eD2k hash collision attacks

2 friends (Uzi Tuvian & Lital Porat), have done a nice research on ed2k collision attacks, here you go :

About the paper:

In the paper we discuss the implications of the MD4 collision attacks that were developed in the past few years on the ed2k protocol (the protocol used in today's eDonkey network).  Since ed2k uses the MD4 hash function to generate unique file identifiers, these collisions allow a well-crafted file to exist in various different versions across the network.  Some of these versions might be legit and some might be malicious, but a user of the current network have to way to distinguish which version of the file he or she is downloading.

Just to be clear - this does not mean that an attacker might inject malicious versions of pre-existing files in the network; It does mean that an attacker (or an organization) might, for example, introduce new colliding files to the network and leverage on the popularity of the legit file to mascaraed the malicious one or even, under some circumstances, send the malicious version to targets of his choice.  One of the scenarios we discuss (one that might already be happening) is of a warez group that can use the network as an attack platform in order to gain access to a selected subset of it's users by distributing illegal content and performing such 'low-profile attacks' on well-chosen targets. These targets can be hosts residing in certain countries or networks, hosts running certain OS versions or whatever parameter which might interest the attacker.

In the paper, we discuss the different techniques that might be used to optimize and hide the attack and it's results, scenarios and attack vectors that are made possible due to this issue, and a tool we've put together that can be used to generate such malicious files in very high efficiency.

You can download the paper from here