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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: randyl
cipher variations:
sboezm tcpfan udqgbo verhcp wfsidq
xgtjer yhukfs zivlgt ajwmhu bkxniv
clyojw dmzpkx enaqly fobrmz gpcsna
hqdtob ireupc jsfvqd ktgwre luhxsf
mviytg nwjzuh oxkavi pylbwj qzmcxk

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: randyl
Cipher: izmwbo

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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: randyl

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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: randyl
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: randyl
Cipher: enaqly

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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: randyl
Cipher: 241133414513

Extended Methods:
Method #1

Plaintext: randyl
method variations:

Method #2
Bifid cipher
The message is converted to its coordinates in the usual manner, but they are written vertically beneath:
r a n d y l 
2 1 3 4 4 1 
4 1 3 1 5 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: randyl
Cipher: bsddcp

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Method #3

Plaintext: randyl
method variations:
dlsqeh lsqehd sqehdl
qehdls ehdlsq hdlsqe

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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: randyl

all 720 cipher variations:
randyl randly ranydl ranyld ranlyd ranldy radnyl radnly radynl radyln radlyn
radlny raydnl raydln rayndl raynld raylnd rayldn raldyn raldny ralydn ralynd
ralnyd ralndy rnadyl rnadly rnaydl rnayld rnalyd rnaldy rndayl rndaly rndyal
rndyla rndlya rndlay rnydal rnydla rnyadl rnyald rnylad rnylda rnldya rnlday
rnlyda rnlyad rnlayd rnlady rdnayl rdnaly rdnyal rdnyla rdnlya rdnlay rdanyl
rdanly rdaynl rdayln rdalyn rdalny rdyanl rdyaln rdynal rdynla rdylna rdylan
rdlayn rdlany rdlyan rdlyna rdlnya rdlnay ryndal ryndla rynadl rynald rynlad
rynlda rydnal rydnla rydanl rydaln rydlan rydlna ryadnl ryadln ryandl ryanld
ryalnd ryaldn ryldan ryldna ryladn ryland rylnad rylnda rlndya rlnday rlnyda
rlnyad rlnayd rlnady rldnya rldnay rldyna rldyan rldayn rldany rlydna rlydan
rlynda rlynad rlyand rlyadn rladyn rladny rlaydn rlaynd rlanyd rlandy arndyl
arndly arnydl arnyld arnlyd arnldy ardnyl ardnly ardynl ardyln ardlyn ardlny
arydnl arydln aryndl arynld arylnd aryldn arldyn arldny arlydn arlynd arlnyd
arlndy anrdyl anrdly anrydl anryld anrlyd anrldy andryl andrly andyrl andylr
andlyr andlry anydrl anydlr anyrdl anyrld anylrd anyldr anldyr anldry anlydr
anlyrd anlryd anlrdy adnryl adnrly adnyrl adnylr adnlyr adnlry adrnyl adrnly
adrynl adryln adrlyn adrlny adyrnl adyrln adynrl adynlr adylnr adylrn adlryn
adlrny adlyrn adlynr adlnyr adlnry ayndrl ayndlr aynrdl aynrld aynlrd aynldr
aydnrl aydnlr aydrnl aydrln aydlrn aydlnr ayrdnl ayrdln ayrndl ayrnld ayrlnd
ayrldn ayldrn ayldnr aylrdn aylrnd aylnrd aylndr alndyr alndry alnydr alnyrd
alnryd alnrdy aldnyr aldnry aldynr aldyrn aldryn aldrny alydnr alydrn alyndr
alynrd alyrnd alyrdn alrdyn alrdny alrydn alrynd alrnyd alrndy nardyl nardly
narydl naryld narlyd narldy nadryl nadrly nadyrl nadylr nadlyr nadlry naydrl
naydlr nayrdl nayrld naylrd nayldr naldyr naldry nalydr nalyrd nalryd nalrdy
nradyl nradly nraydl nrayld nralyd nraldy nrdayl nrdaly nrdyal nrdyla nrdlya
nrdlay nrydal nrydla nryadl nryald nrylad nrylda nrldya nrlday nrlyda nrlyad
nrlayd nrlady ndrayl ndraly ndryal ndryla ndrlya ndrlay ndaryl ndarly ndayrl
ndaylr ndalyr ndalry ndyarl ndyalr ndyral ndyrla ndylra ndylar ndlayr ndlary
ndlyar ndlyra ndlrya ndlray nyrdal nyrdla nyradl nyrald nyrlad nyrlda nydral
nydrla nydarl nydalr nydlar nydlra nyadrl nyadlr nyardl nyarld nyalrd nyaldr
nyldar nyldra nyladr nylard nylrad nylrda nlrdya nlrday nlryda nlryad nlrayd
nlrady nldrya nldray nldyra nldyar nldayr nldary nlydra nlydar nlyrda nlyrad
nlyard nlyadr nladyr nladry nlaydr nlayrd nlaryd nlardy danryl danrly danyrl
danylr danlyr danlry darnyl darnly darynl daryln darlyn darlny dayrnl dayrln
daynrl daynlr daylnr daylrn dalryn dalrny dalyrn dalynr dalnyr dalnry dnaryl
dnarly dnayrl dnaylr dnalyr dnalry dnrayl dnraly dnryal dnryla dnrlya dnrlay
dnyral dnyrla dnyarl dnyalr dnylar dnylra dnlrya dnlray dnlyra dnlyar dnlayr
dnlary drnayl drnaly drnyal drnyla drnlya drnlay dranyl dranly draynl drayln
dralyn dralny dryanl dryaln drynal drynla drylna drylan drlayn drlany drlyan
drlyna drlnya drlnay dynral dynrla dynarl dynalr dynlar dynlra dyrnal dyrnla
dyranl dyraln dyrlan dyrlna dyarnl dyarln dyanrl dyanlr dyalnr dyalrn dylran
dylrna dylarn dylanr dylnar dylnra dlnrya dlnray dlnyra dlnyar dlnayr dlnary
dlrnya dlrnay dlryna dlryan dlrayn dlrany dlyrna dlyran dlynra dlynar dlyanr
dlyarn dlaryn dlarny dlayrn dlaynr dlanyr dlanry yandrl yandlr yanrdl yanrld
yanlrd yanldr yadnrl yadnlr yadrnl yadrln yadlrn yadlnr yardnl yardln yarndl
yarnld yarlnd yarldn yaldrn yaldnr yalrdn yalrnd yalnrd yalndr ynadrl ynadlr
ynardl ynarld ynalrd ynaldr yndarl yndalr yndral yndrla yndlra yndlar ynrdal
ynrdla ynradl ynrald ynrlad ynrlda ynldra ynldar ynlrda ynlrad ynlard ynladr
ydnarl ydnalr ydnral ydnrla ydnlra ydnlar ydanrl ydanlr ydarnl ydarln ydalrn
ydalnr ydranl ydraln ydrnal ydrnla ydrlna ydrlan ydlarn ydlanr ydlran ydlrna
ydlnra ydlnar yrndal yrndla yrnadl yrnald yrnlad yrnlda yrdnal yrdnla yrdanl
yrdaln yrdlan yrdlna yradnl yradln yrandl yranld yralnd yraldn yrldan yrldna
yrladn yrland yrlnad yrlnda ylndra ylndar ylnrda ylnrad ylnard ylnadr yldnra
yldnar yldrna yldran yldarn yldanr ylrdna ylrdan ylrnda ylrnad ylrand ylradn
yladrn yladnr ylardn ylarnd ylanrd ylandr landyr landry lanydr lanyrd lanryd
lanrdy ladnyr ladnry ladynr ladyrn ladryn ladrny laydnr laydrn layndr laynrd
layrnd layrdn lardyn lardny larydn larynd larnyd larndy lnadyr lnadry lnaydr
lnayrd lnaryd lnardy lndayr lndary lndyar lndyra lndrya lndray lnydar lnydra
lnyadr lnyard lnyrad lnyrda lnrdya lnrday lnryda lnryad lnrayd lnrady ldnayr
ldnary ldnyar ldnyra ldnrya ldnray ldanyr ldanry ldaynr ldayrn ldaryn ldarny
ldyanr ldyarn ldynar ldynra ldyrna ldyran ldrayn ldrany ldryan ldryna ldrnya
ldrnay lyndar lyndra lynadr lynard lynrad lynrda lydnar lydnra lydanr lydarn
lydran lydrna lyadnr lyadrn lyandr lyanrd lyarnd lyardn lyrdan lyrdna lyradn
lyrand lyrnad lyrnda lrndya lrnday lrnyda lrnyad lrnayd lrnady lrdnya lrdnay
lrdyna lrdyan lrdayn lrdany lrydna lrydan lrynda lrynad lryand lryadn lradyn
lradny lraydn lraynd lranyd lrandy

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History of cryptography
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