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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: lictor
cipher variations:
mjdups nkevqt olfwru pmgxsv qnhytw
roizux spjavy tqkbwz urlcxa vsmdyb
wtnezc xuofad yvpgbe zwqhcf axridg
bysjeh cztkfi daulgj ebvmhk fcwnil
gdxojm heypkn ifzqlo jgarmp khbsnq

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: lictor
Cipher: orxgli

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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: lictor

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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: lictor
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: lictor
Cipher: yvpgbe

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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: lictor
Cipher: 134231444324

Extended Methods:
Method #1

Plaintext: lictor
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
l i c t o r 
1 4 3 4 4 2 
3 2 1 4 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: lictor
Cipher: qsihqs

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Method #3

Plaintext: lictor
method variations:
smqthd mqthds qthdsm
thdsmq hdsmqt dsmqth

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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: lictor

all 720 cipher variations:
lictor lictro licotr licort licrot licrto litcor litcro litocr litorc litroc
litrco liotcr liotrc lioctr liocrt liorct liortc lirtoc lirtco lirotc liroct
lircot lircto lcitor lcitro lciotr lciort lcirot lcirto lctior lctiro lctoir
lctori lctroi lctrio lcotir lcotri lcoitr lcoirt lcorit lcorti lcrtoi lcrtio
lcroti lcroit lcriot lcrito ltcior ltciro ltcoir ltcori ltcroi ltcrio lticor
lticro ltiocr ltiorc ltiroc ltirco ltoicr ltoirc ltocir ltocri ltorci ltoric
ltrioc ltrico ltroic ltroci ltrcoi ltrcio loctir loctri locitr locirt locrit
locrti lotcir lotcri loticr lotirc lotric lotrci loitcr loitrc loictr loicrt
loirct loirtc lortic lortci loritc lorict lorcit lorcti lrctoi lrctio lrcoti
lrcoit lrciot lrcito lrtcoi lrtcio lrtoci lrtoic lrtioc lrtico lrotci lrotic
lrocti lrocit lroict lroitc lritoc lritco lriotc lrioct lricot lricto ilctor
ilctro ilcotr ilcort ilcrot ilcrto iltcor iltcro iltocr iltorc iltroc iltrco
ilotcr ilotrc iloctr ilocrt ilorct ilortc ilrtoc ilrtco ilrotc ilroct ilrcot
ilrcto icltor icltro iclotr iclort iclrot iclrto ictlor ictlro ictolr ictorl
ictrol ictrlo icotlr icotrl icoltr icolrt icorlt icortl icrtol icrtlo icrotl
icrolt icrlot icrlto itclor itclro itcolr itcorl itcrol itcrlo itlcor itlcro
itlocr itlorc itlroc itlrco itolcr itolrc itoclr itocrl itorcl itorlc itrloc
itrlco itrolc itrocl itrcol itrclo ioctlr ioctrl iocltr ioclrt iocrlt iocrtl
iotclr iotcrl iotlcr iotlrc iotrlc iotrcl ioltcr ioltrc iolctr iolcrt iolrct
iolrtc iortlc iortcl iorltc iorlct iorclt iorctl irctol irctlo ircotl ircolt
irclot irclto irtcol irtclo irtocl irtolc irtloc irtlco irotcl irotlc iroctl
iroclt irolct iroltc irltoc irltco irlotc irloct irlcot irlcto ciltor ciltro
cilotr cilort cilrot cilrto citlor citlro citolr citorl citrol citrlo ciotlr
ciotrl cioltr ciolrt ciorlt ciortl cirtol cirtlo cirotl cirolt cirlot cirlto
clitor clitro cliotr cliort clirot clirto cltior cltiro cltoir cltori cltroi
cltrio clotir clotri cloitr cloirt clorit clorti clrtoi clrtio clroti clroit
clriot clrito ctlior ctliro ctloir ctlori ctlroi ctlrio ctilor ctilro ctiolr
ctiorl ctirol ctirlo ctoilr ctoirl ctolir ctolri ctorli ctoril ctriol ctrilo
ctroil ctroli ctrloi ctrlio coltir coltri colitr colirt colrit colrti cotlir
cotlri cotilr cotirl cotril cotrli coitlr coitrl coiltr coilrt coirlt coirtl
cortil cortli coritl corilt corlit corlti crltoi crltio crloti crloit crliot
crlito crtloi crtlio crtoli crtoil crtiol crtilo crotli crotil crolti crolit
croilt croitl critol critlo criotl criolt crilot crilto ticlor ticlro ticolr
ticorl ticrol ticrlo tilcor tilcro tilocr tilorc tilroc tilrco tiolcr tiolrc
tioclr tiocrl tiorcl tiorlc tirloc tirlco tirolc tirocl tircol tirclo tcilor
tcilro tciolr tciorl tcirol tcirlo tclior tcliro tcloir tclori tclroi tclrio
tcolir tcolri tcoilr tcoirl tcoril tcorli tcrloi tcrlio tcroli tcroil tcriol
tcrilo tlcior tlciro tlcoir tlcori tlcroi tlcrio tlicor tlicro tliocr tliorc
tliroc tlirco tloicr tloirc tlocir tlocri tlorci tloric tlrioc tlrico tlroic
tlroci tlrcoi tlrcio toclir toclri tocilr tocirl tocril tocrli tolcir tolcri
tolicr tolirc tolric tolrci toilcr toilrc toiclr toicrl toircl toirlc torlic
torlci torilc toricl torcil torcli trcloi trclio trcoli trcoil trciol trcilo
trlcoi trlcio trloci trloic trlioc trlico trolci trolic trocli trocil troicl
troilc triloc trilco triolc triocl tricol triclo oictlr oictrl oicltr oiclrt
oicrlt oicrtl oitclr oitcrl oitlcr oitlrc oitrlc oitrcl oiltcr oiltrc oilctr
oilcrt oilrct oilrtc oirtlc oirtcl oirltc oirlct oirclt oirctl ocitlr ocitrl
ociltr ocilrt ocirlt ocirtl octilr octirl octlir octlri octrli octril ocltir
ocltri oclitr oclirt oclrit oclrti ocrtli ocrtil ocrlti ocrlit ocrilt ocritl
otcilr otcirl otclir otclri otcrli otcril oticlr oticrl otilcr otilrc otirlc
otircl otlicr otlirc otlcir otlcri otlrci otlric otrilc otricl otrlic otrlci
otrcli otrcil olctir olctri olcitr olcirt olcrit olcrti oltcir oltcri olticr
oltirc oltric oltrci olitcr olitrc olictr olicrt olirct olirtc olrtic olrtci
olritc olrict olrcit olrcti orctli orctil orclti orclit orcilt orcitl ortcli
ortcil ortlci ortlic ortilc orticl orltci orltic orlcti orlcit orlict orlitc
oritlc oritcl oriltc orilct oriclt orictl rictol rictlo ricotl ricolt riclot
riclto ritcol ritclo ritocl ritolc ritloc ritlco riotcl riotlc rioctl rioclt
riolct rioltc riltoc riltco rilotc riloct rilcot rilcto rcitol rcitlo rciotl
rciolt rcilot rcilto rctiol rctilo rctoil rctoli rctloi rctlio rcotil rcotli
rcoitl rcoilt rcolit rcolti rcltoi rcltio rcloti rcloit rcliot rclito rtciol
rtcilo rtcoil rtcoli rtcloi rtclio rticol rticlo rtiocl rtiolc rtiloc rtilco
rtoicl rtoilc rtocil rtocli rtolci rtolic rtlioc rtlico rtloic rtloci rtlcoi
rtlcio roctil roctli rocitl rocilt roclit roclti rotcil rotcli roticl rotilc
rotlic rotlci roitcl roitlc roictl roiclt roilct roiltc roltic roltci rolitc
rolict rolcit rolcti rlctoi rlctio rlcoti rlcoit rlciot rlcito rltcoi rltcio
rltoci rltoic rltioc rltico rlotci rlotic rlocti rlocit rloict rloitc rlitoc
rlitco rliotc rlioct rlicot rlicto

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History of cryptography
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