ASCII Shift Cipher

The ASCII shift cipher is a substitution cipher method, which, as its name suggests, will use the ASCII table and shift each character by a certain number of positions.

This process is an extension of the Caesar cipher (which is limited to letters) to all ASCII characters (i.e. alphabetic, uppercase, lowercase, numeric and symbolic).

To encode a text with the ASCII shift cipher:

— Identify the ASCII code of each character in the plain text (the ASCII table is composed of 128 characters with a code between 0 and 127).

— Add a fixed numerical shift (also called the encryption key) to each ASCII code. This key can take the format of a number (between 1 and 127, negative numbers are possible, this amounts to a shift in the other direction) or an ASCII character (in this case the character code is used as a number).

— Convert the new codes into characters to obtain the encrypted text. The shift is circular (moving after the end of the alphabet returns to the beginning), if the code is greater than or equal to 128, the limit of the ASCII table, return to the beginning 0.

Decrypting an ASCII offset is the same as encrypting it, but with the offset in the other direction. Instead of adding, the operation is to subtract the offset used during encryption (the equivalent of encrypting with a negative offset).

The message is composed only of ASCII characters.

Frequency analysis should emphasize groups of characters more often (those corresponding to the letters of the plain message).

dCode allows you to test the 127 offsets and displays the most probable results automatically.

The shift ciphers are numerous, the most known is the Caesar cipher, but ROT-47 is probably the closest to ASCII shift as it is limited to printable characters and is reversible.