Re: [Help-gnunet] Questions about GNUnet

[ng0]

Christian Grothoff transcribed 8.3K bytes:
> Hi Philipp,
> 
> Some answers inline below.
> 
> On 04/18/2017 09:18 AM, Philipp wrote:
> > Hello everyone,
> > I am currently working on my master's thesis at the University of Ulm.
> > As a part of my thesis, I performed a literature survey on some systems
> > that offer anonymity properties in P2P environments, among them GNUnet.
> > 
> > I have a few questions regarding GNUnet. I hope it is fine to post them
> > here on the mailing list. Unfortunately, when visiting the FAQ website
> > https://gnunet.org/faq-page I just get an emtpy page, so I couldn't
> > figure out whether there are already answers posted to some of the
> > questions I have.

Christian, do you know what happened to the page? It really is empty.
If there was a page, we should get it back or delete the menu link. 

> > I would be very grateful for help on some of these topics.
> > 
> > 1) In [1], it is mentioned that nodes observe the behavior of
> > neighboring nodes. It also states that a node might pass files (or
> > possbily blocks of a file) to other nodes depending on how trustworthy
> > they seem. Are these trust values derived based on the scheme described
> > in [2]?
> 
> Nodes will pass blocks of files (never files) based on available
> bandwidth (trying to keep their traffic profile constant).  However, IF
> a peer has earned trust ([2]) and IF that peer made a prioritized
> request, nodes will prioritize such requests (possibly doing less work
> for others, dropping other peer's blocks) over other requests from nodes
> that either did not earn trust OR did not make a prioritized request.
> Trust is lost/reduced/reassigned when making prioritized requests.
> 
> > 2) As far as I understood, files that I want to publish are always
> > placed on my local node and not actively distributed into the network. 
> 
> The files will be actively distributed into the network IF your
> configuration allows it (CONTENT_PUSHING = YES).
> 
> > I can, however, decide whether I want to generate a copy and place it in
> > my local store in encrypted form or whether I just want to create the
> > index and blocks are encrypted "on-the-fly" when requested.
> 
> That's an orthogonal concept; indexing vs. insertion is about how
> locally-published files are stored (kept in clear in FS or encrypted in
> DB).  This has no impact on the pushing strategy (see above).
> 
> > In [3], the
> > term "content migration" is used. Are blocks actively pushed to other
> > nodes even without requests on them?
> 
> Yes, see CONTENT_PUSHING and CONTENT_CACHING options.
> 
> > 3) https://gnunet.org/file-sharing-concepts mentions a replication level
> > for blocks. What exactly is the purpose for this and how does it affect
> > replication?
> 
> If you enable CONTENT_PUSHING, the peer will prioritize making
> replication-level PUSH operations of each block of your file before
> going back to making "random" pushes.  Basically, it's a way to give new
> blocks a 'push' in terms of visibility.
> 
> > 4) In the GAP approach described in [4], a peer, say A, can decide to
> > skip the source rewriting step. On the return path, the successor of A
> > needs to communicate directly with the predecessor of A. However, GNUnet
> > uses encrypted links. Does this imply that these nodes need to perform a
> > session key exchange before being able to send the result along the
> > return path?
> 
> Yes.
> 
> > 5) Taking a look at [3] or [4], the network is described as a rather
> > unstructured P2P network. I know also about the DHT based R5N [5] which
> > is a structured approach. How does these two play together in terms of
> > network management? Are there separate routing tables and maintenance
> > protocols?
> 
> Yes, the DHT's routing table is separate from (anonymous) FS, and the
> DHT uses R5N's topology maintenance while FS uses 'topology' (F2F,
> gossip, etc.).  However, these do interact some, as core-level encrypted
> connections found by one may be used immediately by the other and vice
> versa.
> 
> > 6) I know R5N is currently used for non-anonymous file sharing.
> 
> Indirectly via CADET, yes.
> 
> > There is
> > not really sender anonymity due to the hop counter that is used to
> > determine when to switch from random to deterministic routing.
> 
> Nope, it's worse as CADET explicitly identifies the end-points and
> creates a multi-hope end-to-end encrypted communication channel.
> 
> > Furthermore, packets are not intentionally delayed to impede traffic
> > analysis. However, would it be possible to apply similar mechanisms just
> > like in GAP and, e.g., replace the hop counter or use probabilistic
> > behavir to achieve sender anonymity in R5N?
> 
> The likelihood that a particular peer issues queries for a particular
> key in a DHT is quite skewed; it'll be tricky to get this "right" for a
> DHT, and I do not think your simple method works sufficiently well for
> the DHT. For FS: see my comment on CADET.
> 
> > 7) Does GNUnet use erasure codes to tolerate the loss of some of the
> > blocks of a file? Or is a file unretrievable if a block is lost?
> 
> We (still) do not use ECC.
> 
> > 8) Are there any performance measurements in a scientific publication
> > about GAP or GNUnets anonymous file sharing in general?
> 
> AFAIK no.  Initially our performance was always limited by database IO
> (even for the largest setups we could manage), and for testbed-style
> setups this would likely still be a problem today.  Also, several people
> said they would script some kind of "realistic behavior" for users (who
> publishes/searches/downloads what), but AFAIK nobody ever actually
> proposed (not to mention implemented) a good benchmark.
> 
> > [1] Grothoff, Christian, et al. "The gnet whitepaper." Purdue University
> > (2002).
> > [2] Grothoff, Christian. "Resource allocation in peer-to-peer networks:
> > An excess-based economic model." Wirtschaftsinformatik 45.3 (2003):
> > 285-292.
> > [3] Bennett, Krista, et al. "Gnunet-a truly anonymous networking
> > infrastructure." In: Proc. Privacy Enhancing Technologies Workshop (PET.
> > 2002.
> > [4] Bennett, Krista, and Christian Grothoff. "GAP–practical anonymous
> > networking." International Workshop on Privacy Enhancing Technologies.
> > Springer Berlin Heidelberg, 2003.
> > [5] Evans, Nathan S., and Christian Grothoff. "R5n: Randomized recursive
> > routing for restricted-route networks." Network and System Security
> > (NSS), 2011 5th International Conference on. IEEE, 2011.
> > 
> > Best regards,
> 
> Happy hacking!
> 
> Christian
> 




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