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2015-02-24 23:04

Six

Registered: Apr 2002
Posts: 287

Punter File Transfer Protocol

Reading the doc here: http://cbmfiles.com/genie/geniefiles/TelcomTools/C1-PROTOCOL-DE..

it outlines what seems like a very simple protocol. Seems easy to implement from scratch. To that end, I set up two tcpser instances, two instance of VICE with CCGMS 11, and began a transfer, observing the logging output of TCPSER.

What Steve Punter describes should go like this:

SENDER
[dummy packet 1]---ACK---[filetype packet]---ACK---[First file packet]---ACK---[Second file packet]....
RECEIVER
----------------GOO---S/B-----------------GOO---S/B------------------GOO---S/B-- ------------------GOO...

Where dummy packet 1 would be just the two checksums, 8 for the "next block size", and a block number of 0000, filetype packet is much the same, but with the filetype as the payload and a larger "next block size"

But what I'm observing looks more like this:

SENDER
--------------------------------------------------0x91---ACK---[odd data block]---ACK---SYN---S/B---ACK---[data block 1]
RECEIVER
GOO(over and over again until the transfer starts)----GOO---S/B---------------GOO---S/B---SYN---GOO---S/B----

Where the odd data block has a next block size of 4, and a block number of 0xffff and appears to have the file type in it.

My next step is going to be to try multi-punter on the same setup, then try a few different terms and see if the peculiarities are specific to this implementation of punter on CCGMS 11.

Has anyone else dug into this, or have any insight into the how/why? Is there a comprehensive documentation of this protocol anywhere?

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2015-02-26 23:37

Six

Registered: Apr 2002
Posts: 287

For receivers, dealing with bad packets.

RECEIVER: BAD<---------------|
SENDER: ACK                  |
RECEIVER: S/B                |
SENDER: RESENDS SAME PACKET  |
RECEIVER: (BAD OR GOO)-------|

2015-02-27 11:27

Tao

Registered: Aug 2002
Posts: 115

@Six: I'd be happy if you'd have a look at the C*Base punter implementation; I have a slight recollection of something being wrong with it...

2015-02-27 21:46

Six

Registered: Apr 2002
Posts: 287

Aye, I'm moving on to that next. I'll have to set up C*base on VICE for sniffing.

BTW, talked to Steve Punter himself about this on facebook. (VERY nice guy, btw, and he cleared some things up about the various versions.) He dispelled my suspicion that he was "high as fuck" when he wrote that document... His initial version did, in fact, work as he described. People took that initial version and made a number of variations on it, some of which were incompatible with it and eachother. Eventually a sort-of-standard seems to have been reached. Multi-punter, for instance, he had nothing to do with.

This is both good and bad for my research. It's good, because it means there is a lot of ground and forensics work to do yet, and that will be interesting, but bad because this means I have to root through every old term and BBS I can find so I can work out the various protocol variations in order to build a gold-standard. Looks like this will be a longer project than I originally assumed.

2015-03-01 03:45

Six

Registered: Apr 2002
Posts: 287

Delving into multi-punter. It seems to be the same for each file transfer, but starts in an odd way from the sender. Each file is preceded by the following exchange:

SENDER: 0x09,0x09,0x09,0x09,0x09,0x09,0x09,0x09,0x09,0x09,0x09,0x09,0x09,0x09,0x09,0x09, FILENAME,P,0x0d
SENDER:GOO
RECEIVER: GOO
SENDER: ACK [and so on as a normal xfer.]

After all files are transferred:

SENDER: 0x09,0x09,0x09,0x09,0x09,0x09,0x09,0x09,0x09,0x09,0x09,0x09,0x09,0x09,0x09,0x09, 0x04,0x04,0x04,0x04,0x04,0x04,0x04,0x04,0x04,0x04,0x04,0x04,0x04,0x04,0x04,0x04, 0x0d

No response from the receiver after this.

2015-03-02 13:54

Tao

Registered: Aug 2002
Posts: 115

Quoting Six

Aye, I'm moving on to that next. I'll have to set up C*base on VICE for sniffing.

Well, the source code is available, which might help ever so slightly. I did, however, not write the code, so if I were you I wouldn't bet on getting sane answers about the code :P

2015-03-02 23:10

Six

Registered: Apr 2002
Posts: 287

Do you recall who did write that version?

2015-03-03 08:35

Tao

Registered: Aug 2002
Posts: 115

Quoting Six

Do you recall who did write that version?

Well, it's most probably written by Gunther Birznieks. Possibly by Jerome P. Yoner.

I've made some minor modifications, but that's all.

2015-03-04 19:48

MagerValp

Registered: Dec 2001
Posts: 1055

Wow that is one seriously fucked up protocol. I don't think I could come up with something slower and more error prone if I tried.

2015-03-04 19:59

Burglar

Registered: Dec 2004
Posts: 1031

Quoting MagerValp

Wow that is one seriously fucked up protocol. I don't think I could come up with something slower and more error prone if I tried.

faster than xmodem! at least the xmodem used by ucbbs and cbase. punter would only work if u didnt have too much delay+linenoise, horrible but the fastest available.

2015-03-04 20:34

Count Zero

Registered: Jan 2003
Posts: 1821

also xmodem padded blocks with a crap byte at the end - argl :) - thats not even an alternative to anything!

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