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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: hanted
cipher variations:
iboufe jcpvgf kdqwhg lerxih mfsyji
ngtzkj ohualk pivbml qjwcnm rkxdon
slyepo tmzfqp unagrq vobhsr wpcits
xqdjut yrekvu zsflwv atgmxw buhnyx
cviozy dwjpaz exkqba fylrcb gzmsdc

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: hanted
Cipher: szmgvw

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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: hanted

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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: hanted
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: hanted
Cipher: unagrq

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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: hanted
Cipher: 321133445141

Extended Methods:
Method #1

Plaintext: hanted
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
h a n t e d 
3 1 3 4 5 4 
2 1 3 4 1 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: hanted
Cipher: csubsa

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Method #3

Plaintext: hanted
method variations:
blsyql lsyqlb syqlbl
yqlbls qlblsy lblsyq

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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: hanted

all 720 cipher variations:
hanted hantde hanetd hanedt handet handte hatned hatnde hatend hatedn hatden
hatdne haetnd haetdn haentd haendt haednt haedtn hadten hadtne hadetn hadent
hadnet hadnte hnated hnatde hnaetd hnaedt hnadet hnadte hntaed hntade hntead
hnteda hntdea hntdae hnetad hnetda hneatd hneadt hnedat hnedta hndtea hndtae
hndeta hndeat hndaet hndate htnaed htnade htnead htneda htndea htndae htaned
htande htaend htaedn htaden htadne hteand hteadn htenad htenda htedna htedan
htdaen htdane htdean htdena htdnea htdnae hentad hentda henatd henadt hendat
hendta hetnad hetnda hetand hetadn hetdan hetdna heatnd heatdn heantd heandt
headnt headtn hedtan hedtna hedatn hedant hednat hednta hdntea hdntae hdneta
hdneat hdnaet hdnate hdtnea hdtnae hdtena hdtean hdtaen hdtane hdetna hdetan
hdenta hdenat hdeant hdeatn hdaten hdatne hdaetn hdaent hdanet hdante ahnted
ahntde ahnetd ahnedt ahndet ahndte ahtned ahtnde ahtend ahtedn ahtden ahtdne
ahetnd ahetdn ahentd ahendt ahednt ahedtn ahdten ahdtne ahdetn ahdent ahdnet
ahdnte anhted anhtde anhetd anhedt anhdet anhdte anthed anthde antehd antedh
antdeh antdhe anethd anetdh anehtd anehdt anedht anedth andteh andthe andeth
andeht andhet andhte atnhed atnhde atnehd atnedh atndeh atndhe athned athnde
athend athedn athden athdne atehnd atehdn atenhd atendh atednh atedhn atdhen
atdhne atdehn atdenh atdneh atdnhe aenthd aentdh aenhtd aenhdt aendht aendth
aetnhd aetndh aethnd aethdn aetdhn aetdnh aehtnd aehtdn aehntd aehndt aehdnt
aehdtn aedthn aedtnh aedhtn aedhnt aednht aednth adnteh adnthe adneth adneht
adnhet adnhte adtneh adtnhe adtenh adtehn adthen adthne adetnh adethn adenth
adenht adehnt adehtn adhten adhtne adhetn adhent adhnet adhnte nahted nahtde
nahetd nahedt nahdet nahdte nathed nathde natehd natedh natdeh natdhe naethd
naetdh naehtd naehdt naedht naedth nadteh nadthe nadeth nadeht nadhet nadhte
nhated nhatde nhaetd nhaedt nhadet nhadte nhtaed nhtade nhtead nhteda nhtdea
nhtdae nhetad nhetda nheatd nheadt nhedat nhedta nhdtea nhdtae nhdeta nhdeat
nhdaet nhdate nthaed nthade nthead ntheda nthdea nthdae ntahed ntahde ntaehd
ntaedh ntadeh ntadhe nteahd nteadh ntehad ntehda ntedha ntedah ntdaeh ntdahe
ntdeah ntdeha ntdhea ntdhae nehtad nehtda nehatd nehadt nehdat nehdta nethad
nethda netahd netadh netdah netdha neathd neatdh neahtd neahdt neadht neadth
nedtah nedtha nedath nedaht nedhat nedhta ndhtea ndhtae ndheta ndheat ndhaet
ndhate ndthea ndthae ndteha ndteah ndtaeh ndtahe ndetha ndetah ndehta ndehat
ndeaht ndeath ndateh ndathe ndaeth ndaeht ndahet ndahte tanhed tanhde tanehd
tanedh tandeh tandhe tahned tahnde tahend tahedn tahden tahdne taehnd taehdn
taenhd taendh taednh taedhn tadhen tadhne tadehn tadenh tadneh tadnhe tnahed
tnahde tnaehd tnaedh tnadeh tnadhe tnhaed tnhade tnhead tnheda tnhdea tnhdae
tnehad tnehda tneahd tneadh tnedah tnedha tndhea tndhae tndeha tndeah tndaeh
tndahe thnaed thnade thnead thneda thndea thndae thaned thande thaend thaedn
thaden thadne theand theadn thenad thenda thedna thedan thdaen thdane thdean
thdena thdnea thdnae tenhad tenhda tenahd tenadh tendah tendha tehnad tehnda
tehand tehadn tehdan tehdna teahnd teahdn teanhd teandh teadnh teadhn tedhan
tedhna tedahn tedanh tednah tednha tdnhea tdnhae tdneha tdneah tdnaeh tdnahe
tdhnea tdhnae tdhena tdhean tdhaen tdhane tdehna tdehan tdenha tdenah tdeanh
tdeahn tdahen tdahne tdaehn tdaenh tdaneh tdanhe eanthd eantdh eanhtd eanhdt
eandht eandth eatnhd eatndh eathnd eathdn eatdhn eatdnh eahtnd eahtdn eahntd
eahndt eahdnt eahdtn eadthn eadtnh eadhtn eadhnt eadnht eadnth enathd enatdh
enahtd enahdt enadht enadth entahd entadh enthad enthda entdha entdah enhtad
enhtda enhatd enhadt enhdat enhdta endtha endtah endhta endhat endaht endath
etnahd etnadh etnhad etnhda etndha etndah etanhd etandh etahnd etahdn etadhn
etadnh ethand ethadn ethnad ethnda ethdna ethdan etdahn etdanh etdhan etdhna
etdnha etdnah ehntad ehntda ehnatd ehnadt ehndat ehndta ehtnad ehtnda ehtand
ehtadn ehtdan ehtdna ehatnd ehatdn ehantd ehandt ehadnt ehadtn ehdtan ehdtna
ehdatn ehdant ehdnat ehdnta edntha edntah ednhta ednhat ednaht ednath edtnha
edtnah edthna edthan edtahn edtanh edhtna edhtan edhnta edhnat edhant edhatn
edathn edatnh edahtn edahnt edanht edanth danteh danthe daneth daneht danhet
danhte datneh datnhe datenh datehn dathen dathne daetnh daethn daenth daenht
daehnt daehtn dahten dahtne dahetn dahent dahnet dahnte dnateh dnathe dnaeth
dnaeht dnahet dnahte dntaeh dntahe dnteah dnteha dnthea dnthae dnetah dnetha
dneath dneaht dnehat dnehta dnhtea dnhtae dnheta dnheat dnhaet dnhate dtnaeh
dtnahe dtneah dtneha dtnhea dtnhae dtaneh dtanhe dtaenh dtaehn dtahen dtahne
dteanh dteahn dtenah dtenha dtehna dtehan dthaen dthane dthean dthena dthnea
dthnae dentah dentha denath denaht denhat denhta detnah detnha detanh detahn
dethan dethna deatnh deathn deanth deanht deahnt deahtn dehtan dehtna dehatn
dehant dehnat dehnta dhntea dhntae dhneta dhneat dhnaet dhnate dhtnea dhtnae
dhtena dhtean dhtaen dhtane dhetna dhetan dhenta dhenat dheant dheatn dhaten
dhatne dhaetn dhaent dhanet dhante

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History of cryptography
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