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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: prouty
cipher variations:
qspvuz rtqwva surxwb tvsyxc uwtzyd
vxuaze wyvbaf xzwcbg yaxdch zbyedi
aczfej bdagfk cebhgl dfcihm egdjin
fhekjo giflkp hjgmlq ikhnmr jlions
kmjpot lnkqpu molrqv npmsrw oqntsx

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: prouty
Cipher: kilfgb

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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: prouty

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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: prouty
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: prouty
Cipher: cebhgl

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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: prouty
Cipher: 532443544445

Extended Methods:
Method #1

Plaintext: prouty
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
p r o u t y 
5 2 4 5 4 4 
3 4 3 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: prouty
Cipher: kytssy

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Method #3

Plaintext: prouty
method variations:
htxttz txttzh xttzht
ttzhtx tzhtxt zhtxtt

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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: prouty

all 720 cipher variations:
prouty prouyt protuy protyu proytu proyut pruoty pruoyt prutoy prutyo pruyto
pruyot prtuoy prtuyo prtouy prtoyu prtyou prtyuo pryuto pryuot prytuo prytou
pryotu pryout poruty poruyt portuy portyu porytu poryut pourty pouryt poutry
poutyr pouytr pouyrt potury potuyr potruy potryu potyru potyur poyutr poyurt
poytur poytru poyrtu poyrut puorty puoryt puotry puotyr puoytr puoyrt puroty
puroyt purtoy purtyo puryto puryot putroy putryo putory putoyr putyor putyro
puyrto puyrot puytro puytor puyotr puyort ptoury ptouyr ptoruy ptoryu ptoyru
ptoyur ptuory ptuoyr pturoy pturyo ptuyro ptuyor ptruoy ptruyo ptrouy ptroyu
ptryou ptryuo ptyuro ptyuor ptyruo ptyrou ptyoru ptyour pyoutr pyourt pyotur
pyotru pyortu pyorut pyuotr pyuort pyutor pyutro pyurto pyurot pytuor pyturo
pytour pytoru pytrou pytruo pyruto pyruot pyrtuo pyrtou pyrotu pyrout rpouty
rpouyt rpotuy rpotyu rpoytu rpoyut rpuoty rpuoyt rputoy rputyo rpuyto rpuyot
rptuoy rptuyo rptouy rptoyu rptyou rptyuo rpyuto rpyuot rpytuo rpytou rpyotu
rpyout roputy ropuyt roptuy roptyu ropytu ropyut roupty roupyt routpy routyp
rouytp rouypt rotupy rotuyp rotpuy rotpyu rotypu rotyup royutp royupt roytup
roytpu royptu royput ruopty ruopyt ruotpy ruotyp ruoytp ruoypt rupoty rupoyt
ruptoy ruptyo rupyto rupyot rutpoy rutpyo rutopy rutoyp rutyop rutypo ruypto
ruypot ruytpo ruytop ruyotp ruyopt rtoupy rtouyp rtopuy rtopyu rtoypu rtoyup
rtuopy rtuoyp rtupoy rtupyo rtuypo rtuyop rtpuoy rtpuyo rtpouy rtpoyu rtpyou
rtpyuo rtyupo rtyuop rtypuo rtypou rtyopu rtyoup ryoutp ryoupt ryotup ryotpu
ryoptu ryoput ryuotp ryuopt ryutop ryutpo ryupto ryupot rytuop rytupo rytoup
rytopu rytpou rytpuo ryputo rypuot ryptuo ryptou rypotu rypout orputy orpuyt
orptuy orptyu orpytu orpyut orupty orupyt orutpy orutyp oruytp oruypt ortupy
ortuyp ortpuy ortpyu ortypu ortyup oryutp oryupt orytup orytpu oryptu oryput
opruty opruyt oprtuy oprtyu oprytu opryut opurty opuryt oputry oputyr opuytr
opuyrt optury optuyr optruy optryu optyru optyur opyutr opyurt opytur opytru
opyrtu opyrut ouprty oupryt ouptry ouptyr oupytr oupyrt ourpty ourpyt ourtpy
ourtyp ourytp ourypt outrpy outryp outpry outpyr outypr outyrp ouyrtp ouyrpt
ouytrp ouytpr ouyptr ouyprt otpury otpuyr otpruy otpryu otpyru otpyur otupry
otupyr oturpy oturyp otuyrp otuypr otrupy otruyp otrpuy otrpyu otrypu otryup
otyurp otyupr otyrup otyrpu otypru otypur oyputr oypurt oyptur oyptru oyprtu
oyprut oyuptr oyuprt oyutpr oyutrp oyurtp oyurpt oytupr oyturp oytpur oytpru
oytrpu oytrup oyrutp oyrupt oyrtup oyrtpu oyrptu oyrput uropty uropyt urotpy
urotyp uroytp uroypt urpoty urpoyt urptoy urptyo urpyto urpyot urtpoy urtpyo
urtopy urtoyp urtyop urtypo urypto urypot urytpo urytop uryotp uryopt uorpty
uorpyt uortpy uortyp uorytp uorypt uoprty uopryt uoptry uoptyr uopytr uopyrt
uotpry uotpyr uotrpy uotryp uotyrp uotypr uoyptr uoyprt uoytpr uoytrp uoyrtp
uoyrpt uporty uporyt upotry upotyr upoytr upoyrt uproty uproyt uprtoy uprtyo
upryto upryot uptroy uptryo uptory uptoyr uptyor uptyro upyrto upyrot upytro
upytor upyotr upyort utopry utopyr utorpy utoryp utoyrp utoypr utpory utpoyr
utproy utpryo utpyro utpyor utrpoy utrpyo utropy utroyp utryop utrypo utypro
utypor utyrpo utyrop utyorp utyopr uyoptr uyoprt uyotpr uyotrp uyortp uyorpt
uypotr uyport uyptor uyptro uyprto uyprot uytpor uytpro uytopr uytorp uytrop
uytrpo uyrpto uyrpot uyrtpo uyrtop uyrotp uyropt troupy trouyp tropuy tropyu
troypu troyup truopy truoyp trupoy trupyo truypo truyop trpuoy trpuyo trpouy
trpoyu trpyou trpyuo tryupo tryuop trypuo trypou tryopu tryoup torupy toruyp
torpuy torpyu torypu toryup tourpy touryp toupry toupyr touypr touyrp topury
topuyr topruy topryu topyru topyur toyupr toyurp toypur toypru toyrpu toyrup
tuorpy tuoryp tuopry tuopyr tuoypr tuoyrp turopy turoyp turpoy turpyo turypo
turyop tuproy tupryo tupory tupoyr tupyor tupyro tuyrpo tuyrop tuypro tuypor
tuyopr tuyorp tpoury tpouyr tporuy tporyu tpoyru tpoyur tpuory tpuoyr tpuroy
tpuryo tpuyro tpuyor tpruoy tpruyo tprouy tproyu tpryou tpryuo tpyuro tpyuor
tpyruo tpyrou tpyoru tpyour tyoupr tyourp tyopur tyopru tyorpu tyorup tyuopr
tyuorp tyupor tyupro tyurpo tyurop typuor typuro typour typoru typrou typruo
tyrupo tyruop tyrpuo tyrpou tyropu tyroup yroutp yroupt yrotup yrotpu yroptu
yroput yruotp yruopt yrutop yrutpo yrupto yrupot yrtuop yrtupo yrtoup yrtopu
yrtpou yrtpuo yrputo yrpuot yrptuo yrptou yrpotu yrpout yorutp yorupt yortup
yortpu yorptu yorput yourtp yourpt youtrp youtpr youptr youprt yoturp yotupr
yotrup yotrpu yotpru yotpur yoputr yopurt yoptur yoptru yoprtu yoprut yuortp
yuorpt yuotrp yuotpr yuoptr yuoprt yurotp yuropt yurtop yurtpo yurpto yurpot
yutrop yutrpo yutorp yutopr yutpor yutpro yuprto yuprot yuptro yuptor yupotr
yuport ytourp ytoupr ytorup ytorpu ytopru ytopur ytuorp ytuopr yturop yturpo
ytupro ytupor ytruop ytrupo ytroup ytropu ytrpou ytrpuo ytpuro ytpuor ytpruo
ytprou ytporu ytpour ypoutr ypourt ypotur ypotru yportu yporut ypuotr ypuort
yputor yputro ypurto ypurot yptuor ypturo yptour yptoru yptrou yptruo ypruto
ypruot yprtuo yprtou yprotu yprout

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History of cryptography
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