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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: shalom
cipher variations:
tibmpn ujcnqo vkdorp wlepsq xmfqtr
yngrus zohsvt apitwu bqjuxv crkvyw
dslwzx etmxay funybz gvozca hwpadb
ixqbec jyrcfd kzsdge latehf mbufig
ncvgjh odwhki pexilj qfyjmk rgzknl

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: shalom
Cipher: hszoln

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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: shalom

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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: shalom
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: shalom
Cipher: funybz

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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: shalom
Cipher: 343211134323

Extended Methods:
Method #1

Plaintext: shalom
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
s h a l o m 
3 3 1 1 4 2 
4 2 1 3 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: shalom
Cipher: naiiln

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Method #3

Plaintext: shalom
method variations:
obashn bashno ashnob
shnoba hnobas nobash

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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: shalom

all 720 cipher variations:
shalom shalmo shaolm shaoml shamol shamlo shlaom shlamo shloam shloma shlmoa
shlmao sholam sholma shoalm shoaml shomal shomla shmloa shmlao shmola shmoal
shmaol shmalo sahlom sahlmo saholm sahoml sahmol sahmlo salhom salhmo salohm
salomh salmoh salmho saolhm saolmh saohlm saohml saomhl saomlh samloh samlho
samolh samohl samhol samhlo slahom slahmo slaohm slaomh slamoh slamho slhaom
slhamo slhoam slhoma slhmoa slhmao sloham slohma sloahm sloamh slomah slomha
slmhoa slmhao slmoha slmoah slmaoh slmaho soalhm soalmh soahlm soahml soamhl
soamlh solahm solamh solham solhma solmha solmah sohlam sohlma sohalm sohaml
sohmal sohmla somlha somlah somhla somhal somahl somalh smaloh smalho smaolh
smaohl smahol smahlo smlaoh smlaho smloah smloha smlhoa smlhao smolah smolha
smoalh smoahl smohal smohla smhloa smhlao smhola smhoal smhaol smhalo hsalom
hsalmo hsaolm hsaoml hsamol hsamlo hslaom hslamo hsloam hsloma hslmoa hslmao
hsolam hsolma hsoalm hsoaml hsomal hsomla hsmloa hsmlao hsmola hsmoal hsmaol
hsmalo haslom haslmo hasolm hasoml hasmol hasmlo halsom halsmo halosm haloms
halmos halmso haolsm haolms haoslm haosml haomsl haomls hamlos hamlso hamols
hamosl hamsol hamslo hlasom hlasmo hlaosm hlaoms hlamos hlamso hlsaom hlsamo
hlsoam hlsoma hlsmoa hlsmao hlosam hlosma hloasm hloams hlomas hlomsa hlmsoa
hlmsao hlmosa hlmoas hlmaos hlmaso hoalsm hoalms hoaslm hoasml hoamsl hoamls
holasm holams holsam holsma holmsa holmas hoslam hoslma hosalm hosaml hosmal
hosmla homlsa homlas homsla homsal homasl homals hmalos hmalso hmaols hmaosl
hmasol hmaslo hmlaos hmlaso hmloas hmlosa hmlsoa hmlsao hmolas hmolsa hmoals
hmoasl hmosal hmosla hmsloa hmslao hmsola hmsoal hmsaol hmsalo ahslom ahslmo
ahsolm ahsoml ahsmol ahsmlo ahlsom ahlsmo ahlosm ahloms ahlmos ahlmso aholsm
aholms ahoslm ahosml ahomsl ahomls ahmlos ahmlso ahmols ahmosl ahmsol ahmslo
ashlom ashlmo asholm ashoml ashmol ashmlo aslhom aslhmo aslohm aslomh aslmoh
aslmho asolhm asolmh asohlm asohml asomhl asomlh asmloh asmlho asmolh asmohl
asmhol asmhlo alshom alshmo alsohm alsomh alsmoh alsmho alhsom alhsmo alhosm
alhoms alhmos alhmso alohsm alohms aloshm alosmh alomsh alomhs almhos almhso
almohs almosh almsoh almsho aoslhm aoslmh aoshlm aoshml aosmhl aosmlh aolshm
aolsmh aolhsm aolhms aolmhs aolmsh aohlsm aohlms aohslm aohsml aohmsl aohmls
aomlhs aomlsh aomhls aomhsl aomshl aomslh amsloh amslho amsolh amsohl amshol
amshlo amlsoh amlsho amlosh amlohs amlhos amlhso amolsh amolhs amoslh amoshl
amohsl amohls amhlos amhlso amhols amhosl amhsol amhslo lhasom lhasmo lhaosm
lhaoms lhamos lhamso lhsaom lhsamo lhsoam lhsoma lhsmoa lhsmao lhosam lhosma
lhoasm lhoams lhomas lhomsa lhmsoa lhmsao lhmosa lhmoas lhmaos lhmaso lahsom
lahsmo lahosm lahoms lahmos lahmso lashom lashmo lasohm lasomh lasmoh lasmho
laoshm laosmh laohsm laohms laomhs laomsh lamsoh lamsho lamosh lamohs lamhos
lamhso lsahom lsahmo lsaohm lsaomh lsamoh lsamho lshaom lshamo lshoam lshoma
lshmoa lshmao lsoham lsohma lsoahm lsoamh lsomah lsomha lsmhoa lsmhao lsmoha
lsmoah lsmaoh lsmaho loashm loasmh loahsm loahms loamhs loamsh losahm losamh
losham loshma losmha losmah lohsam lohsma lohasm lohams lohmas lohmsa lomsha
lomsah lomhsa lomhas lomahs lomash lmasoh lmasho lmaosh lmaohs lmahos lmahso
lmsaoh lmsaho lmsoah lmsoha lmshoa lmshao lmosah lmosha lmoash lmoahs lmohas
lmohsa lmhsoa lmhsao lmhosa lmhoas lmhaos lmhaso ohalsm ohalms ohaslm ohasml
ohamsl ohamls ohlasm ohlams ohlsam ohlsma ohlmsa ohlmas ohslam ohslma ohsalm
ohsaml ohsmal ohsmla ohmlsa ohmlas ohmsla ohmsal ohmasl ohmals oahlsm oahlms
oahslm oahsml oahmsl oahmls oalhsm oalhms oalshm oalsmh oalmsh oalmhs oaslhm
oaslmh oashlm oashml oasmhl oasmlh oamlsh oamlhs oamslh oamshl oamhsl oamhls
olahsm olahms olashm olasmh olamsh olamhs olhasm olhams olhsam olhsma olhmsa
olhmas olsham olshma olsahm olsamh olsmah olsmha olmhsa olmhas olmsha olmsah
olmash olmahs osalhm osalmh osahlm osahml osamhl osamlh oslahm oslamh oslham
oslhma oslmha oslmah oshlam oshlma oshalm oshaml oshmal oshmla osmlha osmlah
osmhla osmhal osmahl osmalh omalsh omalhs omaslh omashl omahsl omahls omlash
omlahs omlsah omlsha omlhsa omlhas omslah omslha omsalh omsahl omshal omshla
omhlsa omhlas omhsla omhsal omhasl omhals mhalos mhalso mhaols mhaosl mhasol
mhaslo mhlaos mhlaso mhloas mhlosa mhlsoa mhlsao mholas mholsa mhoals mhoasl
mhosal mhosla mhsloa mhslao mhsola mhsoal mhsaol mhsalo mahlos mahlso mahols
mahosl mahsol mahslo malhos malhso malohs malosh malsoh malsho maolhs maolsh
maohls maohsl maoshl maoslh masloh maslho masolh masohl mashol mashlo mlahos
mlahso mlaohs mlaosh mlasoh mlasho mlhaos mlhaso mlhoas mlhosa mlhsoa mlhsao
mlohas mlohsa mloahs mloash mlosah mlosha mlshoa mlshao mlsoha mlsoah mlsaoh
mlsaho moalhs moalsh moahls moahsl moashl moaslh molahs molash molhas molhsa
molsha molsah mohlas mohlsa mohals mohasl mohsal mohsla moslha moslah moshla
moshal mosahl mosalh msaloh msalho msaolh msaohl msahol msahlo mslaoh mslaho
msloah msloha mslhoa mslhao msolah msolha msoalh msoahl msohal msohla mshloa
mshlao mshola mshoal mshaol mshalo

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History of cryptography
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