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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: nerkuu
cipher variations:
ofslvv pgtmww qhunxx rivoyy sjwpzz
tkxqaa ulyrbb vmzscc wnatdd xobuee
ypcvff zqdwgg arexhh bsfyii ctgzjj
duhakk evibll fwjcmm gxkdnn hyleoo
izmfpp jangqq kbohrr lcpiss mdqjtt

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: nerkuu
Cipher: mvipff

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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: nerkuu

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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: nerkuu
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: nerkuu
Cipher: arexhh

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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: nerkuu
Cipher: 335124525454

Extended Methods:
Method #1

Plaintext: nerkuu
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
n e r k u u 
3 5 2 5 5 5 
3 1 4 2 4 4 
They are then read out in rows:
Then divided up into pairs again, and the pairs turned back into letters using the square:
Plain: nerkuu
Cipher: xwzcit

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Method #3

Plaintext: nerkuu
method variations:
xfywyo fywyox ywyoxf
wyoxfy yoxfyw oxfywy

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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: nerkuu

all 720 cipher variations:
nerkuu nerkuu neruku neruuk neruuk neruku nekruu nekruu nekuru nekuur nekuur
nekuru neukru neukur neurku neuruk neuurk neuukr neukur neukru neuukr neuurk
neuruk neurku nrekuu nrekuu nreuku nreuuk nreuuk nreuku nrkeuu nrkeuu nrkueu
nrkuue nrkuue nrkueu nrukeu nrukue nrueku nrueuk nruuek nruuke nrukue nrukeu
nruuke nruuek nrueuk nrueku nkreuu nkreuu nkrueu nkruue nkruue nkrueu nkeruu
nkeruu nkeuru nkeuur nkeuur nkeuru nkueru nkueur nkureu nkurue nkuure nkuuer
nkueur nkueru nkuuer nkuure nkurue nkureu nurkeu nurkue nureku nureuk nuruek
nuruke nukreu nukrue nukeru nukeur nukuer nukure nuekru nuekur nuerku nueruk
nueurk nueukr nuuker nuukre nuuekr nuuerk nuurek nuurke nurkue nurkeu nuruke
nuruek nureuk nureku nukrue nukreu nukure nukuer nukeur nukeru nuukre nuuker
nuurke nuurek nuuerk nuuekr nuekur nuekru nueukr nueurk nueruk nuerku enrkuu
enrkuu enruku enruuk enruuk enruku enkruu enkruu enkuru enkuur enkuur enkuru
enukru enukur enurku enuruk enuurk enuukr enukur enukru enuukr enuurk enuruk
enurku ernkuu ernkuu ernuku ernuuk ernuuk ernuku erknuu erknuu erkunu erkuun
erkuun erkunu eruknu erukun erunku erunuk eruunk eruukn erukun eruknu eruukn
eruunk erunuk erunku ekrnuu ekrnuu ekrunu ekruun ekruun ekrunu eknruu eknruu
eknuru eknuur eknuur eknuru ekunru ekunur ekurnu ekurun ekuurn ekuunr ekunur
ekunru ekuunr ekuurn ekurun ekurnu eurknu eurkun eurnku eurnuk eurunk eurukn
eukrnu eukrun euknru euknur eukunr eukurn eunkru eunkur eunrku eunruk eunurk
eunukr euuknr euukrn euunkr euunrk euurnk euurkn eurkun eurknu eurukn eurunk
eurnuk eurnku eukrun eukrnu eukurn eukunr euknur euknru euukrn euuknr euurkn
euurnk euunrk euunkr eunkur eunkru eunukr eunurk eunruk eunrku renkuu renkuu
renuku renuuk renuuk renuku reknuu reknuu rekunu rekuun rekuun rekunu reuknu
reukun reunku reunuk reuunk reuukn reukun reuknu reuukn reuunk reunuk reunku
rnekuu rnekuu rneuku rneuuk rneuuk rneuku rnkeuu rnkeuu rnkueu rnkuue rnkuue
rnkueu rnukeu rnukue rnueku rnueuk rnuuek rnuuke rnukue rnukeu rnuuke rnuuek
rnueuk rnueku rkneuu rkneuu rknueu rknuue rknuue rknueu rkenuu rkenuu rkeunu
rkeuun rkeuun rkeunu rkuenu rkueun rkuneu rkunue rkuune rkuuen rkueun rkuenu
rkuuen rkuune rkunue rkuneu runkeu runkue runeku runeuk runuek runuke rukneu
ruknue rukenu rukeun rukuen rukune rueknu ruekun ruenku ruenuk rueunk rueukn
ruuken ruukne ruuekn ruuenk ruunek ruunke runkue runkeu runuke runuek runeuk
runeku ruknue rukneu rukune rukuen rukeun rukenu ruukne ruuken ruunke ruunek
ruuenk ruuekn ruekun rueknu rueukn rueunk ruenuk ruenku kernuu kernuu kerunu
keruun keruun kerunu kenruu kenruu kenuru kenuur kenuur kenuru keunru keunur
keurnu keurun keuurn keuunr keunur keunru keuunr keuurn keurun keurnu krenuu
krenuu kreunu kreuun kreuun kreunu krneuu krneuu krnueu krnuue krnuue krnueu
kruneu krunue kruenu krueun kruuen kruune krunue kruneu kruune kruuen krueun
kruenu knreuu knreuu knrueu knruue knruue knrueu kneruu kneruu kneuru kneuur
kneuur kneuru knueru knueur knureu knurue knuure knuuer knueur knueru knuuer
knuure knurue knureu kurneu kurnue kurenu kureun kuruen kurune kunreu kunrue
kuneru kuneur kunuer kunure kuenru kuenur kuernu kuerun kueurn kueunr kuuner
kuunre kuuenr kuuern kuuren kuurne kurnue kurneu kurune kuruen kureun kurenu
kunrue kunreu kunure kunuer kuneur kuneru kuunre kuuner kuurne kuuren kuuern
kuuenr kuenur kuenru kueunr kueurn kuerun kuernu uerknu uerkun uernku uernuk
uerunk uerukn uekrnu uekrun ueknru ueknur uekunr uekurn uenkru uenkur uenrku
uenruk uenurk uenukr ueuknr ueukrn ueunkr ueunrk ueurnk ueurkn ureknu urekun
urenku urenuk ureunk ureukn urkenu urkeun urkneu urknue urkune urkuen urnkeu
urnkue urneku urneuk urnuek urnuke urukne uruken urunke urunek uruenk uruekn
ukrenu ukreun ukrneu ukrnue ukrune ukruen ukernu ukerun ukenru ukenur ukeunr
ukeurn ukneru ukneur uknreu uknrue uknure uknuer ukuenr ukuern ukuner ukunre
ukurne ukuren unrkeu unrkue unreku unreuk unruek unruke unkreu unkrue unkeru
unkeur unkuer unkure unekru unekur unerku uneruk uneurk uneukr unuker unukre
unuekr unuerk unurek unurke uurkne uurken uurnke uurnek uurenk uurekn uukrne
uukren uuknre uukner uukenr uukern uunkre uunker uunrke uunrek uunerk uunekr
uueknr uuekrn uuenkr uuenrk uuernk uuerkn uerkun uerknu uerukn uerunk uernuk
uernku uekrun uekrnu uekurn uekunr ueknur ueknru ueukrn ueuknr ueurkn ueurnk
ueunrk ueunkr uenkur uenkru uenukr uenurk uenruk uenrku urekun ureknu ureukn
ureunk urenuk urenku urkeun urkenu urkuen urkune urknue urkneu uruken urukne
uruekn uruenk urunek urunke urnkue urnkeu urnuke urnuek urneuk urneku ukreun
ukrenu ukruen ukrune ukrnue ukrneu ukerun ukernu ukeurn ukeunr ukenur ukenru
ukuern ukuenr ukuren ukurne ukunre ukuner ukneur ukneru uknuer uknure uknrue
uknreu uurken uurkne uurekn uurenk uurnek uurnke uukren uukrne uukern uukenr
uukner uuknre uuekrn uueknr uuerkn uuernk uuenrk uuenkr uunker uunkre uunekr
uunerk uunrek uunrke unrkue unrkeu unruke unruek unreuk unreku unkrue unkreu
unkure unkuer unkeur unkeru unukre unuker unurke unurek unuerk unuekr unekur
unekru uneukr uneurk uneruk unerku

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History of cryptography
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