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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: formem
cipher variations:
gpsnfn hqtogo iruphp jsvqiq ktwrjr
luxsks mvytlt nwzumu oxavnv pybwow
qzcxpx radyqy sbezrz tcfasa udgbtb
vehcuc wfidvd xgjewe yhkfxf zilgyg
ajmhzh bkniai clojbj dmpkck enqldl

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: formem
Cipher: ulinvn

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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: formem

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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: formem
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: formem
Cipher: sbezrz

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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: formem
Cipher: 124324235123

Extended Methods:
Method #1

Plaintext: formem
method variations:

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

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Method #3

Plaintext: formem
method variations:
rhixfc hixfcr ixfcrh
xfcrhi fcrhix crhixf

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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: formem

all 720 cipher variations:
formem formme foremm foremm formem formme fomrem fomrme fomerm fomemr fommer
fommre foemrm foemmr foermm foermm foemrm foemmr fommer fommre fomemr fomerm
fomrem fomrme fromem fromme froemm froemm fromem fromme frmoem frmome frmeom
frmemo frmmeo frmmoe fremom fremmo freomm freomm fremom fremmo frmmeo frmmoe
frmemo frmeom frmoem frmome fmroem fmrome fmreom fmremo fmrmeo fmrmoe fmorem
fmorme fmoerm fmoemr fmomer fmomre fmeorm fmeomr fmerom fmermo fmemro fmemor
fmmoer fmmore fmmeor fmmero fmmreo fmmroe fermom fermmo feromm feromm fermom
fermmo femrom femrmo femorm femomr femmor femmro feomrm feommr feormm feormm
feomrm feommr femmor femmro femomr femorm femrom femrmo fmrmeo fmrmoe fmremo
fmreom fmroem fmrome fmmreo fmmroe fmmero fmmeor fmmoer fmmore fmemro fmemor
fmermo fmerom fmeorm fmeomr fmomer fmomre fmoemr fmoerm fmorem fmorme ofrmem
ofrmme ofremm ofremm ofrmem ofrmme ofmrem ofmrme ofmerm ofmemr ofmmer ofmmre
ofemrm ofemmr ofermm ofermm ofemrm ofemmr ofmmer ofmmre ofmemr ofmerm ofmrem
ofmrme orfmem orfmme orfemm orfemm orfmem orfmme ormfem ormfme ormefm ormemf
ormmef ormmfe oremfm oremmf orefmm orefmm oremfm oremmf ormmef ormmfe ormemf
ormefm ormfem ormfme omrfem omrfme omrefm omremf omrmef omrmfe omfrem omfrme
omferm omfemr omfmer omfmre omefrm omefmr omerfm omermf omemrf omemfr ommfer
ommfre ommefr ommerf ommref ommrfe oermfm oermmf oerfmm oerfmm oermfm oermmf
oemrfm oemrmf oemfrm oemfmr oemmfr oemmrf oefmrm oefmmr oefrmm oefrmm oefmrm
oefmmr oemmfr oemmrf oemfmr oemfrm oemrfm oemrmf omrmef omrmfe omremf omrefm
omrfem omrfme ommref ommrfe ommerf ommefr ommfer ommfre omemrf omemfr omermf
omerfm omefrm omefmr omfmer omfmre omfemr omferm omfrem omfrme rofmem rofmme
rofemm rofemm rofmem rofmme romfem romfme romefm romemf rommef rommfe roemfm
roemmf roefmm roefmm roemfm roemmf rommef rommfe romemf romefm romfem romfme
rfomem rfomme rfoemm rfoemm rfomem rfomme rfmoem rfmome rfmeom rfmemo rfmmeo
rfmmoe rfemom rfemmo rfeomm rfeomm rfemom rfemmo rfmmeo rfmmoe rfmemo rfmeom
rfmoem rfmome rmfoem rmfome rmfeom rmfemo rmfmeo rmfmoe rmofem rmofme rmoefm
rmoemf rmomef rmomfe rmeofm rmeomf rmefom rmefmo rmemfo rmemof rmmoef rmmofe
rmmeof rmmefo rmmfeo rmmfoe refmom refmmo refomm refomm refmom refmmo remfom
remfmo remofm remomf remmof remmfo reomfm reommf reofmm reofmm reomfm reommf
remmof remmfo remomf remofm remfom remfmo rmfmeo rmfmoe rmfemo rmfeom rmfoem
rmfome rmmfeo rmmfoe rmmefo rmmeof rmmoef rmmofe rmemfo rmemof rmefmo rmefom
rmeofm rmeomf rmomef rmomfe rmoemf rmoefm rmofem rmofme morfem morfme morefm
moremf mormef mormfe mofrem mofrme moferm mofemr mofmer mofmre moefrm moefmr
moerfm moermf moemrf moemfr momfer momfre momefr momerf momref momrfe mrofem
mrofme mroefm mroemf mromef mromfe mrfoem mrfome mrfeom mrfemo mrfmeo mrfmoe
mrefom mrefmo mreofm mreomf mremof mremfo mrmfeo mrmfoe mrmefo mrmeof mrmoef
mrmofe mfroem mfrome mfreom mfremo mfrmeo mfrmoe mforem mforme mfoerm mfoemr
mfomer mfomre mfeorm mfeomr mferom mfermo mfemro mfemor mfmoer mfmore mfmeor
mfmero mfmreo mfmroe merfom merfmo merofm meromf mermof mermfo mefrom mefrmo
meform mefomr mefmor mefmro meofrm meofmr meorfm meormf meomrf meomfr memfor
memfro memofr memorf memrof memrfo mmrfeo mmrfoe mmrefo mmreof mmroef mmrofe
mmfreo mmfroe mmfero mmfeor mmfoer mmfore mmefro mmefor mmerfo mmerof mmeorf
mmeofr mmofer mmofre mmoefr mmoerf mmoref mmorfe eormfm eormmf eorfmm eorfmm
eormfm eormmf eomrfm eomrmf eomfrm eomfmr eommfr eommrf eofmrm eofmmr eofrmm
eofrmm eofmrm eofmmr eommfr eommrf eomfmr eomfrm eomrfm eomrmf eromfm erommf
erofmm erofmm eromfm erommf ermofm ermomf ermfom ermfmo ermmfo ermmof erfmom
erfmmo erfomm erfomm erfmom erfmmo ermmfo ermmof ermfmo ermfom ermofm ermomf
emrofm emromf emrfom emrfmo emrmfo emrmof emorfm emormf emofrm emofmr emomfr
emomrf emform emfomr emfrom emfrmo emfmro emfmor emmofr emmorf emmfor emmfro
emmrfo emmrof efrmom efrmmo efromm efromm efrmom efrmmo efmrom efmrmo efmorm
efmomr efmmor efmmro efomrm efommr eformm eformm efomrm efommr efmmor efmmro
efmomr efmorm efmrom efmrmo emrmfo emrmof emrfmo emrfom emrofm emromf emmrfo
emmrof emmfro emmfor emmofr emmorf emfmro emfmor emfrmo emfrom emform emfomr
emomfr emomrf emofmr emofrm emorfm emormf mormef mormfe moremf morefm morfem
morfme momref momrfe momerf momefr momfer momfre moemrf moemfr moermf moerfm
moefrm moefmr mofmer mofmre mofemr moferm mofrem mofrme mromef mromfe mroemf
mroefm mrofem mrofme mrmoef mrmofe mrmeof mrmefo mrmfeo mrmfoe mremof mremfo
mreomf mreofm mrefom mrefmo mrfmeo mrfmoe mrfemo mrfeom mrfoem mrfome mmroef
mmrofe mmreof mmrefo mmrfeo mmrfoe mmoref mmorfe mmoerf mmoefr mmofer mmofre
mmeorf mmeofr mmerof mmerfo mmefro mmefor mmfoer mmfore mmfeor mmfero mmfreo
mmfroe mermof mermfo meromf merofm merfom merfmo memrof memrfo memorf memofr
memfor memfro meomrf meomfr meormf meorfm meofrm meofmr mefmor mefmro mefomr
meform mefrom mefrmo mfrmeo mfrmoe mfremo mfreom mfroem mfrome mfmreo mfmroe
mfmero mfmeor mfmoer mfmore mfemro mfemor mfermo mferom mfeorm mfeomr mfomer
mfomre mfoemr mfoerm mforem mforme

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History of cryptography
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