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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: rewall
cipher variations:
sfxbmm tgycnn uhzdoo viaepp wjbfqq
xkcgrr yldhss zmeitt anfjuu bogkvv
cphlww dqimxx erjnyy fskozz gtlpaa
humqbb ivnrcc jwosdd kxptee lyquff
mzrvgg naswhh obtxii pcuyjj qdvzkk

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: rewall
Cipher: ivdzoo

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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: rewall

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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: rewall
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: rewall
Cipher: erjnyy

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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: rewall
Cipher: 245125111313

Extended Methods:
Method #1

Plaintext: rewall
method variations:

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

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Method #3

Plaintext: rewall
method variations:
yfeach feachy eachyf
achyfe chyfea hyfeac

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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: rewall

all 720 cipher variations:
rewall rewall rewlal rewlla rewlla rewlal reawll reawll realwl reallw reallw
realwl relawl relalw relwal relwla rellwa rellaw relalw relawl rellaw rellwa
relwla relwal rweall rweall rwelal rwella rwella rwelal rwaell rwaell rwalel
rwalle rwalle rwalel rwlael rwlale rwleal rwlela rwllea rwllae rwlale rwlael
rwllae rwllea rwlela rwleal rawell rawell rawlel rawlle rawlle rawlel raewll
raewll raelwl raellw raellw raelwl ralewl ralelw ralwel ralwle rallwe rallew
ralelw ralewl rallew rallwe ralwle ralwel rlwael rlwale rlweal rlwela rlwlea
rlwlae rlawel rlawle rlaewl rlaelw rlalew rlalwe rleawl rlealw rlewal rlewla
rlelwa rlelaw rllaew rllawe rlleaw rllewa rllwea rllwae rlwale rlwael rlwlae
rlwlea rlwela rlweal rlawle rlawel rlalwe rlalew rlaelw rlaewl rllawe rllaew
rllwae rllwea rllewa rlleaw rlealw rleawl rlelaw rlelwa rlewla rlewal erwall
erwall erwlal erwlla erwlla erwlal erawll erawll eralwl erallw erallw eralwl
erlawl erlalw erlwal erlwla erllwa erllaw erlalw erlawl erllaw erllwa erlwla
erlwal ewrall ewrall ewrlal ewrlla ewrlla ewrlal ewarll ewarll ewalrl ewallr
ewallr ewalrl ewlarl ewlalr ewlral ewlrla ewllra ewllar ewlalr ewlarl ewllar
ewllra ewlrla ewlral eawrll eawrll eawlrl eawllr eawllr eawlrl earwll earwll
earlwl earllw earllw earlwl ealrwl ealrlw ealwrl ealwlr eallwr eallrw ealrlw
ealrwl eallrw eallwr ealwlr ealwrl elwarl elwalr elwral elwrla elwlra elwlar
elawrl elawlr elarwl elarlw elalrw elalwr elrawl elralw elrwal elrwla elrlwa
elrlaw ellarw ellawr ellraw ellrwa ellwra ellwar elwalr elwarl elwlar elwlra
elwrla elwral elawlr elawrl elalwr elalrw elarlw elarwl ellawr ellarw ellwar
ellwra ellrwa ellraw elralw elrawl elrlaw elrlwa elrwla elrwal werall werall
werlal werlla werlla werlal wearll wearll wealrl weallr weallr wealrl welarl
welalr welral welrla wellra wellar welalr welarl wellar wellra welrla welral
wreall wreall wrelal wrella wrella wrelal wraell wraell wralel wralle wralle
wralel wrlael wrlale wrleal wrlela wrllea wrllae wrlale wrlael wrllae wrllea
wrlela wrleal warell warell warlel warlle warlle warlel waerll waerll waelrl
waellr waellr waelrl walerl walelr walrel walrle wallre waller walelr walerl
waller wallre walrle walrel wlrael wlrale wlreal wlrela wlrlea wlrlae wlarel
wlarle wlaerl wlaelr wlaler wlalre wlearl wlealr wleral wlerla wlelra wlelar
wllaer wllare wllear wllera wllrea wllrae wlrale wlrael wlrlae wlrlea wlrela
wlreal wlarle wlarel wlalre wlaler wlaelr wlaerl wllare wllaer wllrae wllrea
wllera wllear wlealr wlearl wlelar wlelra wlerla wleral aewrll aewrll aewlrl
aewllr aewllr aewlrl aerwll aerwll aerlwl aerllw aerllw aerlwl aelrwl aelrlw
aelwrl aelwlr aellwr aellrw aelrlw aelrwl aellrw aellwr aelwlr aelwrl awerll
awerll awelrl awellr awellr awelrl awrell awrell awrlel awrlle awrlle awrlel
awlrel awlrle awlerl awlelr awller awllre awlrle awlrel awllre awller awlelr
awlerl arwell arwell arwlel arwlle arwlle arwlel arewll arewll arelwl arellw
arellw arelwl arlewl arlelw arlwel arlwle arllwe arllew arlelw arlewl arllew
arllwe arlwle arlwel alwrel alwrle alwerl alwelr alwler alwlre alrwel alrwle
alrewl alrelw alrlew alrlwe alerwl alerlw alewrl alewlr alelwr alelrw allrew
allrwe allerw allewr allwer allwre alwrle alwrel alwlre alwler alwelr alwerl
alrwle alrwel alrlwe alrlew alrelw alrewl allrwe allrew allwre allwer allewr
allerw alerlw alerwl alelrw alelwr alewlr alewrl lewarl lewalr lewral lewrla
lewlra lewlar leawrl leawlr learwl learlw lealrw lealwr lerawl leralw lerwal
lerwla lerlwa lerlaw lelarw lelawr lelraw lelrwa lelwra lelwar lwearl lwealr
lweral lwerla lwelra lwelar lwaerl lwaelr lwarel lwarle lwalre lwaler lwrael
lwrale lwreal lwrela lwrlea lwrlae lwlare lwlaer lwlrae lwlrea lwlera lwlear
lawerl lawelr lawrel lawrle lawlre lawler laewrl laewlr laerwl laerlw laelrw
laelwr larewl larelw larwel larwle larlwe larlew lalerw lalewr lalrew lalrwe
lalwre lalwer lrwael lrwale lrweal lrwela lrwlea lrwlae lrawel lrawle lraewl
lraelw lralew lralwe lreawl lrealw lrewal lrewla lrelwa lrelaw lrlaew lrlawe
lrleaw lrlewa lrlwea lrlwae llware llwaer llwrae llwrea llwera llwear llawre
llawer llarwe llarew llaerw llaewr llrawe llraew llrwae llrwea llrewa llreaw
llearw lleawr lleraw llerwa llewra llewar lewalr lewarl lewlar lewlra lewrla
lewral leawlr leawrl lealwr lealrw learlw learwl lelawr lelarw lelwar lelwra
lelrwa lelraw leralw lerawl lerlaw lerlwa lerwla lerwal lwealr lwearl lwelar
lwelra lwerla lweral lwaelr lwaerl lwaler lwalre lwarle lwarel lwlaer lwlare
lwlear lwlera lwlrea lwlrae lwrale lwrael lwrlae lwrlea lwrela lwreal lawelr
lawerl lawler lawlre lawrle lawrel laewlr laewrl laelwr laelrw laerlw laerwl
lalewr lalerw lalwer lalwre lalrwe lalrew larelw larewl larlew larlwe larwle
larwel llwaer llware llwear llwera llwrea llwrae llawer llawre llaewr llaerw
llarew llarwe lleawr llearw llewar llewra llerwa lleraw llraew llrawe llreaw
llrewa llrwea llrwae lrwale lrwael lrwlae lrwlea lrwela lrweal lrawle lrawel
lralwe lralew lraelw lraewl lrlawe lrlaew lrlwae lrlwea lrlewa lrleaw lrealw
lreawl lrelaw lrelwa lrewla lrewal

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History of cryptography
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