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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: rivale
cipher variations:
sjwbmf tkxcng ulydoh vmzepi wnafqj
xobgrk ypchsl zqditm arejun bsfkvo
ctglwp duhmxq evinyr fwjozs gxkpat
hylqbu izmrcv jansdw kbotex lcpufy
mdqvgz nerwha ofsxib pgtyjc qhuzkd

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: rivale
Cipher: irezov

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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: rivale

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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: rivale
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: rivale
Cipher: evinyr

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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: rivale
Cipher: 244215111351

Extended Methods:
Method #1

Plaintext: rivale
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 v a l e 
2 4 1 1 1 5 
4 2 5 1 3 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: rivale
Cipher: raviec

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Method #3

Plaintext: rivale
method variations:
tbeaxf beaxft eaxftb
axftbe xftbea ftbeax

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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: rivale

all 720 cipher variations:
rivale rivael rivlae rivlea rivela riveal riavle riavel rialve rialev riaelv
riaevl rilave rilaev rilvae rilvea rileva rileav riealv rieavl rielav rielva
rievla rieval rviale rviael rvilae rvilea rviela rvieal rvaile rvaiel rvalie
rvalei rvaeli rvaeil rvlaie rvlaei rvliae rvliea rvleia rvleai rveali rveail
rvelai rvelia rveila rveial ravile raviel ravlie ravlei raveli raveil raivle
raivel railve railev raielv raievl ralive raliev ralvie ralvei ralevi raleiv
raeilv raeivl raeliv raelvi raevli raevil rlvaie rlvaei rlviae rlviea rlveia
rlveai rlavie rlavei rlaive rlaiev rlaeiv rlaevi rliave rliaev rlivae rlivea
rlieva rlieav rleaiv rleavi rleiav rleiva rlevia rlevai revali revail revlai
revlia revila revial reavli reavil realvi realiv reailv reaivl relavi relaiv
relvai relvia reliva reliav reialv reiavl reilav reilva reivla reival irvale
irvael irvlae irvlea irvela irveal iravle iravel iralve iralev iraelv iraevl
irlave irlaev irlvae irlvea irleva irleav irealv ireavl irelav irelva irevla
ireval ivrale ivrael ivrlae ivrlea ivrela ivreal ivarle ivarel ivalre ivaler
ivaelr ivaerl ivlare ivlaer ivlrae ivlrea ivlera ivlear ivealr ivearl ivelar
ivelra iverla iveral iavrle iavrel iavlre iavler iavelr iaverl iarvle iarvel
iarlve iarlev iarelv iarevl ialrve ialrev ialvre ialver ialevr ialerv iaerlv
iaervl iaelrv iaelvr iaevlr iaevrl ilvare ilvaer ilvrae ilvrea ilvera ilvear
ilavre ilaver ilarve ilarev ilaerv ilaevr ilrave ilraev ilrvae ilrvea ilreva
ilreav ilearv ileavr ilerav ilerva ilevra ilevar ievalr ievarl ievlar ievlra
ievrla ievral ieavlr ieavrl iealvr iealrv iearlv iearvl ielavr ielarv ielvar
ielvra ielrva ielrav ieralv ieravl ierlav ierlva iervla ierval virale virael
virlae virlea virela vireal viarle viarel vialre vialer viaelr viaerl vilare
vilaer vilrae vilrea vilera vilear viealr viearl vielar vielra vierla vieral
vriale vriael vrilae vrilea vriela vrieal vraile vraiel vralie vralei vraeli
vraeil vrlaie vrlaei vrliae vrliea vrleia vrleai vreali vreail vrelai vrelia
vreila vreial varile variel varlie varlei vareli vareil vairle vairel vailre
vailer vaielr vaierl valire valier valrie valrei valeri valeir vaeilr vaeirl
vaelir vaelri vaerli vaeril vlraie vlraei vlriae vlriea vlreia vlreai vlarie
vlarei vlaire vlaier vlaeir vlaeri vliare vliaer vlirae vlirea vliera vliear
vleair vleari vleiar vleira vleria vlerai verali verail verlai verlia verila
verial vearli vearil vealri vealir veailr veairl velari velair velrai velria
velira veliar veialr veiarl veilar veilra veirla veiral aivrle aivrel aivlre
aivler aivelr aiverl airvle airvel airlve airlev airelv airevl ailrve ailrev
ailvre ailver ailevr ailerv aierlv aiervl aielrv aielvr aievlr aievrl avirle
avirel avilre aviler avielr avierl avrile avriel avrlie avrlei avreli avreil
avlrie avlrei avlire avlier avleir avleri averli averil avelri avelir aveilr
aveirl arvile arviel arvlie arvlei arveli arveil arivle arivel arilve arilev
arielv arievl arlive arliev arlvie arlvei arlevi arleiv areilv areivl areliv
arelvi arevli arevil alvrie alvrei alvire alvier alveir alveri alrvie alrvei
alrive alriev alreiv alrevi alirve alirev alivre aliver alievr alierv aleriv
alervi aleirv aleivr alevir alevri aevrli aevril aevlri aevlir aevilr aevirl
aervli aervil aerlvi aerliv aerilv aerivl aelrvi aelriv aelvri aelvir aelivr
aelirv aeirlv aeirvl aeilrv aeilvr aeivlr aeivrl livare livaer livrae livrea
livera livear liavre liaver liarve liarev liaerv liaevr lirave liraev lirvae
lirvea lireva lireav liearv lieavr lierav lierva lievra lievar lviare lviaer
lvirae lvirea lviera lviear lvaire lvaier lvarie lvarei lvaeri lvaeir lvraie
lvraei lvriae lvriea lvreia lvreai lveari lveair lverai lveria lveira lveiar
lavire lavier lavrie lavrei laveri laveir laivre laiver lairve lairev laierv
laievr larive lariev larvie larvei larevi lareiv laeirv laeivr laeriv laervi
laevri laevir lrvaie lrvaei lrviae lrviea lrveia lrveai lravie lravei lraive
lraiev lraeiv lraevi lriave lriaev lrivae lrivea lrieva lrieav lreaiv lreavi
lreiav lreiva lrevia lrevai levari levair levrai levria levira leviar leavri
leavir learvi leariv leairv leaivr leravi leraiv lervai lervia leriva leriav
leiarv leiavr leirav leirva leivra leivar eivalr eivarl eivlar eivlra eivrla
eivral eiavlr eiavrl eialvr eialrv eiarlv eiarvl eilavr eilarv eilvar eilvra
eilrva eilrav eiralv eiravl eirlav eirlva eirvla eirval evialr eviarl evilar
evilra evirla eviral evailr evairl evalir evalri evarli evaril evlair evlari
evliar evlira evlria evlrai evrali evrail evrlai evrlia evrila evrial eavilr
eavirl eavlir eavlri eavrli eavril eaivlr eaivrl eailvr eailrv eairlv eairvl
ealivr ealirv ealvir ealvri ealrvi ealriv earilv earivl earliv earlvi earvli
earvil elvair elvari elviar elvira elvria elvrai elavir elavri elaivr elairv
elariv elarvi eliavr eliarv elivar elivra elirva elirav elraiv elravi elriav
elriva elrvia elrvai ervali ervail ervlai ervlia ervila ervial eravli eravil
eralvi eraliv erailv eraivl erlavi erlaiv erlvai erlvia erliva erliav erialv
eriavl erilav erilva erivla erival

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History of cryptography
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