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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: macbob
cipher variations:
nbdcpc ocedqd pdfere qegfsf rfhgtg
sgihuh thjivi uikjwj vjlkxk wkmlyl
xlnmzm ymonan znpobo aoqpcp bprqdq
cqsrer drtsfs esutgt ftvuhu guwviv
hvxwjw iwyxkx jxzyly kyazmz lzbana

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: macbob
Cipher: nzxyly

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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: macbob

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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: macbob
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: macbob
Cipher: znpobo

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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: macbob
Cipher: 231131214321

Extended Methods:
Method #1

Plaintext: macbob
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
m a c b o b 
2 1 3 2 4 2 
3 1 1 1 3 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: macbob
Cipher: bhicac

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Method #3

Plaintext: macbob
method variations:
clfqhf lfqhfc fqhfcl
qhfclf hfclfq fclfqh

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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: macbob

all 720 cipher variations:
macbob macbbo macobb macobb macbob macbbo mabcob mabcbo mabocb mabobc mabboc
mabbco maobcb maobbc maocbb maocbb maobcb maobbc mabboc mabbco mabobc mabocb
mabcob mabcbo mcabob mcabbo mcaobb mcaobb mcabob mcabbo mcbaob mcbabo mcboab
mcboba mcbboa mcbbao mcobab mcobba mcoabb mcoabb mcobab mcobba mcbboa mcbbao
mcboba mcboab mcbaob mcbabo mbcaob mbcabo mbcoab mbcoba mbcboa mbcbao mbacob
mbacbo mbaocb mbaobc mbaboc mbabco mboacb mboabc mbocab mbocba mbobca mbobac
mbbaoc mbbaco mbboac mbboca mbbcoa mbbcao mocbab mocbba mocabb mocabb mocbab
mocbba mobcab mobcba mobacb mobabc mobbac mobbca moabcb moabbc moacbb moacbb
moabcb moabbc mobbac mobbca mobabc mobacb mobcab mobcba mbcboa mbcbao mbcoba
mbcoab mbcaob mbcabo mbbcoa mbbcao mbboca mbboac mbbaoc mbbaco mbobca mbobac
mbocba mbocab mboacb mboabc mbaboc mbabco mbaobc mbaocb mbacob mbacbo amcbob
amcbbo amcobb amcobb amcbob amcbbo ambcob ambcbo ambocb ambobc ambboc ambbco
amobcb amobbc amocbb amocbb amobcb amobbc ambboc ambbco ambobc ambocb ambcob
ambcbo acmbob acmbbo acmobb acmobb acmbob acmbbo acbmob acbmbo acbomb acbobm
acbbom acbbmo acobmb acobbm acombb acombb acobmb acobbm acbbom acbbmo acbobm
acbomb acbmob acbmbo abcmob abcmbo abcomb abcobm abcbom abcbmo abmcob abmcbo
abmocb abmobc abmboc abmbco abomcb abombc abocmb abocbm abobcm abobmc abbmoc
abbmco abbomc abbocm abbcom abbcmo aocbmb aocbbm aocmbb aocmbb aocbmb aocbbm
aobcmb aobcbm aobmcb aobmbc aobbmc aobbcm aombcb aombbc aomcbb aomcbb aombcb
aombbc aobbmc aobbcm aobmbc aobmcb aobcmb aobcbm abcbom abcbmo abcobm abcomb
abcmob abcmbo abbcom abbcmo abbocm abbomc abbmoc abbmco abobcm abobmc abocbm
abocmb abomcb abombc abmboc abmbco abmobc abmocb abmcob abmcbo cambob cambbo
camobb camobb cambob cambbo cabmob cabmbo cabomb cabobm cabbom cabbmo caobmb
caobbm caombb caombb caobmb caobbm cabbom cabbmo cabobm cabomb cabmob cabmbo
cmabob cmabbo cmaobb cmaobb cmabob cmabbo cmbaob cmbabo cmboab cmboba cmbboa
cmbbao cmobab cmobba cmoabb cmoabb cmobab cmobba cmbboa cmbbao cmboba cmboab
cmbaob cmbabo cbmaob cbmabo cbmoab cbmoba cbmboa cbmbao cbamob cbambo cbaomb
cbaobm cbabom cbabmo cboamb cboabm cbomab cbomba cbobma cbobam cbbaom cbbamo
cbboam cbboma cbbmoa cbbmao combab combba comabb comabb combab combba cobmab
cobmba cobamb cobabm cobbam cobbma coabmb coabbm coambb coambb coabmb coabbm
cobbam cobbma cobabm cobamb cobmab cobmba cbmboa cbmbao cbmoba cbmoab cbmaob
cbmabo cbbmoa cbbmao cbboma cbboam cbbaom cbbamo cbobma cbobam cbomba cbomab
cboamb cboabm cbabom cbabmo cbaobm cbaomb cbamob cbambo bacmob bacmbo bacomb
bacobm bacbom bacbmo bamcob bamcbo bamocb bamobc bamboc bambco baomcb baombc
baocmb baocbm baobcm baobmc babmoc babmco babomc babocm babcom babcmo bcamob
bcambo bcaomb bcaobm bcabom bcabmo bcmaob bcmabo bcmoab bcmoba bcmboa bcmbao
bcomab bcomba bcoamb bcoabm bcobam bcobma bcbmoa bcbmao bcboma bcboam bcbaom
bcbamo bmcaob bmcabo bmcoab bmcoba bmcboa bmcbao bmacob bmacbo bmaocb bmaobc
bmaboc bmabco bmoacb bmoabc bmocab bmocba bmobca bmobac bmbaoc bmbaco bmboac
bmboca bmbcoa bmbcao bocmab bocmba bocamb bocabm bocbam bocbma bomcab bomcba
bomacb bomabc bombac bombca boamcb boambc boacmb boacbm boabcm boabmc bobmac
bobmca bobamc bobacm bobcam bobcma bbcmoa bbcmao bbcoma bbcoam bbcaom bbcamo
bbmcoa bbmcao bbmoca bbmoac bbmaoc bbmaco bbomca bbomac bbocma bbocam bboacm
bboamc bbamoc bbamco bbaomc bbaocm bbacom bbacmo oacbmb oacbbm oacmbb oacmbb
oacbmb oacbbm oabcmb oabcbm oabmcb oabmbc oabbmc oabbcm oambcb oambbc oamcbb
oamcbb oambcb oambbc oabbmc oabbcm oabmbc oabmcb oabcmb oabcbm ocabmb ocabbm
ocambb ocambb ocabmb ocabbm ocbamb ocbabm ocbmab ocbmba ocbbma ocbbam ocmbab
ocmbba ocmabb ocmabb ocmbab ocmbba ocbbma ocbbam ocbmba ocbmab ocbamb ocbabm
obcamb obcabm obcmab obcmba obcbma obcbam obacmb obacbm obamcb obambc obabmc
obabcm obmacb obmabc obmcab obmcba obmbca obmbac obbamc obbacm obbmac obbmca
obbcma obbcam omcbab omcbba omcabb omcabb omcbab omcbba ombcab ombcba ombacb
ombabc ombbac ombbca omabcb omabbc omacbb omacbb omabcb omabbc ombbac ombbca
ombabc ombacb ombcab ombcba obcbma obcbam obcmba obcmab obcamb obcabm obbcma
obbcam obbmca obbmac obbamc obbacm obmbca obmbac obmcba obmcab obmacb obmabc
obabmc obabcm obambc obamcb obacmb obacbm bacbom bacbmo bacobm bacomb bacmob
bacmbo babcom babcmo babocm babomc babmoc babmco baobcm baobmc baocbm baocmb
baomcb baombc bamboc bambco bamobc bamocb bamcob bamcbo bcabom bcabmo bcaobm
bcaomb bcamob bcambo bcbaom bcbamo bcboam bcboma bcbmoa bcbmao bcobam bcobma
bcoabm bcoamb bcomab bcomba bcmboa bcmbao bcmoba bcmoab bcmaob bcmabo bbcaom
bbcamo bbcoam bbcoma bbcmoa bbcmao bbacom bbacmo bbaocm bbaomc bbamoc bbamco
bboacm bboamc bbocam bbocma bbomca bbomac bbmaoc bbmaco bbmoac bbmoca bbmcoa
bbmcao bocbam bocbma bocabm bocamb bocmab bocmba bobcam bobcma bobacm bobamc
bobmac bobmca boabcm boabmc boacbm boacmb boamcb boambc bombac bombca bomabc
bomacb bomcab bomcba bmcboa bmcbao bmcoba bmcoab bmcaob bmcabo bmbcoa bmbcao
bmboca bmboac bmbaoc bmbaco bmobca bmobac bmocba bmocab bmoacb bmoabc bmaboc
bmabco bmaobc bmaocb bmacob bmacbo

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History of cryptography
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