6,419 research outputs found
Theoretical Bitcoin Attacks with less than Half of the Computational Power (draft)
A widespread security claim of the Bitcoin system, presented in the original
Bitcoin white-paper, states that the security of the system is guaranteed as
long as there is no attacker in possession of half or more of the total
computational power used to maintain the system. This claim, however, is proved
based on theoretically flawed assumptions.
In the paper we analyze two kinds of attacks based on two theoretical flaws:
the Block Discarding Attack and the Difficulty Raising Attack. We argue that
the current theoretical limit of attacker's fraction of total computational
power essential for the security of the system is in a sense not
but a bit less than , and outline proposals for protocol change
that can raise this limit to be as close to as we want.
The basic idea of the Block Discarding Attack has been noted as early as
2010, and lately was independently though-of and analyzed by both author of
this paper and authors of a most recently pre-print published paper. We thus
focus on the major differences of our analysis, and try to explain the
unfortunate surprising coincidence. To the best of our knowledge, the second
attack is presented here for the first time
A study of accuracy in selected numerical-analysis integration techniques
Report discusses several methods of performing numerical integration with computer. When data can be expressed as state vector that is dependent variable in a differential equation, self-starting integrators can be used to predict future data
If you don’t let us dream, we won’t let you sleep
No description supplie
Space shuttle navigation filter development
Problems encountered in developing a high speed trajectory data processor for the shuttle ascent and entry phases are described. The development of a 19 state acceleration filter for the processor is reported
Pocket nickel cadmium cell and battery evaluation
The Nickel Cadmium 129-ampere hour cell was tested in order to characterize the cell under controlled conditions. Results of charge characterization and discharge characterization are reported. Ampere hour efficiency, open circuit stand, and cycle life operation results are included. The battery is briefly described
Refraction corrections for surveying
Optical measurements of range and elevation angle are distorted by the earth's atmosphere. High precision refraction correction equations are presented which are ideally suited for surveying because their inputs are optically measured range and optically measured elevation angle. The outputs are true straight line range and true geometric elevation angle. The 'short distances' used in surveying allow the calculations of true range and true elevation angle to be quickly made using a programmable pocket calculator. Topics covered include the spherical form of Snell's Law; ray path equations; and integrating the equations. Short-, medium-, and long-range refraction corrections are presented in tables
Least squares polynomial fits and their accuracy
Equations are presented which attempt to fit least squares polynomials to tables of date. It is concluded that much data are needed to reduce the measurement error standard deviation by a significant amount, however at certain points great accuracy is attained
Inversion and approximation of Laplace transforms
A method of inverting Laplace transforms by using a set of orthonormal functions is reported. As a byproduct of the inversion, approximation of complicated Laplace transforms by a transform with a series of simple poles along the left half plane real axis is shown. The inversion and approximation process is simple enough to be put on a programmable hand calculator
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