Tool to decrypt/encrypt with Caesar. Caesar cipher (or Caesar code) is a shift cipher, one of the most easy and most famous encryption system. It uses the substitution of a letter by another one further in the alphabet.

Caesar Cipher - dCode

Tag(s) : Cryptography,Substitution Cipher

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Tool to decrypt/encrypt with Caesar. Caesar cipher (or Caesar code) is a shift cipher, one of the most easy and most famous encryption system. It uses the substitution of a letter by another one further in the alphabet.

Encryption with Caesar code is a simple substitution (one letter replaces another). Caesar code remplace is with an alphabet shift : a letter further in the alphabet.

One wants to crypt DCODEX with a shift of 3

To encrypt D, one takes the alphabet and look 3 letters after : G. So D is crypted with G.

To encrypt X, one must loop the alphabet : after X : Y, after Y : Z, after Z : A. So X is crypted A.

Another way to crypt, more mathematical, one can note A = 0, B = 1, ..., Z = 25, and add a constant (the shift), then the result modulo 26 (alphabet length) is the coded text.

D = 4, 4+3 = 7 and 7 = G, so D is crypted with G

X = 23, 23+3 = 26 and 26 mod 26 = 0, 0 = A, so X is crypted with A, etc.

DCODEX becomes GFRGHA

Caesar code decryption replaces a letter another with an inverse alphabet shift : a previous letter in the alphabet.

One wants to de crypt GFRGHA with a shift of 3

To decrypt G, one takes the alphabet and look 3 letters before : D. So G is decrypted with D.

To decrypt X, one must loop the alphabet : before A : Z, before Z : Y, before Y : X. So A is decrypted X.

Another way to de crypt, more mathematical, one can note A = 0, B = 1, ..., Z = 25, and substract a constant (the shift), then the result modulo 26 (alphabet length) is the plain text.

G = 7, 7-3 = 4 and 4 = D, so G is decrypted with D

A = 0, 0-3 = -3 and -3 mod 26 = 23, 23 = X, so A is decrypted with X, etc.

GFRGHA becomes DCODEX.

A shifted ciphered message have an indice of coincidence similar to the language of the plain text.

The easiest method consist in testing all shifts, if the alphabet has 26 letters, it takes only 25 tries.

Caesar cipher is best known with a shift of 3, all other shifts are possible. Some shifts are known with other cipher names.

Another variant changes the alphabet, an can introduce letters for example.

Caesar used this technique for comme correspondances, especially military, for example with Ciceron (shift of 3).

August Cipher is the name given to Caesar Cipher with a shift of 1.

DBFTBS, ECGUCT, FDHVDU, GEIWEV, HFJXFW, IGKYGX, JHLZHY, KIMAIZ, LJNBJA, MKOCKB, NLPDLC, OMQEMD, PNRFNE, QOSGOF, RPTHPG, SQUIQH, TRVJRI, USWKSJ, VTXLTK, WUYMUL, XVZNVM, YWAOWN, ZXBPXO, AYCQYP, BZDRZQ

For N from 1 to Text Length Do

Take C = Nth character of Text

Calculate R = the rank of C in the alphabet

Calculate R2 = (R + Shift) Modulo 26

Write the letter with rank R2 in the alphabet

End For Loop

Unknown, but Caesar is born in 100 before JC

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- How to encrypt using Caesar cipher?
- How to decrypt Caesar cipher?
- How to recognize Caesar ciphered text?
- How to decipher Caesar without knowing the shift?
- What are the variants of the Caesar cipher?
- Why the name Caesar Cipher?
- What is August Cipher?
- What are other Caesar Cipher names?
- How to cipher CAESAR with the Caesar code?
- How to write Caesar Cipher in pseudo-code?
- When Caesar Cipher have been invented ?

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