Bifid Cipher

Mix Polybius square coordinates in fixed-size blocks to create a fractionating classical cipher.

Key square

Each letter becomes a row, column pair inside a 5x5 square. Bifid mixes those coordinates in blocks before converting them back into letters.

Type: Polybius fractionation Square: 5 x 5 I/J: Merged

Keyword

Only A-Z letters are used. Duplicates are removed automatically, and J is merged into I.

Sanitized keyword None

Square alphabet ABCDEFGHIKLMNOPQRSTUVWXYZ

Options

Block size

Preserve case

Keep punctuation & numbers

Remove whitespace

Group letters

Block size is the real Bifid period. Group letters is only display formatting.

Output stats

Mode: Encrypt Input letters: 0 Input chars: 0 Output chars: 0 Cipher blocks: 0 Display groups: 0

Example: with keyword CIPHER and block size 5, DEFEND THE EAST WALL encrypts to RRMZZD CHT ZDUA MALL.

Input

Output

Using This Tool: Guide & Notes Show guide

The Bifid cipher combines Polybius coordinates with fractionation, mixing row and column numbers inside fixed periods.

How to use it

Set the keyword or square used for the Polybius grid.
Choose the period length.
Paste plaintext or ciphertext into the input box.
Use the coordinate preview to see how rows and columns are split and recombined.

Options and settings

Keyword changes the Polybius square and therefore every coordinate.
Period controls how many letters are mixed together before output is produced.
I/J handling affects how the 25-cell square represents the alphabet.
Grouping formats the final ciphertext for easier reading.

Notes

A longer period mixes letters more widely, but this is still a historical cipher.
Wrong period or square settings prevent clean decryption.

Bifid Cipher guide coming soon

The matching article is not published yet. This tool is ready now, and the guide can be added through the shared article template when it is written.

Guide coming soon

Signal acquired

A note from the team

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