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a significant efficiency improvement over the large universe Key-Policy ABE systems of Lewko-Waters and Lewko. Both schemes are selectively secure in the standard model under two \"q-type\" assumptions similar to ones used in prior works. Our work brings back \"program and cancel\" techniques to this problem.
We provide implementations and benchmarks of our constructions
in Charm; a programming environment for rapid prototyping of cryptographic primitives.
payment system in which all the transactions are publicly
accessible (but in an anonymous way). We downloaded the full history
of this scheme, and analyzed many statistical properties of its
associated transaction graph. In this paper we answer for the
first time a variety of interesting questions about the typical
behavior of account owners, how they acquire and how they spend
their Bitcoins, the balance of Bitcoins they keep in their
accounts, and how they move Bitcoins between their various
accounts in order to better protect their privacy. In addition, we
isolated all the large transactions in the system, and discovered
that almost all of them are closely related to a single large
transaction that took place in November 2010, even though the
associated users apparently tried to hide this fact with many
strange looking long chains and fork-merge structures in the
compared to the modular exponentiation required in number-theoretic schemes. Courtois, Finiasz and Sendrier proposed the only practical code-based signature(CFS signature) . It can be used to realise
many cryptographic primitives. But the signature is currently not provably secure due to the existence
of the high rate distinguisher . In this paper, we make use of an alternate key-construct for the CFS
signature, and thus prove its existential unforgeability under chosen message attacks (EUF-CMA). Also,
we propose a code-based signcryption scheme and proved its security. To the best of our knowledge,
this is the first code-based, provably secure signature and signcryption scheme in literature.