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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: hpscid
cipher variations:
iqtdje jruekf ksvflg ltwgmh muxhni
nvyioj owzjpk pxakql qyblrm rzcmsn
sadnto tbeoup ucfpvq vdgqwr wehrxs
xfisyt ygjtzu zhkuav ailvbw bjmwcx
cknxdy dloyez empzfa fnqagb gorbhc

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: hpscid
Cipher: skhxrw

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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: hpscid

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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: hpscid
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: hpscid
Cipher: ucfpvq

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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: hpscid
Cipher: 325334314241

Extended Methods:
Method #1

Plaintext: hpscid
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
h p s c i d 
3 5 3 3 4 4 
2 3 4 1 2 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: hpscid
Cipher: xntmdb

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Method #3

Plaintext: hpscid
method variations:
wnoqrl noqrlw oqrlwn
qrlwno rlwnoq lwnoqr

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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: hpscid

all 720 cipher variations:
hpscid hpscdi hpsicd hpsidc hpsdic hpsdci hpcsid hpcsdi hpcisd hpcids hpcdis
hpcdsi hpicsd hpicds hpiscd hpisdc hpidsc hpidcs hpdcis hpdcsi hpdics hpdisc
hpdsic hpdsci hspcid hspcdi hspicd hspidc hspdic hspdci hscpid hscpdi hscipd
hscidp hscdip hscdpi hsicpd hsicdp hsipcd hsipdc hsidpc hsidcp hsdcip hsdcpi
hsdicp hsdipc hsdpic hsdpci hcspid hcspdi hcsipd hcsidp hcsdip hcsdpi hcpsid
hcpsdi hcpisd hcpids hcpdis hcpdsi hcipsd hcipds hcispd hcisdp hcidsp hcidps
hcdpis hcdpsi hcdips hcdisp hcdsip hcdspi hiscpd hiscdp hispcd hispdc hisdpc
hisdcp hicspd hicsdp hicpsd hicpds hicdps hicdsp hipcsd hipcds hipscd hipsdc
hipdsc hipdcs hidcps hidcsp hidpcs hidpsc hidspc hidscp hdscip hdscpi hdsicp
hdsipc hdspic hdspci hdcsip hdcspi hdcisp hdcips hdcpis hdcpsi hdicsp hdicps
hdiscp hdispc hdipsc hdipcs hdpcis hdpcsi hdpics hdpisc hdpsic hdpsci phscid
phscdi phsicd phsidc phsdic phsdci phcsid phcsdi phcisd phcids phcdis phcdsi
phicsd phicds phiscd phisdc phidsc phidcs phdcis phdcsi phdics phdisc phdsic
phdsci pshcid pshcdi pshicd pshidc pshdic pshdci pschid pschdi pscihd pscidh
pscdih pscdhi psichd psicdh psihcd psihdc psidhc psidch psdcih psdchi psdich
psdihc psdhic psdhci pcshid pcshdi pcsihd pcsidh pcsdih pcsdhi pchsid pchsdi
pchisd pchids pchdis pchdsi pcihsd pcihds pcishd pcisdh pcidsh pcidhs pcdhis
pcdhsi pcdihs pcdish pcdsih pcdshi pischd piscdh pishcd pishdc pisdhc pisdch
picshd picsdh pichsd pichds picdhs picdsh pihcsd pihcds pihscd pihsdc pihdsc
pihdcs pidchs pidcsh pidhcs pidhsc pidshc pidsch pdscih pdschi pdsich pdsihc
pdshic pdshci pdcsih pdcshi pdcish pdcihs pdchis pdchsi pdicsh pdichs pdisch
pdishc pdihsc pdihcs pdhcis pdhcsi pdhics pdhisc pdhsic pdhsci sphcid sphcdi
sphicd sphidc sphdic sphdci spchid spchdi spcihd spcidh spcdih spcdhi spichd
spicdh spihcd spihdc spidhc spidch spdcih spdchi spdich spdihc spdhic spdhci
shpcid shpcdi shpicd shpidc shpdic shpdci shcpid shcpdi shcipd shcidp shcdip
shcdpi shicpd shicdp shipcd shipdc shidpc shidcp shdcip shdcpi shdicp shdipc
shdpic shdpci schpid schpdi schipd schidp schdip schdpi scphid scphdi scpihd
scpidh scpdih scpdhi sciphd scipdh scihpd scihdp scidhp scidph scdpih scdphi
scdiph scdihp scdhip scdhpi sihcpd sihcdp sihpcd sihpdc sihdpc sihdcp sichpd
sichdp sicphd sicpdh sicdph sicdhp sipchd sipcdh siphcd siphdc sipdhc sipdch
sidcph sidchp sidpch sidphc sidhpc sidhcp sdhcip sdhcpi sdhicp sdhipc sdhpic
sdhpci sdchip sdchpi sdcihp sdciph sdcpih sdcphi sdichp sdicph sdihcp sdihpc
sdiphc sdipch sdpcih sdpchi sdpich sdpihc sdphic sdphci cpshid cpshdi cpsihd
cpsidh cpsdih cpsdhi cphsid cphsdi cphisd cphids cphdis cphdsi cpihsd cpihds
cpishd cpisdh cpidsh cpidhs cpdhis cpdhsi cpdihs cpdish cpdsih cpdshi csphid
csphdi cspihd cspidh cspdih cspdhi cshpid cshpdi cshipd cshidp cshdip cshdpi
csihpd csihdp csiphd csipdh csidph csidhp csdhip csdhpi csdihp csdiph csdpih
csdphi chspid chspdi chsipd chsidp chsdip chsdpi chpsid chpsdi chpisd chpids
chpdis chpdsi chipsd chipds chispd chisdp chidsp chidps chdpis chdpsi chdips
chdisp chdsip chdspi cishpd cishdp cisphd cispdh cisdph cisdhp cihspd cihsdp
cihpsd cihpds cihdps cihdsp ciphsd ciphds cipshd cipsdh cipdsh cipdhs cidhps
cidhsp cidphs cidpsh cidsph cidshp cdship cdshpi cdsihp cdsiph cdspih cdsphi
cdhsip cdhspi cdhisp cdhips cdhpis cdhpsi cdihsp cdihps cdishp cdisph cdipsh
cdiphs cdphis cdphsi cdpihs cdpish cdpsih cdpshi ipschd ipscdh ipshcd ipshdc
ipsdhc ipsdch ipcshd ipcsdh ipchsd ipchds ipcdhs ipcdsh iphcsd iphcds iphscd
iphsdc iphdsc iphdcs ipdchs ipdcsh ipdhcs ipdhsc ipdshc ipdsch ispchd ispcdh
isphcd isphdc ispdhc ispdch iscphd iscpdh ischpd ischdp iscdhp iscdph ishcpd
ishcdp ishpcd ishpdc ishdpc ishdcp isdchp isdcph isdhcp isdhpc isdphc isdpch
icsphd icspdh icshpd icshdp icsdhp icsdph icpshd icpsdh icphsd icphds icpdhs
icpdsh ichpsd ichpds ichspd ichsdp ichdsp ichdps icdphs icdpsh icdhps icdhsp
icdshp icdsph ihscpd ihscdp ihspcd ihspdc ihsdpc ihsdcp ihcspd ihcsdp ihcpsd
ihcpds ihcdps ihcdsp ihpcsd ihpcds ihpscd ihpsdc ihpdsc ihpdcs ihdcps ihdcsp
ihdpcs ihdpsc ihdspc ihdscp idschp idscph idshcp idshpc idsphc idspch idcshp
idcsph idchsp idchps idcphs idcpsh idhcsp idhcps idhscp idhspc idhpsc idhpcs
idpchs idpcsh idphcs idphsc idpshc idpsch dpscih dpschi dpsich dpsihc dpshic
dpshci dpcsih dpcshi dpcish dpcihs dpchis dpchsi dpicsh dpichs dpisch dpishc
dpihsc dpihcs dphcis dphcsi dphics dphisc dphsic dphsci dspcih dspchi dspich
dspihc dsphic dsphci dscpih dscphi dsciph dscihp dschip dschpi dsicph dsichp
dsipch dsiphc dsihpc dsihcp dshcip dshcpi dshicp dshipc dshpic dshpci dcspih
dcsphi dcsiph dcsihp dcship dcshpi dcpsih dcpshi dcpish dcpihs dcphis dcphsi
dcipsh dciphs dcisph dcishp dcihsp dcihps dchpis dchpsi dchips dchisp dchsip
dchspi discph dischp dispch disphc dishpc dishcp dicsph dicshp dicpsh dicphs
dichps dichsp dipcsh dipchs dipsch dipshc diphsc diphcs dihcps dihcsp dihpcs
dihpsc dihspc dihscp dhscip dhscpi dhsicp dhsipc dhspic dhspci dhcsip dhcspi
dhcisp dhcips dhcpis dhcpsi dhicsp dhicps dhiscp dhispc dhipsc dhipcs dhpcis
dhpcsi dhpics dhpisc dhpsic dhpsci

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History of cryptography
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