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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: rupial
cipher variations:
svqjbm twrkcn uxsldo vytmep wzunfq
xavogr ybwphs zcxqit adyrju bezskv
cfatlw dgbumx ehcvny fidwoz gjexpa
hkfyqb ilgzrc jmhasd knibte lojcuf
mpkdvg nqlewh ormfxi psngyj qtohzk

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: rupial
Cipher: ifkrzo

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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: rupial

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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: rupial
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: rupial
Cipher: ehcvny

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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: rupial
Cipher: 245453421113

Extended Methods:
Method #1

Plaintext: rupial
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
r u p i a l 
2 5 5 4 1 1 
4 4 3 2 1 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: rupial
Cipher: wuathl

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Method #3

Plaintext: rupial
method variations:
yysbah ysbahy sbahyy
bahyys ahyysb hyysba

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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: rupial

all 720 cipher variations:
rupial rupila rupail rupali ruplai ruplia ruipal ruipla ruiapl ruialp ruilap
ruilpa ruaipl ruailp ruapil ruapli rualpi rualip ruliap rulipa rulaip rulapi
rulpai rulpia rpuial rpuila rpuail rpuali rpulai rpulia rpiual rpiula rpiaul
rpialu rpilau rpilua rpaiul rpailu rpauil rpauli rpalui rpaliu rpliau rpliua
rplaiu rplaui rpluai rpluia ripual ripula ripaul ripalu riplau riplua riupal
riupla riuapl riualp riulap riulpa riaupl riaulp riapul riaplu rialpu rialup
riluap rilupa rilaup rilapu rilpau rilpua rapiul rapilu rapuil rapuli raplui
rapliu raipul raiplu raiupl raiulp railup railpu rauipl rauilp raupil raupli
raulpi raulip raliup ralipu raluip ralupi ralpui ralpiu rlpiau rlpiua rlpaiu
rlpaui rlpuai rlpuia rlipau rlipua rliapu rliaup rliuap rliupa rlaipu rlaiup
rlapiu rlapui rlaupi rlauip rluiap rluipa rluaip rluapi rlupai rlupia urpial
urpila urpail urpali urplai urplia uripal uripla uriapl urialp urilap urilpa
uraipl urailp urapil urapli uralpi uralip urliap urlipa urlaip urlapi urlpai
urlpia uprial uprila uprail uprali uprlai uprlia upiral upirla upiarl upialr
upilar upilra upairl upailr uparil uparli upalri upalir upliar uplira uplair
uplari uplrai uplria uipral uiprla uiparl uipalr uiplar uiplra uirpal uirpla
uirapl uiralp uirlap uirlpa uiarpl uiarlp uiaprl uiaplr uialpr uialrp uilrap
uilrpa uilarp uilapr uilpar uilpra uapirl uapilr uapril uaprli uaplri uaplir
uaiprl uaiplr uairpl uairlp uailrp uailpr uaripl uarilp uarpil uarpli uarlpi
uarlip ualirp ualipr ualrip ualrpi ualpri ualpir ulpiar ulpira ulpair ulpari
ulprai ulpria ulipar ulipra uliapr uliarp ulirap ulirpa ulaipr ulairp ulapir
ulapri ularpi ularip ulriap ulripa ulraip ulrapi ulrpai ulrpia purial purila
purail purali purlai purlia puiral puirla puiarl puialr puilar puilra puairl
puailr puaril puarli pualri pualir puliar pulira pulair pulari pulrai pulria
pruial pruila pruail pruali prulai prulia priual priula priaul prialu prilau
prilua praiul prailu prauil prauli pralui praliu prliau prliua prlaiu prlaui
prluai prluia pirual pirula piraul piralu pirlau pirlua piural piurla piuarl
piualr piular piulra piaurl piaulr piarul piarlu pialru pialur piluar pilura
pilaur pilaru pilrau pilrua pariul parilu paruil paruli parlui parliu pairul
pairlu paiurl paiulr pailur pailru pauirl pauilr pauril paurli paulri paulir
paliur paliru paluir paluri palrui palriu plriau plriua plraiu plraui plruai
plruia plirau plirua pliaru pliaur pliuar pliura plairu plaiur plariu plarui
plauri plauir pluiar pluira pluair pluari plurai pluria iupral iuprla iuparl
iupalr iuplar iuplra iurpal iurpla iurapl iuralp iurlap iurlpa iuarpl iuarlp
iuaprl iuaplr iualpr iualrp iulrap iulrpa iularp iulapr iulpar iulpra ipural
ipurla ipuarl ipualr ipular ipulra iprual iprula ipraul ipralu iprlau iprlua
iparul iparlu ipaurl ipaulr ipalur ipalru iplrau iplrua iplaru iplaur ipluar
iplura irpual irpula irpaul irpalu irplau irplua irupal irupla iruapl irualp
irulap irulpa iraupl iraulp irapul iraplu iralpu iralup irluap irlupa irlaup
irlapu irlpau irlpua iaprul iaprlu iapurl iapulr iaplur iaplru iarpul iarplu
iarupl iarulp iarlup iarlpu iaurpl iaurlp iauprl iauplr iaulpr iaulrp ialrup
ialrpu ialurp ialupr ialpur ialpru ilprau ilprua ilparu ilpaur ilpuar ilpura
ilrpau ilrpua ilrapu ilraup ilruap ilrupa ilarpu ilarup ilapru ilapur ilaupr
ilaurp ilurap ilurpa iluarp iluapr ilupar ilupra aupirl aupilr aupril auprli
auplri auplir auiprl auiplr auirpl auirlp auilrp auilpr auripl aurilp aurpil
aurpli aurlpi aurlip aulirp aulipr aulrip aulrpi aulpri aulpir apuirl apuilr
apuril apurli apulri apulir apiurl apiulr apirul apirlu apilru apilur apriul
aprilu apruil apruli aprlui aprliu apliru apliur aplriu aplrui apluri apluir
aipurl aipulr aiprul aiprlu aiplru aiplur aiuprl aiuplr aiurpl aiurlp aiulrp
aiulpr airupl airulp airpul airplu airlpu airlup ailurp ailupr ailrup ailrpu
ailpru ailpur arpiul arpilu arpuil arpuli arplui arpliu aripul ariplu ariupl
ariulp arilup arilpu aruipl aruilp arupil arupli arulpi arulip arliup arlipu
arluip arlupi arlpui arlpiu alpiru alpiur alpriu alprui alpuri alpuir alipru
alipur alirpu alirup aliurp aliupr alripu alriup alrpiu alrpui alrupi alruip
aluirp aluipr alurip alurpi alupri alupir lupiar lupira lupair lupari luprai
lupria luipar luipra luiapr luiarp luirap luirpa luaipr luairp luapir luapri
luarpi luarip luriap luripa luraip lurapi lurpai lurpia lpuiar lpuira lpuair
lpuari lpurai lpuria lpiuar lpiura lpiaur lpiaru lpirau lpirua lpaiur lpairu
lpauir lpauri lparui lpariu lpriau lpriua lpraiu lpraui lpruai lpruia lipuar
lipura lipaur liparu liprau liprua liupar liupra liuapr liuarp liurap liurpa
liaupr liaurp liapur liapru liarpu liarup liruap lirupa liraup lirapu lirpau
lirpua lapiur lapiru lapuir lapuri laprui lapriu laipur laipru laiupr laiurp
lairup lairpu lauipr lauirp laupir laupri laurpi laurip lariup laripu laruip
larupi larpui larpiu lrpiau lrpiua lrpaiu lrpaui lrpuai lrpuia lripau lripua
lriapu lriaup lriuap lriupa lraipu lraiup lrapiu lrapui lraupi lrauip lruiap
lruipa lruaip lruapi lrupai lrupia

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History of cryptography
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