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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: flossi
cipher variations:
gmpttj hnquuk iorvvl jpswwm kqtxxn
lruyyo msvzzp ntwaaq ouxbbr pvyccs
qwzddt rxaeeu sybffv tzcggw uadhhx
vbeiiy wcfjjz xdgkka yehllb zfimmc
agjnnd bhkooe cilppf djmqqg eknrrh

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: flossi
Cipher: uolhhr

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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: flossi

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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: flossi
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: flossi
Cipher: sybffv

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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: flossi
Cipher: 121343343442

Extended Methods:
Method #1

Plaintext: flossi
method variations:

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

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Method #3

Plaintext: flossi
method variations:
bsnotb snotbb notbbs
otbbsn tbbsno bbsnot

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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: flossi

all 720 cipher variations:
flossi flosis flossi flosis floiss floiss flsosi flsois flssoi flssio flsiso
flsios flssoi flssio flsosi flsois flsios flsiso flisso flisos flisso flisos
flioss flioss folssi folsis folssi folsis foliss foliss foslsi foslis fossli
fossil fosisl fosils fossli fossil foslsi foslis fosils fosisl foissl foisls
foissl foisls foilss foilss fsolsi fsolis fsosli fsosil fsoisl fsoils fslosi
fslois fslsoi fslsio fsliso fslios fssloi fsslio fssoli fssoil fssiol fssilo
fsilso fsilos fsislo fsisol fsiosl fsiols fsosli fsosil fsolsi fsolis fsoils
fsoisl fssoli fssoil fssloi fsslio fssilo fssiol fslsoi fslsio fslosi fslois
fslios fsliso fsislo fsisol fsilso fsilos fsiols fsiosl fiossl fiosls fiossl
fiosls fiolss fiolss fisosl fisols fissol fisslo fislso fislos fissol fisslo
fisosl fisols fislos fislso filsso filsos filsso filsos filoss filoss lfossi
lfosis lfossi lfosis lfoiss lfoiss lfsosi lfsois lfssoi lfssio lfsiso lfsios
lfssoi lfssio lfsosi lfsois lfsios lfsiso lfisso lfisos lfisso lfisos lfioss
lfioss lofssi lofsis lofssi lofsis lofiss lofiss losfsi losfis lossfi lossif
losisf losifs lossfi lossif losfsi losfis losifs losisf loissf loisfs loissf
loisfs loifss loifss lsofsi lsofis lsosfi lsosif lsoisf lsoifs lsfosi lsfois
lsfsoi lsfsio lsfiso lsfios lssfoi lssfio lssofi lssoif lssiof lssifo lsifso
lsifos lsisfo lsisof lsiosf lsiofs lsosfi lsosif lsofsi lsofis lsoifs lsoisf
lssofi lssoif lssfoi lssfio lssifo lssiof lsfsoi lsfsio lsfosi lsfois lsfios
lsfiso lsisfo lsisof lsifso lsifos lsiofs lsiosf liossf liosfs liossf liosfs
liofss liofss lisosf lisofs lissof lissfo lisfso lisfos lissof lissfo lisosf
lisofs lisfos lisfso lifsso lifsos lifsso lifsos lifoss lifoss olfssi olfsis
olfssi olfsis olfiss olfiss olsfsi olsfis olssfi olssif olsisf olsifs olssfi
olssif olsfsi olsfis olsifs olsisf olissf olisfs olissf olisfs olifss olifss
oflssi oflsis oflssi oflsis ofliss ofliss ofslsi ofslis ofssli ofssil ofsisl
ofsils ofssli ofssil ofslsi ofslis ofsils ofsisl ofissl ofisls ofissl ofisls
ofilss ofilss osflsi osflis osfsli osfsil osfisl osfils oslfsi oslfis oslsfi
oslsif oslisf oslifs osslfi osslif ossfli ossfil ossifl ossilf osilsf osilfs
osislf osisfl osifsl osifls osfsli osfsil osflsi osflis osfils osfisl ossfli
ossfil osslfi osslif ossilf ossifl oslsfi oslsif oslfsi oslfis oslifs oslisf
osislf osisfl osilsf osilfs osifls osifsl oifssl oifsls oifssl oifsls oiflss
oiflss oisfsl oisfls oissfl oisslf oislsf oislfs oissfl oisslf oisfsl oisfls
oislfs oislsf oilssf oilsfs oilssf oilsfs oilfss oilfss slofsi slofis slosfi
slosif sloisf sloifs slfosi slfois slfsoi slfsio slfiso slfios slsfoi slsfio
slsofi slsoif slsiof slsifo slifso slifos slisfo slisof sliosf sliofs solfsi
solfis solsfi solsif solisf solifs soflsi soflis sofsli sofsil sofisl sofils
sosfli sosfil soslfi soslif sosilf sosifl soifsl soifls soisfl soislf soilsf
soilfs sfolsi sfolis sfosli sfosil sfoisl sfoils sflosi sflois sflsoi sflsio
sfliso sflios sfsloi sfslio sfsoli sfsoil sfsiol sfsilo sfilso sfilos sfislo
sfisol sfiosl sfiols ssofli ssofil ssolfi ssolif ssoilf ssoifl ssfoli ssfoil
ssfloi ssflio ssfilo ssfiol sslfoi sslfio sslofi ssloif ssliof sslifo ssiflo
ssifol ssilfo ssilof ssiolf ssiofl siofsl siofls siosfl sioslf siolsf siolfs
sifosl sifols sifsol sifslo siflso siflos sisfol sisflo sisofl sisolf sislof
sislfo silfso silfos silsfo silsof silosf silofs slosfi slosif slofsi slofis
sloifs sloisf slsofi slsoif slsfoi slsfio slsifo slsiof slfsoi slfsio slfosi
slfois slfios slfiso slisfo slisof slifso slifos sliofs sliosf solsfi solsif
solfsi solfis solifs solisf soslfi soslif sosfli sosfil sosifl sosilf sofsli
sofsil soflsi soflis sofils sofisl soisfl soislf soifsl soifls soilfs soilsf
ssolfi ssolif ssofli ssofil ssoifl ssoilf sslofi ssloif sslfoi sslfio sslifo
ssliof ssfloi ssflio ssfoli ssfoil ssfiol ssfilo ssilfo ssilof ssiflo ssifol
ssiofl ssiolf sfosli sfosil sfolsi sfolis sfoils sfoisl sfsoli sfsoil sfsloi
sfslio sfsilo sfsiol sflsoi sflsio sflosi sflois sflios sfliso sfislo sfisol
sfilso sfilos sfiols sfiosl siosfl sioslf siofsl siofls siolfs siolsf sisofl
sisolf sisfol sisflo sislfo sislof sifsol sifslo sifosl sifols siflos siflso
silsfo silsof silfso silfos silofs silosf ilossf ilosfs ilossf ilosfs ilofss
ilofss ilsosf ilsofs ilssof ilssfo ilsfso ilsfos ilssof ilssfo ilsosf ilsofs
ilsfos ilsfso ilfsso ilfsos ilfsso ilfsos ilfoss ilfoss iolssf iolsfs iolssf
iolsfs iolfss iolfss ioslsf ioslfs iosslf iossfl iosfsl iosfls iosslf iossfl
ioslsf ioslfs iosfls iosfsl iofssl iofsls iofssl iofsls ioflss ioflss isolsf
isolfs isoslf isosfl isofsl isofls islosf islofs islsof islsfo islfso islfos
isslof isslfo issolf issofl issfol issflo isflso isflos isfslo isfsol isfosl
isfols isoslf isosfl isolsf isolfs isofls isofsl issolf issofl isslof isslfo
issflo issfol islsof islsfo islosf islofs islfos islfso isfslo isfsol isflso
isflos isfols isfosl ifossl ifosls ifossl ifosls ifolss ifolss ifsosl ifsols
ifssol ifsslo ifslso ifslos ifssol ifsslo ifsosl ifsols ifslos ifslso iflsso
iflsos iflsso iflsos ifloss ifloss

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History of cryptography
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