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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: schatz
cipher variations:
tdibua uejcvb vfkdwc wglexd xhmfye
yingzf zjohag akpibh blqjci cmrkdj
dnslek eotmfl fpungm gqvohn hrwpio
isxqjp jtyrkq kuzslr lvatms mwbunt
nxcvou oydwpv pzexqw qafyrx rbgzsy

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: schatz
Cipher: hxszga

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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: schatz

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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: schatz
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: schatz
Cipher: fpungm

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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: schatz
Cipher: 343132114455

Extended Methods:
Method #1

Plaintext: schatz
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
s c h a t z 
3 3 3 1 4 5 
4 1 2 1 4 5 
They are then read out in rows:
Then divided up into pairs again, and the pairs turned back into letters using the square:
Plain: schatz
Cipher: ncydby

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Method #3

Plaintext: schatz
method variations:
olbqyp lbqypo bqypol
qypolb ypolbq polbqy

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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: schatz

all 720 cipher variations:
schatz schazt schtaz schtza schzta schzat scahtz scahzt scathz scatzh scazth
scazht sctahz sctazh scthaz scthza sctzha sctzah sczath sczaht scztah scztha
sczhta sczhat shcatz shcazt shctaz shctza shczta shczat shactz shaczt shatcz
shatzc shaztc shazct shtacz shtazc shtcaz shtcza shtzca shtzac shzatc shzact
shztac shztca shzcta shzcat sahctz sahczt sahtcz sahtzc sahztc sahzct sachtz
sachzt sacthz sactzh saczth saczht satchz satczh sathcz sathzc satzhc satzch
sazcth sazcht saztch sazthc sazhtc sazhct sthacz sthazc sthcaz sthcza sthzca
sthzac stahcz stahzc stachz staczh stazch stazhc stcahz stcazh stchaz stchza
stczha stczah stzach stzahc stzcah stzcha stzhca stzhac szhatc szhact szhtac
szhtca szhcta szhcat szahtc szahct szathc szatch szacth szacht sztahc sztach
szthac szthca sztcha sztcah szcath szcaht szctah szctha szchta szchat cshatz
cshazt cshtaz cshtza cshzta cshzat csahtz csahzt csathz csatzh csazth csazht
cstahz cstazh csthaz csthza cstzha cstzah cszath cszaht csztah csztha cszhta
cszhat chsatz chsazt chstaz chstza chszta chszat chastz chaszt chatsz chatzs
chazts chazst chtasz chtazs chtsaz chtsza chtzsa chtzas chzats chzast chztas
chztsa chzsta chzsat cahstz cahszt cahtsz cahtzs cahzts cahzst cashtz cashzt
casthz castzh caszth caszht catshz catszh cathsz cathzs catzhs catzsh cazsth
cazsht caztsh cazths cazhts cazhst cthasz cthazs cthsaz cthsza cthzsa cthzas
ctahsz ctahzs ctashz ctaszh ctazsh ctazhs ctsahz ctsazh ctshaz ctshza ctszha
ctszah ctzash ctzahs ctzsah ctzsha ctzhsa ctzhas czhats czhast czhtas czhtsa
czhsta czhsat czahts czahst czaths czatsh czasth czasht cztahs cztash czthas
czthsa cztsha cztsah czsath czsaht czstah czstha czshta czshat hcsatz hcsazt
hcstaz hcstza hcszta hcszat hcastz hcaszt hcatsz hcatzs hcazts hcazst hctasz
hctazs hctsaz hctsza hctzsa hctzas hczats hczast hcztas hcztsa hczsta hczsat
hscatz hscazt hsctaz hsctza hsczta hsczat hsactz hsaczt hsatcz hsatzc hsaztc
hsazct hstacz hstazc hstcaz hstcza hstzca hstzac hszatc hszact hsztac hsztca
hszcta hszcat hasctz hasczt hastcz hastzc hasztc haszct hacstz hacszt hactsz
hactzs haczts haczst hatcsz hatczs hatscz hatszc hatzsc hatzcs hazcts hazcst
haztcs haztsc hazstc hazsct htsacz htsazc htscaz htscza htszca htszac htascz
htaszc htacsz htaczs htazcs htazsc htcasz htcazs htcsaz htcsza htczsa htczas
htzacs htzasc htzcas htzcsa htzsca htzsac hzsatc hzsact hzstac hzstca hzscta
hzscat hzastc hzasct hzatsc hzatcs hzacts hzacst hztasc hztacs hztsac hztsca
hztcsa hztcas hzcats hzcast hzctas hzctsa hzcsta hzcsat achstz achszt achtsz
achtzs achzts achzst acshtz acshzt acsthz acstzh acszth acszht actshz actszh
acthsz acthzs actzhs actzsh aczsth aczsht acztsh aczths aczhts aczhst ahcstz
ahcszt ahctsz ahctzs ahczts ahczst ahsctz ahsczt ahstcz ahstzc ahsztc ahszct
ahtscz ahtszc ahtcsz ahtczs ahtzcs ahtzsc ahzstc ahzsct ahztsc ahztcs ahzcts
ahzcst ashctz ashczt ashtcz ashtzc ashztc ashzct aschtz aschzt ascthz asctzh
asczth asczht astchz astczh asthcz asthzc astzhc astzch aszcth aszcht asztch
aszthc aszhtc aszhct athscz athszc athcsz athczs athzcs athzsc atshcz atshzc
atschz atsczh atszch atszhc atcshz atcszh atchsz atchzs atczhs atczsh atzsch
atzshc atzcsh atzchs atzhcs atzhsc azhstc azhsct azhtsc azhtcs azhcts azhcst
azshtc azshct azsthc azstch azscth azscht aztshc aztsch azthsc azthcs aztchs
aztcsh azcsth azcsht azctsh azcths azchts azchst tchasz tchazs tchsaz tchsza
tchzsa tchzas tcahsz tcahzs tcashz tcaszh tcazsh tcazhs tcsahz tcsazh tcshaz
tcshza tcszha tcszah tczash tczahs tczsah tczsha tczhsa tczhas thcasz thcazs
thcsaz thcsza thczsa thczas thacsz thaczs thascz thaszc thazsc thazcs thsacz
thsazc thscaz thscza thszca thszac thzasc thzacs thzsac thzsca thzcsa thzcas
tahcsz tahczs tahscz tahszc tahzsc tahzcs tachsz tachzs tacshz tacszh taczsh
taczhs taschz tasczh tashcz tashzc taszhc taszch tazcsh tazchs tazsch tazshc
tazhsc tazhcs tshacz tshazc tshcaz tshcza tshzca tshzac tsahcz tsahzc tsachz
tsaczh tsazch tsazhc tscahz tscazh tschaz tschza tsczha tsczah tszach tszahc
tszcah tszcha tszhca tszhac tzhasc tzhacs tzhsac tzhsca tzhcsa tzhcas tzahsc
tzahcs tzashc tzasch tzacsh tzachs tzsahc tzsach tzshac tzshca tzscha tzscah
tzcash tzcahs tzcsah tzcsha tzchsa tzchas zchats zchast zchtas zchtsa zchsta
zchsat zcahts zcahst zcaths zcatsh zcasth zcasht zctahs zctash zcthas zcthsa
zctsha zctsah zcsath zcsaht zcstah zcstha zcshta zcshat zhcats zhcast zhctas
zhctsa zhcsta zhcsat zhacts zhacst zhatcs zhatsc zhastc zhasct zhtacs zhtasc
zhtcas zhtcsa zhtsca zhtsac zhsatc zhsact zhstac zhstca zhscta zhscat zahcts
zahcst zahtcs zahtsc zahstc zahsct zachts zachst zacths zactsh zacsth zacsht
zatchs zatcsh zathcs zathsc zatshc zatsch zascth zascht zastch zasthc zashtc
zashct zthacs zthasc zthcas zthcsa zthsca zthsac ztahcs ztahsc ztachs ztacsh
ztasch ztashc ztcahs ztcash ztchas ztchsa ztcsha ztcsah ztsach ztsahc ztscah
ztscha ztshca ztshac zshatc zshact zshtac zshtca zshcta zshcat zsahtc zsahct
zsathc zsatch zsacth zsacht zstahc zstach zsthac zsthca zstcha zstcah zscath
zscaht zsctah zsctha zschta zschat

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History of cryptography
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