Re: [gnet] doubt in building packets

[gnet mm quex org]

On Thu, Jan 06, 2005 at 01:28:43AM -0800, malathy chenniappan wrote:

>            I'm a final year student doing my project
> in network security.My project title is "Steganography
> throu TCP/IP header.
> 
> project details:
>         1.capturing packet from active/passive network
>         2.extracting the TCP header
>         3.Replacing the unused 6 bits in the header
> with encoded data.
>         4.sending the packet into network again
>         5.Reverse processing to get data back at
> receiver end.
> 
>        I started with building packets using raw
> sockets.I've got the idea of creating packet and
> sending using sendto() function.
> 
>        My doubt is how to receive them?.Give idea abt
> the project implementation.Is path right?.

First thing that comes to my mind is libpcap, which is closely
associated with the tcpdump utility: http://www.tcpdump.org
This allows you to "sniff" traffic on a network, and get at
the entire contents of the packet from Layer 2 (e.g. the
Ethernet frame).

I'm not sure about 1+4 - you can't really "steal" a packet from
the network... unless you're responsible for routing it to the
appropriate place.  On a regular network, the receiver would
see both the original packet and your modified version.