Tool for automatic Shift Cipher that consists in replacing a letter by another one in the alphabet using a shifting system, a basic or complex sequence of numbers.

Shift Cipher - dCode

Tag(s) : Substitution Cipher

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A shift cipher is a substitution cipher, the principle of which is to shift the letters by one or more values in the alphabet.

__Example:__ The letter `A` shifted by 1 place in the alphabet becomes `B`

The Caesar cipher is a shift cipher, usually presented with a shift key of value 3.

The shift cipher encryption uses an alphabet and a key (made up of one or more values) that shifts 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 take it at the beginning (imagine the alphabet as cyclical)

__Example:__ `Z` shifted by `1` gives `A`.

It is thus possible to define different types of shifts, some shifts correspond to known encryption algorithms:

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

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

A mathematical shift, the easier is progressive, shifting the nth letter of the value `n` is the Trithemius 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`.

__Example:__ The word `TIJGU` is decoded with an offset of 1 as `SHIFT`

The shift cipher can take a date as key (called *date shift cipher*), generally in the formats YYYYMMDD is used as it contains a series of 8 digits which can be used as the shift key.

__Example:__ `DATECODE` coded with the date `2020/10/10` or (`2,0,2,0,1,0,1,0`) becomes `FAVEDOEE`

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