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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: drolly
cipher variations:
espmmz ftqnna guroob hvsppc iwtqqd
jxurre kyvssf lzwttg maxuuh nbyvvi
oczwwj pdaxxk qebyyl rfczzm sgdaan
thebbo uifccp vjgddq wkheer xliffs
ymjggt znkhhu aoliiv bpmjjw cqnkkx

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: drolly
Cipher: wiloob

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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: drolly

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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: drolly
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: drolly
Cipher: qebyyl

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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: drolly
Cipher: 412443131345

Extended Methods:
Method #1

Plaintext: drolly
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
d r o l l y 
4 2 4 1 1 4 
1 4 3 3 3 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: drolly
Cipher: idqqnx

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Method #3

Plaintext: drolly
method variations:
ftccsu tccsuf ccsuft
csuftc suftcc uftccs

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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: drolly

all 720 cipher variations:
drolly drolyl drolly drolyl droyll droyll drloly drloyl drlloy drllyo drlylo
drlyol drlloy drllyo drloly drloyl drlyol drlylo dryllo drylol dryllo drylol
dryoll dryoll dorlly dorlyl dorlly dorlyl doryll doryll dolrly dolryl dollry
dollyr dolylr dolyrl dollry dollyr dolrly dolryl dolyrl dolylr doyllr doylrl
doyllr doylrl doyrll doyrll dlorly dloryl dlolry dlolyr dloylr dloyrl dlroly
dlroyl dlrloy dlrlyo dlrylo dlryol dllroy dllryo dllory dlloyr dllyor dllyro
dlyrlo dlyrol dlylro dlylor dlyolr dlyorl dlolry dlolyr dlorly dloryl dloyrl
dloylr dllory dlloyr dllroy dllryo dllyro dllyor dlrloy dlrlyo dlroly dlroyl
dlryol dlrylo dlylro dlylor dlyrlo dlyrol dlyorl dlyolr dyollr dyolrl dyollr
dyolrl dyorll dyorll dylolr dylorl dyllor dyllro dylrlo dylrol dyllor dyllro
dylolr dylorl dylrol dylrlo dyrllo dyrlol dyrllo dyrlol dyroll dyroll rdolly
rdolyl rdolly rdolyl rdoyll rdoyll rdloly rdloyl rdlloy rdllyo rdlylo rdlyol
rdlloy rdllyo rdloly rdloyl rdlyol rdlylo rdyllo rdylol rdyllo rdylol rdyoll
rdyoll rodlly rodlyl rodlly rodlyl rodyll rodyll roldly roldyl rolldy rollyd
rolyld rolydl rolldy rollyd roldly roldyl rolydl rolyld roylld royldl roylld
royldl roydll roydll rlodly rlodyl rloldy rlolyd rloyld rloydl rldoly rldoyl
rldloy rldlyo rldylo rldyol rlldoy rlldyo rllody rlloyd rllyod rllydo rlydlo
rlydol rlyldo rlylod rlyold rlyodl rloldy rlolyd rlodly rlodyl rloydl rloyld
rllody rlloyd rlldoy rlldyo rllydo rllyod rldloy rldlyo rldoly rldoyl rldyol
rldylo rlyldo rlylod rlydlo rlydol rlyodl rlyold ryolld ryoldl ryolld ryoldl
ryodll ryodll rylold rylodl ryllod rylldo ryldlo ryldol ryllod rylldo rylold
rylodl ryldol ryldlo rydllo rydlol rydllo rydlol rydoll rydoll ordlly ordlyl
ordlly ordlyl ordyll ordyll orldly orldyl orlldy orllyd orlyld orlydl orlldy
orllyd orldly orldyl orlydl orlyld orylld oryldl orylld oryldl orydll orydll
odrlly odrlyl odrlly odrlyl odryll odryll odlrly odlryl odllry odllyr odlylr
odlyrl odllry odllyr odlrly odlryl odlyrl odlylr odyllr odylrl odyllr odylrl
odyrll odyrll oldrly oldryl oldlry oldlyr oldylr oldyrl olrdly olrdyl olrldy
olrlyd olryld olrydl ollrdy ollryd olldry olldyr ollydr ollyrd olyrld olyrdl
olylrd olyldr olydlr olydrl oldlry oldlyr oldrly oldryl oldyrl oldylr olldry
olldyr ollrdy ollryd ollyrd ollydr olrldy olrlyd olrdly olrdyl olrydl olryld
olylrd olyldr olyrld olyrdl olydrl olydlr oydllr oydlrl oydllr oydlrl oydrll
oydrll oyldlr oyldrl oylldr oyllrd oylrld oylrdl oylldr oyllrd oyldlr oyldrl
oylrdl oylrld oyrlld oyrldl oyrlld oyrldl oyrdll oyrdll lrodly lrodyl lroldy
lrolyd lroyld lroydl lrdoly lrdoyl lrdloy lrdlyo lrdylo lrdyol lrldoy lrldyo
lrlody lrloyd lrlyod lrlydo lrydlo lrydol lryldo lrylod lryold lryodl lordly
lordyl lorldy lorlyd loryld lorydl lodrly lodryl lodlry lodlyr lodylr lodyrl
loldry loldyr lolrdy lolryd lolyrd lolydr loydlr loydrl loyldr loylrd loyrld
loyrdl ldorly ldoryl ldolry ldolyr ldoylr ldoyrl ldroly ldroyl ldrloy ldrlyo
ldrylo ldryol ldlroy ldlryo ldlory ldloyr ldlyor ldlyro ldyrlo ldyrol ldylro
ldylor ldyolr ldyorl llodry llodyr llordy lloryd lloyrd lloydr lldory lldoyr
lldroy lldryo lldyro lldyor llrdoy llrdyo llrody llroyd llryod llrydo llydro
llydor llyrdo llyrod llyord llyodr lyodlr lyodrl lyoldr lyolrd lyorld lyordl
lydolr lydorl lydlor lydlro lydrlo lydrol lyldor lyldro lylodr lylord lylrod
lylrdo lyrdlo lyrdol lyrldo lyrlod lyrold lyrodl lroldy lrolyd lrodly lrodyl
lroydl lroyld lrlody lrloyd lrldoy lrldyo lrlydo lrlyod lrdloy lrdlyo lrdoly
lrdoyl lrdyol lrdylo lryldo lrylod lrydlo lrydol lryodl lryold lorldy lorlyd
lordly lordyl lorydl loryld lolrdy lolryd loldry loldyr lolydr lolyrd lodlry
lodlyr lodrly lodryl lodyrl lodylr loyldr loylrd loydlr loydrl loyrdl loyrld
llordy lloryd llodry llodyr lloydr lloyrd llrody llroyd llrdoy llrdyo llrydo
llryod lldroy lldryo lldory lldoyr lldyor lldyro llyrdo llyrod llydro llydor
llyodr llyord ldolry ldolyr ldorly ldoryl ldoyrl ldoylr ldlory ldloyr ldlroy
ldlryo ldlyro ldlyor ldrloy ldrlyo ldroly ldroyl ldryol ldrylo ldylro ldylor
ldyrlo ldyrol ldyorl ldyolr lyoldr lyolrd lyodlr lyodrl lyordl lyorld lylodr
lylord lyldor lyldro lylrdo lylrod lydlor lydlro lydolr lydorl lydrol lydrlo
lyrldo lyrlod lyrdlo lyrdol lyrodl lyrold yrolld yroldl yrolld yroldl yrodll
yrodll yrlold yrlodl yrllod yrlldo yrldlo yrldol yrllod yrlldo yrlold yrlodl
yrldol yrldlo yrdllo yrdlol yrdllo yrdlol yrdoll yrdoll yorlld yorldl yorlld
yorldl yordll yordll yolrld yolrdl yollrd yolldr yoldlr yoldrl yollrd yolldr
yolrld yolrdl yoldrl yoldlr yodllr yodlrl yodllr yodlrl yodrll yodrll ylorld
ylordl ylolrd yloldr ylodlr ylodrl ylrold ylrodl ylrlod ylrldo ylrdlo ylrdol
yllrod yllrdo yllord yllodr ylldor ylldro yldrlo yldrol yldlro yldlor yldolr
yldorl ylolrd yloldr ylorld ylordl ylodrl ylodlr yllord yllodr yllrod yllrdo
ylldro ylldor ylrlod ylrldo ylrold ylrodl ylrdol ylrdlo yldlro yldlor yldrlo
yldrol yldorl yldolr ydollr ydolrl ydollr ydolrl ydorll ydorll ydlolr ydlorl
ydllor ydllro ydlrlo ydlrol ydllor ydllro ydlolr ydlorl ydlrol ydlrlo ydrllo
ydrlol ydrllo ydrlol ydroll ydroll

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History of cryptography
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