Reverse engineering Samsung's Bluetooth Chat from old dumbphones

Some old Samsung dumbphones have a feature called Bluetooth Chat. Its a small proprietary chat protocol that relies on Bluetooth, allowing users to create small local chats between each other.

According to yet another BS suggestion by russian government, using Internet now can lead to any of your data being accessed by the feds. If there's one thing I would like to not happen to my data, its feds looking at it and misunderstanding my jokes. So, an old decentralized service is exactly what we need, eh?

My Samsung B5722 Duos sends chat messages as .vnt notes. Old Samsung phones use .vnt as a common format for regular text notes, so if you try to send a Bluetooth Chat message to, say, Star 5230 (that does not have bluetooth chat), it goes to Notes.

A sample note looks like this:

BEGIN:VNOTE
VERSION:1.1
BODY;ENCODING=QUOTED-PRINTABLE;CHARSET=UTF-8:Sample Text
DCREATED:20220612T221205
X-SAMSUNG-BTM:SUPPORT
END:VNOTE

Its a text file. Yeah. The text is put into the end of the third line. Not providing any text can crash some phones.

DCREATED is the date, tho it usually does not matter in the Bluetooth Chat context.

X-SAMSUNG-BTM seems to be the flag that tells the phone that this Note is not a regular Note, but a Chat message.

A linux bash script is provided by me to try and send sample notes to phones.