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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: letaba
cipher variations:
mfubcb ngvcdc ohwded pixefe qjyfgf
rkzghg slahih tmbiji uncjkj vodklk
wpelml xqfmnm yrgnon zshopo atipqp
bujqrq cvkrsr dwlsts exmtut fynuvu
gzovwv hapwxw ibqxyx jcryzy kdszaz

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: letaba
Cipher: ovgzyz

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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: letaba

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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: letaba
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: letaba
Cipher: yrgnon

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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: letaba
Cipher: 135144112111

Extended Methods:
Method #1

Plaintext: letaba
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
l e t a b a 
1 5 4 1 2 1 
3 1 4 1 1 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: letaba
Cipher: vdbcda

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Method #3

Plaintext: letaba
method variations:
xqdfaa qdfaax dfaaxq
faaxqd aaxqdf axqdfa

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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: letaba

all 720 cipher variations:
letaba letaab letbaa letbaa letaba letaab leatba leatab leabta leabat leaabt
leaatb lebata lebaat lebtaa lebtaa lebata lebaat leaabt leaatb leabat leabta
leatba leatab lteaba lteaab ltebaa ltebaa lteaba lteaab ltaeba ltaeab ltabea
ltabae ltaabe ltaaeb ltbaea ltbaae ltbeaa ltbeaa ltbaea ltbaae ltaabe ltaaeb
ltabae ltabea ltaeba ltaeab lateba lateab latbea latbae latabe lataeb laetba
laetab laebta laebat laeabt laeatb labeta labeat labtea labtae labate labaet
laaebt laaetb laabet laabte laatbe laateb lbtaea lbtaae lbteaa lbteaa lbtaea
lbtaae lbatea lbatae lbaeta lbaeat lbaaet lbaate lbeata lbeaat lbetaa lbetaa
lbeata lbeaat lbaaet lbaate lbaeat lbaeta lbatea lbatae latabe lataeb latbae
latbea lateba lateab laatbe laateb laabte laabet laaebt laaetb labate labaet
labtae labtea labeta labeat laeabt laeatb laebat laebta laetba laetab eltaba
eltaab eltbaa eltbaa eltaba eltaab elatba elatab elabta elabat elaabt elaatb
elbata elbaat elbtaa elbtaa elbata elbaat elaabt elaatb elabat elabta elatba
elatab etlaba etlaab etlbaa etlbaa etlaba etlaab etalba etalab etabla etabal
etaabl etaalb etbala etbaal etblaa etblaa etbala etbaal etaabl etaalb etabal
etabla etalba etalab eatlba eatlab eatbla eatbal eatabl eatalb ealtba ealtab
ealbta ealbat ealabt ealatb eablta eablat eabtla eabtal eabatl eabalt eaalbt
eaaltb eaablt eaabtl eaatbl eaatlb ebtala ebtaal ebtlaa ebtlaa ebtala ebtaal
ebatla ebatal ebalta ebalat ebaalt ebaatl eblata eblaat ebltaa ebltaa eblata
eblaat ebaalt ebaatl ebalat ebalta ebatla ebatal eatabl eatalb eatbal eatbla
eatlba eatlab eaatbl eaatlb eaabtl eaablt eaalbt eaaltb eabatl eabalt eabtal
eabtla eablta eablat ealabt ealatb ealbat ealbta ealtba ealtab telaba telaab
telbaa telbaa telaba telaab tealba tealab teabla teabal teaabl teaalb tebala
tebaal teblaa teblaa tebala tebaal teaabl teaalb teabal teabla tealba tealab
tleaba tleaab tlebaa tlebaa tleaba tleaab tlaeba tlaeab tlabea tlabae tlaabe
tlaaeb tlbaea tlbaae tlbeaa tlbeaa tlbaea tlbaae tlaabe tlaaeb tlabae tlabea
tlaeba tlaeab taleba taleab talbea talbae talabe talaeb taelba taelab taebla
taebal taeabl taealb tabela tabeal tablea tablae tabale tabael taaebl taaelb
taabel taable taalbe taaleb tblaea tblaae tbleaa tbleaa tblaea tblaae tbalea
tbalae tbaela tbaeal tbaael tbaale tbeala tbeaal tbelaa tbelaa tbeala tbeaal
tbaael tbaale tbaeal tbaela tbalea tbalae talabe talaeb talbae talbea taleba
taleab taalbe taaleb taable taabel taaebl taaelb tabale tabael tablae tablea
tabela tabeal taeabl taealb taebal taebla taelba taelab aetlba aetlab aetbla
aetbal aetabl aetalb aeltba aeltab aelbta aelbat aelabt aelatb aeblta aeblat
aebtla aebtal aebatl aebalt aealbt aealtb aeablt aeabtl aeatbl aeatlb atelba
atelab atebla atebal ateabl atealb atleba atleab atlbea atlbae atlabe atlaeb
atblea atblae atbela atbeal atbael atbale atalbe ataleb atable atabel ataebl
ataelb alteba alteab altbea altbae altabe altaeb aletba aletab alebta alebat
aleabt aleatb albeta albeat albtea albtae albate albaet alaebt alaetb alabet
alabte alatbe alateb abtlea abtlae abtela abteal abtael abtale abltea abltae
ableta ableat ablaet ablate abelta abelat abetla abetal abeatl abealt abalet
abalte abaelt abaetl abatel abatle aatlbe aatleb aatble aatbel aatebl aatelb
aaltbe aalteb aalbte aalbet aalebt aaletb aablte aablet aabtle aabtel aabetl
aabelt aaelbt aaeltb aaeblt aaebtl aaetbl aaetlb betala betaal betlaa betlaa
betala betaal beatla beatal bealta bealat beaalt beaatl belata belaat beltaa
beltaa belata belaat beaalt beaatl bealat bealta beatla beatal bteala bteaal
btelaa btelaa bteala bteaal btaela btaeal btalea btalae btaale btaael btlaea
btlaae btleaa btleaa btlaea btlaae btaale btaael btalae btalea btaela btaeal
batela bateal batlea batlae batale batael baetla baetal baelta baelat baealt
baeatl baleta baleat baltea baltae balate balaet baaelt baaetl baalet baalte
baatle baatel bltaea bltaae blteaa blteaa bltaea bltaae blatea blatae blaeta
blaeat blaaet blaate bleata bleaat bletaa bletaa bleata bleaat blaaet blaate
blaeat blaeta blatea blatae batale batael batlae batlea batela bateal baatle
baatel baalte baalet baaelt baaetl balate balaet baltae baltea baleta baleat
baealt baeatl baelat baelta baetla baetal aetabl aetalb aetbal aetbla aetlba
aetlab aeatbl aeatlb aeabtl aeablt aealbt aealtb aebatl aebalt aebtal aebtla
aeblta aeblat aelabt aelatb aelbat aelbta aeltba aeltab ateabl atealb atebal
atebla atelba atelab ataebl ataelb atabel atable atalbe ataleb atbael atbale
atbeal atbela atblea atblae atlabe atlaeb atlbae atlbea atleba atleab aatebl
aatelb aatbel aatble aatlbe aatleb aaetbl aaetlb aaebtl aaeblt aaelbt aaeltb
aabetl aabelt aabtel aabtle aablte aablet aalebt aaletb aalbet aalbte aaltbe
aalteb abtael abtale abteal abtela abtlea abtlae abatel abatle abaetl abaelt
abalet abalte abeatl abealt abetal abetla abelta abelat ablaet ablate ableat
ableta abltea abltae altabe altaeb altbae altbea alteba alteab alatbe alateb
alabte alabet alaebt alaetb albate albaet albtae albtea albeta albeat aleabt
aleatb alebat alebta aletba aletab

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History of cryptography
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