  Providing unrestricted access to sensitive content such as news and software
is difficult in the presence of adaptive and resourceful surveillance and
censoring adversaries. In this paper we leverage the distributed and resilient
nature of commercial Satoshi blockchains to develop the first provably secure,
censorship resistant, cost-efficient storage system with anonymous and private
access, built on top of commercial cryptocurrency transactions. We introduce
max-rate transactions, a practical construct to persist data of arbitrary size
entirely in a Satoshi blockchain. We leverage max-rate transactions to develop
UWeb, a blockchain-based storage system that charges publishers to self-sustain
its decentralized infrastructure. UWeb organizes blockchainstored content for
easy retrieval, and enables clients to store and access content with provable
anonymity, privacy and censorship resistance properties.
  We present results from UWeb experiments with writing 268.21 MB of data into
the live Litecoin blockchain, including 4.5 months of live-feed BBC articles,
and 41 censorship resistant tools. The max-rate writing throughput (183 KB/s)
and blockchain utilization (88%) exceed those of state-of-the-art solutions by
2-3 orders of magnitude and broke Litecoin's record of the daily average block
size. Our simulations with up to 3,000 concurrent UWeb writers confirm that
UWeb does not impact the confirmation delays of financial transactions.
