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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: quiret
cipher variations:
rvjsfu swktgv txluhw uymvix vznwjy
waoxkz xbpyla ycqzmb zdranc aesbod
bftcpe cgudqf dhverg eiwfsh fjxgti
gkyhuj hlzivk imajwl jnbkxm koclyn
lpdmzo mqenap nrfobq osgpcr pthqds

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: quiret
Cipher: jfrivg

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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: quiret

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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: quiret
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: quiret
Cipher: dhverg

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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: quiret
Cipher: 145442245144

Extended Methods:
Method #1

Plaintext: quiret
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
q u i r e t 
1 5 4 2 5 4 
4 4 2 4 1 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: quiret
Cipher: viutrq

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Method #3

Plaintext: quiret
method variations:
ytgyqd tgyqdy gyqdyt
yqdytg qdytgy dytgyq

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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: quiret

all 720 cipher variations:
quiret quirte quiert quietr quiter quitre quriet qurite qureit qureti qurtei
qurtie querit querti queirt queitr quetir quetri qutrei qutrie quteri quteir
qutier qutire qiuret qiurte qiuert qiuetr qiuter qiutre qiruet qirute qireut
qiretu qirteu qirtue qierut qiertu qieurt qieutr qietur qietru qitreu qitrue
qiteru qiteur qituer qiture qriuet qriute qrieut qrietu qriteu qritue qruiet
qruite qrueit qrueti qrutei qrutie qreuit qreuti qreiut qreitu qretiu qretui
qrtuei qrtuie qrteui qrteiu qrtieu qrtiue qeirut qeirtu qeiurt qeiutr qeitur
qeitru qeriut qeritu qeruit qeruti qertui qertiu qeurit qeurti qeuirt qeuitr
qeutir qeutri qetrui qetriu qeturi qetuir qetiur qetiru qtireu qtirue qtieru
qtieur qtiuer qtiure qtrieu qtriue qtreiu qtreui qtruei qtruie qteriu qterui
qteiru qteiur qteuir qteuri qturei qturie qtueri qtueir qtuier qtuire uqiret
uqirte uqiert uqietr uqiter uqitre uqriet uqrite uqreit uqreti uqrtei uqrtie
uqerit uqerti uqeirt uqeitr uqetir uqetri uqtrei uqtrie uqteri uqteir uqtier
uqtire uiqret uiqrte uiqert uiqetr uiqter uiqtre uirqet uirqte uireqt uiretq
uirteq uirtqe uierqt uiertq uieqrt uieqtr uietqr uietrq uitreq uitrqe uiterq
uiteqr uitqer uitqre uriqet uriqte urieqt urietq uriteq uritqe urqiet urqite
urqeit urqeti urqtei urqtie ureqit ureqti ureiqt ureitq uretiq uretqi urtqei
urtqie urteqi urteiq urtieq urtiqe ueirqt ueirtq ueiqrt ueiqtr ueitqr ueitrq
ueriqt ueritq uerqit uerqti uertqi uertiq ueqrit ueqrti ueqirt ueqitr ueqtir
ueqtri uetrqi uetriq uetqri uetqir uetiqr uetirq utireq utirqe utierq utieqr
utiqer utiqre utrieq utriqe utreiq utreqi utrqei utrqie uteriq uterqi uteirq
uteiqr uteqir uteqri utqrei utqrie utqeri utqeir utqier utqire iuqret iuqrte
iuqert iuqetr iuqter iuqtre iurqet iurqte iureqt iuretq iurteq iurtqe iuerqt
iuertq iueqrt iueqtr iuetqr iuetrq iutreq iutrqe iuterq iuteqr iutqer iutqre
iquret iqurte iquert iquetr iquter iqutre iqruet iqrute iqreut iqretu iqrteu
iqrtue iqerut iqertu iqeurt iqeutr iqetur iqetru iqtreu iqtrue iqteru iqteur
iqtuer iqture irquet irqute irqeut irqetu irqteu irqtue iruqet iruqte irueqt
iruetq iruteq irutqe ireuqt ireutq irequt ireqtu iretqu iretuq irtueq irtuqe
irteuq irtequ irtqeu irtque ieqrut ieqrtu iequrt iequtr ieqtur ieqtru ierqut
ierqtu ieruqt ierutq iertuq iertqu ieurqt ieurtq ieuqrt ieuqtr ieutqr ieutrq
ietruq ietrqu ieturq ietuqr ietqur ietqru itqreu itqrue itqeru itqeur itquer
itqure itrqeu itrque itrequ itreuq itrueq itruqe iterqu iteruq iteqru itequr
iteuqr iteurq itureq iturqe ituerq itueqr ituqer ituqre ruiqet ruiqte ruieqt
ruietq ruiteq ruitqe ruqiet ruqite ruqeit ruqeti ruqtei ruqtie rueqit rueqti
rueiqt rueitq ruetiq ruetqi rutqei rutqie ruteqi ruteiq rutieq rutiqe riuqet
riuqte riueqt riuetq riuteq riutqe riquet riqute riqeut riqetu riqteu riqtue
riequt rieqtu rieuqt rieutq rietuq rietqu ritqeu ritque ritequ riteuq ritueq
rituqe rqiuet rqiute rqieut rqietu rqiteu rqitue rquiet rquite rqueit rqueti
rqutei rqutie rqeuit rqeuti rqeiut rqeitu rqetiu rqetui rqtuei rqtuie rqteui
rqteiu rqtieu rqtiue reiqut reiqtu reiuqt reiutq reituq reitqu reqiut reqitu
requit requti reqtui reqtiu reuqit reuqti reuiqt reuitq reutiq reutqi retqui
retqiu retuqi retuiq retiuq retiqu rtiqeu rtique rtiequ rtieuq rtiueq rtiuqe
rtqieu rtqiue rtqeiu rtqeui rtquei rtquie rteqiu rtequi rteiqu rteiuq rteuiq
rteuqi rtuqei rtuqie rtueqi rtueiq rtuieq rtuiqe euirqt euirtq euiqrt euiqtr
euitqr euitrq euriqt euritq eurqit eurqti eurtqi eurtiq euqrit euqrti euqirt
euqitr euqtir euqtri eutrqi eutriq eutqri eutqir eutiqr eutirq eiurqt eiurtq
eiuqrt eiuqtr eiutqr eiutrq eiruqt eirutq eirqut eirqtu eirtqu eirtuq eiqrut
eiqrtu eiqurt eiqutr eiqtur eiqtru eitrqu eitruq eitqru eitqur eituqr eiturq
eriuqt eriutq eriqut eriqtu eritqu erituq eruiqt eruitq eruqit eruqti erutqi
erutiq erquit erquti erqiut erqitu erqtiu erqtui ertuqi ertuiq ertqui ertqiu
ertiqu ertiuq eqirut eqirtu eqiurt eqiutr eqitur eqitru eqriut eqritu eqruit
eqruti eqrtui eqrtiu equrit equrti equirt equitr equtir equtri eqtrui eqtriu
eqturi eqtuir eqtiur eqtiru etirqu etiruq etiqru etiqur etiuqr etiurq etriqu
etriuq etrqiu etrqui etruqi etruiq etqriu etqrui etqiru etqiur etquir etquri
eturqi eturiq etuqri etuqir etuiqr etuirq tuireq tuirqe tuierq tuieqr tuiqer
tuiqre turieq turiqe tureiq tureqi turqei turqie tueriq tuerqi tueirq tueiqr
tueqir tueqri tuqrei tuqrie tuqeri tuqeir tuqier tuqire tiureq tiurqe tiuerq
tiueqr tiuqer tiuqre tirueq tiruqe tireuq tirequ tirqeu tirque tieruq tierqu
tieurq tieuqr tiequr tieqru tiqreu tiqrue tiqeru tiqeur tiquer tiqure triueq
triuqe trieuq triequ triqeu trique truieq truiqe trueiq trueqi truqei truqie
treuiq treuqi treiuq treiqu treqiu trequi trquei trquie trqeui trqeiu trqieu
trqiue teiruq teirqu teiurq teiuqr teiqur teiqru teriuq teriqu teruiq teruqi
terqui terqiu teuriq teurqi teuirq teuiqr teuqir teuqri teqrui teqriu tequri
tequir teqiur teqiru tqireu tqirue tqieru tqieur tqiuer tqiure tqrieu tqriue
tqreiu tqreui tqruei tqruie tqeriu tqerui tqeiru tqeiur tqeuir tqeuri tqurei
tqurie tqueri tqueir tquier tquire

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History of cryptography
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