abkysl abkyls abksyl abksly abklsy
abklys abskyl abskly absykl absylk abslyk abslky ablksy ablkys ablsky ablsyk
ablysk ablyks asybkl asyblk asykbl asyklb asylkb asylbk asbykl asbylk asbkyl
asbkly asblky asblyk askbyl askbly askybl askylb asklyb asklby aslbky aslbyk
aslkby aslkyb aslykb aslybk alybsk alybks alysbk alyskb alyksb alykbs albysk
albyks albsyk albsky albksy albkys alsbyk alsbky alsybk alsykb alskyb alskby
alkbsy alkbys alksby alksyb alkysb alkybs lkybas lkybsa lkyabs lkyasb lkysab
lkysba lkbyas lkbysa lkbays lkbasy lkbsay lkbsya lkabys lkabsy lkaybs lkaysb
lkasyb lkasby lksbay lksbya lksaby lksayb lksyab lksyba lykbas lykbsa lykabs
lykasb lyksab lyksba lybkas lybksa lybaks lybask lybsak lybska lyabks lyabsk
lyakbs lyaksb lyaskb lyasbk lysbak lysbka lysabk lysakb lyskab lyskba lbykas
lbyksa lbyaks lbyask lbysak lbyska lbkyas lbkysa lbkays lbkasy lbksay lbksya
lbakys lbaksy lbayks lbaysk lbasyk lbasky lbskay lbskya lbsaky lbsayk lbsyak
lbsyka laybks laybsk laykbs layksb layskb laysbk labyks labysk labkys labksy
labsky labsyk lakbys lakbsy lakybs lakysb laksyb laksby lasbky lasbyk laskby
laskyb lasykb lasybk lsybak lsybka lsyabk lsyakb lsykab lsykba lsbyak lsbyka
lsbayk lsbaky lsbkay lsbkya lsabyk lsabky lsaybk lsaykb lsakyb lsakby lskbay
lskbya lskaby lskayb lskyab lskyba

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History of cryptography
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