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Re: security in P2P
From: "Rajiv D" <rajiv.ceh () gmail com>
Date: Sun, 29 Jul 2012 08:09:54 +0000

I agree to what Jeff said that MD5 is broken way long time. However we don't see this much in local campuses. Only 
sophisticated or motivated crackers use these to get through to their victim. 

One more thing is P2P use chunks and uses these combination to club the full file. If one of the chunk is of wrong size 
or is simply invalid. The P2P download stops saying size mismatch etc. 
-- Rajiv

-----Original Message-----
From: Jeffrey Walton <noloader () gmail com>
Date: Sat, 28 Jul 2012 19:19:02 
To: <rajiv.ceh () gmail com>
Reply-To: noloader () gmail com
Cc: Pratik Narang<pratik.cse.bits () gmail com>; <listbounce () securityfocus com>; <security-basics () securityfocus 
Subject: Re: security in P2P

On Fri, Jul 27, 2012 at 1:00 PM, Rajiv D <rajiv.ceh () gmail com> wrote:
Hi Pratik,

P2P systems uses what is called hashing.  Before you can share it on the network it should be hashed. P2P generally 
uses MD5. So any file that you are downloading should have same hash in all the peers. So if two users have the EXACT 
same file then only the hash will match and it will be downloaded from them. If some malware has been Introduced in 
the file then the hash will change and it will be treated as a separate file. The real problem comes when you 
download from a user and that particular file is malicious. In that case any HIPS can help you out.

Not necessarily - MD5 is broken and should not be used. The same file
will hash to the same digest (expected); and different files can hash
to the same digest (unexpected). Confer: Flame and the chosen prefix
collision attack.

Will anyone be surprised when tripwire-like programs are defeated by a
sophisticated attacker?


-----Original Message-----
From: Pratik Narang <pratik.cse.bits () gmail com>
Sender: listbounce () securityfocus com
Date: Fri, 27 Jul 2012 12:38:37
To: <security-basics () securityfocus com>
Subject: security in P2P

Hi all,

Consider a situation involving (only) Peer to Peer traffic in a small
or medium sized network.

Peer A does a search for file qwerty.mp3, and then starts pulling the
file, in pieces, from different Peers- B, C, D and E.

Now say Mr. C is a malicious peer, and the file at his end contains a
malware/virus/trojan etc. Or better still, Mr. C decides to target
peer A and injects a malware/trojan etc. into one of the pieces of the

As a network admin, what one may do that innocent peers like A are
protected from such situations. I need a solution involving use of
IDS/IPS with signature based and/or anomaly based detection.

Kindly do not suggest actions or measures relating to the end user.
Whatever has to be done, must be done in the network design/plan- say
use Snort or some other IDS/IPS and write rules to an Open source
firewall using the IDS/IPS for this specific scenario.

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