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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: ydalir
cipher variations:
zebmjs afcnkt bgdolu chepmv difqnw
ejgrox fkhspy glitqz hmjura inkvsb
jolwtc kpmxud lqnyve mrozwf nspaxg
otqbyh purczi qvsdaj rwtebk sxufcl
tyvgdm uzwhen vaxifo wbyjgp xczkhq

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: ydalir
Cipher: bwzori

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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: ydalir

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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: ydalir
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: ydalir
Cipher: lqnyve

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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: ydalir
Cipher: 454111134224

Extended Methods:
Method #1

Plaintext: ydalir
method variations:

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

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Method #3

Plaintext: ydalir
method variations:
uaasgt aasgtu asgtua
sgtuaa gtuaas tuaasg

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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: ydalir

all 720 cipher variations:
ydalir ydalri ydailr ydairl ydaril ydarli ydlair ydlari ydliar ydlira ydlria
ydlrai ydilar ydilra ydialr ydiarl ydiral ydirla ydrlia ydrlai ydrila ydrial
ydrail ydrali yadlir yadlri yadilr yadirl yadril yadrli yaldir yaldri yalidr
yalird yalrid yalrdi yaildr yailrd yaidlr yaidrl yairdl yairld yarlid yarldi
yarild yaridl yardil yardli yladir yladri ylaidr ylaird ylarid ylardi yldair
yldari yldiar yldira yldria yldrai ylidar ylidra yliadr yliard ylirad ylirda
ylrdia ylrdai ylrida ylriad ylraid ylradi yialdr yialrd yiadlr yiadrl yiardl
yiarld yiladr yilard yildar yildra yilrda yilrad yidlar yidlra yidalr yidarl
yidral yidrla yirlda yirlad yirdla yirdal yiradl yirald yralid yraldi yraild
yraidl yradil yradli yrlaid yrladi yrliad yrlida yrldia yrldai yrilad yrilda
yriald yriadl yridal yridla yrdlia yrdlai yrdila yrdial yrdail yrdali dyalir
dyalri dyailr dyairl dyaril dyarli dylair dylari dyliar dylira dylria dylrai
dyilar dyilra dyialr dyiarl dyiral dyirla dyrlia dyrlai dyrila dyrial dyrail
dyrali daylir daylri dayilr dayirl dayril dayrli dalyir dalyri daliyr daliry
dalriy dalryi dailyr dailry daiylr daiyrl dairyl dairly darliy darlyi darily
dariyl daryil daryli dlayir dlayri dlaiyr dlairy dlariy dlaryi dlyair dlyari
dlyiar dlyira dlyria dlyrai dliyar dliyra dliayr dliary dliray dlirya dlryia
dlryai dlriya dlriay dlraiy dlrayi dialyr dialry diaylr diayrl diaryl diarly
dilayr dilary dilyar dilyra dilrya dilray diylar diylra diyalr diyarl diyral
diyrla dirlya dirlay diryla diryal dirayl diraly draliy dralyi draily draiyl
drayil drayli drlaiy drlayi drliay drliya drlyia drlyai drilay drilya drialy
driayl driyal driyla drylia drylai dryila dryial dryail dryali adylir adylri
adyilr adyirl adyril adyrli adlyir adlyri adliyr adliry adlriy adlryi adilyr
adilry adiylr adiyrl adiryl adirly adrliy adrlyi adrily adriyl adryil adryli
aydlir aydlri aydilr aydirl aydril aydrli ayldir ayldri aylidr aylird aylrid
aylrdi ayildr ayilrd ayidlr ayidrl ayirdl ayirld ayrlid ayrldi ayrild ayridl
ayrdil ayrdli alydir alydri alyidr alyird alyrid alyrdi aldyir aldyri aldiyr
aldiry aldriy aldryi alidyr alidry aliydr aliyrd aliryd alirdy alrdiy alrdyi
alridy alriyd alryid alrydi aiyldr aiylrd aiydlr aiydrl aiyrdl aiyrld ailydr
ailyrd aildyr aildry ailrdy ailryd aidlyr aidlry aidylr aidyrl aidryl aidrly
airldy airlyd airdly airdyl airydl airyld arylid aryldi aryild aryidl arydil
arydli arlyid arlydi arliyd arlidy arldiy arldyi arilyd arildy ariyld ariydl
aridyl aridly ardliy ardlyi ardily ardiyl ardyil ardyli ldayir ldayri ldaiyr
ldairy ldariy ldaryi ldyair ldyari ldyiar ldyira ldyria ldyrai ldiyar ldiyra
ldiayr ldiary ldiray ldirya ldryia ldryai ldriya ldriay ldraiy ldrayi ladyir
ladyri ladiyr ladiry ladriy ladryi laydir laydri layidr layird layrid layrdi
laiydr laiyrd laidyr laidry lairdy lairyd laryid larydi lariyd laridy lardiy
lardyi lyadir lyadri lyaidr lyaird lyarid lyardi lydair lydari lydiar lydira
lydria lydrai lyidar lyidra lyiadr lyiard lyirad lyirda lyrdia lyrdai lyrida
lyriad lyraid lyradi liaydr liayrd liadyr liadry liardy liaryd liyadr liyard
liydar liydra liyrda liyrad lidyar lidyra lidayr lidary lidray lidrya liryda
liryad lirdya lirday lirady lirayd lrayid lraydi lraiyd lraidy lradiy lradyi
lryaid lryadi lryiad lryida lrydia lrydai lriyad lriyda lriayd lriady lriday
lridya lrdyia lrdyai lrdiya lrdiay lrdaiy lrdayi idalyr idalry idaylr idayrl
idaryl idarly idlayr idlary idlyar idlyra idlrya idlray idylar idylra idyalr
idyarl idyral idyrla idrlya idrlay idryla idryal idrayl idraly iadlyr iadlry
iadylr iadyrl iadryl iadrly ialdyr ialdry ialydr ialyrd ialryd ialrdy iayldr
iaylrd iaydlr iaydrl iayrdl iayrld iarlyd iarldy iaryld iarydl iardyl iardly
iladyr iladry ilaydr ilayrd ilaryd ilardy ildayr ildary ildyar ildyra ildrya
ildray ilydar ilydra ilyadr ilyard ilyrad ilyrda ilrdya ilrday ilryda ilryad
ilrayd ilrady iyaldr iyalrd iyadlr iyadrl iyardl iyarld iyladr iylard iyldar
iyldra iylrda iylrad iydlar iydlra iydalr iydarl iydral iydrla iyrlda iyrlad
iyrdla iyrdal iyradl iyrald iralyd iraldy irayld iraydl iradyl iradly irlayd
irlady irlyad irlyda irldya irlday irylad irylda iryald iryadl irydal irydla
irdlya irdlay irdyla irdyal irdayl irdaly rdaliy rdalyi rdaily rdaiyl rdayil
rdayli rdlaiy rdlayi rdliay rdliya rdlyia rdlyai rdilay rdilya rdialy rdiayl
rdiyal rdiyla rdylia rdylai rdyila rdyial rdyail rdyali radliy radlyi radily
radiyl radyil radyli raldiy raldyi ralidy raliyd ralyid ralydi raildy railyd
raidly raidyl raiydl raiyld raylid rayldi rayild rayidl raydil raydli rladiy
rladyi rlaidy rlaiyd rlayid rlaydi rldaiy rldayi rldiay rldiya rldyia rldyai
rliday rlidya rliady rliayd rliyad rliyda rlydia rlydai rlyida rlyiad rlyaid
rlyadi rialdy rialyd riadly riadyl riaydl riayld rilady rilayd rilday rildya
rilyda rilyad ridlay ridlya ridaly ridayl ridyal ridyla riylda riylad riydla
riydal riyadl riyald ryalid ryaldi ryaild ryaidl ryadil ryadli rylaid ryladi
ryliad rylida ryldia ryldai ryilad ryilda ryiald ryiadl ryidal ryidla rydlia
rydlai rydila rydial rydail rydali

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History of cryptography
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