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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: drossy
cipher variations:
espttz ftquua gurvvb hvswwc iwtxxd
jxuyye kyvzzf lzwaag maxbbh nbycci
oczddj pdaeek qebffl rfcggm sgdhhn
theiio uifjjp vjgkkq wkhllr xlimms
ymjnnt znkoou aolppv bpmqqw cqnrrx

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: drossy
Cipher: wilhhb

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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: drossy

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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: drossy
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: drossy
Cipher: qebffl

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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: drossy
Cipher: 412443343445

Extended Methods:
Method #1

Plaintext: drossy
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
d r o s s y 
4 2 4 3 3 4 
1 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: drossy
Cipher: iosqsy

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Method #3

Plaintext: drossy
method variations:
ftnotu tnotuf notuft
otuftn tuftno uftnot

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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: drossy

all 720 cipher variations:
drossy drosys drossy drosys droyss droyss drsosy drsoys drssoy drssyo drsyso
drsyos drssoy drssyo drsosy drsoys drsyos drsyso drysso drysos drysso drysos
dryoss dryoss dorssy dorsys dorssy dorsys doryss doryss dosrsy dosrys dossry
dossyr dosysr dosyrs dossry dossyr dosrsy dosrys dosyrs dosysr doyssr doysrs
doyssr doysrs doyrss doyrss dsorsy dsorys dsosry dsosyr dsoysr dsoyrs dsrosy
dsroys dsrsoy dsrsyo dsryso dsryos dssroy dssryo dssory dssoyr dssyor dssyro
dsyrso dsyros dsysro dsysor dsyosr dsyors dsosry dsosyr dsorsy dsorys dsoyrs
dsoysr dssory dssoyr dssroy dssryo dssyro dssyor dsrsoy dsrsyo dsrosy dsroys
dsryos dsryso dsysro dsysor dsyrso dsyros dsyors dsyosr dyossr dyosrs dyossr
dyosrs dyorss dyorss dysosr dysors dyssor dyssro dysrso dysros dyssor dyssro
dysosr dysors dysros dysrso dyrsso dyrsos dyrsso dyrsos dyross dyross rdossy
rdosys rdossy rdosys rdoyss rdoyss rdsosy rdsoys rdssoy rdssyo rdsyso rdsyos
rdssoy rdssyo rdsosy rdsoys rdsyos rdsyso rdysso rdysos rdysso rdysos rdyoss
rdyoss rodssy rodsys rodssy rodsys rodyss rodyss rosdsy rosdys rossdy rossyd
rosysd rosyds rossdy rossyd rosdsy rosdys rosyds rosysd royssd roysds royssd
roysds roydss roydss rsodsy rsodys rsosdy rsosyd rsoysd rsoyds rsdosy rsdoys
rsdsoy rsdsyo rsdyso rsdyos rssdoy rssdyo rssody rssoyd rssyod rssydo rsydso
rsydos rsysdo rsysod rsyosd rsyods rsosdy rsosyd rsodsy rsodys rsoyds rsoysd
rssody rssoyd rssdoy rssdyo rssydo rssyod rsdsoy rsdsyo rsdosy rsdoys rsdyos
rsdyso rsysdo rsysod rsydso rsydos rsyods rsyosd ryossd ryosds ryossd ryosds
ryodss ryodss rysosd rysods ryssod ryssdo rysdso rysdos ryssod ryssdo rysosd
rysods rysdos rysdso rydsso rydsos rydsso rydsos rydoss rydoss ordssy ordsys
ordssy ordsys ordyss ordyss orsdsy orsdys orssdy orssyd orsysd orsyds orssdy
orssyd orsdsy orsdys orsyds orsysd oryssd orysds oryssd orysds orydss orydss
odrssy odrsys odrssy odrsys odryss odryss odsrsy odsrys odssry odssyr odsysr
odsyrs odssry odssyr odsrsy odsrys odsyrs odsysr odyssr odysrs odyssr odysrs
odyrss odyrss osdrsy osdrys osdsry osdsyr osdysr osdyrs osrdsy osrdys osrsdy
osrsyd osrysd osryds ossrdy ossryd ossdry ossdyr ossydr ossyrd osyrsd osyrds
osysrd osysdr osydsr osydrs osdsry osdsyr osdrsy osdrys osdyrs osdysr ossdry
ossdyr ossrdy ossryd ossyrd ossydr osrsdy osrsyd osrdsy osrdys osryds osrysd
osysrd osysdr osyrsd osyrds osydrs osydsr oydssr oydsrs oydssr oydsrs oydrss
oydrss oysdsr oysdrs oyssdr oyssrd oysrsd oysrds oyssdr oyssrd oysdsr oysdrs
oysrds oysrsd oyrssd oyrsds oyrssd oyrsds oyrdss oyrdss srodsy srodys srosdy
srosyd sroysd sroyds srdosy srdoys srdsoy srdsyo srdyso srdyos srsdoy srsdyo
srsody srsoyd srsyod srsydo srydso srydos srysdo srysod sryosd sryods sordsy
sordys sorsdy sorsyd sorysd soryds sodrsy sodrys sodsry sodsyr sodysr sodyrs
sosdry sosdyr sosrdy sosryd sosyrd sosydr soydsr soydrs soysdr soysrd soyrsd
soyrds sdorsy sdorys sdosry sdosyr sdoysr sdoyrs sdrosy sdroys sdrsoy sdrsyo
sdryso sdryos sdsroy sdsryo sdsory sdsoyr sdsyor sdsyro sdyrso sdyros sdysro
sdysor sdyosr sdyors ssodry ssodyr ssordy ssoryd ssoyrd ssoydr ssdory ssdoyr
ssdroy ssdryo ssdyro ssdyor ssrdoy ssrdyo ssrody ssroyd ssryod ssrydo ssydro
ssydor ssyrdo ssyrod ssyord ssyodr syodsr syodrs syosdr syosrd syorsd syords
sydosr sydors sydsor sydsro sydrso sydros sysdor sysdro sysodr sysord sysrod
sysrdo syrdso syrdos syrsdo syrsod syrosd syrods srosdy srosyd srodsy srodys
sroyds sroysd srsody srsoyd srsdoy srsdyo srsydo srsyod srdsoy srdsyo srdosy
srdoys srdyos srdyso srysdo srysod srydso srydos sryods sryosd sorsdy sorsyd
sordsy sordys soryds sorysd sosrdy sosryd sosdry sosdyr sosydr sosyrd sodsry
sodsyr sodrsy sodrys sodyrs sodysr soysdr soysrd soydsr soydrs soyrds soyrsd
ssordy ssoryd ssodry ssodyr ssoydr ssoyrd ssrody ssroyd ssrdoy ssrdyo ssrydo
ssryod ssdroy ssdryo ssdory ssdoyr ssdyor ssdyro ssyrdo ssyrod ssydro ssydor
ssyodr ssyord sdosry sdosyr sdorsy sdorys sdoyrs sdoysr sdsory sdsoyr sdsroy
sdsryo sdsyro sdsyor sdrsoy sdrsyo sdrosy sdroys sdryos sdryso sdysro sdysor
sdyrso sdyros sdyors sdyosr syosdr syosrd syodsr syodrs syords syorsd sysodr
sysord sysdor sysdro sysrdo sysrod sydsor sydsro sydosr sydors sydros sydrso
syrsdo syrsod syrdso syrdos syrods syrosd yrossd yrosds yrossd yrosds yrodss
yrodss yrsosd yrsods yrssod yrssdo yrsdso yrsdos yrssod yrssdo yrsosd yrsods
yrsdos yrsdso yrdsso yrdsos yrdsso yrdsos yrdoss yrdoss yorssd yorsds yorssd
yorsds yordss yordss yosrsd yosrds yossrd yossdr yosdsr yosdrs yossrd yossdr
yosrsd yosrds yosdrs yosdsr yodssr yodsrs yodssr yodsrs yodrss yodrss ysorsd
ysords ysosrd ysosdr ysodsr ysodrs ysrosd ysrods ysrsod ysrsdo ysrdso ysrdos
yssrod yssrdo yssord yssodr yssdor yssdro ysdrso ysdros ysdsro ysdsor ysdosr
ysdors ysosrd ysosdr ysorsd ysords ysodrs ysodsr yssord yssodr yssrod yssrdo
yssdro yssdor ysrsod ysrsdo ysrosd ysrods ysrdos ysrdso ysdsro ysdsor ysdrso
ysdros ysdors ysdosr ydossr ydosrs ydossr ydosrs ydorss ydorss ydsosr ydsors
ydssor ydssro ydsrso ydsros ydssor ydssro ydsosr ydsors ydsros ydsrso ydrsso
ydrsos ydrsso ydrsos ydross ydross

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History of cryptography
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