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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: praemo
cipher variations:
qsbfnp rtcgoq sudhpr tveiqs uwfjrt
vxgksu wyhltv xzimuw yajnvx zbkowy
aclpxz bdmqya cenrzb dfosac egptbd
fhquce girvdf hjsweg iktxfh jluygi
kmvzhj lnwaik moxbjl npyckm oqzdln

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: praemo
Cipher: kizvnl

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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: praemo

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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: praemo
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: praemo
Cipher: cenrzb

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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: praemo
Cipher: 532411512343

Extended Methods:
Method #1

Plaintext: praemo
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
p r a e m o 
5 2 1 5 2 4 
3 4 1 1 3 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: praemo
Cipher: kvrsan

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Method #3

Plaintext: praemo
method variations:
hdvfsx dvfsxh vfsxhd
fsxhdv sxhdvf xhdvfs

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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: praemo

all 720 cipher variations:
praemo praeom prameo pramoe praome praoem preamo preaom premao premoa preoma
preoam prmeao prmeoa prmaeo prmaoe prmoae prmoea proema proeam promea promae
proame proaem paremo pareom parmeo parmoe parome paroem paermo paerom paemro
paemor paeomr paeorm pamero pameor pamreo pamroe pamore pamoer paoemr paoerm
paomer paomre paorme paorem pearmo pearom peamro peamor peaomr peaorm peramo
peraom permao permoa peroma peroam pemrao pemroa pemaro pemaor pemoar pemora
peorma peoram peomra peomar peoamr peoarm pmaero pmaeor pmareo pmaroe pmaore
pmaoer pmearo pmeaor pmerao pmeroa pmeora pmeoar pmreao pmreoa pmraeo pmraoe
pmroae pmroea pmoera pmoear pmorea pmorae pmoare pmoaer poaemr poaerm poamer
poamre poarme poarem poeamr poearm poemar poemra poerma poeram pomear pomera
pomaer pomare pomrae pomrea porema poream pormea pormae porame poraem rpaemo
rpaeom rpameo rpamoe rpaome rpaoem rpeamo rpeaom rpemao rpemoa rpeoma rpeoam
rpmeao rpmeoa rpmaeo rpmaoe rpmoae rpmoea rpoema rpoeam rpomea rpomae rpoame
rpoaem rapemo rapeom rapmeo rapmoe rapome rapoem raepmo raepom raempo raemop
raeomp raeopm ramepo rameop rampeo rampoe ramope ramoep raoemp raoepm raomep
raompe raopme raopem reapmo reapom reampo reamop reaomp reaopm repamo repaom
repmao repmoa repoma repoam rempao rempoa remapo remaop remoap remopa reopma
reopam reompa reomap reoamp reoapm rmaepo rmaeop rmapeo rmapoe rmaope rmaoep
rmeapo rmeaop rmepao rmepoa rmeopa rmeoap rmpeao rmpeoa rmpaeo rmpaoe rmpoae
rmpoea rmoepa rmoeap rmopea rmopae rmoape rmoaep roaemp roaepm roamep roampe
roapme roapem roeamp roeapm roemap roempa roepma roepam romeap romepa romaep
romape rompae rompea ropema ropeam ropmea ropmae ropame ropaem arpemo arpeom
arpmeo arpmoe arpome arpoem arepmo arepom arempo aremop areomp areopm armepo
armeop armpeo armpoe armope armoep aroemp aroepm aromep arompe aropme aropem
apremo apreom aprmeo aprmoe aprome aproem apermo aperom apemro apemor apeomr
apeorm apmero apmeor apmreo apmroe apmore apmoer apoemr apoerm apomer apomre
aporme aporem aeprmo aeprom aepmro aepmor aepomr aeporm aerpmo aerpom aermpo
aermop aeromp aeropm aemrpo aemrop aempro aempor aemopr aemorp aeormp aeorpm
aeomrp aeompr aeopmr aeoprm ampero ampeor ampreo amproe ampore ampoer amepro
amepor amerpo amerop ameorp ameopr amrepo amreop amrpeo amrpoe amrope amroep
amoerp amoepr amorep amorpe amopre amoper aopemr aoperm aopmer aopmre aoprme
aoprem aoepmr aoeprm aoempr aoemrp aoermp aoerpm aomepr aomerp aomper aompre
aomrpe aomrep aoremp aorepm aormep aormpe aorpme aorpem erapmo erapom erampo
eramop eraomp eraopm erpamo erpaom erpmao erpmoa erpoma erpoam ermpao ermpoa
ermapo ermaop ermoap ermopa eropma eropam erompa eromap eroamp eroapm earpmo
earpom earmpo earmop earomp earopm eaprmo eaprom eapmro eapmor eapomr eaporm
eampro eampor eamrpo eamrop eamorp eamopr eaopmr eaoprm eaompr eaomrp eaormp
eaorpm eparmo eparom epamro epamor epaomr epaorm epramo epraom eprmao eprmoa
eproma eproam epmrao epmroa epmaro epmaor epmoar epmora eporma eporam epomra
epomar epoamr epoarm emapro emapor emarpo emarop emaorp emaopr emparo empaor
emprao emproa empora empoar emrpao emrpoa emrapo emraop emroap emropa emopra
emopar emorpa emorap emoarp emoapr eoapmr eoaprm eoampr eoamrp eoarmp eoarpm
eopamr eoparm eopmar eopmra eoprma eopram eompar eompra eomapr eomarp eomrap
eomrpa eorpma eorpam eormpa eormap eoramp eorapm mraepo mraeop mrapeo mrapoe
mraope mraoep mreapo mreaop mrepao mrepoa mreopa mreoap mrpeao mrpeoa mrpaeo
mrpaoe mrpoae mrpoea mroepa mroeap mropea mropae mroape mroaep marepo mareop
marpeo marpoe marope maroep maerpo maerop maepro maepor maeopr maeorp mapero
mapeor mapreo maproe mapore mapoer maoepr maoerp maoper maopre maorpe maorep
mearpo mearop meapro meapor meaopr meaorp merapo meraop merpao merpoa meropa
meroap meprao meproa meparo mepaor mepoar mepora meorpa meorap meopra meopar
meoapr meoarp mpaero mpaeor mpareo mparoe mpaore mpaoer mpearo mpeaor mperao
mperoa mpeora mpeoar mpreao mpreoa mpraeo mpraoe mproae mproea mpoera mpoear
mporea mporae mpoare mpoaer moaepr moaerp moaper moapre moarpe moarep moeapr
moearp moepar moepra moerpa moerap mopear mopera mopaer mopare moprae moprea
morepa moreap morpea morpae morape moraep oraemp oraepm oramep orampe orapme
orapem oreamp oreapm oremap orempa orepma orepam ormeap ormepa ormaep ormape
ormpae ormpea orpema orpeam orpmea orpmae orpame orpaem oaremp oarepm oarmep
oarmpe oarpme oarpem oaermp oaerpm oaemrp oaempr oaepmr oaeprm oamerp oamepr
oamrep oamrpe oampre oamper oapemr oaperm oapmer oapmre oaprme oaprem oearmp
oearpm oeamrp oeampr oeapmr oeaprm oeramp oerapm oermap oermpa oerpma oerpam
oemrap oemrpa oemarp oemapr oempar oempra oeprma oepram oepmra oepmar oepamr
oeparm omaerp omaepr omarep omarpe omapre omaper omearp omeapr omerap omerpa
omepra omepar omreap omrepa omraep omrape omrpae omrpea ompera ompear omprea
omprae ompare ompaer opaemr opaerm opamer opamre oparme oparem opeamr opearm
opemar opemra operma operam opmear opmera opmaer opmare opmrae opmrea oprema
opream oprmea oprmae oprame opraem

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History of cryptography
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