How is this different from a classic Vigenère cipher?

Classic Vigenère uses a 26-letter alphabet and ignores spaces and punctuation. This extended version uses all 95 printable ASCII characters (codes 32 to 126), so spaces, digits, and symbols are enciphered too and the keystream advances on every character.

What characters can I use in the key?

Any printable ASCII character from space (code 32) up to tilde (code 126). Each key character contributes a shift equal to its offset from code 32. Characters outside this range are not valid key material.

What happens to characters outside printable ASCII?

Characters with codes below 32 or above 126 — such as newlines, tabs, or non-Latin letters — are passed through unchanged so the layout of multi-line text is preserved.

Is decoding just the reverse shift?

Yes. Encoding adds the key offset modulo 95 and decoding subtracts it modulo 95. Using the exact same key for decode recovers the original text precisely.

Is this secure for real secrets?

No. Vigenère, even over full ASCII, is a classical cipher that falls to frequency and Kasiski analysis. Use it for puzzles and learning, not for protecting sensitive data; use modern authenticated encryption for that.

Extended Vigenère (Full ASCII)

The extended Vigenère cipher widens the classic polyalphabetic cipher from the 26-letter alphabet to the full set of 95 printable ASCII characters. Because spaces, digits, and punctuation become part of the alphabet, every visible character in your message is enciphered and the keystream advances on each one.

How it works

Each printable character is treated as a number from 0 to 94 by subtracting the ASCII code of space (32). The repeating key is converted the same way, and the two are combined modulo 95:

P = charCode(plain) - 32      (0..94)
K = charCode(keyChar) - 32    (0..94)
encode: C = (P + K) mod 95
decode: P = (C - K + 95) mod 95
output char = String.fromCharCode(result + 32)

The key index only advances for printable characters, so any non-printable character (newline, tab, accented letter) is emitted untouched and does not consume key material.

Example and notes

With the key Gera!, the plaintext Hello, World! enciphers to a string of printable symbols where even the comma and space have shifted. Decoding the same ciphertext with the same key returns Hello, World! exactly. Keep your key secret and reasonably long: a one-character key collapses this into a simple Caesar-style shift across all 95 characters and is trivial to break.