21,897 research outputs found
Balanced Allocations and Double Hashing
Double hashing has recently found more common usage in schemes that use
multiple hash functions. In double hashing, for an item , one generates two
hash values and , and then uses combinations for to generate multiple hash values from the initial two. We
first perform an empirical study showing that, surprisingly, the performance
difference between double hashing and fully random hashing appears negligible
in the standard balanced allocation paradigm, where each item is placed in the
least loaded of choices, as well as several related variants. We then
provide theoretical results that explain the behavior of double hashing in this
context.Comment: Further updated, small improvements/typos fixe
Asymptotic Analysis of Plausible Tree Hash Modes for SHA-3
Discussions about the choice of a tree hash mode of operation for a
standardization have recently been undertaken. It appears that a single tree
mode cannot address adequately all possible uses and specifications of a
system. In this paper, we review the tree modes which have been proposed, we
discuss their problems and propose remedies. We make the reasonable assumption
that communicating systems have different specifications and that software
applications are of different types (securing stored content or live-streamed
content). Finally, we propose new modes of operation that address the resource
usage problem for the three most representative categories of devices and we
analyse their asymptotic behavior
Parallel Recursive State Compression for Free
This paper focuses on reducing memory usage in enumerative model checking,
while maintaining the multi-core scalability obtained in earlier work. We
present a tree-based multi-core compression method, which works by leveraging
sharing among sub-vectors of state vectors.
An algorithmic analysis of both worst-case and optimal compression ratios
shows the potential to compress even large states to a small constant on
average (8 bytes). Our experiments demonstrate that this holds up in practice:
the median compression ratio of 279 measured experiments is within 17% of the
optimum for tree compression, and five times better than the median compression
ratio of SPIN's COLLAPSE compression.
Our algorithms are implemented in the LTSmin tool, and our experiments show
that for model checking, multi-core tree compression pays its own way: it comes
virtually without overhead compared to the fastest hash table-based methods.Comment: 19 page
Parallel Searching for a First Solution
A parallel algorithm for conducting a search for a first solution to the problem of generating minimal perfect hash functions is presented. A message-based distributed memory computer is assumed as a model for parallel computations. A data structure, called reverse trie (r-trie), was devised to carry out the search. The algorithm was implemented on a transputer network. The experiments showed that the algorithm exhibits a consistent and almost linear speed-up. The r-trie structure proved to be highly memory efficient
Keeping Authorities "Honest or Bust" with Decentralized Witness Cosigning
The secret keys of critical network authorities - such as time, name,
certificate, and software update services - represent high-value targets for
hackers, criminals, and spy agencies wishing to use these keys secretly to
compromise other hosts. To protect authorities and their clients proactively
from undetected exploits and misuse, we introduce CoSi, a scalable witness
cosigning protocol ensuring that every authoritative statement is validated and
publicly logged by a diverse group of witnesses before any client will accept
it. A statement S collectively signed by W witnesses assures clients that S has
been seen, and not immediately found erroneous, by those W observers. Even if S
is compromised in a fashion not readily detectable by the witnesses, CoSi still
guarantees S's exposure to public scrutiny, forcing secrecy-minded attackers to
risk that the compromise will soon be detected by one of the W witnesses.
Because clients can verify collective signatures efficiently without
communication, CoSi protects clients' privacy, and offers the first
transparency mechanism effective against persistent man-in-the-middle attackers
who control a victim's Internet access, the authority's secret key, and several
witnesses' secret keys. CoSi builds on existing cryptographic multisignature
methods, scaling them to support thousands of witnesses via signature
aggregation over efficient communication trees. A working prototype
demonstrates CoSi in the context of timestamping and logging authorities,
enabling groups of over 8,000 distributed witnesses to cosign authoritative
statements in under two seconds.Comment: 20 pages, 7 figure
BaseFs - Basically Acailable, Soft State, Eventually Consistent Filesystem for Cluster Management
A peer-to-peer distributed filesystem for community cloud management. https://github.com/glic3rinu/basef
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