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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: yowled
cipher variations:
zpxmfe aqyngf brzohg csapih dtbqji
eucrkj fvdslk gwetml hxfunm iygvon
jzhwpo kaixqp lbjyrq mckzsr ndlats
oembut pfncvu qgodwv rhpexw siqfyx
tjrgzy ukshaz vltiba wmujcb xnvkdc

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: yowled
Cipher: bldovw

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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: yowled

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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: yowled
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: yowled
Cipher: lbjyrq

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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: yowled
Cipher: 454325135141

Extended Methods:
Method #1

Plaintext: yowled
method variations:

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

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Method #3

Plaintext: yowled
method variations:
uhexqq hexqqu exqquh
xqquhe qquhex quhexq

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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: yowled

all 720 cipher variations:
yowled yowlde yoweld yowedl yowdel yowdle yolwed yolwde yolewd yoledw yoldew
yoldwe yoelwd yoeldw yoewld yoewdl yoedwl yoedlw yodlew yodlwe yodelw yodewl
yodwel yodwle ywoled ywolde ywoeld ywoedl ywodel ywodle ywloed ywlode ywleod
ywledo ywldeo ywldoe ywelod yweldo yweold yweodl ywedol ywedlo ywdleo ywdloe
ywdelo ywdeol ywdoel ywdole ylwoed ylwode ylweod ylwedo ylwdeo ylwdoe ylowed
ylowde yloewd yloedw ylodew ylodwe yleowd yleodw ylewod ylewdo yledwo yledow
yldoew yldowe yldeow yldewo yldweo yldwoe yewlod yewldo yewold yewodl yewdol
yewdlo yelwod yelwdo yelowd yelodw yeldow yeldwo yeolwd yeoldw yeowld yeowdl
yeodwl yeodlw yedlow yedlwo yedolw yedowl yedwol yedwlo ydwleo ydwloe ydwelo
ydweol ydwoel ydwole ydlweo ydlwoe ydlewo ydleow ydloew ydlowe ydelwo ydelow
ydewlo ydewol ydeowl ydeolw ydolew ydolwe ydoelw ydoewl ydowel ydowle oywled
oywlde oyweld oywedl oywdel oywdle oylwed oylwde oylewd oyledw oyldew oyldwe
oyelwd oyeldw oyewld oyewdl oyedwl oyedlw oydlew oydlwe oydelw oydewl oydwel
oydwle owyled owylde owyeld owyedl owydel owydle owlyed owlyde owleyd owledy
owldey owldye owelyd oweldy oweyld oweydl owedyl owedly owdley owdlye owdely
owdeyl owdyel owdyle olwyed olwyde olweyd olwedy olwdey olwdye olywed olywde
olyewd olyedw olydew olydwe oleywd oleydw olewyd olewdy oledwy oledyw oldyew
oldywe oldeyw oldewy oldwey oldwye oewlyd oewldy oewyld oewydl oewdyl oewdly
oelwyd oelwdy oelywd oelydw oeldyw oeldwy oeylwd oeyldw oeywld oeywdl oeydwl
oeydlw oedlyw oedlwy oedylw oedywl oedwyl oedwly odwley odwlye odwely odweyl
odwyel odwyle odlwey odlwye odlewy odleyw odlyew odlywe odelwy odelyw odewly
odewyl odeywl odeylw odylew odylwe odyelw odyewl odywel odywle woyled woylde
woyeld woyedl woydel woydle wolyed wolyde woleyd woledy woldey woldye woelyd
woeldy woeyld woeydl woedyl woedly wodley wodlye wodely wodeyl wodyel wodyle
wyoled wyolde wyoeld wyoedl wyodel wyodle wyloed wylode wyleod wyledo wyldeo
wyldoe wyelod wyeldo wyeold wyeodl wyedol wyedlo wydleo wydloe wydelo wydeol
wydoel wydole wlyoed wlyode wlyeod wlyedo wlydeo wlydoe wloyed wloyde wloeyd
wloedy wlodey wlodye wleoyd wleody wleyod wleydo wledyo wledoy wldoey wldoye
wldeoy wldeyo wldyeo wldyoe weylod weyldo weyold weyodl weydol weydlo welyod
welydo weloyd welody weldoy weldyo weolyd weoldy weoyld weoydl weodyl weodly
wedloy wedlyo wedoly wedoyl wedyol wedylo wdyleo wdyloe wdyelo wdyeol wdyoel
wdyole wdlyeo wdlyoe wdleyo wdleoy wdloey wdloye wdelyo wdeloy wdeylo wdeyol
wdeoyl wdeoly wdoley wdolye wdoely wdoeyl wdoyel wdoyle lowyed lowyde loweyd
lowedy lowdey lowdye loywed loywde loyewd loyedw loydew loydwe loeywd loeydw
loewyd loewdy loedwy loedyw lodyew lodywe lodeyw lodewy lodwey lodwye lwoyed
lwoyde lwoeyd lwoedy lwodey lwodye lwyoed lwyode lwyeod lwyedo lwydeo lwydoe
lweyod lweydo lweoyd lweody lwedoy lwedyo lwdyeo lwdyoe lwdeyo lwdeoy lwdoey
lwdoye lywoed lywode lyweod lywedo lywdeo lywdoe lyowed lyowde lyoewd lyoedw
lyodew lyodwe lyeowd lyeodw lyewod lyewdo lyedwo lyedow lydoew lydowe lydeow
lydewo lydweo lydwoe lewyod lewydo lewoyd lewody lewdoy lewdyo leywod leywdo
leyowd leyodw leydow leydwo leoywd leoydw leowyd leowdy leodwy leodyw ledyow
ledywo ledoyw ledowy ledwoy ledwyo ldwyeo ldwyoe ldweyo ldweoy ldwoey ldwoye
ldyweo ldywoe ldyewo ldyeow ldyoew ldyowe ldeywo ldeyow ldewyo ldewoy ldeowy
ldeoyw ldoyew ldoywe ldoeyw ldoewy ldowey ldowye eowlyd eowldy eowyld eowydl
eowdyl eowdly eolwyd eolwdy eolywd eolydw eoldyw eoldwy eoylwd eoyldw eoywld
eoywdl eoydwl eoydlw eodlyw eodlwy eodylw eodywl eodwyl eodwly ewolyd ewoldy
ewoyld ewoydl ewodyl ewodly ewloyd ewlody ewlyod ewlydo ewldyo ewldoy ewylod
ewyldo ewyold ewyodl ewydol ewydlo ewdlyo ewdloy ewdylo ewdyol ewdoyl ewdoly
elwoyd elwody elwyod elwydo elwdyo elwdoy elowyd elowdy eloywd eloydw elodyw
elodwy elyowd elyodw elywod elywdo elydwo elydow eldoyw eldowy eldyow eldywo
eldwyo eldwoy eywlod eywldo eywold eywodl eywdol eywdlo eylwod eylwdo eylowd
eylodw eyldow eyldwo eyolwd eyoldw eyowld eyowdl eyodwl eyodlw eydlow eydlwo
eydolw eydowl eydwol eydwlo edwlyo edwloy edwylo edwyol edwoyl edwoly edlwyo
edlwoy edlywo edlyow edloyw edlowy edylwo edylow edywlo edywol edyowl edyolw
edolyw edolwy edoylw edoywl edowyl edowly dowley dowlye dowely doweyl dowyel
dowyle dolwey dolwye dolewy doleyw dolyew dolywe doelwy doelyw doewly doewyl
doeywl doeylw doylew doylwe doyelw doyewl doywel doywle dwoley dwolye dwoely
dwoeyl dwoyel dwoyle dwloey dwloye dwleoy dwleyo dwlyeo dwlyoe dweloy dwelyo
dweoly dweoyl dweyol dweylo dwyleo dwyloe dwyelo dwyeol dwyoel dwyole dlwoey
dlwoye dlweoy dlweyo dlwyeo dlwyoe dlowey dlowye dloewy dloeyw dloyew dloywe
dleowy dleoyw dlewoy dlewyo dleywo dleyow dlyoew dlyowe dlyeow dlyewo dlyweo
dlywoe dewloy dewlyo dewoly dewoyl dewyol dewylo delwoy delwyo delowy deloyw
delyow delywo deolwy deolyw deowly deowyl deoywl deoylw deylow deylwo deyolw
deyowl deywol deywlo dywleo dywloe dywelo dyweol dywoel dywole dylweo dylwoe
dylewo dyleow dyloew dylowe dyelwo dyelow dyewlo dyewol dyeowl dyeolw dyolew
dyolwe dyoelw dyoewl dyowel dyowle

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History of cryptography
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