RE: *warning* student question

["David Gillett" <gillettdavid () fhda edu>]

  What on earth is a "random CRC"?

  A CRC is a value calculated using a specific algorithm.  A
recipient that wants to validate the CRC executes the same
algorithm and either arrives at the same result, or does not.
  IF it's a CRC, then the interloper can (and must) recalculate
it as part of tweaking the packet.

  I haven't looked closely at this part of IPv6.  It's possible
that this value depends on some kind of key that is not present 
in the packet itself.  If that's true, then

(a) only the end-point recipient can check it, so it can't be
    dropped by routers as "invalid", and

(b) it's not really a CRC, it's probably a "hash".

  In no case, however, is it "random".

David Gillett


> -----Original Message-----
> From: Aaron Scribner [mailto:awscrib () comcast net]
> Sent: January 19, 2004 09:55
> To: security-basics () securityfocus com
> Subject: *warning* student question
>
>
> I have been lurking on this list for about 3 months 
> now....and I am more 
> clueless now than when I signed up.
>
> One day talking to my prof after a UNIX/TCP class, we started 
> talking about 
> raw socket programming.  My prof introduced the idea of being able to 
> program with raw sockets to "hijack" a connection.  He 
> presented this to a 
> buddy of mine and I as a self-study in the Network Lab.  
> Basically, be able 
> to get into a system without a trace and be able to receive 
> the packets 
> back.  I know you can change the IP and MAC ID of the IP 
> header, but then 
> you have to worry about the random CRC of IPv6 (and being on 
> this list and 
> reading, I found out most routers will just drop invalid packets).  I 
> COMPLETELY have not a clue where to start.  I read whatever I 
> could get my 
> hands on over the winter break, but I know nothing when it 
> comes to network 
> security, just network communication through code.  I have a 
> background in 
> c/c++ and a couple years of game development (then went back 
> to school 
> after the game flopped), so network security is far from my specialty.
>
> The point of this email, is this even possible to accomplish? 
>  We have 
> another project that we can work on that we will be able to 
> complete to 85% 
> no problems.  Should we attempt to take on the "network 
> hijacking" project 
> or just look at something else.  I do not need a solution to 
> the problem, 
> as that would defeat the purpose of the class, just curious 
> if anyone has 
> researched this or attempted to do it themselves.
>
> Thanks for the bandwidth,
>
> Aaron
>
>
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---------------------------------------------------------------------------
Ethical Hacking at InfoSec Institute. Mention this ad and get $720 off any 
course! All of our class sizes are guaranteed to be 10 students or less. 
We provide Ethical Hacking, Advanced Ethical Hacking, Intrusion Prevention, 
and many other technical hands on courses. 
Visit us at http://www.infosecinstitute.com/securityfocus to get $720 off 
any course!  
----------------------------------------------------------------------------