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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: vrabie
cipher variations:
wsbcjf xtcdkg yudelh zvefmi awfgnj
bxghok cyhipl dzijqm eajkrn fbklso
gclmtp hdmnuq ienovr jfopws kgpqxt
lhqryu mirszv njstaw oktubx pluvcy
qmvwdz rnwxea soxyfb tpyzgc uqzahd

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: vrabie
Cipher: eizyrv

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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: vrabie

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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: vrabie
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: vrabie
Cipher: ienovr

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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: vrabie
Cipher: 152411214251

Extended Methods:
Method #1

Plaintext: vrabie
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
v r a b i e 
1 2 1 2 4 5 
5 4 1 1 2 1 
They are then read out in rows:
Then divided up into pairs again, and the pairs turned back into letters using the square:
Plain: vrabie
Cipher: ffyuab

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Method #3

Plaintext: vrabie
method variations:
kdfqwa dfqwak fqwakd
qwakdf wakdfq akdfqw

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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: vrabie

all 720 cipher variations:
vrabie vrabei vraibe vraieb vraeib vraebi vrbaie vrbaei vrbiae vrbiea vrbeia
vrbeai vribae vribea vriabe vriaeb vrieab vrieba vrebia vrebai vreiba vreiab
vreaib vreabi varbie varbei varibe varieb vareib varebi vabrie vabrei vabire
vabier vabeir vaberi vaibre vaiber vairbe vaireb vaierb vaiebr vaebir vaebri
vaeibr vaeirb vaerib vaerbi vbarie vbarei vbaire vbaier vbaeir vbaeri vbraie
vbraei vbriae vbriea vbreia vbreai vbirae vbirea vbiare vbiaer vbiear vbiera
vberia vberai vbeira vbeiar vbeair vbeari viabre viaber viarbe viareb viaerb
viaebr vibare vibaer vibrae vibrea vibera vibear virbae virbea virabe viraeb
vireab vireba viebra viebar vierba vierab viearb vieabr veabir veabri veaibr
veairb vearib vearbi vebair vebari vebiar vebira vebria vebrai veibar veibra
veiabr veiarb veirab veirba verbia verbai veriba veriab veraib verabi rvabie
rvabei rvaibe rvaieb rvaeib rvaebi rvbaie rvbaei rvbiae rvbiea rvbeia rvbeai
rvibae rvibea rviabe rviaeb rvieab rvieba rvebia rvebai rveiba rveiab rveaib
rveabi ravbie ravbei ravibe ravieb raveib ravebi rabvie rabvei rabive rabiev
rabeiv rabevi raibve raibev raivbe raiveb raievb raiebv raebiv raebvi raeibv
raeivb raevib raevbi rbavie rbavei rbaive rbaiev rbaeiv rbaevi rbvaie rbvaei
rbviae rbviea rbveia rbveai rbivae rbivea rbiave rbiaev rbieav rbieva rbevia
rbevai rbeiva rbeiav rbeaiv rbeavi riabve riabev riavbe riaveb riaevb riaebv
ribave ribaev ribvae ribvea ribeva ribeav rivbae rivbea rivabe rivaeb riveab
riveba riebva riebav rievba rievab rieavb rieabv reabiv reabvi reaibv reaivb
reavib reavbi rebaiv rebavi rebiav rebiva rebvia rebvai reibav reibva reiabv
reiavb reivab reivba revbia revbai reviba reviab revaib revabi arvbie arvbei
arvibe arvieb arveib arvebi arbvie arbvei arbive arbiev arbeiv arbevi aribve
aribev arivbe ariveb arievb ariebv arebiv arebvi areibv areivb arevib arevbi
avrbie avrbei avribe avrieb avreib avrebi avbrie avbrei avbire avbier avbeir
avberi avibre aviber avirbe avireb avierb aviebr avebir avebri aveibr aveirb
averib averbi abvrie abvrei abvire abvier abveir abveri abrvie abrvei abrive
abriev abreiv abrevi abirve abirev abivre abiver abievr abierv aberiv abervi
abeirv abeivr abevir abevri aivbre aivber aivrbe aivreb aiverb aivebr aibvre
aibver aibrve aibrev aiberv aibevr airbve airbev airvbe airveb airevb airebv
aiebrv aiebvr aierbv aiervb aievrb aievbr aevbir aevbri aevibr aevirb aevrib
aevrbi aebvir aebvri aebivr aebirv aebriv aebrvi aeibvr aeibrv aeivbr aeivrb
aeirvb aeirbv aerbiv aerbvi aeribv aerivb aervib aervbi bravie bravei braive
braiev braeiv braevi brvaie brvaei brviae brviea brveia brveai brivae brivea
briave briaev brieav brieva brevia brevai breiva breiav breaiv breavi barvie
barvei barive bariev bareiv barevi bavrie bavrei bavire bavier baveir baveri
baivre baiver bairve bairev baierv baievr baevir baevri baeivr baeirv baeriv
baervi bvarie bvarei bvaire bvaier bvaeir bvaeri bvraie bvraei bvriae bvriea
bvreia bvreai bvirae bvirea bviare bviaer bviear bviera bveria bverai bveira
bveiar bveair bveari biavre biaver biarve biarev biaerv biaevr bivare bivaer
bivrae bivrea bivera bivear birvae birvea birave biraev bireav bireva bievra
bievar bierva bierav biearv bieavr beavir beavri beaivr beairv beariv bearvi
bevair bevari beviar bevira bevria bevrai beivar beivra beiavr beiarv beirav
beirva bervia bervai beriva beriav beraiv beravi irabve irabev iravbe iraveb
iraevb iraebv irbave irbaev irbvae irbvea irbeva irbeav irvbae irvbea irvabe
irvaeb irveab irveba irebva irebav irevba irevab ireavb ireabv iarbve iarbev
iarvbe iarveb iarevb iarebv iabrve iabrev iabvre iabver iabevr iaberv iavbre
iavber iavrbe iavreb iaverb iavebr iaebvr iaebrv iaevbr iaevrb iaervb iaerbv
ibarve ibarev ibavre ibaver ibaevr ibaerv ibrave ibraev ibrvae ibrvea ibreva
ibreav ibvrae ibvrea ibvare ibvaer ibvear ibvera iberva iberav ibevra ibevar
ibeavr ibearv ivabre ivaber ivarbe ivareb ivaerb ivaebr ivbare ivbaer ivbrae
ivbrea ivbera ivbear ivrbae ivrbea ivrabe ivraeb ivreab ivreba ivebra ivebar
iverba iverab ivearb iveabr ieabvr ieabrv ieavbr ieavrb iearvb iearbv iebavr
iebarv iebvar iebvra iebrva iebrav ievbar ievbra ievabr ievarb ievrab ievrba
ierbva ierbav iervba iervab ieravb ierabv erabiv erabvi eraibv eraivb eravib
eravbi erbaiv erbavi erbiav erbiva erbvia erbvai eribav eribva eriabv eriavb
erivab erivba ervbia ervbai erviba erviab ervaib ervabi earbiv earbvi earibv
earivb earvib earvbi eabriv eabrvi eabirv eabivr eabvir eabvri eaibrv eaibvr
eairbv eairvb eaivrb eaivbr eavbir eavbri eavibr eavirb eavrib eavrbi ebariv
ebarvi ebairv ebaivr ebavir ebavri ebraiv ebravi ebriav ebriva ebrvia ebrvai
ebirav ebirva ebiarv ebiavr ebivar ebivra ebvria ebvrai ebvira ebviar ebvair
ebvari eiabrv eiabvr eiarbv eiarvb eiavrb eiavbr eibarv eibavr eibrav eibrva
eibvra eibvar eirbav eirbva eirabv eiravb eirvab eirvba eivbra eivbar eivrba
eivrab eivarb eivabr evabir evabri evaibr evairb evarib evarbi evbair evbari
evbiar evbira evbria evbrai evibar evibra eviabr eviarb evirab evirba evrbia
evrbai evriba evriab evraib evrabi

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History of cryptography
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