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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: dressy
cipher variations:
esfttz ftguua guhvvb hviwwc iwjxxd
jxkyye kylzzf lzmaag manbbh nbocci
ocpddj pdqeek qerffl rfsggm sgthhn
thuiio uivjjp vjwkkq wkxllr xlymms
ymznnt znaoou aobppv bpcqqw cqdrrx

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: dressy
Cipher: wivhhb

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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: dressy

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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: dressy
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: dressy
Cipher: qerffl

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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: dressy
Cipher: 412451343445

Extended Methods:
Method #1

Plaintext: dressy
method variations:

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

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Method #3

Plaintext: dressy
method variations:
fylotu ylotuf lotufy
otufyl tufylo ufylot

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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: dressy

all 720 cipher variations:
dressy dresys dressy dresys dreyss dreyss drsesy drseys drssey drssye drsyse
drsyes drssey drssye drsesy drseys drsyes drsyse drysse dryses drysse dryses
dryess dryess derssy dersys derssy dersys deryss deryss desrsy desrys dessry
dessyr desysr desyrs dessry dessyr desrsy desrys desyrs desysr deyssr deysrs
deyssr deysrs deyrss deyrss dsersy dserys dsesry dsesyr dseysr dseyrs dsresy
dsreys dsrsey dsrsye dsryse dsryes dssrey dssrye dssery dsseyr dssyer dssyre
dsyrse dsyres dsysre dsyser dsyesr dsyers dsesry dsesyr dsersy dserys dseyrs
dseysr dssery dsseyr dssrey dssrye dssyre dssyer dsrsey dsrsye dsresy dsreys
dsryes dsryse dsysre dsyser dsyrse dsyres dsyers dsyesr dyessr dyesrs dyessr
dyesrs dyerss dyerss dysesr dysers dysser dyssre dysrse dysres dysser dyssre
dysesr dysers dysres dysrse dyrsse dyrses dyrsse dyrses dyress dyress rdessy
rdesys rdessy rdesys rdeyss rdeyss rdsesy rdseys rdssey rdssye rdsyse rdsyes
rdssey rdssye rdsesy rdseys rdsyes rdsyse rdysse rdyses rdysse rdyses rdyess
rdyess redssy redsys redssy redsys redyss redyss resdsy resdys ressdy ressyd
resysd resyds ressdy ressyd resdsy resdys resyds resysd reyssd reysds reyssd
reysds reydss reydss rsedsy rsedys rsesdy rsesyd rseysd rseyds rsdesy rsdeys
rsdsey rsdsye rsdyse rsdyes rssdey rssdye rssedy rsseyd rssyed rssyde rsydse
rsydes rsysde rsysed rsyesd rsyeds rsesdy rsesyd rsedsy rsedys rseyds rseysd
rssedy rsseyd rssdey rssdye rssyde rssyed rsdsey rsdsye rsdesy rsdeys rsdyes
rsdyse rsysde rsysed rsydse rsydes rsyeds rsyesd ryessd ryesds ryessd ryesds
ryedss ryedss rysesd ryseds ryssed ryssde rysdse rysdes ryssed ryssde rysesd
ryseds rysdes rysdse rydsse rydses rydsse rydses rydess rydess erdssy erdsys
erdssy erdsys erdyss erdyss ersdsy ersdys erssdy erssyd ersysd ersyds erssdy
erssyd ersdsy ersdys ersyds ersysd eryssd erysds eryssd erysds erydss erydss
edrssy edrsys edrssy edrsys edryss edryss edsrsy edsrys edssry edssyr edsysr
edsyrs edssry edssyr edsrsy edsrys edsyrs edsysr edyssr edysrs edyssr edysrs
edyrss edyrss esdrsy esdrys esdsry esdsyr esdysr esdyrs esrdsy esrdys esrsdy
esrsyd esrysd esryds essrdy essryd essdry essdyr essydr essyrd esyrsd esyrds
esysrd esysdr esydsr esydrs esdsry esdsyr esdrsy esdrys esdyrs esdysr essdry
essdyr essrdy essryd essyrd essydr esrsdy esrsyd esrdsy esrdys esryds esrysd
esysrd esysdr esyrsd esyrds esydrs esydsr eydssr eydsrs eydssr eydsrs eydrss
eydrss eysdsr eysdrs eyssdr eyssrd eysrsd eysrds eyssdr eyssrd eysdsr eysdrs
eysrds eysrsd eyrssd eyrsds eyrssd eyrsds eyrdss eyrdss sredsy sredys sresdy
sresyd sreysd sreyds srdesy srdeys srdsey srdsye srdyse srdyes srsdey srsdye
srsedy srseyd srsyed srsyde srydse srydes srysde srysed sryesd sryeds serdsy
serdys sersdy sersyd serysd seryds sedrsy sedrys sedsry sedsyr sedysr sedyrs
sesdry sesdyr sesrdy sesryd sesyrd sesydr seydsr seydrs seysdr seysrd seyrsd
seyrds sdersy sderys sdesry sdesyr sdeysr sdeyrs sdresy sdreys sdrsey sdrsye
sdryse sdryes sdsrey sdsrye sdsery sdseyr sdsyer sdsyre sdyrse sdyres sdysre
sdyser sdyesr sdyers ssedry ssedyr sserdy sseryd sseyrd sseydr ssdery ssdeyr
ssdrey ssdrye ssdyre ssdyer ssrdey ssrdye ssredy ssreyd ssryed ssryde ssydre
ssyder ssyrde ssyred ssyerd ssyedr syedsr syedrs syesdr syesrd syersd syerds
sydesr syders sydser sydsre sydrse sydres sysder sysdre sysedr syserd sysred
sysrde syrdse syrdes syrsde syrsed syresd syreds sresdy sresyd sredsy sredys
sreyds sreysd srsedy srseyd srsdey srsdye srsyde srsyed srdsey srdsye srdesy
srdeys srdyes srdyse srysde srysed srydse srydes sryeds sryesd sersdy sersyd
serdsy serdys seryds serysd sesrdy sesryd sesdry sesdyr sesydr sesyrd sedsry
sedsyr sedrsy sedrys sedyrs sedysr seysdr seysrd seydsr seydrs seyrds seyrsd
sserdy sseryd ssedry ssedyr sseydr sseyrd ssredy ssreyd ssrdey ssrdye ssryde
ssryed ssdrey ssdrye ssdery ssdeyr ssdyer ssdyre ssyrde ssyred ssydre ssyder
ssyedr ssyerd sdesry sdesyr sdersy sderys sdeyrs sdeysr sdsery sdseyr sdsrey
sdsrye sdsyre sdsyer sdrsey sdrsye sdresy sdreys sdryes sdryse sdysre sdyser
sdyrse sdyres sdyers sdyesr syesdr syesrd syedsr syedrs syerds syersd sysedr
syserd sysder sysdre sysrde sysred sydser sydsre sydesr syders sydres sydrse
syrsde syrsed syrdse syrdes syreds syresd yressd yresds yressd yresds yredss
yredss yrsesd yrseds yrssed yrssde yrsdse yrsdes yrssed yrssde yrsesd yrseds
yrsdes yrsdse yrdsse yrdses yrdsse yrdses yrdess yrdess yerssd yersds yerssd
yersds yerdss yerdss yesrsd yesrds yessrd yessdr yesdsr yesdrs yessrd yessdr
yesrsd yesrds yesdrs yesdsr yedssr yedsrs yedssr yedsrs yedrss yedrss ysersd
yserds ysesrd ysesdr ysedsr ysedrs ysresd ysreds ysrsed ysrsde ysrdse ysrdes
yssred yssrde ysserd yssedr yssder yssdre ysdrse ysdres ysdsre ysdser ysdesr
ysders ysesrd ysesdr ysersd yserds ysedrs ysedsr ysserd yssedr yssred yssrde
yssdre yssder ysrsed ysrsde ysresd ysreds ysrdes ysrdse ysdsre ysdser ysdrse
ysdres ysders ysdesr ydessr ydesrs ydessr ydesrs yderss yderss ydsesr ydsers
ydsser ydssre ydsrse ydsres ydsser ydssre ydsesr ydsers ydsres ydsrse ydrsse
ydrses ydrsse ydrses ydress ydress

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History of cryptography
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