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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: rietty
cipher variations:
sjfuuz tkgvva ulhwwb vmixxc wnjyyd
xokzze yplaaf zqmbbg arncch bsoddi
ctpeej duqffk evrggl fwshhm gxtiin
hyujjo izvkkp jawllq kbxmmr lcynns
mdzoot neappu ofbqqv pgcrrw qhdssx

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: rietty
Cipher: irvggb

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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: rietty

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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: rietty
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: rietty
Cipher: evrggl

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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: rietty
Cipher: 244251444445

Extended Methods:
Method #1

Plaintext: rietty
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
r i e t t y 
2 4 5 4 4 4 
4 2 1 4 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: rietty
Cipher: rutiqy

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Method #3

Plaintext: rietty
method variations:
twqttk wqttkt qttktw
ttktwq tktwqt ktwqtt

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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: rietty

all 720 cipher variations:
rietty rietyt rietty rietyt rieytt rieytt ritety riteyt rittey rittye rityte
rityet rittey rittye ritety riteyt rityet rityte riytte riytet riytte riytet
riyett riyett reitty reityt reitty reityt reiytt reiytt retity retiyt rettiy
rettyi retyti retyit rettiy rettyi retity retiyt retyit retyti reytti reytit
reytti reytit reyitt reyitt rteity rteiyt rtetiy rtetyi rteyti rteyit rtiety
rtieyt rtitey rtitye rtiyte rtiyet rttiey rttiye rtteiy rtteyi rttyei rttyie
rtyite rtyiet rtytie rtytei rtyeti rtyeit rtetiy rtetyi rteity rteiyt rteyit
rteyti rtteiy rtteyi rttiey rttiye rttyie rttyei rtitey rtitye rtiety rtieyt
rtiyet rtiyte rtytie rtytei rtyite rtyiet rtyeit rtyeti ryetti ryetit ryetti
ryetit ryeitt ryeitt ryteti ryteit ryttei ryttie rytite rytiet ryttei ryttie
ryteti ryteit rytiet rytite ryitte ryitet ryitte ryitet ryiett ryiett iretty
iretyt iretty iretyt ireytt ireytt irtety irteyt irttey irttye irtyte irtyet
irttey irttye irtety irteyt irtyet irtyte irytte irytet irytte irytet iryett
iryett iertty iertyt iertty iertyt ierytt ierytt ietrty ietryt iettry iettyr
ietytr ietyrt iettry iettyr ietrty ietryt ietyrt ietytr ieyttr ieytrt ieyttr
ieytrt ieyrtt ieyrtt iterty iteryt itetry itetyr iteytr iteyrt itrety itreyt
itrtey itrtye itryte itryet ittrey ittrye ittery itteyr ittyer ittyre ityrte
ityret itytre ityter ityetr ityert itetry itetyr iterty iteryt iteyrt iteytr
ittery itteyr ittrey ittrye ittyre ittyer itrtey itrtye itrety itreyt itryet
itryte itytre ityter ityrte ityret ityert ityetr iyettr iyetrt iyettr iyetrt
iyertt iyertt iytetr iytert iytter iyttre iytrte iytret iytter iyttre iytetr
iytert iytret iytrte iyrtte iyrtet iyrtte iyrtet iyrett iyrett eirtty eirtyt
eirtty eirtyt eirytt eirytt eitrty eitryt eittry eittyr eitytr eityrt eittry
eittyr eitrty eitryt eityrt eitytr eiyttr eiytrt eiyttr eiytrt eiyrtt eiyrtt
eritty erityt eritty erityt eriytt eriytt ertity ertiyt erttiy erttyi ertyti
ertyit erttiy erttyi ertity ertiyt ertyit ertyti erytti erytit erytti erytit
eryitt eryitt etrity etriyt etrtiy etrtyi etryti etryit etirty etiryt etitry
etityr etiytr etiyrt ettiry ettiyr ettriy ettryi ettyri ettyir etyitr etyirt
etytir etytri etyrti etyrit etrtiy etrtyi etrity etriyt etryit etryti ettriy
ettryi ettiry ettiyr ettyir ettyri etitry etityr etirty etiryt etiyrt etiytr
etytir etytri etyitr etyirt etyrit etyrti eyrtti eyrtit eyrtti eyrtit eyritt
eyritt eytrti eytrit eyttri eyttir eytitr eytirt eyttri eyttir eytrti eytrit
eytirt eytitr eyittr eyitrt eyittr eyitrt eyirtt eyirtt tierty tieryt tietry
tietyr tieytr tieyrt tirety tireyt tirtey tirtye tiryte tiryet titrey titrye
titery titeyr tityer tityre tiyrte tiyret tiytre tiyter tiyetr tiyert teirty
teiryt teitry teityr teiytr teiyrt terity teriyt tertiy tertyi teryti teryit
tetriy tetryi tetiry tetiyr tetyir tetyri teyrti teyrit teytri teytir teyitr
teyirt treity treiyt tretiy tretyi treyti treyit triety trieyt tritey tritye
triyte triyet trtiey trtiye trteiy trteyi trtyei trtyie tryite tryiet trytie
trytei tryeti tryeit tteriy tteryi tteiry tteiyr tteyir tteyri ttreiy ttreyi
ttriey ttriye ttryie ttryei ttirey ttirye ttiery ttieyr ttiyer ttiyre ttyrie
ttyrei ttyire ttyier ttyeir ttyeri tyerti tyerit tyetri tyetir tyeitr tyeirt
tyreti tyreit tyrtei tyrtie tyrite tyriet tytrei tytrie tyteri tyteir tytier
tytire tyirte tyiret tyitre tyiter tyietr tyiert tietry tietyr tierty tieryt
tieyrt tieytr titery titeyr titrey titrye tityre tityer tirtey tirtye tirety
tireyt tiryet tiryte tiytre tiyter tiyrte tiyret tiyert tiyetr teitry teityr
teirty teiryt teiyrt teiytr tetiry tetiyr tetriy tetryi tetyri tetyir tertiy
tertyi terity teriyt teryit teryti teytri teytir teyrti teyrit teyirt teyitr
tteiry tteiyr tteriy tteryi tteyri tteyir ttiery ttieyr ttirey ttirye ttiyre
ttiyer ttriey ttriye ttreiy ttreyi ttryei ttryie ttyire ttyier ttyrie ttyrei
ttyeri ttyeir tretiy tretyi treity treiyt treyit treyti trteiy trteyi trtiey
trtiye trtyie trtyei tritey tritye triety trieyt triyet triyte trytie trytei
tryite tryiet tryeit tryeti tyetri tyetir tyerti tyerit tyeirt tyeitr tyteri
tyteir tytrei tytrie tytire tytier tyrtei tyrtie tyreti tyreit tyriet tyrite
tyitre tyiter tyirte tyiret tyiert tyietr yiettr yietrt yiettr yietrt yiertt
yiertt yitetr yitert yitter yittre yitrte yitret yitter yittre yitetr yitert
yitret yitrte yirtte yirtet yirtte yirtet yirett yirett yeittr yeitrt yeittr
yeitrt yeirtt yeirtt yetitr yetirt yettir yettri yetrti yetrit yettir yettri
yetitr yetirt yetrit yetrti yertti yertit yertti yertit yeritt yeritt yteitr
yteirt ytetir ytetri yterti yterit ytietr ytiert ytiter ytitre ytirte ytiret
yttier yttire ytteir ytteri yttrei yttrie ytrite ytriet ytrtie ytrtei ytreti
ytreit ytetir ytetri yteitr yteirt yterit yterti ytteir ytteri yttier yttire
yttrie yttrei ytiter ytitre ytietr ytiert ytiret ytirte ytrtie ytrtei ytrite
ytriet ytreit ytreti yretti yretit yretti yretit yreitt yreitt yrteti yrteit
yrttei yrttie yrtite yrtiet yrttei yrttie yrteti yrteit yrtiet yrtite yritte
yritet yritte yritet yriett yriett

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History of cryptography
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