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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: mothra
cipher variations:
npuisb oqvjtc prwkud qsxlve rtymwf
suznxg tvaoyh uwbpzi vxcqaj wydrbk
xzescl yaftdm zbguen achvfo bdiwgp
cejxhq dfkyir eglzjs fhmakt ginblu
hjocmv ikpdnw jlqeox kmrfpy lnsgqz

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: mothra
Cipher: nlgsiz

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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: mothra

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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: mothra
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: mothra
Cipher: zbguen

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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: mothra
Cipher: 234344322411

Extended Methods:
Method #1

Plaintext: mothra
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
m o t h r a 
2 4 4 3 2 1 
3 3 4 2 4 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: mothra
Cipher: robnid

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Method #3

Plaintext: mothra
method variations:
ssogdf sogdfs ogdfss
gdfsso dfssog fssogd

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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: mothra

all 720 cipher variations:
mothra mothar motrha motrah motarh motahr mohtra mohtar mohrta mohrat mohart
mohatr morhta morhat mortha mortah morath moraht moahrt moahtr moarht moarth
moatrh moathr mtohra mtohar mtorha mtorah mtoarh mtoahr mthora mthoar mthroa
mthrao mtharo mthaor mtrhoa mtrhao mtroha mtroah mtraoh mtraho mtahro mtahor
mtarho mtaroh mtaorh mtaohr mhtora mhtoar mhtroa mhtrao mhtaro mhtaor mhotra
mhotar mhorta mhorat mhoart mhoatr mhrota mhroat mhrtoa mhrtao mhrato mhraot
mhaort mhaotr mharot mharto mhatro mhator mrthoa mrthao mrtoha mrtoah mrtaoh
mrtaho mrhtoa mrhtao mrhota mrhoat mrhaot mrhato mrohta mrohat mrotha mrotah
mroath mroaht mrahot mrahto mraoht mraoth mratoh mratho mathro mathor matrho
matroh matorh matohr mahtro mahtor mahrto mahrot mahort mahotr marhto marhot
martho martoh maroth maroht maohrt maohtr maorht maorth maotrh maothr omthra
omthar omtrha omtrah omtarh omtahr omhtra omhtar omhrta omhrat omhart omhatr
omrhta omrhat omrtha omrtah omrath omraht omahrt omahtr omarht omarth omatrh
omathr otmhra otmhar otmrha otmrah otmarh otmahr othmra othmar othrma othram
otharm othamr otrhma otrham otrmha otrmah otramh otrahm otahrm otahmr otarhm
otarmh otamrh otamhr ohtmra ohtmar ohtrma ohtram ohtarm ohtamr ohmtra ohmtar
ohmrta ohmrat ohmart ohmatr ohrmta ohrmat ohrtma ohrtam ohratm ohramt ohamrt
ohamtr oharmt ohartm ohatrm ohatmr orthma ortham ortmha ortmah ortamh ortahm
orhtma orhtam orhmta orhmat orhamt orhatm ormhta ormhat ormtha ormtah ormath
ormaht orahmt orahtm oramht oramth oratmh orathm oathrm oathmr oatrhm oatrmh
oatmrh oatmhr oahtrm oahtmr oahrtm oahrmt oahmrt oahmtr oarhtm oarhmt oarthm
oartmh oarmth oarmht oamhrt oamhtr oamrht oamrth oamtrh oamthr tomhra tomhar
tomrha tomrah tomarh tomahr tohmra tohmar tohrma tohram toharm tohamr torhma
torham tormha tormah toramh torahm toahrm toahmr toarhm toarmh toamrh toamhr
tmohra tmohar tmorha tmorah tmoarh tmoahr tmhora tmhoar tmhroa tmhrao tmharo
tmhaor tmrhoa tmrhao tmroha tmroah tmraoh tmraho tmahro tmahor tmarho tmaroh
tmaorh tmaohr thmora thmoar thmroa thmrao thmaro thmaor thomra thomar thorma
thoram thoarm thoamr throma throam thrmoa thrmao thramo thraom thaorm thaomr
tharom tharmo thamro thamor trmhoa trmhao trmoha trmoah trmaoh trmaho trhmoa
trhmao trhoma trhoam trhaom trhamo trohma troham tromha tromah troamh troahm
trahom trahmo traohm traomh tramoh tramho tamhro tamhor tamrho tamroh tamorh
tamohr tahmro tahmor tahrmo tahrom tahorm tahomr tarhmo tarhom tarmho tarmoh
taromh tarohm taohrm taohmr taorhm taormh taomrh taomhr hotmra hotmar hotrma
hotram hotarm hotamr homtra homtar homrta homrat homart homatr hormta hormat
hortma hortam horatm horamt hoamrt hoamtr hoarmt hoartm hoatrm hoatmr htomra
htomar htorma htoram htoarm htoamr htmora htmoar htmroa htmrao htmaro htmaor
htrmoa htrmao htroma htroam htraom htramo htamro htamor htarmo htarom htaorm
htaomr hmtora hmtoar hmtroa hmtrao hmtaro hmtaor hmotra hmotar hmorta hmorat
hmoart hmoatr hmrota hmroat hmrtoa hmrtao hmrato hmraot hmaort hmaotr hmarot
hmarto hmatro hmator hrtmoa hrtmao hrtoma hrtoam hrtaom hrtamo hrmtoa hrmtao
hrmota hrmoat hrmaot hrmato hromta hromat hrotma hrotam hroatm hroamt hramot
hramto hraomt hraotm hratom hratmo hatmro hatmor hatrmo hatrom hatorm hatomr
hamtro hamtor hamrto hamrot hamort hamotr harmto harmot hartmo hartom harotm
haromt haomrt haomtr haormt haortm haotrm haotmr rothma rotham rotmha rotmah
rotamh rotahm rohtma rohtam rohmta rohmat rohamt rohatm romhta romhat romtha
romtah romath romaht roahmt roahtm roamht roamth roatmh roathm rtohma rtoham
rtomha rtomah rtoamh rtoahm rthoma rthoam rthmoa rthmao rthamo rthaom rtmhoa
rtmhao rtmoha rtmoah rtmaoh rtmaho rtahmo rtahom rtamho rtamoh rtaomh rtaohm
rhtoma rhtoam rhtmoa rhtmao rhtamo rhtaom rhotma rhotam rhomta rhomat rhoamt
rhoatm rhmota rhmoat rhmtoa rhmtao rhmato rhmaot rhaomt rhaotm rhamot rhamto
rhatmo rhatom rmthoa rmthao rmtoha rmtoah rmtaoh rmtaho rmhtoa rmhtao rmhota
rmhoat rmhaot rmhato rmohta rmohat rmotha rmotah rmoath rmoaht rmahot rmahto
rmaoht rmaoth rmatoh rmatho rathmo rathom ratmho ratmoh ratomh ratohm rahtmo
rahtom rahmto rahmot rahomt rahotm ramhto ramhot ramtho ramtoh ramoth ramoht
raohmt raohtm raomht raomth raotmh raothm aothrm aothmr aotrhm aotrmh aotmrh
aotmhr aohtrm aohtmr aohrtm aohrmt aohmrt aohmtr aorhtm aorhmt aorthm aortmh
aormth aormht aomhrt aomhtr aomrht aomrth aomtrh aomthr atohrm atohmr atorhm
atormh atomrh atomhr athorm athomr athrom athrmo athmro athmor atrhom atrhmo
atrohm atromh atrmoh atrmho atmhro atmhor atmrho atmroh atmorh atmohr ahtorm
ahtomr ahtrom ahtrmo ahtmro ahtmor ahotrm ahotmr ahortm ahormt ahomrt ahomtr
ahrotm ahromt ahrtom ahrtmo ahrmto ahrmot ahmort ahmotr ahmrot ahmrto ahmtro
ahmtor arthom arthmo artohm artomh artmoh artmho arhtom arhtmo arhotm arhomt
arhmot arhmto arohtm arohmt arothm arotmh aromth aromht armhot armhto armoht
armoth armtoh armtho amthro amthor amtrho amtroh amtorh amtohr amhtro amhtor
amhrto amhrot amhort amhotr amrhto amrhot amrtho amrtoh amroth amroht amohrt
amohtr amorht amorth amotrh amothr

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History of cryptography
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