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"Wiretapping" my internet connection

Discussion in 'Electronic Design' started by MikeMandaville, Mar 1, 2004.

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  1. Hello, everyone,

    I have an idea which I would like some feedback on. I am thinking about
    installing an external modem on my computer, and then designing a box which
    will go in between my computer and the modem. The purpose of this box would be
    to eavesdrop upon the communications which take place between my computer and
    the internet. The box would also be programmable, and I would use it to
    program MIDI files, and then to send those files to my computer. The idea here
    is that I would first locate a random MIDI file on the internet, set it up for
    downloading, and then, before clicking on the download button, I would push a
    button on the box, which would disconnect my computer from the internet, and
    connect it instead to the box. As far as my computer is concerned, it would be
    downloading the file from the internet. My purpose in eavesdropping upon the
    communications which take place between my computer and the internet is that I
    would like to also be able to send whatever additional signals my computer
    might require in order to facilitate these downloads. I would appreciate any
    comments which any of you might have regarding this project.

    Michael "Chip Monk" Mandaville
  2. Ken Taylor

    Ken Taylor Guest

    I have to ask: 'why?'. Instead of going in at what appears to be the V.xx
    end of things, why not do it at the TCP side via a network card. Build your
    'box' so that it can be mapped as a network drive and store on that drive
    rather than in your PC. An external box something like a single-board
    computer would do the trick.

    Or if that doesn't fit the bill, why not a USB hard drive. Even better, use
    a USB-Hard-Drive-on-a-watch (for true geek value!). If you want to actually
    play the MIDI file on the 'box' later, get a MIDI/MPEG player with a USB


  3. Richard

    Richard Guest

    Sure, it can be done. But you'll likely have a lot of learning to do,
    and it may cost quite a bit before you're done. Probably an excellent
    learning experience, if that's the intent.

    You'd need at least a fast microcontroller with a couple UARTs, a bit of
    RAM, a lot of code space, and some RS-232 line drivers. Add storage on
    flash or hard disk (for extra complexity). While you're at it, build in
    the modem via an add-on module.

    Starting to get more complex. Now your box needs to know PPP, IP, TCP,
    and a few other protocols. This can add a lot of time to your
    development, and size to your code.

    Now your widget needs some storage. Flash if it's small enough, or disk
    (which adds complexity for the hardware interface and file system).

    Why even disconnect it from the Internet, or require a button keypress?
    Your device would be in an excellent position to detect when a MIDI
    filetype was being downloaded and substitute its own content instead,
    all the while leaving your PC connected to the Internet for other uses.

    Yes, this would be necessary. Your widget would have to "spoof"
    (pretend to be) the server to your computer, and vice-versa during this

    Sounds like an odd project. And very complex - not very feasible for a
    first-time system. It's hard enough to put devices online; to "hijack"
    your PC's Internet connectivity will be even harder. Plan to spend a
    LOT of time on this project.

    I'd suggest you start with an established platform so you can focus on
    building your project, not conquering fundamentals. would be a good place to start; the
    dev kit will cost you ~$350 to get started. Look for something that has
    2 UARTs on-board and ask whether it can drive both interfaces at the
    line rate you'll need.

    Also, perhaps the BASIC Stamp platform, though I wonder if they'd have
    the horsepower. You'll need a fair amount of power to analyze & spoof
    the data stream while copying it between the modem and PC ports.

    Lastly, check out comp.arch.embedded.
  4. What is the purpose? Why not simply download the file?
  5. Active8

    Active8 Guest

    On 01 Mar 2004 03:58:47 GMT, said...
    I really don't know from WTF you are talking, but I think you're
    asking for a packet sniffer.

    On Linux, these are free, but don't necessarily offer the value
    added shit you can get from CommView by Tamo Soft. It won't break
    you, but you'll get ASCII views as well as IP, UDP, TCP, etc,
    views, port info, blah, blah, am I over your head yet?

    Check it out.
  6. Active8

    Active8 Guest

    On 01 Mar 2004 03:58:47 GMT, said...
    The commo between your box and an external modem is *not* inet,
    i.e., TCP/IP, etc. via PPPoE, but RS-232.
    Use the computer to program MIDI files.
    not what you said above. entering the nebulous zone here.
    Your computer only needs to send a text command "GET" to the URL
    from whence the download comes. Additionally, browsers can send
    queries to find out the size of the file so they know WTF to expect
    and set up a buffer, progress bar or "downloading file.gif 23k of
    100k" typr of status window stuff.
  7. Monitoring the telephony side is a looser - it is *by far* much easier to
    monitor the IP layer; One such tool "Ethereal" is preconfigured for most
    situations and can be customised to whatever you want to do.
  8. Tim Auton

    Tim Auton Guest

    You want to build a hardware sniffer, but is what you really want a
    proxy server? Either way, it's far easier to do in software.

  9. RS232 is the electrical connection and outside wrapper, the protocol would be PPP and in
    that TCP or UDP or whatever, and even then RS232 is NOT implied, he could be using
    a USB modem, or USB ADSL, or Ethernet ADSL, or whatever laptop on a GSM, or I dunno.
    Its a daft idea.
    Just download the midi file, and upload / send / copy / burn / etc.. it to wherever you want it.
    In case of a RS232 V90 modem, all the modem does is some compression, quadrature
    modulation, handshaking to find the maximum line speed, but it does NOT change or add
    the TCP layer.
  10. Active8

    Active8 Guest

    This is true.
    So's that.
  11. Ian Stirling

    Ian Stirling Guest

    You can even get MP3 players on a watch.
  12. Joel Murray

    Joel Murray Guest

    Why not just use a port sniffer program to log the data coming from your
    computer? If its a serial modem you could probably just loopback into com2
    and run hyper terminal to see everything that is sent, but it would make no
    I use a Ethereal on linux for packet capture, but I think
    it works on windows as well.
    Designing something yourself that interprets TCP/IP is going to be very hard
    to do.
  13. Wim Ton

    Wim Ton Guest

    Get a protocol analyser, Ebay or from a second hand dealer. New they are
    quite expensive

  14. Hello again, fellows,

    And thanks for the responses, which I hope will continue. I admit that my idea
    is an unconventional one. By the way, here is the computer which I am using:

    I installed the operating system myself, and it is Windows XP Home. Since I
    haven't bought the external modem yet, I suppose that I will have my choice of
    either an RS232 modem, or a USB modem. I am leaning towards the RS232 modem,
    because I think that I might have an easier time understanding the signals that
    way, though I might be wrong about that.

    I first got the idea of "wiretapping" a computer-to-modem connection after I
    bought Don Lancaster's "TV Typewriter Cookbook", and before I had a computer of
    my own, so you can see how my thinking has evelved on this matter. I also have
    purchased some music software which I have found to be unusable. In addition
    to these things, I have discovered that my simple "Notepad" program is the most
    efficient way for me to build web pages, regardless of the "more efficient"
    higher level programs.

    I have a couple of MIDI keyboards, a book which explains the MIDI language, a
    couple of dozen breadboards, all of which haven seen good use, and no aversion
    to programming in machine language, especially since I am confident that I
    could design some firmware to bring me up to another level.

    Please keep in mind that my MIDI files will only need to be "stowaways" for the
    short time that it will take to get them from my MIDI sequencer box to my
    desktop. Since my computer will be disconnected from the internet at this time
    (although it will "think" that it is connected) I will only need to worry about
    handling the handshaking signals, or whatever additional signals might be
    required other than the actual MIDI file itself, from my own computer's side of
    the equation.

    I have recently discovered Jan Axelson's books relating to the designing of
    computer peripherals, though her books seem to involve purchasing developmental
    platforms and Visual Basic. I am still at the point where I think that a
    hardware port sniffer will be the way for me to go. Again, I don't mind
    "slugging it out" at the low end, although I don't know how long I will be able
    to hold out. I built a non-standard music sequencer before I even had a MIDI
    music keyboard, and it worked just fine, so this has given me a lot of
    confidence in my ability as a hardware designer.

    If nothing else, I will keep you all posted on my progress. I will be starting
    my mowing season next Monday, so this is the time of year when I come out of
    hibernation, and start following through with the wild-eyed schemes that I
    dream up during the off season.

    Michael "Chip Monk" Mandaville
  15. Active8

    Active8 Guest

    On 01 Mar 2004 20:26:12 GMT, said...
    Well, whatever.

    I still think the CommView packet sniffer and an internal modem is
    all you need. CommView installs a virtual NIC and you can sniff web
    traffing and internal network traffic. The basic license IIRC was
    for one machine one OS.
  16. Richard

    Richard Guest

    To say the least. But hey, what do we know? (I can imagine plausible
    reasons, but they're a stretch... ;-) Care to share why on earth you're
    doing this?

    Yes, if you go the hardware route, you'll probably find the RS-232 will
    be the easier path. Incidentally, it looks like Rabbit has a dev kit
    for under $250 with an MCU that may do what you're after.

    However, consider software instead... a couple options: proxy and
    packet filter. Both will work without any hardware investment, and it'd
    be portable to DSL, Cable, etc.

    Proxy is almost a trivial afternoon project. Just listen on one port,
    fetch the requests on another, and send them back to the client
    software. All on the same PC. The only "gotcha" is that the client
    software needs to support proxies. (Browsers do, enterprise software
    does sometimes, consumer products rarely do.)

    Packet filter is more complex, but equally possible. It sits in the
    protocol stack and handles every packet coming & going. Look for an
    open-source firewall product that you can modify.

    Good luck!
  17. Chaos Master

    Chaos Master Guest

    MikeMandaville tava com a mulhegada quando eu cheguei gritando:
    If I understand you correctly, you want to make a device that accesses Internet
    when your main computer is connected and you "pass" the file to the given "box".

    So you could use a PC in a small CPU, running Linux, in a network with your main
    PC. This would be the simpler way to do it.

    Or you'd have to implement TCP/IP, networking (PPP? Ethernet? You didn't say if
    it is a DSL/ISDN modem - I don't know the exact term for this, but here on
    Brazil they're known as "Cable Modems" or "ADSL modems" - or a dial-up modem)
    and HTTP/FTP protocols in a microcontroller (not easy, I think).

    by Chaos Master® - MSN:

    "A Elbereth Gilthoniel, silivren penna miriel o menel aglar elenath!
    Na-chaered palan-diriel o galadhremmin ennorath,
    Fanuilos, le linnathon nef aear, si nef aearon!" - The Lord of the Rings

    Linux User #327480 / GNU-Win32 / Cygwin / Win98 + LiteStep
  18. I still think the CommView packet sniffer and an internal modem is
    Hello again, Mike, and All,

    Since I could evidently get a free packet sniffer with a free Linux, maybe I
    will just download Linux from the internet, and do a dual boot.

    Actually, I have been thinking about building a Z80 computer for a long time
    now, and I think that this project might just be the excuse which I need to
    finally build one. My first computer was the Z80-based five-chip Sinclair,
    with onboard TINI BASIC. Evidently TINI is one of the platforms which Jan
    Axelson works with also, so this would be a plus, since I could refer to her
    books for reference.

    You fellows have given me a lot of good ideas, and I am confident that I will
    eventually succeed with my project.

    Mike "Chip Monk" Mandaville
  19. Fred Bloggs

    Fred Bloggs Guest

    Your purpose in eavesdropping is to illegally download music and think
    you can get away with it....
  20. Konstantin

    Konstantin Guest

    Why are you still using such unhandy thing as Hyper Terminal? Recently
    I've found an interesting program - Flash Terminal. It is really Hyper
    Terminal killer. With Flash Terminal you can chat and exchange files
    via modem (including v.90, ISDN, ADSL, GPRS) and null-modem
    simultaneously without Internet! You can exchange up to 255 files at
    once with unlimited transfer resuming after connection break. Program
    includes large amount of nice avatars.
    Direct link for downloading:
    Direct link for Win95 version downloading:
    Developers site:
    More info:
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