  Decentralized data storage systems like the Interplanetary Filesystem (IPFS)
are becoming increasingly popular, e.g., as a data layer in blockchain
applications and for sharing content in a censorship-resistant manner. In IPFS,
data is hosted by an open set of peers, requests to which are broadcast to all
directly connected peers and routed via a DHT. In this paper, we showcase how
the monitoring of said data requests allows for profound insights about the
IPFS network while simultaneously breaching individual users' privacy. To this
end, we present a passive monitoring methodology that enables us to collect all
data requests of a significant and upscalable portion of the total IPFS node
population. Using a measurement setup implementing our approach and data
collected over a period of nine months, we demonstrate the estimation of, among
other things: the size of the IPFS network, activity levels and structure, and
content popularity distributions. We furthermore present how our methodology
can be abused for attacks on users' privacy. As a demonstration, we identify
and successfully surveil public IPFS/HTTP gateways, thereby also uncovering
their (normally hidden) node identifiers. We give a detailed analysis of the
mechanics and reasons behind implied privacy threats and discuss possible
countermeasures.
