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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: pcmcl
cipher variations:
qdndm reoen sfpfo tgqgp uhrhq
visir wjtjs xkukt ylvlu zmwmv
anxnw boyox cpzpy dqaqz erbra
fscsb gtdtc hueud ivfve jwgwf
kxhxg lyiyh mzjzi nakaj oblbk

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: pcmcl
Cipher: kxnxo

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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: pcmcl
Cipher: ABBBA AAABA ABABB AAABA ABABA

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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: pcmcl
cipher variations:
qdndmuhlhiyljlecphpagtftwkxdxssfzfkwjxjg
anvncertryivrvumzpzqreoenvimijzmkmfdqiqb
huguxlyeyttgaglxkykhbowodfsuszjwswvnaqar
sfpfowjnjkanlngerjrcivhvymzfzuuhbhmylzli
cpxpegtvtakxtxwobrbstgqgpxkoklbomohfsksd
jwiwznagavvicinzmamjdqyqfhuwublyuyxpcsct
uhrhqylplmcpnpigtltekxjxaobhbwwjdjoanbnk
erzrgivxvcmzvzyqdtduvisirzmqmndqoqjhumuf
lykybpcicxxkekpbocolfsashjwywdnawazreuev
wjtjsanrnoerprkivnvgmzlzcqdjdyylflqcpdpm
gtbtikxzxeobxbasfvfwxkuktbosopfsqsljwowh
namadrekezzmgmrdqeqnhucujlyayfpcycbtgwgx
ylvlucptpqgtrtmkxpxiobnbesflfaanhnserfro
ivdvkmzbzgqdzdcuhxhyzmwmvdquqrhusunlyqyj
pcocftgmgbboiotfsgspjwewlnacahreaedviyiz
anxnwervrsivtvomzrzkqdpdguhnhccpjpugthtq
kxfxmobdbisfbfewjzjaboyoxfswstjwuwpnasal
reqehvioiddqkqvhuiurlygynpcecjtgcgfxkakb
cpzpygtxtukxvxqobtbmsfrfiwjpjeerlrwivjvs
mzhzoqdfdkuhdhgylblcdqaqzhuyuvlywyrpcucn
tgsgjxkqkffsmsxjwkwtnaiapregelvieihzmcmd
erbraivzvwmzxzsqdvdouhthkylrlggtntykxlxu
objbqsfhfmwjfjiandnefscsbjwawxnayatrewep
viuilzmsmhhuouzlymyvpckcrtgignxkgkjboeof
gtdtckxbxyobzbusfxfqwjvjmantniivpvamznzw
qdldsuhjhoylhlkcpfpghueudlycyzpcacvtgygr
xkwknbouojjwqwbnaoaxremetvikipzmimldqgqh
ivfvemzdzaqdbdwuhzhsylxlocpvpkkxrxcobpby
sfnfuwjljqanjnmerhrijwgwfnaeabrecexviait
zmympdqwqllysydpcqcztgogvxkmkrbokonfsisj
kxhxgobfbcsfdfywjbjuanznqerxrmmztzeqdrda
uhphwylnlscplpogtjtklyiyhpcgcdtgegzxkckv
boaorfsysnnauafresebviqixzmomtdqmqphukul
mzjziqdhdeuhfhayldlwcpbpsgtztoobvbgsftfc
wjrjyanpnuernrqivlvmnakajreiefvigibzmemx
dqcqthuauppcwchtgugdxkskzboqovfsosrjwmwn
oblbksfjfgwjhjcanfnyerdruivbvqqdxdiuhvhe
yltlacprpwgtptskxnxopcmcltgkghxkikdbogoz
fsesvjwcwrreyejviwifzmumbdqsqxhuqutlyoyp

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: pcmcl
Cipher: cpzpy

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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: pcmcl
Cipher: 5331233113

Extended Methods:
Method #1

Plaintext: pcmcl
method variations:
uhrhqznwnvesbsakxgxf

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
p c m c l 
5 3 2 3 1 
3 1 3 1 3 
They are then read out in rows:
5323131313
Then divided up into pairs again, and the pairs turned back into letters using the square:
Plain: pcmcl
Cipher: pmlll

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Method #3

Plaintext: pcmcl
method variations:
nfnax fnaxn naxnf
axnfn xnfna

Read more ...[RUS] , [EN]

 

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: pcmcl

all 120 cipher variations:
pcmcl pcmlc pccml pcclm pclcm pclmc pmccl pmclc pmccl pmclc pmlcc
pmlcc pcmcl pcmlc pccml pcclm pclcm pclmc plmcc plmcc plcmc plccm
plccm plcmc cpmcl cpmlc cpcml cpclm cplcm cplmc cmpcl cmplc cmcpl
cmclp cmlcp cmlpc ccmpl ccmlp ccpml ccplm cclpm cclmp clmcp clmpc
clcmp clcpm clpcm clpmc mcpcl mcplc mccpl mcclp mclcp mclpc mpccl
mpclc mpccl mpclc mplcc mplcc mcpcl mcplc mccpl mcclp mclcp mclpc
mlpcc mlpcc mlcpc mlccp mlccp mlcpc ccmpl ccmlp ccpml ccplm cclpm
cclmp cmcpl cmclp cmpcl cmplc cmlpc cmlcp cpmcl cpmlc cpcml cpclm
cplcm cplmc clmpc clmcp clpmc clpcm clcpm clcmp lcmcp lcmpc lccmp
lccpm lcpcm lcpmc lmccp lmcpc lmccp lmcpc lmpcc lmpcc lcmcp lcmpc
lccmp lccpm lcpcm lcpmc lpmcc lpmcc lpcmc lpccm lpccm lpcmc

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

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