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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: copan
cipher variations:
dpqbo eqrcp frsdq gster htufs
iuvgt jvwhu kwxiv lxyjw myzkx
nzaly oabmz pbcna qcdob rdepc
sefqd tfgre ughsf vhitg wijuh
xjkvi yklwj zlmxk amnyl bnozm

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: copan
Cipher: xlkzm

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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: copan
Cipher: AAABA ABBAB ABBBA AAAAA ABBAA

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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: copan
cipher variations:
dpqbohruboltybopvcbotxgboxzkbofdsbojfwbo
nhaborjebovliboznmboeqrcpisvcpmuzcpqwdcp
uyhcpyalcpgetcpkgxcpoibcpskfcpwmjcpaoncp
frsdqjtwdqnvadqrxedqvzidqzbmdqhfudqlhydq
pjcdqtlgdqxnkdqbpodqgsterkuxerowbersyfer
wajeracnerigvermizerqkderumheryolercqper
htufslvyfspxcfstzgfsxbkfsbdofsjhwfsnjafs
rlefsvnifszpmfsdrqfsiuvgtmwzgtqydgtuahgt
yclgtcepgtkixgtokbgtsmfgtwojgtaqngtesrgt
jvwhunxahurzehuvbihuzdmhudfqhuljyhuplchu
tnghuxpkhubrohuftshukwxivoybivsafivwcjiv
aenivegrivmkzivqmdivuohivyqlivcspivgutiv
lxyjwpzcjwtbgjwxdkjwbfojwfhsjwnlajwrnejw
vpijwzrmjwdtqjwhvujwmyzkxqadkxuchkxyelkx
cgpkxgitkxombkxsofkxwqjkxasnkxeurkxiwvkx
nzalyrbelyvdilyzfmlydhqlyhjulypnclytpgly
xrklybtolyfvslyjxwlyoabmzscfmzwejmzagnmz
eirmzikvmzqodmzuqhmzyslmzcupmzgwtmzkyxmz
pbcnatdgnaxfknabhonafjsnajlwnarpenavrina
ztmnadvqnahxunalzynaqcdobuehobyglobcipob
gktobkmxobsqfobwsjobaunobewrobiyvobmazob
rdepcvfipczhmpcdjqpchlupclnypctrgpcxtkpc
bvopcfxspcjzwpcnbapcsefqdwgjqdainqdekrqd
imvqdmozqdushqdyulqdcwpqdgytqdkaxqdocbqd
tfgrexhkrebjoreflsrejnwrenparevtirezvmre
dxqrehzurelbyrepdcreughsfyilsfckpsfgmtsf
koxsfoqbsfwujsfawnsfeyrsfiavsfmczsfqedsf
vhitgzjmtgdlqtghnutglpytgprctgxvktgbxotg
fzstgjbwtgndatgrfetgwijuhaknuhemruhiovuh
mqzuhqsduhywluhcypuhgatuhkcxuhoebuhsgfuh
xjkviblovifnsvijpwvinravirtevizxmvidzqvi
hbuvildyvipfcvithgviyklwjcmpwjgotwjkqxwj
osbwjsufwjaynwjearwjicvwjmezwjqgdwjuihwj
zlmxkdnqxkhpuxklryxkptcxktvgxkbzoxkfbsxk
jdwxknfaxkrhexkvjixkamnyleoryliqvylmszyl
qudyluwhylcapylgctylkexylogbylsifylwkjyl
bnozmfpszmjrwzmntazmrvezmvxizmdbqzmhduzm
lfyzmphczmtjgzmxlkzmcopangqtanksxanouban
swfanwyjanecranievanmgzanqidanukhanymlan

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: copan
Cipher: pbcna

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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: copan
Cipher: 3143531133

Extended Methods:
Method #1

Plaintext: copan
method variations:
htufsnyzlxsdeqcxikvh

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
c o p a n 
3 4 5 1 3 
1 3 3 1 3 
They are then read out in rows:
3451313313
Then divided up into pairs again, and the pairs turned back into letters using the square:
Plain: copan
Cipher: secnl

Read more ...
Method #3

Plaintext: copan
method variations:
qxcln xclnq clnqx
lnqxc nqxcl

Read more ...[RUS] , [EN]

 

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: copan

all 120 cipher variations:
copan copna coapn coanp conap conpa cpoan cpona cpaon cpano cpnao
cpnoa capon capno caopn caonp canop canpo cnpao cnpoa cnapo cnaop
cnoap cnopa ocpan ocpna ocapn ocanp ocnap ocnpa opcan opcna opacn
opanc opnac opnca oapcn oapnc oacpn oacnp oancp oanpc onpac onpca
onapc onacp oncap oncpa pocan pocna poacn poanc ponac ponca pcoan
pcona pcaon pcano pcnao pcnoa pacon pacno paocn paonc panoc panco
pncao pncoa pnaco pnaoc pnoac pnoca aopcn aopnc aocpn aocnp aoncp
aonpc apocn aponc apcon apcno apnco apnoc acpon acpno acopn aconp
acnop acnpo anpco anpoc ancpo ancop anocp anopc nopac nopca noapc
noacp nocap nocpa npoac npoca npaoc npaco npcao npcoa napoc napco
naopc naocp nacop nacpo ncpao ncpoa ncapo ncaop ncoap ncopa

Read more ...[1] , [2] , [3]

History of cryptography
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