Descent on the Picard variety of a degenerating curve

Speaker: 

Shahed Sharif

Institution: 

California State University San Marcos

Time: 

Thursday, May 31, 2012 - 3:00pm

Location: 

RH 306

Let $C$ be a curve over a local field whose reduction is totally
degenerate. We discuss the related problems of 1) determining the
group structure of the torsion subgroup of the Jacobian of $C$, and 2)
determining if a given line bundle on $C$ is divisible by a given
integer $r$. Under certain hypotheses on the reduction of $C$, we
exhibit explicit algorithms for answering these two questions.

Lattice Algorithms: State of the Art and Open Problems

Speaker: 

Daniele Micciancio

Institution: 

UCSD

Time: 

Wednesday, March 14, 2012 - 2:00am

Host: 

Location: 

RH 306

TITLE: Lattice Algorithms: State of the Art and Open Problems
SPEAKER: Daniele Micciancio (UCSD)

ABSTRACT
Computational problems on point lattices play an important role in
many areas of computer science and mathematics. Since the discovery of
the LLL basis reduction algorithm in the early '80s, much effort has
gone into the development of better (faster, or more accurate)
algorithms, largely motivated by applications in cryptanalysis. Today,
with the flourishing of lattice based cryptography (i.e.,
cryptographic function whose security rests on the computational
intractability of lattice problems, including the recent development
of fully homomorphic encryption schemes), improving our understanding
of the effort required to solve lattice problems has never been more
important, as it plays a critical role determining appropriate key
sizes. In this talk I will describe the current state of the art in
lattice algorithms, including the asymptotically fastest known
algorithm of Micciancio and Voulgaris, as well as less understood but
practically effective heuristics, and a panoramic of the many research
problems that are still open in the area.

Bio sketch: Daniele Micciancio got his PhD from MIT in 1998, and
joined the UCSD CSE faculty in 1999. He is the recipient of several
awards, including an NSF CAREER award, Sloan Fellowship and Hellman
Fellowship. He is most known for his research on the complexity of
lattice problems, which spans the whole spectrum from computational
complexity and algorithms, to cryptography. His most notable
achievements include the first significant inapproximability result
for the Shortest Vector Problem, pioneering the use of cyclic and
ideal lattices from algebraic number theory for the construction of
very efficient cryptographic primitives based on worst-case complexity
assumptions, and the discovery of the first single exponential time
algorithm to solve all the most important computational problems on
point lattices.

Approximate common divisors via lattices

Speaker: 

Nadia Heninger

Institution: 

UCSD Department of Computer Science and Engineering

Time: 

Tuesday, November 15, 2011 - 3:00pm

Location: 

RH 340N

Given two integers, we can compute their greatest common divisor
efficiently using Euclid's algorithm. Howgrave-Graham formulated
an approximate version of this question, asking ``What if instead of
exact multiples of some common divisor, we only know approximations?''
This problem has many applications in cryptography, particularly
partial key recovery for RSA. In this talk, I will show how to extend
Howgrave-Graham's algorithm from two approximate multiples to many
approximate multiples. This gives a more detailed analysis of the
hardness assumption underlying the recent fully homomorphic
cryptosystem of van Dijk, Gentry, Halevi, and Vaikuntanathan. While
these results do not challenge the suggested parameters, a
$2^{n^{2/3}$ approximation algorithm for lattice basis reduction in
$n$ dimensions could be used to break these parameters.

Joint work with Henry Cohn

Toward Making Homomorphic Encryption Practical

Speaker: 

Craig Gentry

Institution: 

IBM

Time: 

Tuesday, October 25, 2011 - 3:00pm

Location: 

RH 340N

Homomorphic encryption allows you to delegate the processing of your data or your query to a "worker" (e.g., the "cloud") without sacrificing your privacy. The worker can process your private data or private query even though it is encrypted, and send back to you the (encrypted) response that you were seeking, without learning anything significant.

This talk will partly be a tutorial designed to give a taste of how homomorphic encryption schemes work, and why they have been so inefficient. Next, the talk will sketch some very recent results that dramatically improve efficiency and give us hope that homomorphic computation may one day be truly practical.

Geometric Flavored Arithmetic on Jacobians of Hyperelliptic Curves

Speaker: 

Craig Costello

Institution: 

UCI & Queensland University of Technology

Time: 

Monday, April 18, 2011 - 4:00pm

Location: 

RH 306

As an alternative to elliptic curve groups, Koblitz (1989) suggested Jacobians of hyperelliptic curves for use in public-key cryptography. Hyperelliptic curves can achieve the same level of discrete log based security as elliptic curves, whilst offering the potential advantage of being defined over much smaller fields. At present however, elliptic curves still outperform hyperelliptic curves in general, because of the significant difference in the complexity of computing group operations. Indeed, when deriving fast explicit formulas for elliptic curve computations, one is aided by the simple geometric "chord-and-tangent" description. In contrast, Cantor's algorithm for arithmetic in Jacobian groups suffers from more computationally heavy operations, such as Euclid's algorithm for finding the gcd of two polynomials, and the chinese remainder theorem. In this talk we discuss recent results which exploit a chord-and-tangent-like analogue for hyperelliptic curves. We give a simple description of higher genus Jacobian arithmetic and show that for genus 2 curves this gives rise to explicit formulas which are significantly faster than their Cantor-based counterparts. This is joint work with Kristin Lauter.

Computing Cryptographic Pairings: the State of the Art

Speaker: 

Craig Costello

Institution: 

UCI & Queensland University of Technology

Time: 

Tuesday, November 2, 2010 - 3:00pm

Location: 

RH 340N

Bilinear pairings, such as the Weil and Tate pairings, have revolutionized
public-key cryptography since they burst onto the scene at the turn of the
century. In the decade that has followed, methods to compute
cryptographically secure pairings have received a great deal of attention
from mathematicians and cryptographers alike, in an effort to accelerate
their speed so that the many new and exciting protocols that pairings
facilitate can be realized in industry. In this talk we give an overview
of the progress in pairing computation, paying particular attention to the
very latest results in the area.

Efficient Arithmetic on Hessian Curves

Speaker: 

Reza Rezaeian Farashahi

Institution: 

Macquarie University

Time: 

Tuesday, October 12, 2010 - 3:00pm

Location: 

RH 340P

In this talk, we present the family of generalized Hessian curves.

The family of generalized Hessian curves covers more isomorphism classes of elliptic curves than Hessian curves.

We provide efficient unified addition formulas for generalized Hessian curves. The formulas even feature completeness for suitably chosen curve parameters.

We also also present extremely fast addition formulas for generalized binary Hessian curves. The fastest projective addition formulas require $9\M+3\s$, where $\M$ is the cost of a field multiplication and $\s$ is the cost of a field squaring. Moreover, very fast differential addition and doubling formulas are provided that need only $5\M+4\s$ when the curve is chosen with small parameters.

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