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[liberationtech] New Anonymity Network for Short Messages

Michael Rogers michael at briarproject.org
Wed Jun 12 06:34:57 PDT 2013


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On 11/06/13 17:52, Sean Cassidy wrote:
> I have created a simple anonymity network that broadcasts all
> messages to participants so that you cannot associate chatters.

Hi Sean,

A few quick questions:

* Do routers subscribe to prefixes, or is it only clients that do so?
If routers subscribe to prefixes, how do you ensure that all routers
subscribed to a given prefix form a connected subgraph?

* A passive observer can pretty quickly tell which prefixes a client
subscribes to by seeing which messages routers send her - her outgoing
messages can be ignored. So can't a global passive observer identify a
group of clients who all subscribe to the same prefix?

> struct dinet_packet { uint8_t id[16]; // prefix + random in the
> default client uint8_t data[1024]; uint8_t checksum[32]; // SHA-256
> checksum of the previous two fields, to avoid flooding the network
> with duplicate packets };

* Why is the checksum included in the packet? Each router can
calculate the hash of the previous two fields itself, and discard the
packet if the hash matches a previously seen hash. If the router
trusts the hash included in the packet, it's possible to poison a
router's duplicate detection cache by sending it a packet that has the
same checksum field as another packet but different data.

Cheers,
Michael

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