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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: barolo
cipher variations:
cbspmp dctqnq eduror fevsps gfwtqt
hgxuru ihyvsv jizwtw kjaxux lkbyvy
mlczwz nmdaxa onebyb pofczc qpgdad
rqhebe srifcf tsjgdg utkheh vulifi
wvmjgj xwnkhk yxolil zypmjm azqnkn

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: barolo
Cipher: yzilol

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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: barolo

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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: barolo
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: barolo
Cipher: onebyb

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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: barolo
Cipher: 211124431343

Extended Methods:
Method #1

Plaintext: barolo
method variations:

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

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Method #3

Plaintext: barolo
method variations:
aftcsh ftcsha tcshaf
cshaft shaftc haftcs

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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: barolo

all 720 cipher variations:
barolo barool barloo barloo barolo barool baorlo baorol baolro baolor baoolr
baoorl baloro baloor balroo balroo baloro baloor baoolr baoorl baolor baolro
baorlo baorol braolo braool braloo braloo braolo braool broalo broaol brolao
broloa broola brooal brloao brlooa brlaoo brlaoo brloao brlooa broola brooal
broloa brolao broalo broaol boralo boraol borlao borloa borola boroal boarlo
boarol boalro boalor boaolr boaorl bolaro bolaor bolrao bolroa bolora boloar
booalr booarl boolar boolra boorla booral blroao blrooa blraoo blraoo blroao
blrooa blorao bloroa bloaro bloaor blooar bloora blaoro blaoor blaroo blaroo
blaoro blaoor blooar bloora bloaor bloaro blorao bloroa borola boroal borloa
borlao boralo boraol boorla booral boolra boolar booalr booarl bolora boloar
bolroa bolrao bolaro bolaor boaolr boaorl boalor boalro boarlo boarol abrolo
abrool abrloo abrloo abrolo abrool aborlo aborol abolro abolor aboolr aboorl
abloro abloor ablroo ablroo abloro abloor aboolr aboorl abolor abolro aborlo
aborol arbolo arbool arbloo arbloo arbolo arbool aroblo arobol arolbo arolob
aroolb aroobl arlobo arloob arlboo arlboo arlobo arloob aroolb aroobl arolob
arolbo aroblo arobol aorblo aorbol aorlbo aorlob aorolb aorobl aobrlo aobrol
aoblro aoblor aobolr aoborl aolbro aolbor aolrbo aolrob aolorb aolobr aooblr
aoobrl aoolbr aoolrb aoorlb aoorbl alrobo alroob alrboo alrboo alrobo alroob
alorbo alorob alobro alobor aloobr aloorb alboro alboor albroo albroo alboro
alboor aloobr aloorb alobor alobro alorbo alorob aorolb aorobl aorlob aorlbo
aorblo aorbol aoorlb aoorbl aoolrb aoolbr aooblr aoobrl aolorb aolobr aolrob
aolrbo aolbro aolbor aobolr aoborl aoblor aoblro aobrlo aobrol rabolo rabool
rabloo rabloo rabolo rabool raoblo raobol raolbo raolob raoolb raoobl ralobo
raloob ralboo ralboo ralobo raloob raoolb raoobl raolob raolbo raoblo raobol
rbaolo rbaool rbaloo rbaloo rbaolo rbaool rboalo rboaol rbolao rboloa rboola
rbooal rbloao rblooa rblaoo rblaoo rbloao rblooa rboola rbooal rboloa rbolao
rboalo rboaol robalo robaol roblao robloa robola roboal roablo roabol roalbo
roalob roaolb roaobl rolabo rolaob rolbao rolboa roloba roloab rooalb rooabl
roolab roolba roobla roobal rlboao rlbooa rlbaoo rlbaoo rlboao rlbooa rlobao
rloboa rloabo rloaob rlooab rlooba rlaobo rlaoob rlaboo rlaboo rlaobo rlaoob
rlooab rlooba rloaob rloabo rlobao rloboa robola roboal robloa roblao robalo
robaol roobla roobal roolba roolab rooalb rooabl roloba roloab rolboa rolbao
rolabo rolaob roaolb roaobl roalob roalbo roablo roabol oarblo oarbol oarlbo
oarlob oarolb oarobl oabrlo oabrol oablro oablor oabolr oaborl oalbro oalbor
oalrbo oalrob oalorb oalobr oaoblr oaobrl oaolbr oaolrb oaorlb oaorbl orablo
orabol oralbo oralob oraolb oraobl orbalo orbaol orblao orbloa orbola orboal
orlbao orlboa orlabo orlaob orloab orloba orobla orobal orolba orolab oroalb
oroabl obralo obraol obrlao obrloa obrola obroal obarlo obarol obalro obalor
obaolr obaorl oblaro oblaor oblrao oblroa oblora obloar oboalr oboarl obolar
obolra oborla oboral olrbao olrboa olrabo olraob olroab olroba olbrao olbroa
olbaro olbaor olboar olbora olabro olabor olarbo olarob olaorb olaobr olobar
olobra oloabr oloarb olorab olorba oorbla oorbal oorlba oorlab ooralb oorabl
oobrla oobral ooblra ooblar oobalr oobarl oolbra oolbar oolrba oolrab oolarb
oolabr ooablr ooabrl ooalbr ooalrb ooarlb ooarbl larobo laroob larboo larboo
larobo laroob laorbo laorob laobro laobor laoobr laoorb laboro laboor labroo
labroo laboro laboor laoobr laoorb laobor laobro laorbo laorob lraobo lraoob
lraboo lraboo lraobo lraoob lroabo lroaob lrobao lroboa lrooba lrooab lrboao
lrbooa lrbaoo lrbaoo lrboao lrbooa lrooba lrooab lroboa lrobao lroabo lroaob
lorabo loraob lorbao lorboa loroba loroab loarbo loarob loabro loabor loaobr
loaorb lobaro lobaor lobrao lobroa lobora loboar looabr looarb loobar loobra
loorba loorab lbroao lbrooa lbraoo lbraoo lbroao lbrooa lborao lboroa lboaro
lboaor lbooar lboora lbaoro lbaoor lbaroo lbaroo lbaoro lbaoor lbooar lboora
lboaor lboaro lborao lboroa loroba loroab lorboa lorbao lorabo loraob loorba
loorab loobra loobar looabr looarb lobora loboar lobroa lobrao lobaro lobaor
loaobr loaorb loabor loabro loarbo loarob oarolb oarobl oarlob oarlbo oarblo
oarbol oaorlb oaorbl oaolrb oaolbr oaoblr oaobrl oalorb oalobr oalrob oalrbo
oalbro oalbor oabolr oaborl oablor oablro oabrlo oabrol oraolb oraobl oralob
oralbo orablo orabol oroalb oroabl orolab orolba orobla orobal orloab orloba
orlaob orlabo orlbao orlboa orbola orboal orbloa orblao orbalo orbaol ooralb
oorabl oorlab oorlba oorbla oorbal ooarlb ooarbl ooalrb ooalbr ooablr ooabrl
oolarb oolabr oolrab oolrba oolbra oolbar oobalr oobarl ooblar ooblra oobrla
oobral olroab olroba olraob olrabo olrbao olrboa olorab olorba oloarb oloabr
olobar olobra olaorb olaobr olarob olarbo olabro olabor olboar olbora olbaor
olbaro olbrao olbroa obrola obroal obrloa obrlao obralo obraol oborla oboral
obolra obolar oboalr oboarl oblora obloar oblroa oblrao oblaro oblaor obaolr
obaorl obalor obalro obarlo obarol

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History of cryptography
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