DOCSLIB.ORG

CAAM 402/502 Spring 2013 Homework 2 Solutions

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
CAAM 402/502 Spring 2013 Homework 2 Solutions CAAM 402/502 Spring 2013 Homework 2 Solutions 1. Problem XVII.1.1 in Lang. Let E be a vector space and let v1; :::; vn 2 E be a basis for E. Show that any linear map λ : E ! F into the normed vector space F is continuous. Proof. Let us denote the norm of F by k·kF . We also equip the finite dimensional vector space E with Pn the norm k · k1 defined in terms of the basis fv1; :::; vng as follows. Given x 2 E, let x = i=1 αivi where the scalars αi are uniquely determined by x. Then kxk1 = maxi jαij. We brake the proof into 2 claims. Claim 1: The linear map λ :(E; k · k1) ! (F; k · kF ) is continuous. Proof: In virtue of the result found in Lang page 455, we may equivalently prove that λ is bounded. Let x 2 E be arbitrary. There Pn exist scalars fα1; :::; αng uniquely determined by x such that x = i=1 αivi. Then n n n X X X kλ(x)kF = αiλ(vi) ≤ jαijkλ(vi)kF ≤ max jαij kλ(vi)kF = Ckxk1 i i=1 F i=1 i=1 Pn where C = i=1 kλ(vi)kF is clearly independent of x. Hence λ is bounded. Claim 2: Let k · kE be any norm on E. Then the linear map λ :(E; k · kE) ! (F; k · kF ) is continuous. Proof: Again we show boundedness. We use Theorem 4.3 (Lang page 145) on the equivalence of norms for finite-dimensional spaces. Then there exists a constant K > 0 such that kxk1 ≤ KkxkE; for all x 2 E Then, from Claim 1, we have that, kλ(x)kF ≤ Ckxk1 ≤ CKkxkE; for all x 2 E which makes λ a bounded map. 2. Let f :[−1; 1] ! R de defined as 3x2; if x 2 \ [−1; 1]; f(x) = Q 0; otherwise. Show that f is not differentiable at any point in [−1; 1] except for x = 0. Proof. Since differentiability implies continuity, then f cannot be differentiable at points where it is not continuous. Now we show that f is differentiable at x = 0 and that f 0(0) = 0. Consider h 6= 0 and 2 f(h) − f(0) f(h) 3h 0 ≤ = ≤ = 3jhj: h jhj jhj So in the limit as h ! 0, we obtain that f 0(0) = 0. 1 3. Problem XVII.1.4 in Lang. Let E, F and G be normed vector spaces. A map λ : E × F ! G is said to be bilinear if it satisfies the conditions, λ(v; w1 + w2) = λ(v; w1) + λ(v; w2) λ(v1 + v2; w) = λ(v1; w) + λ(v2; w) λ(cv; w) = cλ(v; w) = λ(v; cw) for all v, vi 2 E, w, wi 2 F and c 2 R (a) Show that a bilinear map λ is continuous if and only if there exists (C > 0) such that for all (v; w) 2 E × F we have jλ(v; w)j ≤ Cjvjjwj Proof. \)", λ is continuous ) λ is continuous at (0; 0). This means that there exist δ1; δ2 > 0 such that jvij ≤ δ1; jwij ≤ δ2 ) jλ(vi; wi) − λ(0; 0)j ≤ 1 We have λ(0; 0) = 0 from third property of bilinear map. Hence jvij ≤ δ1; jwij ≤ δ2 ) jλ(vi; wi)j ≤ 1 v w Consider for any v 2 E, w 2 F , v = δ and w = δ . Clearly jv j = δ and jw j = δ . i jvj 1 i jwj 2 i 1 i 2 Therefore we have, v w δ1 δ2 1 λ δ1; δ2 ≤ 1 ) jλ(v; w)j ≤ 1 ) jλ(v; w)j ≤ jvjjwj ) jλ(v; w)j ≤ Cjvjjwj jvj jwj jvj jwj δ1δ2 1 with C = . δ1δ2 \(" Assume that there exists C > 0 such that jλ(v; w)j ≤ Cjvjjwj for all (v; w) 2 E × F . For any > 0 and (vi; wi) 2 E × F , pick δ = min 1; C(1 + jvij + jwij) jλ(v; w) − λ(vi; wi)j = jλ(v − vi; wi) + λ(v − vi; w − wi) + λ(vi; w − wi)j ≤ jλ(v − vi; wi)j + jλ(v − vi; w − wi)j + jλ(vi; w − wi)j ≤ Cjv − vijjwij + Cjv − vijjw − wij + Cjvijjw − wij 2 < Cδjwij + Cδ + Cδjvij for jv − vij < δ; jw − wij < δ < Hence λ is continuous at every (vi; wi) 2 E × F (b) Let v 2 E be fixed. Show that if λ is continuous, then the map λv : F ! G given by w ! λ(v; w) is a continous linear map. Proof. Let α; β 2 R and w1; w2 2 F . λv(αw1+βw2) = λ(v; αw1+βw2) = λ(v; αw1)+λ(v; βw2) = αλ(v; w1)+βλ(v; w2) = αλv(w1)+βλv(w2) Hence λv is linear. jλv(w)j = jλ(v; w)j ≤ Cjvjjwj = Cvjwj ) jλv(w)j ≤ Cvjwj Cv = Cjvj Hence λv is bounded and linear. Hence λv is a continuous linear map. 2 4. Let S be an open and connected set in Rn, and consider the differentiable function f : S ! Rm with derivative f 0(c) = 0 (the linear map zero), for all c 2 S. Prove that f is constant. Hint: Use the result of Problem 1 below, which says that S is polygonally connected. Proof. Fix a 2 S and let x 2 S. Since S is open and connected, it is polygonally connected (Problem 1 for 502). Thus, there exist points x0 = a; x1; ··· ; xk = x such that L(xj−1; xj) (line segment between two points) is in S for all j = 1; ··· ; k. By the fundamental theorem of calculus we have that Z 1 0 f(xj) − f(xj−1) = f (txj + (1 − t)xj−1)dt (xj − xj−1) = 0 0 for j = 1; ··· ; k. Summing over j we get k X 0 = (f(xj) − f(xj−1)) = f(x) − f(a): j=1 Hence, f(x) = f(a) for all x 2 S, that is, f is constant. 3 ADDITIONAL PROBLEMS FOR CAAM 502 1. Let S be an open and connected set in Rn. Prove that S is polygonally connected, ie., any two points x and y in S can be joined by a polygonal line. Proof. Since S is connected, then the only set two sets in S that are both open and closed (with respect to S) are the whole set S and the empty set . Assume that S is not empty and let a 2 S. Let C ⊂ S denote the set of all the points in S that are polygonally connected to a. This set C is clearly nonempty since a is polygonally to itself. Now we claim that C is both open and closed with respect to S. We proceed to prove openness first. Let x 2 C ⊂ S. Since S is open in Rn, then there exists r > 0 such that Br(x) ⊂ S. Let y 2 Br(x) be arbitrary. Notice that the line segment from x to y stays within Br(x) ⊂ S (by convexity). Now since x 2 C there is a polygonal line in S from a to x. We simply join this line with the line segment from x to y to obtain the desired polygonal line from a to y. Hence we have that Br(x) ⊂ C which implies that C is open in S. Finally we proceed to show that C is closed with respect to S or equivalent that the complement S n C is open. Take x 2 S n C arbitrary (no polygonall line from a to x). Since S is open in Rn, then there exists r > 0 such that Br(x) 2 S. No point y in the ball Br(x) can belong to C, otherwise (like before) we could join a line segment to connected to the center of the ball which is x, and this cannot happen since x2 = C. Hence Br(x) ⊂ S n C which makes S n C open in S. Since a was chosen arbitrarily in S, then we conclude that S is polygonally connected. 2. Let E and F be normed vector spaces and denote by L2(E; F ) the space of continuous bilinear maps of E × E ! F . Let λ 2 L2(E; F ) and define kλk to be the greatest lower bound of all numbers C > 0 such that kλ(v1; v2)kF ≤ Ckv1kEkv2kE 8v1; v2 2 E Show that kλk is a norm in λ 2 L2(E; F ) and verify that its definition is equivalent to kλ(v ; v )k kλk = sup 1 2 F v1;v26=0 kv1kEkv2kE Proof. First we verify the equivalence of definitions. This follows from the fact that the greatest lower bound of all C's that satisfy the above inequality coincides with the least upper bound of all C's that do not satisfy the same inequality. Now we check the axioms of a norm. N1. kλk ≥ 0 and kλk = 0 iff λ = 0 kλk is the greatest lower bound of all C's that satisfy the above inequality. Hence kλ(v ; v )k 1 2 F ≤ kλk kv1kEkv2kE k·kF is a norm, hence kλ(v1; v2)kF ≥ 0 ) kλk ≥ 0. If kλk = 0 ) kλ(v1; v2)kF = 0, 8v1; v2 2 E ) λ(v1; v2) = 0 , 8v1; v2 2 E. Hence λ = 0 N2. For any α 2 R kαλk = jαjkλk For any C > 0 satisfying the given inequality, we have kαλ(v1; v2)kF = jαjkλ(v1; v2)kF ≤ jαjCkv1kEkv2kE If kλk is the greatest lower bound of all possible numbers C, jαjkλk is the greatest lower bound of all possible numbers jαjC.
Load more

Recommended publications
  • A Note on Bilinear Forms
    A note on bilinear forms Darij Grinberg July 9, 2020 Contents 1. Introduction1 2. Bilinear maps and forms1 3. Left and right orthogonal spaces4 4. Interlude: Symmetric and antisymmetric bilinear forms 14 5. The morphism of quotients I 15 6. The morphism of quotients II 20 7. More on orthogonal spaces 24 1. Introduction In this note, we shall prove some elementary linear-algebraic properties of bi- linear forms. These properties generalize some of the standard facts about non- degenerate bilinear forms on finite-dimensional vector spaces (e.g., the fact that ? V? = V for a vector subspace V of a vector space A equipped with a nonde- generate symmetric bilinear form) to bilinear forms which may be degenerate. They are unlikely to be new, but I have not found them explored anywhere, whence this note. 2. Bilinear maps and forms We fix a field k. This field will be fixed for the rest of this note. The notion of a “vector space” will always be understood to mean “k-vector space”. The 1 A note on bilinear forms July 9, 2020 word “subspace” will always mean “k-vector subspace”. The word “linear” will always mean “k-linear”. If V and W are two k-vector spaces, then Hom (V, W) denotes the vector space of all linear maps from V to W. If S is a subset of a vector space V, then span S will mean the span of S (that is, the subspace of V spanned by S). We recall the definition of a bilinear map: Definition 2.1.
    [Show full text]
  • Bornologically Isomorphic Representations of Tensor Distributions
    Bornologically isomorphic representations of distributions on manifolds E. Nigsch Thursday 15th November, 2018 Abstract Distributional tensor fields can be regarded as multilinear mappings with distributional values or as (classical) tensor fields with distribu- tional coefficients. We show that the corresponding isomorphisms hold also in the bornological setting. 1 Introduction ′ ′ ′r s ′ Let D (M) := Γc(M, Vol(M)) and Ds (M) := Γc(M, Tr(M) ⊗ Vol(M)) be the strong duals of the space of compactly supported sections of the volume s bundle Vol(M) and of its tensor product with the tensor bundle Tr(M) over a manifold; these are the spaces of scalar and tensor distributions on M as defined in [?, ?]. A property of the space of tensor distributions which is fundamental in distributional geometry is given by the C∞(M)-module isomorphisms ′r ∼ s ′ ∼ r ′ Ds (M) = LC∞(M)(Tr (M), D (M)) = Ts (M) ⊗C∞(M) D (M) (1) (cf. [?, Theorem 3.1.12 and Corollary 3.1.15]) where C∞(M) is the space of smooth functions on M. In[?] a space of Colombeau-type nonlinear generalized tensor fields was constructed. This involved handling smooth functions (in the sense of convenient calculus as developed in [?]) in par- arXiv:1105.1642v1 [math.FA] 9 May 2011 ∞ r ′ ticular on the C (M)-module tensor products Ts (M) ⊗C∞(M) D (M) and Γ(E) ⊗C∞(M) Γ(F ), where Γ(E) denotes the space of smooth sections of a vector bundle E over M. In[?], however, only minor attention was paid to questions of topology on these tensor products.
    [Show full text]
  • A Symplectic Banach Space with No Lagrangian Subspaces
    transactions of the american mathematical society Volume 273, Number 1, September 1982 A SYMPLECTIC BANACHSPACE WITH NO LAGRANGIANSUBSPACES BY N. J. KALTON1 AND R. C. SWANSON Abstract. In this paper we construct a symplectic Banach space (X, Ü) which does not split as a direct sum of closed isotropic subspaces. Thus, the question of whether every symplectic Banach space is isomorphic to one of the canonical form Y X Y* is settled in the negative. The proof also shows that £(A") admits a nontrivial continuous homomorphism into £(//) where H is a Hilbert space. 1. Introduction. Given a Banach space E, a linear symplectic form on F is a continuous bilinear map ß: E X E -> R which is alternating and nondegenerate in the (strong) sense that the induced map ß: E — E* given by Û(e)(f) = ü(e, f) is an isomorphism of E onto E*. A Banach space with such a form is called a symplectic Banach space. It can be shown, by essentially the argument of Lemma 2 below, that any symplectic Banach space can be renormed so that ß is an isometry. Any symplectic Banach space is reflexive. Standard examples of symplectic Banach spaces all arise in the following way. Let F be a reflexive Banach space and set E — Y © Y*. Define the linear symplectic form fiyby Qy[(^. y% (z>z*)] = z*(y) ~y*(z)- We define two symplectic spaces (£,, ß,) and (E2, ß2) to be equivalent if there is an isomorphism A : Ex -» E2 such that Q2(Ax, Ay) = ß,(x, y). A. Weinstein [10] has asked the question whether every symplectic Banach space is equivalent to one of the form (Y © Y*, üy).
    [Show full text]
  • Self-Bilinear Map from One Way Encoding System and Indistinguishability Obfuscation
    Self-bilinear Map from One Way Encoding System and Indistinguishability Obfuscation Huang Zhang1,4, Fangguo Zhang1,4, Baodian Wei2,4, and Yusong Du3 1 School of Information Science and Technology, Sun Yat-sen University 2 School of Data and Computer Science, Sun Yat-sen University 3 School of Information Management, Sun Yat-sen University 4 Guangdong Key Laboratory of Information Security Technology Guangzhou 510006, China [email protected] Abstract. The bilinear map whose domain and target sets are identical is called the self-bilinear map. Original self-bilinear maps are defined over cyclic groups. This brings a lot of limitations to construct secure self-bilinear schemes. Since the map itself reveals information about the underlying cyclic group, hardness assumptions on DDHP and CDHP may not hold any more. In this paper, we used iO to construct a self-bilinear map from generic sets. These sets should own several properties. A new notion, One Way Encoding System (OWES), is proposed to describe formally the properties those sets should hold. An Encoding Division Problem is defined to complete the security proof. As an instance of the generic construction, we propose a concrete scheme built on the GGH graded encoding system and state that any 1-graded encoding system may satisfy the requirements of OWES. Finally, we discuss the hardness of EDP in the GGH graded encoding system. Keywords: self-bilinear map, multi-linear map, indistinguishability obfus- cation, one way encoding system. 1 Introduction The bilinear map is a very useful cryptographic primitive. It provides solutions for many cryptographic applications such as identity-based encryptions [2], non- interactive zero-knowledge proof systems [16], attribute-based encryptions [21] and short signatures [3, 23], etc.
    [Show full text]
  • A Bilinear Version of Orlicz-Pettis Theorem. a Bilinear Version of Orlicz-Pettis Theorem
    A bilinear version of Orlicz-Pettis theorem. O. Blasco 1 Department of Mathematics. Universitat de Val`encia.Burjassot 46100 (Val`encia), Spain. J.M. Calabuig ∗,2 Instituto Universitario de Matem´atica Pura y Aplicada. Universitat Polit`ecnica de Val`encia. Val`encia46022, Spain. T. Signes 3 Department of Applied Mathematics. Universidad de Murcia. Espinardo 30100 (Murcia), Spain. A bilinear version of Orlicz-Pettis theorem. O. Blasco Department of Mathematics. Universitat de Val`encia.Burjassot 46100 (Val`encia), Spain. J.M. Calabuig Instituto Universitario de Matem´atica Pura y Aplicada. Universitat Polit`ecnica de Val`encia. Val`encia46022, Spain. T. Signes Department of Applied Mathematics. Universidad de Murcia. Espinardo 30100 (Murcia), Spain. Abstract Given three Banach spaces X, Y and Z and a bounded bilinear map B : X×Y → Z, P∞ a sequence x = (xn)n ⊆ X is called B-absolutely summable if n=1 kB(xn, y)kZ < 1 ∞ for any y ∈ Y . Connections of this space with `weak(X) are presented. A sequence P∞ ∗ x = (xn)n ⊆ X is called B-unconditionally summable if n=1 |hB(xn, y), z i| < ∞ Preprint submitted to Elsevier 21 December 2007 ∗ ∗ for any y ∈ Y and z ∈ Z and for any M ⊆ N there exists xM ∈ X for which P ∗ ∗ ∗ ∗ n∈M hB(xn, y), z i = hB(xM , y), z i for all y ∈ Y and z ∈ Z . A bilinear version of Orlicz-Pettis theorem is given in this setting and some applications are presented. Key words: 40F05 Absolute and strong summability, 46A45 Sequence spaces, 46B45 Banach sequence spaces. 1 Notation and preliminaries.
    [Show full text]
  • Multiplication Algorithms : Bilinear Complexity and Fast Asymptotic Methods Svyatoslav Covanov
    Multiplication algorithms : bilinear complexity and fast asymptotic methods Svyatoslav Covanov To cite this version: Svyatoslav Covanov. Multiplication algorithms : bilinear complexity and fast asymptotic methods. Symbolic Computation [cs.SC]. Université de Lorraine, 2018. English. NNT : 2018LORR0057. tel- 01825744 HAL Id: tel-01825744 https://tel.archives-ouvertes.fr/tel-01825744 Submitted on 28 Jun 2018 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Ecole´ doctorale IAEM Lorraine Algorithmes de multiplication : complexit´ebilin´eaireet m´ethodes asymptotiquement rapides THESE` pr´esent´eeet soutenue publiquement le 5 juin 2018 pour l'obtention du Doctorat de l'Universit´ede Lorraine (mention informatique) par Svyatoslav Covanov Composition du jury Rapporteurs : Daniel Augot Directeur de recherche, Inria Saclay Cl´ement Pernet Ma^ıtrede Conf´erences(HDR), Universit´eGrenoble-Alpes Encadrants : Emmanuel Thom´e Directeur de recherche, Inria Nancy J´er´emieDetrey Charg´ede recherche, Inria Nancy Examinatrices : Sylvie Boldo Directrice de recherche, Inria Saclay Natacha Portier Ma^ıtre de Conf´erences, ENS´ Lyon Laboratoire Lorrain de Recherche en Informatique et ses Applications | UMR 7503 Mis en page avec la classe thesul. i Remerciements «Avant, je ne savais pas que la beauté avait un sens.
    [Show full text]
  • Bilinear Ideals in Operator Spaces 3
    BILINEAR IDEALS IN OPERATOR SPACES VERÓNICA DIMANT AND MAITE FERNÁNDEZ-UNZUETA Abstract. We introduce a concept of bilinear ideal of jointly completely bounded mappings between operator spaces. In particular, we study the bilinear ideals N of completely nuclear, I of completely integral, E of completely extendible bilinear mappings, MB multiplicatively bounded and its symmetrization SMB. We prove some basic properties of them, one of which is the fact that I is naturally identified with the ideal of (linear) completely integral mappings on the injective operator space tensor product. 1. Introduction and Preliminaries Let V,W and X be operator spaces. If we consider the underlying vector space structure, the relations ν ρ (1) Bil(V × W, X) ≃ L(V ⊗ W, X) ≃ L(V, L(W, X)) hold through the two natural linear isomorphisms ν, ρ. In order for ν and ρ to induce natural morphisms in the operator space category, it is necessary to have appropriately defined an oper- ator space tensor norm on V ⊗W and specific classes of linear and bilinear mappings. This is the case, for instance, of the so called projective operator space tensor norm k · k∧, the completely bounded maps and the jointly completely bounded bilinear mappings, where ν and ρ induce the following completely bounded isometric isomorphisms: JCB(V × W, X) ≃ CB(V ⊗W, X) ≃ CB(V, CB(W, X)). There are many possible ways to provide V ⊗ W with an operator space tensor norm and, of b course, to define classes of mappings. Several authors, inspired by the success that the study of arXiv:1306.3411v3 [math.OA] 26 Mar 2015 the relations between tensor products and mappings has had in the Banach space setting, have systematically study some analogous relations for operator spaces.
    [Show full text]
  • Orthosymmetric Bilinear Map on Riesz Spaces
    Comment.Math.Univ.Carolin. 56,3 (2015) 307–317 307 Orthosymmetric bilinear map on Riesz spaces Elmiloud Chil, Mohamed Mokaddem, Bourokba Hassen Abstract. Let E be a Riesz space, F a Hausdorff topological vector space (t.v.s.). We prove, under a certain separation condition, that any orthosymmetric bilinear map T : E × E → F is automatically symmetric. This generalizes in certain way an earlier result by F. Ben Amor [On orthosymmetric bilinear maps, Positivity 14 (2010), 123–134]. As an application, we show that under a certain separation condition, any orthogonally additive homogeneous polynomial P : E → F is linearly represented. This fits in the type of results by Y. Benyamini, S. Lassalle and J.L.G. Llavona [Homogeneous orthogonally additive polynomials on Banach lattices, Bulletin of the London Mathematical Society 38 (2006), no. 3 123–134]. Keywords: orthosymmetric multilinear map; homogeneous polynomial; Riesz space Classification: 06F25, 46A40 1. Introduction One of the relevant problems in operator theory is to describe orthogonally ad- ditive polynomials via linear operators. This problem can be treated in a different manner, depending on domains and co-domains on which polynomials act. Inter- est in orthogonally additive polynomials on Banach lattices originates in the work of K. Sundaresan [19] where the space of n-homogeneous orthogonally additive polynomials on the Banach lattices lp and Lp [0, 1] was characterized. It is only recently that the class of such mappings has been getting more attention. We are thinking here about works on orthogonally additive polynomials and holomorphic functions and orthosymmetric multilinear mappings on different Banach lattices and also C∗-algebras, see for instance [3], [6], [7], [18] and [8], [13], [14], [17].
    [Show full text]
  • Orthosymmetric Maps and Polynomial Valuations
    University of Mississippi eGrove Electronic Theses and Dissertations Graduate School 2017 Orthosymmetric Maps And Polynomial Valuations Stephan Christopher Roberts University of Mississippi Follow this and additional works at: https://egrove.olemiss.edu/etd Part of the Mathematics Commons Recommended Citation Roberts, Stephan Christopher, "Orthosymmetric Maps And Polynomial Valuations" (2017). Electronic Theses and Dissertations. 680. https://egrove.olemiss.edu/etd/680 This Dissertation is brought to you for free and open access by the Graduate School at eGrove. It has been accepted for inclusion in Electronic Theses and Dissertations by an authorized administrator of eGrove. For more information, please contact [email protected]. ORTHOSYMMETRIC MAPS AND POLYNOMIAL VALUATIONS A Dissertation presented in partial fulfillment of requirements for the degree of Doctor of Philosophy in the Department of Mathematics The University of Mississippi by STEPHAN CHRISTOPHER ROBERTS December 2017 Copyright Stephan Christopher Roberts 2017 ALL RIGHTS RESERVED ABSTRACT We present a characterization of orthogonally additive polynomials on vector lattices as orthosymmetric multilinear maps. Our proof avoids partitionaly orthosymmetric maps and results that represent orthogonally additive polynomials as linear maps on a power. We also prove band characterizations for order bounded polynomial valuations and for order continuous polynomials of order bounded variation. Finally, we use polynomial valuations to prove that a certain restriction of the Arens extension
    [Show full text]
  • Encryption Schemes from Bilinear Maps
    Encryption Schemes from Bilinear Maps Eu-Jin Goh September 8, 2007 Dedication This thesis is dedicated to my parents, Goh Ah Hock and Tan Chor Ngan, my aunt Tan Chor Koon, my sister Goh Yen-Li, and my wife Serene Koh. It is also dedicated to the memory of my late grandmother Tan Poh Tee. Acknowledgements This thesis would have been impossible without the unstinting support and mentoring of my advisor, Dan Boneh, and also the members of both the Applied Crypto and the Security Group at Stanford; in particular, Hovav Shacham, Nagendra Modadugu, Stanis law Jarecki, Philippe Golle, and John Mitchell. 1 Abstract Encryption schemes are designed to provide data confidentiality and are a fundamental crypto- graphic primitive with many applications in higher-level protocols. Groups with a bilinear map allow us to build public key encryption schemes with new properties that are otherwise difficult to obtain using groups without a bilinear map. We support our thesis by presenting two encryption schemes based on bilinear groups; the first is a partial solution to the open problem on doubly homomorphic encryption proposed by Rivest et al. in 1978, and the second is the most efficient hierarchical identity based encryption scheme to date. Our main result deals with homomorphic encryption. Using bilinear groups, we developed a homomorphic encryption scheme based on the subgroup decision complexity assumption; this encryption scheme is additively homomorphic and also possesses an additional limited (single) multiplicative homomorphism. Even with such limitations, our encryption scheme allows us to evaluate on encrypted inputs useful formulas such as polynomials of total degree at most two and dot products.
    [Show full text]
  • Arxiv:Math/0512611V2 [Math.FA] 6 Mar 2009
    ON TOPOLOGICAL TENSOR PRODUCTS OF FUNCTIONAL FRECHET´ AND DF SPACES A. G. SMIRNOV Abstract. A convenient technique for calculating completed topological ten- sor products of functional Fr´echet and DF spaces is developed. The general construction is applied to proving kernel theorems for a wide class of weighted spaces of smooth and entire analytic functions. 1. Introduction Let X and Y be sets and F , G, and H be locally convex spaces consisting of func- tions defined on X, Y , and X × Y respectively. If the function (x, y) → f(x)g(y) belongs to H for any f ∈ F and g ∈ G, then F ⊗ G is identified with a linear subspace of H. In applications, it is often important to find out whether H can be interpreted as the completion of F ⊗G with respect to some natural tensor product topology. Results of this type (or rather their reformulations in terms of bilinear forms) for concrete functional spaces are known as kernel theorems. For example, Schwartz’s kernel theorem for tempered distributions amounts to the statement that the space S(Rk1+k2 ) of rapidly decreasing smooth functions on Rk1+k2 is iden- k1 k2 k1 k2 tical to the completion S(R )⊗πS(R ) of S(R ) ⊗ S(R ) with respect to the projective1 topology. Very general conditions ensuring the algebraic coincidence of H with F ⊗πG can be derived fromb the description of completed tensor products of functional spaces given by Grothendieck ([5], Chapitre 2, Th´eor`eme 13). Namely, suppose bothb F and G are Hausdorff and complete, F is nuclear and representable as an inductive limit of Fr´echet spaces, and the topology of F is stronger than that of simple convergence.
    [Show full text]
  • Finding Optimal Formulae for Bilinear Maps
    Finding Optimal Formulae for Bilinear Maps Razvan Barbulescu, J´er´emieDetrey, Nicolas Estibals, and Paul Zimmermann CARAMEL project-team, LORIA, Universit´ede Lorraine / INRIA / CNRS, Campus Scientifique, BP 239, 54506 Vandœuvre-l`es-NancyCedex, France Abstract. We describe a unified framework to search for optimal formulae evaluating bi- linear | or quadratic | maps. This framework applies to polynomial multiplication and squaring, finite field arithmetic, matrix multiplication, etc. We then propose a new algorithm to solve problems in this unified framework. With an implementation of this algorithm, we prove the optimality of various published upper bounds, and find improved upper bounds. Keywords: optimal algorithms, polynomial multiplication and squaring, finite field arith- metic, tensor rank, bilinear map, bilinear rank 1 Introduction This article studies the bilinear rank problem. Given a field K, this problem naturally arises when considering the computational complexity of formulae (or algorithms) for evaluating bilinear maps over K [4, Ch. 14]. For instance, typical bilinear maps include | but are not limited to | the multiplication of two n-term polynomials of K[X], or of two r × r square matrices of Kr×r. Note that, given an algorithm for computing a bilinear map over K, this algorithm can be naturally extended to compute the same bilinear map over any larger K-algebra K. For instance, given a formula for computing the product of two n-term polynomials over K = F2, the exact same formula can also be used to compute the product of two n-term polynomials over any field extension K = F2m , or even the product of two n-term r×r polynomials of F2 [X], i.e., polynomials having binary r × r matrices as coefficients.
    [Show full text]