[BitTorrent] Free rider problem

guanying_wang guanying_wang at yahoo.com.cn
Thu Dec 23 01:25:27 EST 2004



I find a way to download via BT but without uploading.  I did as follows:
1. Revise the source code, comment out the code telling peers about my
blocks, then peers will think I have nothing, and never ask me for any
block.
2. Of course, I will be snubbed after some time.  But I find that if I
close the connection and wait for it to be rebuilt, such as from
remote passively or until next announce to tracker, then peers will
not recognize me, thinking I'm a new comer.  And they will upload to
me again.  Next time they snub me, I just close the connection one
more time.

I tested this in my college LAN, and it works against BitComet, which
is commonly used in the LAN.  Everybody upload to me, and I finished
together with others.  I tried once against BitTorrent 3.4.2, and it's
even more vulnerable than BitComet.  Tests against BitTornado is not
very convincible, I did the test only with 4 peers, and BitTornado
kept uploading to me, like BitTorrent.

I have figured out a solution, but I have never implemented it. 
First, I assume the peers bind to unique IP addresses.   So I can just
remember every IP and their total upload to me, and base on these
info, decide which peers should I choke.  Another restriction is only
one connection per ip, because I have to remember IP-total pairs, two
connections from the same ip will be confusing.

GuanYing






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