[chord] A research project in Sweden

[Emil Sit]

On Thu, 31 March 2005 at 19:51 (+0000), Thomas Andersson wrote:
> I have some more questions I would be very grateful if you could
> answer for me.

In the future, please direct your queries to the chord mailing list.
Thanks.

> Can a file be revoked from the network?
> 
> Can the permission to revoke a file be given to someone else? Can it be done 
> without risking the security of the person who originally injected the file?

Chord by itself is merely a lookup protocol, a means for establishing
a rendezvous point.   What is done at the rendezvous point is up to
other layers.

DHash does not support revocation of data.  In some sense, it is hard
to actually delete data since it may be stored on nodes that are not
currently available.  Some work in this area (e.g. the Bamboo DHT)
requires that the person inserting the data specify an expiration
time, after which the data is lost.  The data owner must periodically
reinsert the data to maintain availability.

> Can a node decide which files it will host?

This depends on the architecture of your application.  You can
use the rendezvous point to store the location of the actual file.
You can read the Arpeggio paper (available off of 
http://iptps05.cs.cornell.edu/IPTPS_pro.htm) for an example of
a DHT-based system (proposal) that does this.

> Can outsiders (for example a PDA or cellphone via WAP/GPRS) access the
> network for a few brief seconds, access one or a few files and then
> disconnect? And if so, would it disturb the network?

Such a device could use a proxy to access the network and not
"join" it per se.

> Does the network protect itself from malicious users?

No.  It is still not clear how best to preserve correctness
in the face of malicious users.  Some early papers in this area
include the Sybil Attack and the Security Considerations
paper from the first IPTPS (http://www.cs.rice.edu/Conferences/IPTPS02/).

-- 
Emil Sit / MIT: CSAIL PDOS, SIPB, OLC / http://web.mit.edu/sit/www/