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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: lentor
cipher variations:
mfoups ngpvqt ohqwru pirxsv qjsytw
rktzux sluavy tmvbwz unwcxa voxdyb
wpyezc xqzfad yragbe zsbhcf atcidg
budjeh cvekfi dwflgj exgmhk fyhnil
gziojm hajpkn ibkqlo jclrmp kdmsnq

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: lentor
Cipher: ovmgli

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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: lentor

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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: lentor
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: lentor
Cipher: yragbe

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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: lentor
Cipher: 135133444324

Extended Methods:
Method #1

Plaintext: lentor
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
l e n t o r 
1 5 3 4 4 2 
3 1 3 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: lentor
Cipher: vsicss

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Method #3

Plaintext: lentor
method variations:
xlsthd lsthdx sthdxl
thdxls hdxlst dxlsth

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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: lentor

all 720 cipher variations:
lentor lentro lenotr lenort lenrot lenrto letnor letnro letonr letorn letron
letrno leotnr leotrn leontr leonrt leornt leortn lerton lertno lerotn leront
lernot lernto lnetor lnetro lneotr lneort lnerot lnerto lnteor lntero lntoer
lntore lntroe lntreo lnoter lnotre lnoetr lnoert lnoret lnorte lnrtoe lnrteo
lnrote lnroet lnreot lnreto ltneor ltnero ltnoer ltnore ltnroe ltnreo ltenor
ltenro lteonr lteorn lteron lterno ltoenr ltoern ltoner ltonre ltorne ltoren
ltreon ltreno ltroen ltrone ltrnoe ltrneo lonter lontre lonetr lonert lonret
lonrte lotner lotnre lotenr lotern lotren lotrne loetnr loetrn loentr loenrt
loernt loertn lorten lortne loretn lorent lornet lornte lrntoe lrnteo lrnote
lrnoet lrneot lrneto lrtnoe lrtneo lrtone lrtoen lrteon lrteno lrotne lroten
lronte lronet lroent lroetn lreton lretno lreotn lreont lrenot lrento elntor
elntro elnotr elnort elnrot elnrto eltnor eltnro eltonr eltorn eltron eltrno
elotnr elotrn elontr elonrt elornt elortn elrton elrtno elrotn elront elrnot
elrnto enltor enltro enlotr enlort enlrot enlrto entlor entlro entolr entorl
entrol entrlo enotlr enotrl enoltr enolrt enorlt enortl enrtol enrtlo enrotl
enrolt enrlot enrlto etnlor etnlro etnolr etnorl etnrol etnrlo etlnor etlnro
etlonr etlorn etlron etlrno etolnr etolrn etonlr etonrl etornl etorln etrlon
etrlno etroln etronl etrnol etrnlo eontlr eontrl eonltr eonlrt eonrlt eonrtl
eotnlr eotnrl eotlnr eotlrn eotrln eotrnl eoltnr eoltrn eolntr eolnrt eolrnt
eolrtn eortln eortnl eorltn eorlnt eornlt eorntl erntol erntlo ernotl ernolt
ernlot ernlto ertnol ertnlo ertonl ertoln ertlon ertlno erotnl erotln erontl
eronlt erolnt eroltn erlton erltno erlotn erlont erlnot erlnto neltor neltro
nelotr nelort nelrot nelrto netlor netlro netolr netorl netrol netrlo neotlr
neotrl neoltr neolrt neorlt neortl nertol nertlo nerotl nerolt nerlot nerlto
nletor nletro nleotr nleort nlerot nlerto nlteor nltero nltoer nltore nltroe
nltreo nloter nlotre nloetr nloert nloret nlorte nlrtoe nlrteo nlrote nlroet
nlreot nlreto ntleor ntlero ntloer ntlore ntlroe ntlreo ntelor ntelro nteolr
nteorl nterol nterlo ntoelr ntoerl ntoler ntolre ntorle ntorel ntreol ntrelo
ntroel ntrole ntrloe ntrleo nolter noltre noletr nolert nolret nolrte notler
notlre notelr noterl notrel notrle noetlr noetrl noeltr noelrt noerlt noertl
nortel nortle noretl norelt norlet norlte nrltoe nrlteo nrlote nrloet nrleot
nrleto nrtloe nrtleo nrtole nrtoel nrteol nrtelo nrotle nrotel nrolte nrolet
nroelt nroetl nretol nretlo nreotl nreolt nrelot nrelto tenlor tenlro tenolr
tenorl tenrol tenrlo telnor telnro telonr telorn telron telrno teolnr teolrn
teonlr teonrl teornl teorln terlon terlno teroln teronl ternol ternlo tnelor
tnelro tneolr tneorl tnerol tnerlo tnleor tnlero tnloer tnlore tnlroe tnlreo
tnoler tnolre tnoelr tnoerl tnorel tnorle tnrloe tnrleo tnrole tnroel tnreol
tnrelo tlneor tlnero tlnoer tlnore tlnroe tlnreo tlenor tlenro tleonr tleorn
tleron tlerno tloenr tloern tloner tlonre tlorne tloren tlreon tlreno tlroen
tlrone tlrnoe tlrneo tonler tonlre tonelr tonerl tonrel tonrle tolner tolnre
tolenr tolern tolren tolrne toelnr toelrn toenlr toenrl toernl toerln torlen
torlne toreln torenl tornel tornle trnloe trnleo trnole trnoel trneol trnelo
trlnoe trlneo trlone trloen trleon trleno trolne trolen tronle tronel troenl
troeln trelon trelno treoln treonl trenol trenlo oentlr oentrl oenltr oenlrt
oenrlt oenrtl oetnlr oetnrl oetlnr oetlrn oetrln oetrnl oeltnr oeltrn oelntr
oelnrt oelrnt oelrtn oertln oertnl oerltn oerlnt oernlt oerntl onetlr onetrl
oneltr onelrt onerlt onertl ontelr onterl ontler ontlre ontrle ontrel onlter
onltre onletr onlert onlret onlrte onrtle onrtel onrlte onrlet onrelt onretl
otnelr otnerl otnler otnlre otnrle otnrel otenlr otenrl otelnr otelrn oterln
oternl otlenr otlern otlner otlnre otlrne otlren otreln otrenl otrlen otrlne
otrnle otrnel olnter olntre olnetr olnert olnret olnrte oltner oltnre oltenr
oltern oltren oltrne oletnr oletrn olentr olenrt olernt olertn olrten olrtne
olretn olrent olrnet olrnte orntle orntel ornlte ornlet ornelt ornetl ortnle
ortnel ortlne ortlen orteln ortenl orltne orlten orlnte orlnet orlent orletn
oretln oretnl oreltn orelnt orenlt orentl rentol rentlo renotl renolt renlot
renlto retnol retnlo retonl retoln retlon retlno reotnl reotln reontl reonlt
reolnt reoltn relton reltno relotn relont relnot relnto rnetol rnetlo rneotl
rneolt rnelot rnelto rnteol rntelo rntoel rntole rntloe rntleo rnotel rnotle
rnoetl rnoelt rnolet rnolte rnltoe rnlteo rnlote rnloet rnleot rnleto rtneol
rtnelo rtnoel rtnole rtnloe rtnleo rtenol rtenlo rteonl rteoln rtelon rtelno
rtoenl rtoeln rtonel rtonle rtolne rtolen rtleon rtleno rtloen rtlone rtlnoe
rtlneo rontel rontle ronetl ronelt ronlet ronlte rotnel rotnle rotenl roteln
rotlen rotlne roetnl roetln roentl roenlt roelnt roeltn rolten roltne roletn
rolent rolnet rolnte rlntoe rlnteo rlnote rlnoet rlneot rlneto rltnoe rltneo
rltone rltoen rlteon rlteno rlotne rloten rlonte rlonet rloent rloetn rleton
rletno rleotn rleont rlenot rlento

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History of cryptography
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