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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: astque
cipher variations:
bturvf cuvswg dvwtxh ewxuyi fxyvzj
gyzwak hzaxbl iabycm jbczdn kcdaeo
ldebfp mefcgq nfgdhr ogheis phifjt
qijgku rjkhlv sklimw tlmjnx umnkoy
vnolpz wopmqa xpqnrb yqrosc zrsptd

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: astque
Cipher: zhgjfv

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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: astque

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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: astque
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: astque
Cipher: nfgdhr

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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: astque
Cipher: 113444145451

Extended Methods:
Method #1

Plaintext: astque
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
a s t q u e 
1 3 4 1 5 5 
1 4 4 4 4 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: astque
Cipher: ldzqtd

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Method #3

Plaintext: astque
method variations:
ltdyya tdyyal dyyalt
yyaltd yaltdy altdyy

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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: astque

all 720 cipher variations:
astque astqeu astuqe astueq asteuq astequ asqtue asqteu asqute asquet asqeut
asqetu asuqte asuqet asutqe asuteq asuetq asueqt asequt aseqtu aseuqt aseutq
asetuq asetqu atsque atsqeu atsuqe atsueq atseuq atsequ atqsue atqseu atquse
atques atqeus atqesu atuqse atuqes atusqe atuseq atuesq atueqs atequs ateqsu
ateuqs ateusq atesuq atesqu aqtsue aqtseu aqtuse aqtues aqteus aqtesu aqstue
aqsteu aqsute aqsuet aqseut aqsetu aquste aquset aqutse aqutes aquets aquest
aqesut aqestu aqeust aqeuts aqetus aqetsu autqse autqes autsqe autseq autesq
auteqs auqtse auqtes auqste auqset auqest auqets ausqte ausqet austqe austeq
ausetq auseqt aueqst aueqts auesqt auestq auetsq auetqs aetqus aetqsu aetuqs
aetusq aetsuq aetsqu aeqtus aeqtsu aequts aequst aeqsut aeqstu aeuqts aeuqst
aeutqs aeutsq aeustq aeusqt aesqut aesqtu aesuqt aesutq aestuq aestqu satque
satqeu satuqe satueq sateuq satequ saqtue saqteu saqute saquet saqeut saqetu
sauqte sauqet sautqe sauteq sauetq saueqt saequt saeqtu saeuqt saeutq saetuq
saetqu staque staqeu stauqe staueq staeuq staequ stqaue stqaeu stquae stquea
stqeua stqeau stuqae stuqea stuaqe stuaeq stueaq stueqa stequa steqau steuqa
steuaq steauq steaqu sqtaue sqtaeu sqtuae sqtuea sqteua sqteau sqatue sqateu
sqaute sqauet sqaeut sqaetu squate squaet squtae squtea squeta squeat sqeaut
sqeatu sqeuat sqeuta sqetua sqetau sutqae sutqea sutaqe sutaeq suteaq suteqa
suqtae suqtea suqate suqaet suqeat suqeta suaqte suaqet suatqe suateq suaetq
suaeqt sueqat sueqta sueaqt sueatq suetaq suetqa setqua setqau setuqa setuaq
setauq setaqu seqtua seqtau sequta sequat seqaut seqatu seuqta seuqat seutqa
seutaq seuatq seuaqt seaqut seaqtu seauqt seautq seatuq seatqu tsaque tsaqeu
tsauqe tsaueq tsaeuq tsaequ tsqaue tsqaeu tsquae tsquea tsqeua tsqeau tsuqae
tsuqea tsuaqe tsuaeq tsueaq tsueqa tsequa tseqau tseuqa tseuaq tseauq tseaqu
tasque tasqeu tasuqe tasueq taseuq tasequ taqsue taqseu taquse taques taqeus
taqesu tauqse tauqes tausqe tauseq tauesq taueqs taequs taeqsu taeuqs taeusq
taesuq taesqu tqasue tqaseu tqause tqaues tqaeus tqaesu tqsaue tqsaeu tqsuae
tqsuea tqseua tqseau tqusae tqusea tquase tquaes tqueas tquesa tqesua tqesau
tqeusa tqeuas tqeaus tqeasu tuaqse tuaqes tuasqe tuaseq tuaesq tuaeqs tuqase
tuqaes tuqsae tuqsea tuqesa tuqeas tusqae tusqea tusaqe tusaeq tuseaq tuseqa
tueqsa tueqas tuesqa tuesaq tueasq tueaqs teaqus teaqsu teauqs teausq teasuq
teasqu teqaus teqasu tequas tequsa teqsua teqsau teuqas teuqsa teuaqs teuasq
teusaq teusqa tesqua tesqau tesuqa tesuaq tesauq tesaqu qstaue qstaeu qstuae
qstuea qsteua qsteau qsatue qsateu qsaute qsauet qsaeut qsaetu qsuate qsuaet
qsutae qsutea qsueta qsueat qseaut qseatu qseuat qseuta qsetua qsetau qtsaue
qtsaeu qtsuae qtsuea qtseua qtseau qtasue qtaseu qtause qtaues qtaeus qtaesu
qtuase qtuaes qtusae qtusea qtuesa qtueas qteaus qteasu qteuas qteusa qtesua
qtesau qatsue qatseu qatuse qatues qateus qatesu qastue qasteu qasute qasuet
qaseut qasetu qauste qauset qautse qautes qauets qauest qaesut qaestu qaeust
qaeuts qaetus qaetsu qutase qutaes qutsae qutsea qutesa quteas quatse quates
quaste quaset quaest quaets qusate qusaet qustae qustea quseta quseat queast
queats quesat questa quetsa quetas qetaus qetasu qetuas qetusa qetsua qetsau
qeatus qeatsu qeauts qeaust qeasut qeastu qeuats qeuast qeutas qeutsa qeusta
qeusat qesaut qesatu qesuat qesuta qestua qestau ustqae ustqea ustaqe ustaeq
usteaq usteqa usqtae usqtea usqate usqaet usqeat usqeta usaqte usaqet usatqe
usateq usaetq usaeqt useqat useqta useaqt useatq usetaq usetqa utsqae utsqea
utsaqe utsaeq utseaq utseqa utqsae utqsea utqase utqaes utqeas utqesa utaqse
utaqes utasqe utaseq utaesq utaeqs uteqas uteqsa uteaqs uteasq utesaq utesqa
uqtsae uqtsea uqtase uqtaes uqteas uqtesa uqstae uqstea uqsate uqsaet uqseat
uqseta uqaste uqaset uqatse uqates uqaets uqaest uqesat uqesta uqeast uqeats
uqetas uqetsa uatqse uatqes uatsqe uatseq uatesq uateqs uaqtse uaqtes uaqste
uaqset uaqest uaqets uasqte uasqet uastqe uasteq uasetq uaseqt uaeqst uaeqts
uaesqt uaestq uaetsq uaetqs uetqas uetqsa uetaqs uetasq uetsaq uetsqa ueqtas
ueqtsa ueqats ueqast ueqsat ueqsta ueaqts ueaqst ueatqs ueatsq ueastq ueasqt
uesqat uesqta uesaqt uesatq uestaq uestqa estqua estqau estuqa estuaq estauq
estaqu esqtua esqtau esquta esquat esqaut esqatu esuqta esuqat esutqa esutaq
esuatq esuaqt esaqut esaqtu esauqt esautq esatuq esatqu etsqua etsqau etsuqa
etsuaq etsauq etsaqu etqsua etqsau etqusa etquas etqaus etqasu etuqsa etuqas
etusqa etusaq etuasq etuaqs etaqus etaqsu etauqs etausq etasuq etasqu eqtsua
eqtsau eqtusa eqtuas eqtaus eqtasu eqstua eqstau eqsuta eqsuat eqsaut eqsatu
equsta equsat equtsa equtas equats equast eqasut eqastu eqaust eqauts eqatus
eqatsu eutqsa eutqas eutsqa eutsaq eutasq eutaqs euqtsa euqtas euqsta euqsat
euqast euqats eusqta eusqat eustqa eustaq eusatq eusaqt euaqst euaqts euasqt
euastq euatsq euatqs eatqus eatqsu eatuqs eatusq eatsuq eatsqu eaqtus eaqtsu
eaquts eaqust eaqsut eaqstu eauqts eauqst eautqs eautsq eaustq eausqt easqut
easqtu easuqt easutq eastuq eastqu

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History of cryptography
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