Bifid Cipher

Bifid is the fractionating cipher that predates and inspires the ADFGX family, invented by the same French cryptographer, Félix Delastelle, in 1901. The core idea: every letter is a coordinate in a Polybius square, so a message becomes two lists of digits (one for rows, one for columns). Bifid's twist is that it fractionates - it concatenates those two lists and reads them back in pairs, so the row and column digits get scrambled together before being turned back into letters. The result is a cipher where the same letter can encrypt to different outputs depending on context, and frequency analysis gets a much harder job than with a plain monoalphabetic substitution.

The one thing that makes Bifid different from nearly everything else in the pack: its key is an integer, not a word. The key input defaults to 10 and the tooltip asks for any non-negative integer. That number is the period - how many letters get fractionated together at a time. A period of 1 is trivially weak (it degenerates toward a plain substitution), and larger periods produce stronger mixing at the cost of making the ciphertext longer to hand-decode. If you want the historical default, period 5 is the classic recommendation.

The inputs that matter

• key (INT) - the period, default 10. This is the entire security story of the node. Pick a sensible value (5 is the textbook one; 10 is fine too) and write it down - decrypt needs the exact same number.
• mode - encrypt/decrypt toggle (on = encrypt).
• text, alphabet, keep_formatting - the standard classical kit, alphabet defaulting to ENGLISH.

Output is the usual single encrypted_txt STRING.

Where people get burned

The integer-key surprise hits everyone once. You reach for "the Bifid cipher," see an INT field, and briefly wonder if you grabbed the wrong node - you didn't, Bifid is period-keyed. The second trap is changing the key between encrypt and decrypt; because the period reshapes the whole digit stream, any difference produces instant garbage with no error. Third: the pack's preprocessing lowercases and strips your message before encrypting, which matters if you're cross-checking against an online Bifid tool - make sure keep_formatting matches on both sides, and keep in mind that implementations differ on whether they pad odd-length groups.

One honesty note: Bifid with a small period is vulnerable to a known-plaintext-style attack, and a knowledgeable solver can crack it by hand given enough ciphertext. It's a great mid-tier puzzle, not a secret-keeper.

Installing it

Standard ARG Toolkit install:

cd ComfyUI/custom_nodes
git clone https://github.com/AzelusLightvale/ComfyUI-ARG-Toolkit

Restart ComfyUI and it's under ARG Toolkit → Cryptography → Classical (or ComfyUI Manager → search "ComfyUI ARG Toolkit"). Classical ciphers use secretpy, installed by Manager or via pip install -r requirements.txt on manual clones. Pure Python, no models.

Troubleshooting

• Decrypt is garbage → period key mismatch, or you changed key between passes.
• "This should take a keyword" → no; Bifid takes an integer period. That's the design.
• Reference tool disagrees → match keep_formatting and confirm the tool uses the same period and alphabet.

Bifid is the cipher that teaches you what "fractionation" actually means, and its period knob is a rare thing in a puzzle cipher: a difficulty dial you can turn yourself.