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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: torfel
cipher variations:
upsgfm vqthgn wruiho xsvjip ytwkjq
zuxlkr avymls bwznmt cxaonu dybpov
ezcqpw fadrqx gbesry hcftsz idguta
jehvub kfiwvc lgjxwd mhkyxe nilzyf
ojmazg pknbah qlocbi rmpdcj snqedk

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: torfel
Cipher: gliuvo

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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: torfel

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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: torfel
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: torfel
Cipher: gbesry

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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: torfel
Cipher: 444324125113

Extended Methods:
Method #1

Plaintext: torfel
method variations:

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

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Method #3

Plaintext: torfel
method variations:
thdwas hdwast dwasth
wasthd asthdw sthdwa

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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: torfel

all 720 cipher variations:
torfel torfle torefl torelf torlef torlfe tofrel tofrle toferl tofelr tofler
toflre toefrl toeflr toerfl toerlf toelrf toelfr tolfer tolfre tolefr tolerf
tolref tolrfe trofel trofle troefl troelf trolef trolfe trfoel trfole trfeol
trfelo trfleo trfloe trefol treflo treofl treolf trelof trelfo trlfeo trlfoe
trlefo trleof trloef trlofe tfroel tfrole tfreol tfrelo tfrleo tfrloe tforel
tforle tfoerl tfoelr tfoler tfolre tfeorl tfeolr tferol tferlo tfelro tfelor
tfloer tflore tfleor tflero tflreo tflroe terfol terflo terofl terolf terlof
terlfo tefrol tefrlo teforl tefolr teflor teflro teofrl teoflr teorfl teorlf
teolrf teolfr telfor telfro telofr telorf telrof telrfo tlrfeo tlrfoe tlrefo
tlreof tlroef tlrofe tlfreo tlfroe tlfero tlfeor tlfoer tlfore tlefro tlefor
tlerfo tlerof tleorf tleofr tlofer tlofre tloefr tloerf tloref tlorfe otrfel
otrfle otrefl otrelf otrlef otrlfe otfrel otfrle otferl otfelr otfler otflre
otefrl oteflr oterfl oterlf otelrf otelfr otlfer otlfre otlefr otlerf otlref
otlrfe ortfel ortfle ortefl ortelf ortlef ortlfe orftel orftle orfetl orfelt
orflet orflte oreftl oreflt oretfl oretlf oreltf orelft orlfet orlfte orleft
orletf orltef orltfe ofrtel ofrtle ofretl ofrelt ofrlet ofrlte oftrel oftrle
ofterl oftelr oftler oftlre ofetrl ofetlr ofertl oferlt ofelrt ofeltr oflter
ofltre ofletr oflert oflret oflrte oerftl oerflt oertfl oertlf oerltf oerlft
oefrtl oefrlt oeftrl oeftlr oefltr oeflrt oetfrl oetflr oetrfl oetrlf oetlrf
oetlfr oelftr oelfrt oeltfr oeltrf oelrtf oelrft olrfet olrfte olreft olretf
olrtef olrtfe olfret olfrte olfert olfetr olfter olftre olefrt oleftr olerft
olertf oletrf oletfr oltfer oltfre oltefr olterf oltref oltrfe rotfel rotfle
rotefl rotelf rotlef rotlfe roftel roftle rofetl rofelt roflet roflte roeftl
roeflt roetfl roetlf roeltf roelft rolfet rolfte roleft roletf roltef roltfe
rtofel rtofle rtoefl rtoelf rtolef rtolfe rtfoel rtfole rtfeol rtfelo rtfleo
rtfloe rtefol rteflo rteofl rteolf rtelof rtelfo rtlfeo rtlfoe rtlefo rtleof
rtloef rtlofe rftoel rftole rfteol rftelo rftleo rftloe rfotel rfotle rfoetl
rfoelt rfolet rfolte rfeotl rfeolt rfetol rfetlo rfelto rfelot rfloet rflote
rfleot rfleto rflteo rfltoe retfol retflo retofl retolf retlof retlfo reftol
reftlo refotl refolt reflot reflto reoftl reoflt reotfl reotlf reoltf reolft
relfot relfto reloft relotf reltof reltfo rltfeo rltfoe rltefo rlteof rltoef
rltofe rlfteo rlftoe rlfeto rlfeot rlfoet rlfote rlefto rlefot rletfo rletof
rleotf rleoft rlofet rlofte rloeft rloetf rlotef rlotfe fortel fortle foretl
forelt forlet forlte fotrel fotrle foterl fotelr fotler fotlre foetrl foetlr
foertl foerlt foelrt foeltr folter foltre foletr folert folret folrte frotel
frotle froetl froelt frolet frolte frtoel frtole frteol frtelo frtleo frtloe
fretol fretlo freotl freolt frelot frelto frlteo frltoe frleto frleot frloet
frlote ftroel ftrole ftreol ftrelo ftrleo ftrloe ftorel ftorle ftoerl ftoelr
ftoler ftolre fteorl fteolr fterol fterlo ftelro ftelor ftloer ftlore ftleor
ftlero ftlreo ftlroe fertol fertlo ferotl ferolt ferlot ferlto fetrol fetrlo
fetorl fetolr fetlor fetlro feotrl feotlr feortl feorlt feolrt feoltr feltor
feltro felotr felort felrot felrto flrteo flrtoe flreto flreot flroet flrote
fltreo fltroe fltero flteor fltoer fltore fletro fletor flerto flerot fleort
fleotr floter flotre floetr floert floret florte eorftl eorflt eortfl eortlf
eorltf eorlft eofrtl eofrlt eoftrl eoftlr eofltr eoflrt eotfrl eotflr eotrfl
eotrlf eotlrf eotlfr eolftr eolfrt eoltfr eoltrf eolrtf eolrft eroftl eroflt
erotfl erotlf eroltf erolft erfotl erfolt erftol erftlo erflto erflot ertfol
ertflo ertofl ertolf ertlof ertlfo erlfto erlfot erltfo erltof erlotf erloft
efrotl efrolt efrtol efrtlo efrlto efrlot efortl eforlt efotrl efotlr efoltr
efolrt eftorl eftolr eftrol eftrlo eftlro eftlor eflotr eflort efltor efltro
eflrto eflrot etrfol etrflo etrofl etrolf etrlof etrlfo etfrol etfrlo etforl
etfolr etflor etflro etofrl etoflr etorfl etorlf etolrf etolfr etlfor etlfro
etlofr etlorf etlrof etlrfo elrfto elrfot elrtfo elrtof elrotf elroft elfrto
elfrot elftro elftor elfotr elfort eltfro eltfor eltrfo eltrof eltorf eltofr
eloftr elofrt elotfr elotrf elortf elorft lorfet lorfte loreft loretf lortef
lortfe lofret lofrte lofert lofetr lofter loftre loefrt loeftr loerft loertf
loetrf loetfr lotfer lotfre lotefr loterf lotref lotrfe lrofet lrofte lroeft
lroetf lrotef lrotfe lrfoet lrfote lrfeot lrfeto lrfteo lrftoe lrefot lrefto
lreoft lreotf lretof lretfo lrtfeo lrtfoe lrtefo lrteof lrtoef lrtofe lfroet
lfrote lfreot lfreto lfrteo lfrtoe lforet lforte lfoert lfoetr lfoter lfotre
lfeort lfeotr lferot lferto lfetro lfetor lftoer lftore lfteor lftero lftreo
lftroe lerfot lerfto leroft lerotf lertof lertfo lefrot lefrto lefort lefotr
leftor leftro leofrt leoftr leorft leortf leotrf leotfr letfor letfro letofr
letorf letrof letrfo ltrfeo ltrfoe ltrefo ltreof ltroef ltrofe ltfreo ltfroe
ltfero ltfeor ltfoer ltfore ltefro ltefor lterfo lterof lteorf lteofr ltofer
ltofre ltoefr ltoerf ltoref ltorfe

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History of cryptography
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