910 research outputs found
Certified lattice reduction
Quadratic form reduction and lattice reduction are fundamental tools in
computational number theory and in computer science, especially in
cryptography. The celebrated Lenstra-Lenstra-Lov\'asz reduction algorithm
(so-called LLL) has been improved in many ways through the past decades and
remains one of the central methods used for reducing integral lattice basis. In
particular, its floating-point variants-where the rational arithmetic required
by Gram-Schmidt orthogonalization is replaced by floating-point arithmetic-are
now the fastest known. However, the systematic study of the reduction theory of
real quadratic forms or, more generally, of real lattices is not widely
represented in the literature. When the problem arises, the lattice is usually
replaced by an integral approximation of (a multiple of) the original lattice,
which is then reduced. While practically useful and proven in some special
cases, this method doesn't offer any guarantee of success in general. In this
work, we present an adaptive-precision version of a generalized LLL algorithm
that covers this case in all generality. In particular, we replace
floating-point arithmetic by Interval Arithmetic to certify the behavior of the
algorithm. We conclude by giving a typical application of the result in
algebraic number theory for the reduction of ideal lattices in number fields.Comment: 23 page
Cosmos greenstone terrane: Insights into an Archaean volcanic arc, associated with komatiite-hosted nickel sulphide mineralisation, from U-Pb dating, volcanic stratigraphy and geochemistry
The Neoarchaean Agnew-Wiluna greenstone belt (AWB) of the Kalgoorlie
Terrane, within the Eastern Goldfields Superterrane (EGS) of the Yilgarn Craton,
Western Australia, contains several world-class, komatiite-hosted, nickel-sulphide ore
bodies. These are commonly associated with felsic volcanic successions, many of
which are considered to have a tonalite-trondhjemite-dacite (TTD) affinity. The
Cosmos greenstone sequence lies on the western edge of the AWB and this previously
unstudied mineralised volcanic succession contrasts markedly in age, geochemistry,
emplacement mechanisms and probable tectonic setting to that of the majority of the
AWB and wider EGS. Detailed subsurface mapping has shown that the footwall to the
Cosmos mineralised ultramafic sequence consists of an intricate succession of both
fragmental and coherent extrusive lithologies, ranging from basaltic andesites through
to rhyolites, plus later-formed felsic and basaltic intrusions. The occurrence of thick
sequences of amygdaloidal intermediate lavas intercalated with extensive sequences
of dacite lapilli tuff, coupled with the absence of marine sediments or hydrovolcanic
products, indicates the succession was formed in a subaerial environment. Chemical
composition of the non-ultramafic lithologies is typified by a high-K calc-alkaline to
shoshonite signature, indicative of formation in a volcanic arc setting. Assimilation-fractional
crystallisation modelling has shown that at least two compositionally
distinct sources must be invoked to explain the observed basaltic andesite to rhyolite
magma suite. High resolution U-Pb dating of several units within the succession
underpins stratigraphic relationships established in the field and indicates that the
emplacement of the Cosmos succession took place between ~2736 Ma and ~2653 Ma,
making it significantly older and longer-lived than most other greenstone successions
within the Kalgoorlie Terrane. Extrusive periodic volcanism spanned ~50 Myrs with
three cycles of bimodal intermediate/felsic and ultramafic volcanism occurring
between ~2736 Ma and ~2685 Ma. Periodic intrusive activity, related to the local
granite plutonism, lasted for a further ~32 Myrs or until ~2653 Ma. The Cosmos
succession either represents a separate, older terrane in its own right or it has an
autochthonous relationship with the AWB but volcanism initiated much earlier in this
region than currently considered. Dating of the Cosmos succession has demonstrated
that high-resolution geochronology within individual greenstone successions can be
achieved and provides more robust platforms for interpreting the evolution of ancient
mineralised volcanic successions. The geochemical affinity of the Cosmos succession
indicates a subduction zone was operating in the Kalgoorlie Terrane by ~2736 Ma,
much earlier than considered in current regional geodynamic models. The Cosmos
volcanic succession provides further evidence that plate tectonics was in operation
during the Neoarchaean, contrary to some recently proposed tectonic models
Fully homomorphic encryption modulo Fermat numbers
In this paper, we recast state-of-the-art constructions for fully
homomorphic encryption in the simple language of arithmetic modulo
large Fermat numbers. The techniques used to construct our scheme
are quite standard in the realm of (R)LWE based
cryptosystems. However, the use of arithmetic in such a simple ring
greatly simplifies exposition of the scheme and makes its
implementation much easier.
In terms of performance, our test implementation of the proposed
scheme is slower than the current speed records but remains within a
comparable range. We hope that the detailed study of our simplified
scheme by the community can make it competitive and provide new
insights into FHE constructions at large
New Complexity Trade-Offs for the (Multiple) Number Field Sieve Algorithm in Non-Prime Fields
The selection of polynomials to represent number fields crucially determines the efficiency of the Number Field Sieve
(NFS) algorithm for solving the discrete logarithm in a finite field. An important recent work due to Barbulescu et al. builds upon
existing works to propose two new methods for polynomial selection when the target field is a non-prime field. These methods are
called the generalised Joux-Lercier (GJL) and the Conjugation methods. In this work, we propose a new method (which we denote
as ) for polynomial selection for the NFS algorithm in fields , with and .
The new method both subsumes and generalises the GJL and the Conjugation methods and provides new trade-offs for both composite
and prime. Let us denote the variant of the (multiple) NFS algorithm using the polynomial selection method ``{X} by (M)NFS-{X}.
Asymptotic analysis is performed for both the NFS- and the MNFS- algorithms.
In particular, when , for , the complexity of NFS- is better than the complexities
of all previous algorithms whether classical or MNFS. The MNFS- algorithm provides lower complexity compared to
NFS- algorithm; for , the complexity of MNFS-
is the same as that of the MNFS-Conjugation and for , the complexity of MNFS-
is lower than that of all previous methods
A General Polynomial Selection Method and New Asymptotic Complexities for the Tower Number Field Sieve Algorithm
In a recent work, Kim and Barbulescu had extended the tower number field sieve algorithm to obtain improved asymptotic complexities in
the medium prime case for the discrete logarithm problem on where is not a prime power. Their method does not work
when is a composite prime power. For this case, we obtain new asymptotic complexities, e.g., (resp.
for the multiple number field variation) when is composite and a power of 2; the previously best known complexity for this
case is (resp. ). These complexities may have consequences to the selection of key sizes for
pairing based cryptography. The new complexities are achieved through a general polynomial selection method.
This method, which we call Algorithm-, extends a previous polynomial selection method proposed at Eurocrypt 2016 to the
tower number field case. As special cases, it is possible to obtain the generalised Joux-Lercier and the Conjugation method of
polynomial selection proposed at Eurocrypt 2015 and the extension of these methods to the tower number field scenario by Kim and Barbulescu.
A thorough analysis of the new algorithm is carried out in both concrete and asymptotic terms
Classical and Quantum Algorithms for Variants of Subset-Sum via Dynamic Programming
Subset-Sum is an NP-complete problem where one must decide if a multiset of n integers contains a subset whose elements sum to a target value m. The best known classical and quantum algorithms run in time O?(2^{n/2}) and O?(2^{n/3}), respectively, based on the well-known meet-in-the-middle technique. Here we introduce a novel classical dynamic-programming-based data structure with applications to Subset-Sum and a number of variants, including Equal-Sums (where one seeks two disjoint subsets with the same sum), 2-Subset-Sum (a relaxed version of Subset-Sum where each item in the input set can be used twice in the summation), and Shifted-Sums, a generalization of both of these variants, where one seeks two disjoint subsets whose sums differ by some specified value.
Given any modulus p, our data structure can be constructed in time O(np), after which queries can be made in time O(n) to the lists of subsets summing to any value modulo p. We use this data structure in combination with variable-time amplitude amplification and a new quantum pair finding algorithm, extending the quantum claw finding algorithm to the multiple solutions case, to give an O(2^{0.504n}) quantum algorithm for Shifted-Sums. This provides a notable improvement on the best known O(2^{0.773n}) classical running time established by Mucha et al. [Mucha et al., 2019]. We also study Pigeonhole Equal-Sums, a variant of Equal-Sums where the existence of a solution is guaranteed by the pigeonhole principle. For this problem we give faster classical and quantum algorithms with running time O?(2^{n/2}) and O?(2^{2n/5}), respectively
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