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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: dargot
cipher variations:
ebshpu fctiqv gdujrw hevksx ifwlty
jgxmuz khynva lizowb mjapxc nkbqyd
olcrze pmdsaf qnetbg rofuch spgvdi
tqhwej urixfk vsjygl wtkzhm xulain
yvmbjo zwnckp axodlq bypemr czqfns

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: dargot
Cipher: wzitlg

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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: dargot

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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: dargot
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: dargot
Cipher: qnetbg

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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: dargot
Cipher: 411124224344

Extended Methods:
Method #1

Plaintext: dargot
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
d a r g o t 
4 1 2 2 4 4 
1 1 4 2 3 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: dargot
Cipher: dgtais

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Method #3

Plaintext: dargot
method variations:
afirst firsta irstaf
rstafi stafir tafirs

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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: dargot

all 720 cipher variations:
dargot dargto darogt darotg dartog dartgo dagrot dagrto dagort dagotr dagtor
dagtro daogrt daogtr daorgt daortg daotrg daotgr datgor datgro datogr datorg
datrog datrgo dragot dragto draogt draotg dratog dratgo drgaot drgato drgoat
drgota drgtoa drgtao drogat drogta droagt droatg drotag drotga drtgoa drtgao
drtoga drtoag drtaog drtago dgraot dgrato dgroat dgrota dgrtoa dgrtao dgarot
dgarto dgaort dgaotr dgator dgatro dgoart dgoatr dgorat dgorta dgotra dgotar
dgtaor dgtaro dgtoar dgtora dgtroa dgtrao dorgat dorgta doragt doratg dortag
dortga dograt dogrta dogart dogatr dogtar dogtra doagrt doagtr doargt doartg
doatrg doatgr dotgar dotgra dotagr dotarg dotrag dotrga dtrgoa dtrgao dtroga
dtroag dtraog dtrago dtgroa dtgrao dtgora dtgoar dtgaor dtgaro dtogra dtogar
dtorga dtorag dtoarg dtoagr dtagor dtagro dtaogr dtaorg dtarog dtargo adrgot
adrgto adrogt adrotg adrtog adrtgo adgrot adgrto adgort adgotr adgtor adgtro
adogrt adogtr adorgt adortg adotrg adotgr adtgor adtgro adtogr adtorg adtrog
adtrgo ardgot ardgto ardogt ardotg ardtog ardtgo argdot argdto argodt argotd
argtod argtdo arogdt arogtd arodgt arodtg arotdg arotgd artgod artgdo artogd
artodg artdog artdgo agrdot agrdto agrodt agrotd agrtod agrtdo agdrot agdrto
agdort agdotr agdtor agdtro agodrt agodtr agordt agortd agotrd agotdr agtdor
agtdro agtodr agtord agtrod agtrdo aorgdt aorgtd aordgt aordtg aortdg aortgd
aogrdt aogrtd aogdrt aogdtr aogtdr aogtrd aodgrt aodgtr aodrgt aodrtg aodtrg
aodtgr aotgdr aotgrd aotdgr aotdrg aotrdg aotrgd atrgod atrgdo atrogd atrodg
atrdog atrdgo atgrod atgrdo atgord atgodr atgdor atgdro atogrd atogdr atorgd
atordg atodrg atodgr atdgor atdgro atdogr atdorg atdrog atdrgo radgot radgto
radogt radotg radtog radtgo ragdot ragdto ragodt ragotd ragtod ragtdo raogdt
raogtd raodgt raodtg raotdg raotgd ratgod ratgdo ratogd ratodg ratdog ratdgo
rdagot rdagto rdaogt rdaotg rdatog rdatgo rdgaot rdgato rdgoat rdgota rdgtoa
rdgtao rdogat rdogta rdoagt rdoatg rdotag rdotga rdtgoa rdtgao rdtoga rdtoag
rdtaog rdtago rgdaot rgdato rgdoat rgdota rgdtoa rgdtao rgadot rgadto rgaodt
rgaotd rgatod rgatdo rgoadt rgoatd rgodat rgodta rgotda rgotad rgtaod rgtado
rgtoad rgtoda rgtdoa rgtdao rodgat rodgta rodagt rodatg rodtag rodtga rogdat
rogdta rogadt rogatd rogtad rogtda roagdt roagtd roadgt roadtg roatdg roatgd
rotgad rotgda rotagd rotadg rotdag rotdga rtdgoa rtdgao rtdoga rtdoag rtdaog
rtdago rtgdoa rtgdao rtgoda rtgoad rtgaod rtgado rtogda rtogad rtodga rtodag
rtoadg rtoagd rtagod rtagdo rtaogd rtaodg rtadog rtadgo gardot gardto garodt
garotd gartod gartdo gadrot gadrto gadort gadotr gadtor gadtro gaodrt gaodtr
gaordt gaortd gaotrd gaotdr gatdor gatdro gatodr gatord gatrod gatrdo gradot
gradto graodt graotd gratod gratdo grdaot grdato grdoat grdota grdtoa grdtao
grodat grodta groadt groatd grotad grotda grtdoa grtdao grtoda grtoad grtaod
grtado gdraot gdrato gdroat gdrota gdrtoa gdrtao gdarot gdarto gdaort gdaotr
gdator gdatro gdoart gdoatr gdorat gdorta gdotra gdotar gdtaor gdtaro gdtoar
gdtora gdtroa gdtrao gordat gordta goradt goratd gortad gortda godrat godrta
godart godatr godtar godtra goadrt goadtr goardt goartd goatrd goatdr gotdar
gotdra gotadr gotard gotrad gotrda gtrdoa gtrdao gtroda gtroad gtraod gtrado
gtdroa gtdrao gtdora gtdoar gtdaor gtdaro gtodra gtodar gtorda gtorad gtoard
gtoadr gtador gtadro gtaodr gtaord gtarod gtardo oargdt oargtd oardgt oardtg
oartdg oartgd oagrdt oagrtd oagdrt oagdtr oagtdr oagtrd oadgrt oadgtr oadrgt
oadrtg oadtrg oadtgr oatgdr oatgrd oatdgr oatdrg oatrdg oatrgd oragdt oragtd
oradgt oradtg oratdg oratgd orgadt orgatd orgdat orgdta orgtda orgtad ordgat
ordgta ordagt ordatg ordtag ordtga ortgda ortgad ortdga ortdag ortadg ortagd
ogradt ogratd ogrdat ogrdta ogrtda ogrtad ogardt ogartd ogadrt ogadtr ogatdr
ogatrd ogdart ogdatr ogdrat ogdrta ogdtra ogdtar ogtadr ogtard ogtdar ogtdra
ogtrda ogtrad odrgat odrgta odragt odratg odrtag odrtga odgrat odgrta odgart
odgatr odgtar odgtra odagrt odagtr odargt odartg odatrg odatgr odtgar odtgra
odtagr odtarg odtrag odtrga otrgda otrgad otrdga otrdag otradg otragd otgrda
otgrad otgdra otgdar otgadr otgard otdgra otdgar otdrga otdrag otdarg otdagr
otagdr otagrd otadgr otadrg otardg otargd targod targdo tarogd tarodg tardog
tardgo tagrod tagrdo tagord tagodr tagdor tagdro taogrd taogdr taorgd taordg
taodrg taodgr tadgor tadgro tadogr tadorg tadrog tadrgo tragod tragdo traogd
traodg tradog tradgo trgaod trgado trgoad trgoda trgdoa trgdao trogad trogda
troagd troadg trodag trodga trdgoa trdgao trdoga trdoag trdaog trdago tgraod
tgrado tgroad tgroda tgrdoa tgrdao tgarod tgardo tgaord tgaodr tgador tgadro
tgoard tgoadr tgorad tgorda tgodra tgodar tgdaor tgdaro tgdoar tgdora tgdroa
tgdrao torgad torgda toragd toradg tordag tordga tograd togrda togard togadr
togdar togdra toagrd toagdr toargd toardg toadrg toadgr todgar todgra todagr
todarg todrag todrga tdrgoa tdrgao tdroga tdroag tdraog tdrago tdgroa tdgrao
tdgora tdgoar tdgaor tdgaro tdogra tdogar tdorga tdorag tdoarg tdoagr tdagor
tdagro tdaogr tdaorg tdarog tdargo

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History of cryptography
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