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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: risdon
cipher variations:
sjtepo tkufqp ulvgrq vmwhsr wnxits
xoyjut ypzkvu zqalwv arbmxw bscnyx
ctdozy duepaz evfqba fwgrcb gxhsdc
hyited izjufe jakvgf kblwhg lcmxih
mdnyji neozkj ofpalk pgqbml qhrcnm

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: risdon
Cipher: irhwlm

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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: risdon

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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: risdon
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: risdon
Cipher: evfqba

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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: risdon
Cipher: 244234414333

Extended Methods:
Method #1

Plaintext: risdon
method variations:

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

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Method #3

Plaintext: risdon
method variations:
tmtqnh mtqnht tqnhtm
qnhtmt nhtmtq htmtqn

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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: risdon

all 720 cipher variations:
risdon risdno risodn risond risnod risndo ridson ridsno ridosn ridons ridnos
ridnso riodsn riodns riosdn riosnd rionsd rionds rindos rindso rinods rinosd
rinsod rinsdo rsidon rsidno rsiodn rsiond rsinod rsindo rsdion rsdino rsdoin
rsdoni rsdnoi rsdnio rsodin rsodni rsoidn rsoind rsonid rsondi rsndoi rsndio
rsnodi rsnoid rsniod rsnido rdsion rdsino rdsoin rdsoni rdsnoi rdsnio rdison
rdisno rdiosn rdions rdinos rdinso rdoisn rdoins rdosin rdosni rdonsi rdonis
rdnios rdniso rdnois rdnosi rdnsoi rdnsio rosdin rosdni rosidn rosind rosnid
rosndi rodsin rodsni rodisn rodins rodnis rodnsi roidsn roidns roisdn roisnd
roinsd roinds rondis rondsi ronids ronisd ronsid ronsdi rnsdoi rnsdio rnsodi
rnsoid rnsiod rnsido rndsoi rndsio rndosi rndois rndios rndiso rnodsi rnodis
rnosdi rnosid rnoisd rnoids rnidos rnidso rniods rniosd rnisod rnisdo irsdon
irsdno irsodn irsond irsnod irsndo irdson irdsno irdosn irdons irdnos irdnso
irodsn irodns irosdn irosnd ironsd ironds irndos irndso irnods irnosd irnsod
irnsdo isrdon isrdno isrodn isrond isrnod isrndo isdron isdrno isdorn isdonr
isdnor isdnro isodrn isodnr isordn isornd isonrd isondr isndor isndro isnodr
isnord isnrod isnrdo idsron idsrno idsorn idsonr idsnor idsnro idrson idrsno
idrosn idrons idrnos idrnso idorsn idorns idosrn idosnr idonsr idonrs idnros
idnrso idnors idnosr idnsor idnsro iosdrn iosdnr iosrdn iosrnd iosnrd iosndr
iodsrn iodsnr iodrsn iodrns iodnrs iodnsr iordsn iordns iorsdn iorsnd iornsd
iornds iondrs iondsr ionrds ionrsd ionsrd ionsdr insdor insdro insodr insord
insrod insrdo indsor indsro indosr indors indros indrso inodsr inodrs inosdr
inosrd inorsd inords inrdos inrdso inrods inrosd inrsod inrsdo sirdon sirdno
sirodn sirond sirnod sirndo sidron sidrno sidorn sidonr sidnor sidnro siodrn
siodnr siordn siornd sionrd siondr sindor sindro sinodr sinord sinrod sinrdo
sridon sridno sriodn sriond srinod srindo srdion srdino srdoin srdoni srdnoi
srdnio srodin srodni sroidn sroind sronid srondi srndoi srndio srnodi srnoid
srniod srnido sdrion sdrino sdroin sdroni sdrnoi sdrnio sdiron sdirno sdiorn
sdionr sdinor sdinro sdoirn sdoinr sdorin sdorni sdonri sdonir sdnior sdniro
sdnoir sdnori sdnroi sdnrio sordin sordni soridn sorind sornid sorndi sodrin
sodrni sodirn sodinr sodnir sodnri soidrn soidnr soirdn soirnd soinrd soindr
sondir sondri sonidr sonird sonrid sonrdi snrdoi snrdio snrodi snroid snriod
snrido sndroi sndrio sndori sndoir sndior sndiro snodri snodir snordi snorid
snoird snoidr snidor snidro sniodr sniord snirod snirdo disron disrno disorn
disonr disnor disnro dirson dirsno dirosn dirons dirnos dirnso diorsn diorns
diosrn diosnr dionsr dionrs dinros dinrso dinors dinosr dinsor dinsro dsiron
dsirno dsiorn dsionr dsinor dsinro dsrion dsrino dsroin dsroni dsrnoi dsrnio
dsorin dsorni dsoirn dsoinr dsonir dsonri dsnroi dsnrio dsnori dsnoir dsnior
dsniro drsion drsino drsoin drsoni drsnoi drsnio drison drisno driosn drions
drinos drinso droisn droins drosin drosni dronsi dronis drnios drniso drnois
drnosi drnsoi drnsio dosrin dosrni dosirn dosinr dosnir dosnri dorsin dorsni
dorisn dorins dornis dornsi doirsn doirns doisrn doisnr doinsr doinrs donris
donrsi donirs donisr donsir donsri dnsroi dnsrio dnsori dnsoir dnsior dnsiro
dnrsoi dnrsio dnrosi dnrois dnrios dnriso dnorsi dnoris dnosri dnosir dnoisr
dnoirs dniros dnirso dniors dniosr dnisor dnisro oisdrn oisdnr oisrdn oisrnd
oisnrd oisndr oidsrn oidsnr oidrsn oidrns oidnrs oidnsr oirdsn oirdns oirsdn
oirsnd oirnsd oirnds oindrs oindsr oinrds oinrsd oinsrd oinsdr osidrn osidnr
osirdn osirnd osinrd osindr osdirn osdinr osdrin osdrni osdnri osdnir osrdin
osrdni osridn osrind osrnid osrndi osndri osndir osnrdi osnrid osnird osnidr
odsirn odsinr odsrin odsrni odsnri odsnir odisrn odisnr odirsn odirns odinrs
odinsr odrisn odrins odrsin odrsni odrnsi odrnis odnirs odnisr odnris odnrsi
odnsri odnsir orsdin orsdni orsidn orsind orsnid orsndi ordsin ordsni ordisn
ordins ordnis ordnsi oridsn oridns orisdn orisnd orinsd orinds orndis orndsi
ornids ornisd ornsid ornsdi onsdri onsdir onsrdi onsrid onsird onsidr ondsri
ondsir ondrsi ondris ondirs ondisr onrdsi onrdis onrsdi onrsid onrisd onrids
onidrs onidsr onirds onirsd onisrd onisdr nisdor nisdro nisodr nisord nisrod
nisrdo nidsor nidsro nidosr nidors nidros nidrso niodsr niodrs niosdr niosrd
niorsd niords nirdos nirdso nirods nirosd nirsod nirsdo nsidor nsidro nsiodr
nsiord nsirod nsirdo nsdior nsdiro nsdoir nsdori nsdroi nsdrio nsodir nsodri
nsoidr nsoird nsorid nsordi nsrdoi nsrdio nsrodi nsroid nsriod nsrido ndsior
ndsiro ndsoir ndsori ndsroi ndsrio ndisor ndisro ndiosr ndiors ndiros ndirso
ndoisr ndoirs ndosir ndosri ndorsi ndoris ndrios ndriso ndrois ndrosi ndrsoi
ndrsio nosdir nosdri nosidr nosird nosrid nosrdi nodsir nodsri nodisr nodirs
nodris nodrsi noidsr noidrs noisdr noisrd noirsd noirds nordis nordsi norids
norisd norsid norsdi nrsdoi nrsdio nrsodi nrsoid nrsiod nrsido nrdsoi nrdsio
nrdosi nrdois nrdios nrdiso nrodsi nrodis nrosdi nrosid nroisd nroids nridos
nridso nriods nriosd nrisod nrisdo

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History of cryptography
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