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Diffstat (limited to 'docs/notes.md')
| -rw-r--r-- | docs/notes.md | 36 |
1 files changed, 24 insertions, 12 deletions
diff --git a/docs/notes.md b/docs/notes.md index e3d1659..c4a72ab 100644 --- a/docs/notes.md +++ b/docs/notes.md @@ -96,14 +96,14 @@ source: <https://git.pipeframe.xyz/fork/melonDS> which appears to be some kind of 16-bit encoding of the username set on the emulator used to capture these packets (this is likely UCS-2 and not UTF-16 as suggested by [masscat-nifi] which specifies UCS-2). +- WEP is not used for local multiplayer. This was verified after using + Wireshark to dissassemble the IEEE802.11 header present in all captured + frames. None of the captured frames had the WEP encrypt flag set. - The messages are not sent as single packets. The Ni-Fi protocol appears to set up a constant stream, and messages are sent across multiple frames. -- A full height filled-in message results in 64 packets (with Wireshark filter - `nifi.type.enum == 1 && pictochat && frame[0x1a] == 0x02 && frame.len == - 246`) - PictoChat does not appear to send messages when you are in a chat room by - yourself, so local multiplayer / Ni-Fi emulation is required for capturing - message content + yourself, so local multiplayer emulation is required for capturing message + content ### Message sizing/cropping @@ -306,18 +306,31 @@ messages from the system that joined later) - <https://www.problemkaputt.de/gbatek.htm#dswifiieee80211frames> - <https://www.problemkaputt.de/gbatek.htm#dswifinintendobeacons> +## Reassembly + +The pictochat protocol itself also seems to be made up of several layers, one +of which splits large messages over multiple frames. After writing more lua +code to reassemble these chunks, the following observations were made: + +- There is a fixed 0x24 (36) byte header before all drawings +- The size of the reassembled messages for pictochat drawings exactly follows + the equation $f(x) = 36 = 2048x$ where $x$ is the number of rows the message + shows up as. The row count of the message does not appear to be stored + anywhere. +- The first 8 bytes of reassembled messages (drawings, room join) consists of a + constant 0x03, a message type indicator (1 byte) and the address of the + author/subject (6 bytes). +- The remaining 28 bytes of the reassembled message header are constant for + drawings. These bytes appear to be some kind of padding as changing them + appears to have no effect and does not show up in the drawing. + ## Unsure/notes - Is the endianness of the DS properly emulated? -- Is the Ni-Fi magic value also present in physical frames or is this something - MelonDS did? -- The DS implemented WEP(?) encryption for connecting to home network - routers/APs, but is this encryption also used when the WiFi module is used in - local multiplayer mode? Does this even matter inside the emulator? +- Where is a message's destination (pictochat room) defined? ## TODO: -- message reassembly field? (how does pictochat know which part a message index is) - are message-resends required or can the packets be dropped? - user identifier / login / announcement procedure? - actual message format @@ -326,5 +339,4 @@ messages from the system that joined later) * palette color indices (pixels are 1 nibble) - what types of pictochat packets are there? (i.e. how are room join/leave events broadcast?) -- `pictochat.msg_type in {10, 24, 86}` message reassembly in dissector |