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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: dispar
cipher variations:
ejtqbs fkurct glvsdu hmwtev inxufw
joyvgx kpzwhy lqaxiz mrbyja nsczkb
otdalc puebmd qvfcne rwgdof sxhepg
tyifqh uzjgri vakhsj wblitk xcmjul
ydnkvm zeolwn afpmxo bgqnyp chrozq

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: dispar
Cipher: wrhkzi

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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: dispar

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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: dispar
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: dispar
Cipher: qvfcne

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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: dispar
Cipher: 414234531124

Extended Methods:
Method #1

Plaintext: dispar
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
d i s p a r 
4 4 3 5 1 2 
1 2 4 3 1 4 
They are then read out in rows:
Then divided up into pairs again, and the pairs turned back into letters using the square:
Plain: dispar
Cipher: txffoq

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Method #3

Plaintext: dispar
method variations:
qmycft mycftq ycftqm
cftqmy ftqmyc tqmycf

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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: dispar

all 720 cipher variations:
dispar dispra disapr disarp disrap disrpa dipsar dipsra dipasr dipars dipras
diprsa diapsr diaprs diaspr diasrp diarsp diarps dirpas dirpsa diraps dirasp
dirsap dirspa dsipar dsipra dsiapr dsiarp dsirap dsirpa dspiar dspira dspair
dspari dsprai dspria dsapir dsapri dsaipr dsairp dsarip dsarpi dsrpai dsrpia
dsrapi dsraip dsriap dsripa dpsiar dpsira dpsair dpsari dpsrai dpsria dpisar
dpisra dpiasr dpiars dpiras dpirsa dpaisr dpairs dpasir dpasri dparsi dparis
dprias dprisa dprais dprasi dprsai dprsia daspir daspri dasipr dasirp dasrip
dasrpi dapsir dapsri dapisr dapirs dapris daprsi daipsr daiprs daispr daisrp
dairsp dairps darpis darpsi darips darisp darsip darspi drspai drspia drsapi
drsaip drsiap drsipa drpsai drpsia drpasi drpais drpias drpisa drapsi drapis
draspi drasip draisp draips dripas dripsa driaps driasp drisap drispa idspar
idspra idsapr idsarp idsrap idsrpa idpsar idpsra idpasr idpars idpras idprsa
idapsr idaprs idaspr idasrp idarsp idarps idrpas idrpsa idraps idrasp idrsap
idrspa isdpar isdpra isdapr isdarp isdrap isdrpa ispdar ispdra ispadr ispard
isprad isprda isapdr isaprd isadpr isadrp isardp isarpd isrpad isrpda israpd
isradp isrdap isrdpa ipsdar ipsdra ipsadr ipsard ipsrad ipsrda ipdsar ipdsra
ipdasr ipdars ipdras ipdrsa ipadsr ipadrs ipasdr ipasrd iparsd ipards iprdas
iprdsa iprads iprasd iprsad iprsda iaspdr iasprd iasdpr iasdrp iasrdp iasrpd
iapsdr iapsrd iapdsr iapdrs iaprds iaprsd iadpsr iadprs iadspr iadsrp iadrsp
iadrps iarpds iarpsd iardps iardsp iarsdp iarspd irspad irspda irsapd irsadp
irsdap irsdpa irpsad irpsda irpasd irpads irpdas irpdsa irapsd irapds iraspd
irasdp iradsp iradps irdpas irdpsa irdaps irdasp irdsap irdspa sidpar sidpra
sidapr sidarp sidrap sidrpa sipdar sipdra sipadr sipard siprad siprda siapdr
siaprd siadpr siadrp siardp siarpd sirpad sirpda sirapd siradp sirdap sirdpa
sdipar sdipra sdiapr sdiarp sdirap sdirpa sdpiar sdpira sdpair sdpari sdprai
sdpria sdapir sdapri sdaipr sdairp sdarip sdarpi sdrpai sdrpia sdrapi sdraip
sdriap sdripa spdiar spdira spdair spdari spdrai spdria spidar spidra spiadr
spiard spirad spirda spaidr spaird spadir spadri spardi sparid spriad sprida
spraid spradi sprdai sprdia sadpir sadpri sadipr sadirp sadrip sadrpi sapdir
sapdri sapidr sapird saprid saprdi saipdr saiprd saidpr saidrp sairdp sairpd
sarpid sarpdi saripd saridp sardip sardpi srdpai srdpia srdapi srdaip srdiap
srdipa srpdai srpdia srpadi srpaid srpiad srpida srapdi srapid sradpi sradip
sraidp sraipd sripad sripda sriapd sriadp sridap sridpa pisdar pisdra pisadr
pisard pisrad pisrda pidsar pidsra pidasr pidars pidras pidrsa piadsr piadrs
piasdr piasrd piarsd piards pirdas pirdsa pirads pirasd pirsad pirsda psidar
psidra psiadr psiard psirad psirda psdiar psdira psdair psdari psdrai psdria
psadir psadri psaidr psaird psarid psardi psrdai psrdia psradi psraid psriad
psrida pdsiar pdsira pdsair pdsari pdsrai pdsria pdisar pdisra pdiasr pdiars
pdiras pdirsa pdaisr pdairs pdasir pdasri pdarsi pdaris pdrias pdrisa pdrais
pdrasi pdrsai pdrsia pasdir pasdri pasidr pasird pasrid pasrdi padsir padsri
padisr padirs padris padrsi paidsr paidrs paisdr paisrd pairsd pairds pardis
pardsi parids parisd parsid parsdi prsdai prsdia prsadi prsaid prsiad prsida
prdsai prdsia prdasi prdais prdias prdisa pradsi pradis prasdi prasid praisd
praids pridas pridsa priads priasd prisad prisda aispdr aisprd aisdpr aisdrp
aisrdp aisrpd aipsdr aipsrd aipdsr aipdrs aiprds aiprsd aidpsr aidprs aidspr
aidsrp aidrsp aidrps airpds airpsd airdps airdsp airsdp airspd asipdr asiprd
asidpr asidrp asirdp asirpd aspidr aspird aspdir aspdri asprdi asprid asdpir
asdpri asdipr asdirp asdrip asdrpi asrpdi asrpid asrdpi asrdip asridp asripd
apsidr apsird apsdir apsdri apsrdi apsrid apisdr apisrd apidsr apidrs apirds
apirsd apdisr apdirs apdsir apdsri apdrsi apdris aprids aprisd aprdis aprdsi
aprsdi aprsid adspir adspri adsipr adsirp adsrip adsrpi adpsir adpsri adpisr
adpirs adpris adprsi adipsr adiprs adispr adisrp adirsp adirps adrpis adrpsi
adrips adrisp adrsip adrspi arspdi arspid arsdpi arsdip arsidp arsipd arpsdi
arpsid arpdsi arpdis arpids arpisd ardpsi ardpis ardspi ardsip ardisp ardips
aripds aripsd aridps aridsp arisdp arispd rispad rispda risapd risadp risdap
risdpa ripsad ripsda ripasd ripads ripdas ripdsa riapsd riapds riaspd riasdp
riadsp riadps ridpas ridpsa ridaps ridasp ridsap ridspa rsipad rsipda rsiapd
rsiadp rsidap rsidpa rspiad rspida rspaid rspadi rspdai rspdia rsapid rsapdi
rsaipd rsaidp rsadip rsadpi rsdpai rsdpia rsdapi rsdaip rsdiap rsdipa rpsiad
rpsida rpsaid rpsadi rpsdai rpsdia rpisad rpisda rpiasd rpiads rpidas rpidsa
rpaisd rpaids rpasid rpasdi rpadsi rpadis rpdias rpdisa rpdais rpdasi rpdsai
rpdsia raspid raspdi rasipd rasidp rasdip rasdpi rapsid rapsdi rapisd rapids
rapdis rapdsi raipsd raipds raispd raisdp raidsp raidps radpis radpsi radips
radisp radsip radspi rdspai rdspia rdsapi rdsaip rdsiap rdsipa rdpsai rdpsia
rdpasi rdpais rdpias rdpisa rdapsi rdapis rdaspi rdasip rdaisp rdaips rdipas
rdipsa rdiaps rdiasp rdisap rdispa

Read more ...[1] , [2] , [3]

History of cryptography
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