Shift Cipher

The encryption uses an alphabet and the position of its letters.

A letter in position N in the alphabet, can be shifted by X into the letter located at position N+X (This is equivalent to using a substitution with a shifted alphabet).

Example: Take the letter E in position 5 in the alphabet ABCDEFGHIJKLMNOPQRSTUVWXYZ, it will be encrypted by a shift of 3 in position 8 or H.

If the shifted position exceeds the number of letters in the alphabet, then we take it at the beginning: Z shifted by 1 gives A.

It is thus possible to define different shifts, some shifts correspond to known encryption algorithms (eg the Caesar code), please visit the dedicated pages for more details.

A single shift (all letters are shifted to the same value) is called Caesar Code.

A multiple shift, according to a key that is repeated (the letters are shifted from each of the key values), it is called Vigenere Cipher.

A mathematical shift, the easiest way is to shift the nth letter of the value n is the Trithemus Cipher or if the shift is more complex Affine Cipher or even Hill Cipher.

Decryption requires knowing the shift used and the alphabet.

Take a letter in position N in the alphabet that has been encrypted by a shift of X, it must be shifted by -X to return to its original position N-X.

Example: The letter H in position 8 in the alphabet ABCDEFGHIJKLMNOPQRSTUVWXYZ, will be decrypted from a shift of 3 in position 8-3=5 or E.