Lecture 18: PSPACE-Completeness, and Randomized Complexity Classes
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On the Randomness Complexity of Interactive Proofs and Statistical Zero-Knowledge Proofs*
On the Randomness Complexity of Interactive Proofs and Statistical Zero-Knowledge Proofs* Benny Applebaum† Eyal Golombek* Abstract We study the randomness complexity of interactive proofs and zero-knowledge proofs. In particular, we ask whether it is possible to reduce the randomness complexity, R, of the verifier to be comparable with the number of bits, CV , that the verifier sends during the interaction. We show that such randomness sparsification is possible in several settings. Specifically, unconditional sparsification can be obtained in the non-uniform setting (where the verifier is modelled as a circuit), and in the uniform setting where the parties have access to a (reusable) common-random-string (CRS). We further show that constant-round uniform protocols can be sparsified without a CRS under a plausible worst-case complexity-theoretic assumption that was used previously in the context of derandomization. All the above sparsification results preserve statistical-zero knowledge provided that this property holds against a cheating verifier. We further show that randomness sparsification can be applied to honest-verifier statistical zero-knowledge (HVSZK) proofs at the expense of increasing the communica- tion from the prover by R−F bits, or, in the case of honest-verifier perfect zero-knowledge (HVPZK) by slowing down the simulation by a factor of 2R−F . Here F is a new measure of accessible bit complexity of an HVZK proof system that ranges from 0 to R, where a maximal grade of R is achieved when zero- knowledge holds against a “semi-malicious” verifier that maliciously selects its random tape and then plays honestly. -
The Randomized Quicksort Algorithm
Outline The Randomized Quicksort Algorithm K. Subramani1 1Lane Department of Computer Science and Electrical Engineering West Virginia University 7 February, 2012 Subramani Sample Analyses Outline Outline 1 The Randomized Quicksort Algorithm Subramani Sample Analyses The Randomized Quicksort Algorithm The Sorting Problem Problem Statement Given an array A of n distinct integers, in the indices A[1] through A[n], Subramani Sample Analyses The Randomized Quicksort Algorithm The Sorting Problem Problem Statement Given an array A of n distinct integers, in the indices A[1] through A[n], permute the elements of A, so that Subramani Sample Analyses The Randomized Quicksort Algorithm The Sorting Problem Problem Statement Given an array A of n distinct integers, in the indices A[1] through A[n], permute the elements of A, so that A[1] < A[2]... A[n]. Subramani Sample Analyses The Randomized Quicksort Algorithm The Sorting Problem Problem Statement Given an array A of n distinct integers, in the indices A[1] through A[n], permute the elements of A, so that A[1] < A[2]... A[n]. Note The assumption of distinctness simplifies the analysis. Subramani Sample Analyses The Randomized Quicksort Algorithm The Sorting Problem Problem Statement Given an array A of n distinct integers, in the indices A[1] through A[n], permute the elements of A, so that A[1] < A[2]... A[n]. Note The assumption of distinctness simplifies the analysis. It has no bearing on the running time. Subramani Sample Analyses The Randomized Quicksort Algorithm The Partition subroutine Function PARTITION(A,p,q) 1: {We partition the sub-array A[p,p + 1,...,q] about A[p].} 2: for (i = (p + 1) to q) do 3: if (A[i] < A[p]) then 4: Insert A[i] into bucket L. -
NP-Completeness Part I
NP-Completeness Part I Outline for Today ● Recap from Last Time ● Welcome back from break! Let's make sure we're all on the same page here. ● Polynomial-Time Reducibility ● Connecting problems together. ● NP-Completeness ● What are the hardest problems in NP? ● The Cook-Levin Theorem ● A concrete NP-complete problem. Recap from Last Time The Limits of Computability EQTM EQTM co-RE R RE LD LD ADD HALT ATM HALT ATM 0*1* The Limits of Efficient Computation P NP R P and NP Refresher ● The class P consists of all problems solvable in deterministic polynomial time. ● The class NP consists of all problems solvable in nondeterministic polynomial time. ● Equivalently, NP consists of all problems for which there is a deterministic, polynomial-time verifier for the problem. Reducibility Maximum Matching ● Given an undirected graph G, a matching in G is a set of edges such that no two edges share an endpoint. ● A maximum matching is a matching with the largest number of edges. AA maximummaximum matching.matching. Maximum Matching ● Jack Edmonds' paper “Paths, Trees, and Flowers” gives a polynomial-time algorithm for finding maximum matchings. ● (This is the same Edmonds as in “Cobham- Edmonds Thesis.) ● Using this fact, what other problems can we solve? Domino Tiling Domino Tiling Solving Domino Tiling Solving Domino Tiling Solving Domino Tiling Solving Domino Tiling Solving Domino Tiling Solving Domino Tiling Solving Domino Tiling Solving Domino Tiling The Setup ● To determine whether you can place at least k dominoes on a crossword grid, do the following: ● Convert the grid into a graph: each empty cell is a node, and any two adjacent empty cells have an edge between them. -
Randomized Algorithms, Quicksort and Randomized Selection Carola Wenk Slides Courtesy of Charles Leiserson with Additions by Carola Wenk
CMPS 2200 – Fall 2014 Randomized Algorithms, Quicksort and Randomized Selection Carola Wenk Slides courtesy of Charles Leiserson with additions by Carola Wenk CMPS 2200 Intro. to Algorithms 1 Deterministic Algorithms Runtime for deterministic algorithms with input size n: • Best-case runtime Attained by one input of size n • Worst-case runtime Attained by one input of size n • Average runtime Averaged over all possible inputs of size n CMPS 2200 Intro. to Algorithms 2 Deterministic Algorithms: Insertion Sort for j=2 to n { key = A[j] // insert A[j] into sorted sequence A[1..j-1] i=j-1 while(i>0 && A[i]>key){ A[i+1]=A[i] i-- } A[i+1]=key } • Best case runtime? • Worst case runtime? CMPS 2200 Intro. to Algorithms 3 Deterministic Algorithms: Insertion Sort Best-case runtime: O(n), input [1,2,3,…,n] Attained by one input of size n • Worst-case runtime: O(n2), input [n, n-1, …,2,1] Attained by one input of size n • Average runtime : O(n2) Averaged over all possible inputs of size n •What kind of inputs are there? • How many inputs are there? CMPS 2200 Intro. to Algorithms 4 Average Runtime • What kind of inputs are there? • Do [1,2,…,n] and [5,6,…,n+5] cause different behavior of Insertion Sort? • No. Therefore it suffices to only consider all permutations of [1,2,…,n] . • How many inputs are there? • There are n! different permutations of [1,2,…,n] CMPS 2200 Intro. to Algorithms 5 Average Runtime Insertion Sort: n=4 • Inputs: 4!=24 [1,2,3,4]0346 [4,1,2,3] [4,1,3,2] [4,3,2,1] [2,1,3,4]1235 [1,4,2,3] [1,4,3,2] [3,4,2,1] [1,3,2,4]1124 [1,2,4,3] [1,3,4,2] [3,2,4,1] [3,1,2,4]2455 [4,2,1,3] [4,3,1,2] [4,2,3,1] [3,2,1,4]3244 [2,1,4,3] [3,4,1,2] [2,4,3,1] [2,3,1,4]2333 [2,4,1,3] [3,1,4,2] [2,3,4,1] • Runtime is proportional to: 3 + #times in while loop • Best: 3+0, Worst: 3+6=9, Average: 3+72/24 = 6 CMPS 2200 Intro. -
Theory of Computation
A Universal Program (4) Theory of Computation Prof. Michael Mascagni Florida State University Department of Computer Science 1 / 33 Recursively Enumerable Sets (4.4) A Universal Program (4) The Parameter Theorem (4.5) Diagonalization, Reducibility, and Rice's Theorem (4.6, 4.7) Enumeration Theorem Definition. We write Wn = fx 2 N j Φ(x; n) #g: Then we have Theorem 4.6. A set B is r.e. if and only if there is an n for which B = Wn. Proof. This is simply by the definition ofΦ( x; n). 2 Note that W0; W1; W2;::: is an enumeration of all r.e. sets. 2 / 33 Recursively Enumerable Sets (4.4) A Universal Program (4) The Parameter Theorem (4.5) Diagonalization, Reducibility, and Rice's Theorem (4.6, 4.7) The Set K Let K = fn 2 N j n 2 Wng: Now n 2 K , Φ(n; n) #, HALT(n; n) This, K is the set of all numbers n such that program number n eventually halts on input n. 3 / 33 Recursively Enumerable Sets (4.4) A Universal Program (4) The Parameter Theorem (4.5) Diagonalization, Reducibility, and Rice's Theorem (4.6, 4.7) K Is r.e. but Not Recursive Theorem 4.7. K is r.e. but not recursive. Proof. By the universality theorem, Φ(n; n) is partially computable, hence K is r.e. If K¯ were also r.e., then by the enumeration theorem, K¯ = Wi for some i. We then arrive at i 2 K , i 2 Wi , i 2 K¯ which is a contradiction. -
Glossary of Complexity Classes
App endix A Glossary of Complexity Classes Summary This glossary includes selfcontained denitions of most complexity classes mentioned in the b o ok Needless to say the glossary oers a very minimal discussion of these classes and the reader is re ferred to the main text for further discussion The items are organized by topics rather than by alphab etic order Sp ecically the glossary is partitioned into two parts dealing separately with complexity classes that are dened in terms of algorithms and their resources ie time and space complexity of Turing machines and complexity classes de ned in terms of nonuniform circuits and referring to their size and depth The algorithmic classes include timecomplexity based classes such as P NP coNP BPP RP coRP PH E EXP and NEXP and the space complexity classes L NL RL and P S P AC E The non k uniform classes include the circuit classes P p oly as well as NC and k AC Denitions and basic results regarding many other complexity classes are available at the constantly evolving Complexity Zoo A Preliminaries Complexity classes are sets of computational problems where each class contains problems that can b e solved with sp ecic computational resources To dene a complexity class one sp ecies a mo del of computation a complexity measure like time or space which is always measured as a function of the input length and a b ound on the complexity of problems in the class We follow the tradition of fo cusing on decision problems but refer to these problems using the terminology of promise problems -
A Study of the NEXP Vs. P/Poly Problem and Its Variants by Barıs
A Study of the NEXP vs. P/poly Problem and Its Variants by Barı¸sAydınlıoglu˘ A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Computer Sciences) at the UNIVERSITY OF WISCONSIN–MADISON 2017 Date of final oral examination: August 15, 2017 This dissertation is approved by the following members of the Final Oral Committee: Eric Bach, Professor, Computer Sciences Jin-Yi Cai, Professor, Computer Sciences Shuchi Chawla, Associate Professor, Computer Sciences Loris D’Antoni, Asssistant Professor, Computer Sciences Joseph S. Miller, Professor, Mathematics © Copyright by Barı¸sAydınlıoglu˘ 2017 All Rights Reserved i To Azadeh ii acknowledgments I am grateful to my advisor Eric Bach, for taking me on as his student, for being a constant source of inspiration and guidance, for his patience, time, and for our collaboration in [9]. I have a story to tell about that last one, the paper [9]. It was a late Monday night, 9:46 PM to be exact, when I e-mailed Eric this: Subject: question Eric, I am attaching two lemmas. They seem simple enough. Do they seem plausible to you? Do you see a proof/counterexample? Five minutes past midnight, Eric responded, Subject: one down, one to go. I think the first result is just linear algebra. and proceeded to give a proof from The Book. I was ecstatic, though only for fifteen minutes because then he sent a counterexample refuting the other lemma. But a third lemma, inspired by his counterexample, tied everything together. All within three hours. On a Monday midnight. I only wish that I had asked to work with him sooner. -
IBM Research Report Derandomizing Arthur-Merlin Games And
H-0292 (H1010-004) October 5, 2010 Computer Science IBM Research Report Derandomizing Arthur-Merlin Games and Approximate Counting Implies Exponential-Size Lower Bounds Dan Gutfreund, Akinori Kawachi IBM Research Division Haifa Research Laboratory Mt. Carmel 31905 Haifa, Israel Research Division Almaden - Austin - Beijing - Cambridge - Haifa - India - T. J. Watson - Tokyo - Zurich LIMITED DISTRIBUTION NOTICE: This report has been submitted for publication outside of IBM and will probably be copyrighted if accepted for publication. It has been issued as a Research Report for early dissemination of its contents. In view of the transfer of copyright to the outside publisher, its distribution outside of IBM prior to publication should be limited to peer communications and specific requests. After outside publication, requests should be filled only by reprints or legally obtained copies of the article (e.g. , payment of royalties). Copies may be requested from IBM T. J. Watson Research Center , P. O. Box 218, Yorktown Heights, NY 10598 USA (email: [email protected]). Some reports are available on the internet at http://domino.watson.ibm.com/library/CyberDig.nsf/home . Derandomization Implies Exponential-Size Lower Bounds 1 DERANDOMIZING ARTHUR-MERLIN GAMES AND APPROXIMATE COUNTING IMPLIES EXPONENTIAL-SIZE LOWER BOUNDS Dan Gutfreund and Akinori Kawachi Abstract. We show that if Arthur-Merlin protocols can be deran- domized, then there is a Boolean function computable in deterministic exponential-time with access to an NP oracle, that cannot be computed by Boolean circuits of exponential size. More formally, if prAM ⊆ PNP then there is a Boolean function in ENP that requires circuits of size 2Ω(n). -
January 30 4.1 a Deterministic Algorithm for Primality Testing
CS271 Randomness & Computation Spring 2020 Lecture 4: January 30 Instructor: Alistair Sinclair Disclaimer: These notes have not been subjected to the usual scrutiny accorded to formal publications. They may be distributed outside this class only with the permission of the Instructor. 4.1 A deterministic algorithm for primality testing We conclude our discussion of primality testing by sketching the route to the first polynomial time determin- istic primality testing algorithm announced in 2002. This is based on another randomized algorithm due to Agrawal and Biswas [AB99], which was subsequently derandomized by Agrawal, Kayal and Saxena [AKS02]. We won’t discuss the derandomization in detail as that is not the main focus of the class. The Agrawal-Biswas algorithm exploits a different number theoretic fact, which is a generalization of Fermat’s Theorem, to find a witness for a composite number. Namely: Fact 4.1 For every a > 1 such that gcd(a, n) = 1, n is a prime iff (x − a)n = xn − a mod n. n Exercise: Prove this fact. [Hint: Use the fact that k = 0 mod n for all 0 < k < n iff n is prime.] The obvious approach for designing an algorithm around this fact is to use the Schwartz-Zippel test to see if (x − a)n − (xn − a) is the zero polynomial. However, this fails for two reasons. The first is that if n is not prime then Zn is not a field (which we assumed in our analysis of Schwartz-Zippel); the second is that the degree of the polynomial is n, which is the same as the cardinality of Zn and thus too large (recall that Schwartz-Zippel requires that values be chosen from a set of size strictly larger than the degree). -
A New Point of NP-Hardness for Unique Games
A new point of NP-hardness for Unique Games Ryan O'Donnell∗ John Wrighty September 30, 2012 Abstract 1 3 We show that distinguishing 2 -satisfiable Unique-Games instances from ( 8 + )-satisfiable instances is NP-hard (for all > 0). A consequence is that we match or improve the best known c vs. s NP-hardness result for Unique-Games for all values of c (except for c very close to 0). For these c, ours is the first hardness result showing that it helps to take the alphabet size larger than 2. Our NP-hardness reductions are quasilinear-size and thus show nearly full exponential time is required, assuming the ETH. ∗Department of Computer Science, Carnegie Mellon University. Supported by NSF grants CCF-0747250 and CCF-0915893, and by a Sloan fellowship. Some of this research performed while the author was a von Neumann Fellow at the Institute for Advanced Study, supported by NSF grants DMS-083537 and CCF-0832797. yDepartment of Computer Science, Carnegie Mellon University. 1 Introduction Thanks largely to the groundbreaking work of H˚astad[H˚as01], we have optimal NP-hardness of approximation results for several constraint satisfaction problems (CSPs), including 3Lin(Z2) and 3Sat. But for many others | including most interesting CSPs with 2-variable constraints | we lack matching algorithmic and NP-hardness results. Take the 2Lin(Z2) problem for example, in which there are Boolean variables with constraints of the form \xi = xj" and \xi 6= xj". The largest approximation ratio known to be achievable in polynomial time is roughly :878 [GW95], whereas it 11 is only known that achieving ratios above 12 ≈ :917 is NP-hard [H˚as01, TSSW00]. -
CMSC 420: Lecture 7 Randomized Search Structures: Treaps and Skip Lists
CMSC 420 Dave Mount CMSC 420: Lecture 7 Randomized Search Structures: Treaps and Skip Lists Randomized Data Structures: A common design techlque in the field of algorithm design in- volves the notion of using randomization. A randomized algorithm employs a pseudo-random number generator to inform some of its decisions. Randomization has proved to be a re- markably useful technique, and randomized algorithms are often the fastest and simplest algorithms for a given application. This may seem perplexing at first. Shouldn't an intelligent, clever algorithm designer be able to make better decisions than a simple random number generator? The issue is that a deterministic decision-making process may be susceptible to systematic biases, which in turn can result in unbalanced data structures. Randomness creates a layer of \independence," which can alleviate these systematic biases. In this lecture, we will consider two famous randomized data structures, which were invented at nearly the same time. The first is a randomized version of a binary tree, called a treap. This data structure's name is a portmanteau (combination) of \tree" and \heap." It was developed by Raimund Seidel and Cecilia Aragon in 1989. (Remarkably, this 1-dimensional data structure is closely related to two 2-dimensional data structures, the Cartesian tree by Jean Vuillemin and the priority search tree of Edward McCreight, both discovered in 1980.) The other data structure is the skip list, which is a randomized version of a linked list where links can point to entries that are separated by a significant distance. This was invented by Bill Pugh (a professor at UMD!). -
Quantum Computational Complexity Theory Is to Un- Derstand the Implications of Quantum Physics to Computational Complexity Theory
Quantum Computational Complexity John Watrous Institute for Quantum Computing and School of Computer Science University of Waterloo, Waterloo, Ontario, Canada. Article outline I. Definition of the subject and its importance II. Introduction III. The quantum circuit model IV. Polynomial-time quantum computations V. Quantum proofs VI. Quantum interactive proof systems VII. Other selected notions in quantum complexity VIII. Future directions IX. References Glossary Quantum circuit. A quantum circuit is an acyclic network of quantum gates connected by wires: the gates represent quantum operations and the wires represent the qubits on which these operations are performed. The quantum circuit model is the most commonly studied model of quantum computation. Quantum complexity class. A quantum complexity class is a collection of computational problems that are solvable by a cho- sen quantum computational model that obeys certain resource constraints. For example, BQP is the quantum complexity class of all decision problems that can be solved in polynomial time by a arXiv:0804.3401v1 [quant-ph] 21 Apr 2008 quantum computer. Quantum proof. A quantum proof is a quantum state that plays the role of a witness or certificate to a quan- tum computer that runs a verification procedure. The quantum complexity class QMA is defined by this notion: it includes all decision problems whose yes-instances are efficiently verifiable by means of quantum proofs. Quantum interactive proof system. A quantum interactive proof system is an interaction between a verifier and one or more provers, involving the processing and exchange of quantum information, whereby the provers attempt to convince the verifier of the answer to some computational problem.