School of Technology and Computer Science - PhD Synopsis Seminar
https://www.tcs.tifr.res.in/event/phd-synopsis-seminar
enA Formal Approach to Exchange Design and Regulation
https://www.tcs.tifr.res.in/events/formal-approach-exchange-design-and-regulation
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<a href="/event/phd-synopsis-seminar" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">PhD Synopsis Seminar</a> </li>
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<div class="field field-name-field-members field-type-entityreference field-label-inline clearfix view-mode-rss clearfix">
<div class="field-label">Speaker: </div>
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<div class="field-item even"><a href="/people/suneel-sarswat">Suneel Sarswat</a>, TIFR</div>
</div>
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<section class="field field-name-field-time field-type-datetime field-label-inline clearfix view-mode-rss"><h2 class="field-label">Time: </h2><div class="field-items"><div class="field-item even"><span class="date-display-single">Friday, 21 July 2023, <span class="date-display-range"><span class="date-display-start" property="dc:date" datatype="xsd:dateTime" content="2023-07-21T14:00:00+05:30">14:00</span> to <span class="date-display-end" property="dc:date" datatype="xsd:dateTime" content="2023-07-21T15:00:00+05:30">15:00</span></span></span></div></div></section><section class="field field-name-field-venue field-type-taxonomy-term-reference field-label-inline clearfix view-mode-rss clearfix">
<h2 class="field-label">Venue: </h2>
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<a href="/venue/a201" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">A201</a> </li>
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</section>
<section class="field field-name-field-organisers field-type-entityreference field-label-inline clearfix view-mode-rss"><h2 class="field-label">Organisers: </h2><div class="field-items"><div class="field-item even"><a href="/people/n-raja">N Raja</a></div></div></section><div class="field field-name-body field-type-text-with-summary field-label-hidden view-mode-rss"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax">
<p>Exchanges such as that of foreign currency, stocks, and commodities are organized marketplaces where trades are conducted by matching buy and sell requests of traders. Several instances have been reported where exchanges have been found violating regulatory guidelines and the stated rules. In this work, we propose a robust approach to exchange design and regulation by presenting a comprehensive framework for formalizing and certifying double auctions, which are the key mechanisms employed by the exchanges to match the buy and sell requests of traders. Typically, two types of double auctions are employed in the exchanges: call auctions and continuous auctions. For call auctions again, there are two main alternatives: uniform price and dynamic price. Our main contributions are as follows.</p>
<p>-- Call auctions: We formalize the various notions of call auctions and provide fully formalized algorithms for uniform and dynamic price auctions along with their correctness proofs.</p>
<p>-- Continuous auctions: We formulate the specifications for continuous double auctions by identifying three simple and necessary properties and formally proving that they are in fact sufficient; they completely determine the input-output relationship. We then formally verify that a natural algorithm satisfies these properties.</p>
<p>-- Uniqueness theorems: We establish new uniqueness theorems for both call and continuous auctions that enable us to build automated checkers that are guaranteed to detect errors in the trade logs of exchanges if they generate transactions that violate the specifications. We extract verified programs of our formalized algorithms to build automated checkers.</p>
<p>-- Tests on real data: We add preprocessing steps that enable us to tailor our general model to a specific exchange. We then run our automated checkers on real data. Furthermore, we report the running times on various input sizes.</p>
<p>-- Efficiency: We obtain tight bounds on the time complexity of all these three matching problems in the comparison model. Specifically, we demonstrate that uniform price matching can be achieved in linear time, which is an improvement over the previous algorithm that takes O(n log n) time to match n requests. For dynamic price matching, we establish a lower bound of Ω(n log n) on the running time, thereby proving that the currently known best algorithm is time-efficient. Furthermore, for continuous double auctions, we show that a natural algorithm takes O(n log n) time, while any algorithm requires at least Ω(n log n) time.</p>
</div>
</div></div></div><section class="field field-name-field-diplay-profile field-type-list-boolean field-label-above view-mode-rss"><h2 class="field-label">Faculty Candidate: </h2><div class="field-items"><div class="field-item even"></div></div></section>Fri, 14 Jul 2023 06:09:52 +0000Chinmayee Kudtarkar4896 at https://www.tcs.tifr.res.inStrategic Decision-Making for Information Freshness
https://www.tcs.tifr.res.in/events/strategic-decision-making-information-freshness
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<a href="/event/phd-synopsis-seminar" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">PhD Synopsis Seminar</a> </li>
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<div class="field-label">Speaker: </div>
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<div class="field-item even"><a href="/people/kumar-saurav">Kumar Saurav</a>, TIFR</div>
</div>
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<section class="field field-name-field-time field-type-datetime field-label-inline clearfix view-mode-rss"><h2 class="field-label">Time: </h2><div class="field-items"><div class="field-item even"><span class="date-display-single">Thursday, 13 July 2023, <span class="date-display-range"><span class="date-display-start" property="dc:date" datatype="xsd:dateTime" content="2023-07-13T16:00:00+05:30">16:00</span> to <span class="date-display-end" property="dc:date" datatype="xsd:dateTime" content="2023-07-13T17:00:00+05:30">17:00</span></span></span></div></div></section><section class="field field-name-field-venue field-type-taxonomy-term-reference field-label-inline clearfix view-mode-rss clearfix">
<h2 class="field-label">Venue: </h2>
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<a href="/venue/a201" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">A201</a> </li>
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</section>
<section class="field field-name-field-organisers field-type-entityreference field-label-inline clearfix view-mode-rss"><h2 class="field-label">Organisers: </h2><div class="field-items"><div class="field-item even"><a href="/people/kumar-saurav">Kumar Saurav</a></div></div></section><div class="field field-name-body field-type-text-with-summary field-label-hidden view-mode-rss"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax">
<p>Classical network scheduling problems have primarily focused on optimizing metrics, such as delay, which pertain to the service provided to individual packets in the network. However, in modern applications like tele-robotics and networked cars, the emphasis is on metrics that capture the freshness of information, specifically, how up-to-date the information is at the receiver (monitor) compared to the transmitter (source). Thus, several metrics have been introduced to quantify information freshness, the most widely used one being the age of information (AoI). The AoI for a source at any given time is equal to the difference between the current time and the generation time of the most recent packet (update) received at the monitor. For modern applications, the scheduling objective is to minimize the AoI for the sources in an online environment, where only causal information is available at any time.</p>
<p>A critical feature of AoI scheduling problems is that not all updates generated at a source need to be transmitted. Depending on the network model, a scheduling algorithm (policy) must choose a subset of updates to transmit. This characteristic gives AoI scheduling problems a combinatorial flavour, making them fundamentally different and analytically challenging compared to classical scheduling problems. In the PhD dissertation, we have addressed some major challenges in AoI scheduling for generic network models, taking into consideration energy consumption, shared transmission link, and the type of scheduler (centralized/decentralized). We have analyzed the various trade-offs involved in decision-making and proposed novel causal algorithms (policies) that strategically handle these trade-offs. Additionally, using analytical techniques, we have derived theoretical performance guarantees, ensuring the efficiency and robustness of the proposed solutions. In this seminar, we will have a comprehensive overview of the above contributions, with all the relevant background.</p>
</div>
</div></div></div><section class="field field-name-field-diplay-profile field-type-list-boolean field-label-above view-mode-rss"><h2 class="field-label">Faculty Candidate: </h2><div class="field-items"><div class="field-item even"></div></div></section>Thu, 06 Jul 2023 08:51:33 +0000Chinmayee Kudtarkar4887 at https://www.tcs.tifr.res.inOn Complexity measures of Boolean functions
https://www.tcs.tifr.res.in/events/complexity-measures-boolean-functions-0
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<a href="/event/phd-synopsis-seminar" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">PhD Synopsis Seminar</a> </li>
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<div class="field-label">Speaker: </div>
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<div class="field-item even"><a href="/people/tulasi-mohan-molli">Tulasi mohan Molli</a>, TIFR</div>
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<section class="field field-name-field-time field-type-datetime field-label-inline clearfix view-mode-rss"><h2 class="field-label">Time: </h2><div class="field-items"><div class="field-item even"><span class="date-display-single">Friday, 15 July 2022, <span class="date-display-range"><span class="date-display-start" property="dc:date" datatype="xsd:dateTime" content="2022-07-15T14:00:00+05:30">14:00</span> to <span class="date-display-end" property="dc:date" datatype="xsd:dateTime" content="2022-07-15T15:00:00+05:30">15:00</span></span></span></div></div></section><section class="field field-name-field-venue field-type-taxonomy-term-reference field-label-inline clearfix view-mode-rss clearfix">
<h2 class="field-label">Venue: </h2>
<ul class="field-items">
<li class="field-item even">
<a href="/venue/zoom" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">Via Zoom</a> </li>
</ul>
</section>
<section class="field field-name-field-organisers field-type-entityreference field-label-inline clearfix view-mode-rss"><h2 class="field-label">Organisers: </h2><div class="field-items"><div class="field-item even"><a href="/people/prahladh-harsha">Prahladh Harsha</a></div></div></section><div class="field field-name-body field-type-text-with-summary field-label-hidden view-mode-rss"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax">
<p>Boolean functions capture various problems and situations arising in computer science and other areas. In this synopsis, we study boolean functions using two complexity measures.</p>
<p>In the first part of the talk, we will focus on the Probabilistic degree of OR over Reals. This is based on joint work with Bhandari, Harsha and Srinivasan. In this part, we will look at the construction of a Probabilistic Polynomial for OR over Reals, which improves on the previous best construction due to Toda-Ogiwara and Beigel, Tarui, Reingold and Speilman. We will also look at a lower bound on the Probabilistic degree of OR which matches our upper bound construction in a restricted setting.</p>
<p> In the second part, we will look at a bunch of complexity measures which arise out of the Fourier representation of Boolean functions and study the relationship between them. This is based on joint work with Chakraborty, Mande, Mittal, Paraashar and Sanyal. In this part, we will focus on a couple of upper bounds on Fourier rank in terms of Fourier sparsity, weight, Fourier max-entropy and Fourier max-rank entropy. We will also exhibit functions which match these bounds.</p>
<p> Meeting URL : <a href="https://zoom.us/j/98513182619?pwd=WjZDWFhVVVdYM0NhZGZjdGtObjhvQT09">https://zoom.us/j/98513182619?pwd=WjZDWFhVVVdYM0NhZGZjdGtObjhvQT09</a><br />
Meeting ID : 98513182619<br />
Passcode : 59290580</p>
</div>
</div></div></div><section class="field field-name-field-diplay-profile field-type-list-boolean field-label-above view-mode-rss"><h2 class="field-label">Faculty Candidate: </h2><div class="field-items"><div class="field-item even"></div></div></section>Mon, 11 Jul 2022 10:09:07 +0000Supriya Pottipati4692 at https://www.tcs.tifr.res.inSecure Multiparty Computation with Limited Connectivity
https://www.tcs.tifr.res.in/events/secure-multiparty-computation-limited-connectivity
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<a href="/event/phd-synopsis-seminar" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">PhD Synopsis Seminar</a> </li>
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<div class="field-label">Speaker: </div>
<div class="field-items">
<div class="field-item even"><a href="/people/varun-narayanan">Varun Narayanan</a>, TIFR</div>
</div>
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<section class="field field-name-field-time field-type-datetime field-label-inline clearfix view-mode-rss"><h2 class="field-label">Time: </h2><div class="field-items"><div class="field-item even"><span class="date-display-single">Monday, 18 January 2021, <span class="date-display-range"><span class="date-display-start" property="dc:date" datatype="xsd:dateTime" content="2021-01-18T11:00:00+05:30">11:00</span> to <span class="date-display-end" property="dc:date" datatype="xsd:dateTime" content="2021-01-18T12:00:00+05:30">12:00</span></span></span></div></div></section><div class="field field-name-body field-type-text-with-summary field-label-hidden view-mode-rss"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax">
<p>Information theoretically secure multiparty computation (MPC) is a central primitive in modern cryptography.<br />
It enables mutually distrusting parties to collaboratively perform computations on their combined data by ensuring that each party's data is kept private from the others.<br />
This is achieved by designing communication protocols which allow the parties to collectively simulate an incorruptible trusted party, who privately receives inputs from the parties, computes the pre-agreed functionality, and delivers the outputs to the appropriate parties privately.</p>
<p>The subject of this dissertation is MPC when there is limited connectivity in the communication network available to the participants.<br />
Our motivations and the progress we made in addressing them follows:</p>
<p>- In many practical scenarios, the parties may only have access to a communication network with limited connectivity, in that, not every pair of parties can communicate privately and reliably with each other.<br />
We characterize the conditions under which a pair of parties can compute any functionality with information theoretic security in an incomplete network of reliable, private links.<br />
Separate characterizations are obtained for honest-but-curious and malicious modes of corruption with security against general adversary structures.</p>
<p>- Many cryptographic tasks can be modelled as secure 2-party computation (2PC) using only one-directional communication.<br />
Garg et al. (Crypto 15) initiated the study of non-interactive 2PC over noisy channels with one-way communication, namely when only one party speaks.<br />
A major question left open by that work was the completeness of finite channels in this model of secure computation.<br />
We show that bit-ROT (i.e., Randomized Oblivious Transfer) channel, which erases one of the two input bits uniformly at random, can compute any functionality with inverse polynomial security error (in the number of channel uses) in this model against a computationally unbounded adversary.<br />
Further, assuming ideal obfuscation, realizable using tamper-proof hardware tokens, naturally occurring channels such as binary symmetric channel (BSC) and binary erasure channel (BEC) are complete in this sense with inverse polynomial security error against a computationally bounded adversary.<br />
To complement this, we show that no channel with finite alphabet is complete in this model with negligible security error even against a computationally bounded adversary.<br />
Finally, we characterize the channels that enable zero-knowledge proofs in this model; the previous result work had presented construction of zero-knowledge proofs using BEC/BSC channels.</p>
<p>- Studying secure computation with limited interaction tends to reveal new frontiers to approach the problem of complexity of several information theoretic primitives: a notoriously hard problem in cryptography.<br />
We introduce a new primitive in information-theoretic cryptography, namely zero-communication reductions (ZCR), with varying levels of security, and relate it with several other important primitives.<br />
Using these connections, we obtain new upper bounds and lower bounds for complexity of several cryptographic primitives.</p>
<p>- MPC provides a meaningful and robust definition of security that can be used for modelling security guarantees for existing models in network information theory.<br />
Index coding is a well studied problem, in which a server wants to efficiently broadcast n messages intended for n users, each with access to a subset of these messages as side information.<br />
We introduce a notion of privacy in index coding, where the receivers do not learn anything more than the message they want from the server and those they have as side information, and study various aspects of its transmission rate and secret consumption rate.</p>
</div>
</div></div></div><section class="field field-name-field-diplay-profile field-type-list-boolean field-label-above view-mode-rss"><h2 class="field-label">Faculty Candidate: </h2><div class="field-items"><div class="field-item even"></div></div></section>Fri, 15 Jan 2021 04:24:44 +0000Supriya Pottipati4443 at https://www.tcs.tifr.res.inHitting Sets for Some Algebraic Models - Constructions and Consequences
https://www.tcs.tifr.res.in/events/hitting-sets-some-algebraic-models-constructions-and-consequences
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<a href="/event/phd-synopsis-seminar" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">PhD Synopsis Seminar</a> </li>
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<div class="field-label">Speaker: </div>
<div class="field-items">
<div class="field-item even"><a href="/people/anamay-tengse">Anamay Tengse</a>, TIFR</div>
</div>
</div>
<section class="field field-name-field-time field-type-datetime field-label-inline clearfix view-mode-rss"><h2 class="field-label">Time: </h2><div class="field-items"><div class="field-item even"><span class="date-display-single">Monday, 23 November 2020, <span class="date-display-range"><span class="date-display-start" property="dc:date" datatype="xsd:dateTime" content="2020-11-23T11:15:00+05:30">11:15</span> to <span class="date-display-end" property="dc:date" datatype="xsd:dateTime" content="2020-11-23T12:15:00+05:30">12:15</span></span></span></div></div></section><section class="field field-name-field-organisers field-type-entityreference field-label-inline clearfix view-mode-rss"><h2 class="field-label">Organisers: </h2><div class="field-items"><div class="field-item even"><a href="/people/ramprasad-saptharishi">Ramprasad Saptharishi</a></div></div></section><div class="field field-name-body field-type-text-with-summary field-label-hidden view-mode-rss"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax">
<p>We study the question of constructing _hitting sets_ for polynomials computed by several algebraic models. For a class of polynomials C, hitting sets for C capture the problem of _deterministic_ blackbox PIT for C - checking if a polynomial from C is zero by querying it on a few points. Formally, a hitting set for a class C is a set H such that for every nonzero f in C, there is some point h in H for which f(h) is nonzero. Owing to its close connections to the search of explicit hard polynomials, finding efficient hitting sets for various classes of polynomials is a central question in algebraic complexity theory.</p>
<p>Our contributions towards this question are as follows. The first set of our results extend the scope of known hitting set constructions to other well studied algebraic models. Next, we show that for any general enough algebraic model, like circuits or formulas, even a mild improvement to the trivial hitting sets for the model leads to almost efficient hitting sets for it. Lastly, we explore how hitting sets for a class of polynomials can assist us in _proving_ lower bounds against that class.</p>
</div>
</div></div></div><section class="field field-name-field-diplay-profile field-type-list-boolean field-label-above view-mode-rss"><h2 class="field-label">Faculty Candidate: </h2><div class="field-items"><div class="field-item even"></div></div></section>Thu, 19 Nov 2020 05:08:50 +0000Supriya Pottipati4431 at https://www.tcs.tifr.res.inPartial Function Extension with Applications to Learning and Property Testing
https://www.tcs.tifr.res.in/events/partial-function-extension-applications-learning-and-property-testing
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<a href="/event/phd-synopsis-seminar" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">PhD Synopsis Seminar</a> </li>
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<div class="field-label">Speaker: </div>
<div class="field-items">
<div class="field-item even"><a href="/people/gunjan-kumar">Gunjan Kumar</a>, TIFR</div>
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<section class="field field-name-field-time field-type-datetime field-label-inline clearfix view-mode-rss"><h2 class="field-label">Time: </h2><div class="field-items"><div class="field-item even"><span class="date-display-single">Tuesday, 20 October 2020, <span class="date-display-range"><span class="date-display-start" property="dc:date" datatype="xsd:dateTime" content="2020-10-20T14:00:00+05:30">14:00</span> to <span class="date-display-end" property="dc:date" datatype="xsd:dateTime" content="2020-10-20T15:00:00+05:30">15:00</span></span></span></div></div></section><div class="field field-name-body field-type-text-with-summary field-label-hidden view-mode-rss"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax">Partial function extension is a basic problem that underpins multiple research topics in optimization, including learning, property testing, and game theory. Here, we are given a partial function consisting of $n$ points from a domain and a function value at each point. Our objective is to determine if this partial function can be extended to a function defined on the domain, that additionally satisfies a given property, such as linearity. We formally study partial function extension for various complement-free functions.
<p>Our contributions are twofold. Firstly, for the properties studied, we give a combinatorial characterization and bounds on the complexity of partial function extension. Secondly, we develop new connections between partial function extension and learning and property testing, and use these to give new results for these problems.</p>
<p>Zoom link: <a href="https://zoom.us/j/91586068203?pwd=Sjk1T1lhR1lYVUhidHN2VVRXeFJoZz09">https://zoom.us/j/91586068203?pwd=Sjk1T1lhR1lYVUhidHN2VVRXeFJoZz09</a>
</p></div>
</div></div></div><section class="field field-name-field-diplay-profile field-type-list-boolean field-label-above view-mode-rss"><h2 class="field-label">Faculty Candidate: </h2><div class="field-items"><div class="field-item even"></div></div></section>Thu, 01 Oct 2020 03:56:37 +0000Supriya Pottipati4418 at https://www.tcs.tifr.res.inCoordination Over Networks: Shared Randomness, Security, and Interaction
https://www.tcs.tifr.res.in/events/coordination-over-networks-shared-randomness-security-and-interaction
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<a href="/event/phd-synopsis-seminar" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">PhD Synopsis Seminar</a> </li>
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<div class="field-label">Speaker: </div>
<div class="field-items">
<div class="field-item even"><a href="/people/gowtham-raghunath-kurri">Gowtham Raghunath Kurri</a>, TIFR</div>
</div>
</div>
<section class="field field-name-field-time field-type-datetime field-label-inline clearfix view-mode-rss"><h2 class="field-label">Time: </h2><div class="field-items"><div class="field-item even"><span class="date-display-single">Friday, 15 November 2019, <span class="date-display-range"><span class="date-display-start" property="dc:date" datatype="xsd:dateTime" content="2019-11-15T11:00:00+05:30">11:00</span> to <span class="date-display-end" property="dc:date" datatype="xsd:dateTime" content="2019-11-15T12:00:00+05:30">12:00</span></span></span></div></div></section><section class="field field-name-field-venue field-type-taxonomy-term-reference field-label-inline clearfix view-mode-rss clearfix">
<h2 class="field-label">Venue: </h2>
<ul class="field-items">
<li class="field-item even">
<a href="/venue/201-stcs-seminar-room" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">A-201 (STCS Seminar Room)</a> </li>
</ul>
</section>
<section class="field field-name-field-organisers field-type-entityreference field-label-inline clearfix view-mode-rss"><h2 class="field-label">Organisers: </h2><div class="field-items"><div class="field-item even"><a href="/people/vinod-m-prabhakaran">Vinod M. Prabhakaran</a></div></div></section><div class="field field-name-body field-type-text-with-summary field-label-hidden view-mode-rss"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax">
<p><strong>Abstract:</strong> In a coordination problem, users in a network observing correlated inputs collaborate to evaluate possibly randomized functions of the inputs. Problems of this kind have been widely studied in the information theory literature. It finds applications in several diverse areas such as in parallel processing, cooperative game theory, distributed control, function computation in networks. The focus of many of the works in the literature has been on the amount of communication needed to achieve coordination. In practice, several other aspects are also of interest such as the amount and form of shared/correlated randomness available, topology of the network used, and security. </p>
<p>In this talk, we present a systematic study of various such aspects, namely, shared randomness, security, and interaction in addition to the amount of communication needed. To this end, the first problem we study is a distributed sampling problem where a set of processors want to output correlated sequences of random variables with the help of a coordinator which has access to several independent sources of randomness and each processor has access to a subset of these sources. We characterize optimal communication and/or shared randomness rates in various cases of this setting. In the second problem, we study interactive secure function computation. The privacy requirement is that the communication should not reveal to either user any extra information about the other user’s input and output other than what can be inferred from the user’s own input and output. We give single-letter expressions for the asymptotic rate regions. Further, we analyse the role of common randomness and interaction. In secure function computation, in practical scenarios, it might be reasonable to give away certain amount of information about the inputs but not about some specific functions of the inputs which the users want to keep private. We study such settings also.</p>
</div>
</div></div></div><section class="field field-name-field-diplay-profile field-type-list-boolean field-label-above view-mode-rss"><h2 class="field-label">Faculty Candidate: </h2><div class="field-items"><div class="field-item even"></div></div></section>Mon, 11 Nov 2019 05:37:44 +0000Supriya Pottipati4270 at https://www.tcs.tifr.res.inSuccinct Representations of Shortest Paths in Graphs
https://www.tcs.tifr.res.in/events/succinct-representations-shortest-paths-graphs
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<a href="/event/phd-synopsis-seminar" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">PhD Synopsis Seminar</a> </li>
</ul>
</div>
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<div class="field field-name-field-members field-type-entityreference field-label-inline clearfix view-mode-rss clearfix">
<div class="field-label">Speaker: </div>
<div class="field-items">
<div class="field-item even"><a href="/people/kshitij-gajjar">Kshitij Gajjar</a>, TIFR</div>
</div>
</div>
<section class="field field-name-field-time field-type-datetime field-label-inline clearfix view-mode-rss"><h2 class="field-label">Time: </h2><div class="field-items"><div class="field-item even"><span class="date-display-single">Friday, 4 January 2019, <span class="date-display-range"><span class="date-display-start" property="dc:date" datatype="xsd:dateTime" content="2019-01-04T17:15:00+05:30">17:15</span> to <span class="date-display-end" property="dc:date" datatype="xsd:dateTime" content="2019-01-04T18:15:00+05:30">18:15</span></span></span></div></div></section><section class="field field-name-field-venue field-type-taxonomy-term-reference field-label-inline clearfix view-mode-rss clearfix">
<h2 class="field-label">Venue: </h2>
<ul class="field-items">
<li class="field-item even">
<a href="/venue/201-stcs-seminar-room" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">A-201 (STCS Seminar Room)</a> </li>
</ul>
</section>
<section class="field field-name-field-organisers field-type-entityreference field-label-inline clearfix view-mode-rss"><h2 class="field-label">Organisers: </h2><div class="field-items"><div class="field-item even"><a href="/people/vinod-m-prabhakaran">Vinod M. Prabhakaran</a></div></div></section><div class="field field-name-body field-type-text-with-summary field-label-hidden view-mode-rss"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax">
<p><strong>Abstract: </strong>Computing and maintaining shortest paths is a fundamental problem in computer science. We consider two ways of succinctly representing shortest paths in graphs: (i) distance-preserving subgraphs, and (ii) parametric shortest paths. In this talk, we will survey our results on these topics. In particular, we will present the following two results in detail.</p>
<p>(i) Given a graph with $k$ special vertices (called terminals), a distance-preserving subgraph of it is a subgraph which has the same pairwise distances between the terminals as in the original graph. We prove that every interval graph with $k$ terminals has a distance-preserving subgraph with $O(k \log k)$ vertices of degree three or more. We also prove that this bound is tight.</p>
<p>(ii) Given a graph with two special vertices $s$ and $t$, and edge weights that vary linearly with a parameter $\lambda$, the parametric shortest path complexity of the graph is the number of times the shortest $s$-$t$ path changes as $\lambda$ varies from $-\infty$ to $+\infty$. We construct a family of planar graphs $(G_n: n\geq 4)$, where $G_n$ has $n$ vertices, such that the parametric shortest path complexity of $G_n$ is $n^{\Omega(\log n)}$. This refutes a conjecture of Nikolova (2009).</p>
</div>
</div></div></div><section class="field field-name-field-diplay-profile field-type-list-boolean field-label-above view-mode-rss"><h2 class="field-label">Faculty Candidate: </h2><div class="field-items"><div class="field-item even"></div></div></section>Wed, 26 Dec 2018 04:49:50 +0000Supriya Pottipati4096 at https://www.tcs.tifr.res.inCommunication Complexity of $\mathsf{XOR}$ Functions
https://www.tcs.tifr.res.in/events/communication-complexity-mathsfxor-functions
<div class="field field-name-field-event-type field-type-taxonomy-term-reference field-label-hidden view-mode-rss clearfix">
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<a href="/event/phd-synopsis-seminar" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">PhD Synopsis Seminar</a> </li>
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<div class="field field-name-field-members field-type-entityreference field-label-inline clearfix view-mode-rss clearfix">
<div class="field-label">Speaker: </div>
<div class="field-items">
<div class="field-item even"><a href="/people/nikhil-s-mande">Nikhil S Mande</a>, TIFR</div>
</div>
</div>
<section class="field field-name-field-time field-type-datetime field-label-inline clearfix view-mode-rss"><h2 class="field-label">Time: </h2><div class="field-items"><div class="field-item even"><span class="date-display-single">Tuesday, 17 April 2018, <span class="date-display-range"><span class="date-display-start" property="dc:date" datatype="xsd:dateTime" content="2018-04-17T16:00:00+05:30">16:00</span> to <span class="date-display-end" property="dc:date" datatype="xsd:dateTime" content="2018-04-17T17:30:00+05:30">17:30</span></span></span></div></div></section><section class="field field-name-field-venue field-type-taxonomy-term-reference field-label-inline clearfix view-mode-rss clearfix">
<h2 class="field-label">Venue: </h2>
<ul class="field-items">
<li class="field-item even">
<a href="/venue/201-stcs-seminar-room" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">A-201 (STCS Seminar Room)</a> </li>
</ul>
</section>
<section class="field field-name-field-organisers field-type-entityreference field-label-inline clearfix view-mode-rss"><h2 class="field-label">Organisers: </h2><div class="field-items"><div class="field-item even"><a href="/people/vinod-m-prabhakaran">Vinod M. Prabhakaran</a></div></div></section><div class="field field-name-body field-type-text-with-summary field-label-hidden view-mode-rss"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax">
<p>Given a boolean function $f : \{0, 1\}^n \rightarrow \{0, 1\}$ define the function $f \circ \mathsf{XOR}$ on $2n$ bits by $f \circ \mathsf{XOR} (x_1, \dots, x_n, y_1, \dots, y_n) = f(x_1 \oplus y_1, \dots, x_n \oplus y_n)$. Such a function is called an $\mathsf{XOR}$ function. A natural communication game for such a function is as follows. Alice is given $x = (x_1, \dots, x_n)$, Bob is given $y = (y_1, \dots, y_n)$, and they jointly wish to compute $f \circ \mathsf{XOR}(x, y)$. They have unbounded computational power individually and wish to minimize the amount of communication between them on the worst case input.</p>
<p>We study the communication complexity of $\mathsf{XOR}$ functions under various randomized models, and resolve several open questions in the areas of communication complexity, boolean circuit complexity and analysis of boolean functions.</p>
<p>1) We characterize the weakly-unbounded error communication complexity of $\mathsf{XOR}$ functions in terms on a certain approximation theoretic property of the outer function. We use this characterization to reprove several known results. Along the way, we also resolve some open questions in the area of analysis of boolean functions.</p>
<p>2) We prove a strong unbounded error communication complexity lower bound for an easily describable function. We then use this to show a boolean circuit complexity class separation that has been open since the early 90's, and first explicitly posed in 2005. This also resolves a recent open problem in communication complexity by separating two communication complexity classes.<br />
We also prove lower bounds against the class of functions efficiently computable by decision lists of linear threshold functions, and prove unbounded error communication complexity lower bounds for $\mathsf{XOR}$ functions when the outer function is symmetric.</p>
<p>3) Finally, we separate two randomized communication complexity classes in the "number on forehead" model of multiparty communication. This also implies boolean circuit class separations.</p>
</div>
</div></div></div><section class="field field-name-field-diplay-profile field-type-list-boolean field-label-above view-mode-rss"><h2 class="field-label">Faculty Candidate: </h2><div class="field-items"><div class="field-item even"></div></div></section>Tue, 10 Apr 2018 06:30:50 +0000Supriya Pottipati3994 at https://www.tcs.tifr.res.inCommunication Complexity and Characterization Results in Secure Computation
https://www.tcs.tifr.res.in/events/communication-complexity-and-characterization-results-secure-computation
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<li class="field-item even">
<a href="/event/phd-synopsis-seminar" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">PhD Synopsis Seminar</a> </li>
</ul>
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<div class="field field-name-field-members field-type-entityreference field-label-inline clearfix view-mode-rss clearfix">
<div class="field-label">Speaker: </div>
<div class="field-items">
<div class="field-item even"><a href="/people/deepesh-data">Deepesh Data</a>, TIFR</div>
</div>
</div>
<section class="field field-name-field-time field-type-datetime field-label-inline clearfix view-mode-rss"><h2 class="field-label">Time: </h2><div class="field-items"><div class="field-item even"><span class="date-display-single">Monday, 31 July 2017, <span class="date-display-range"><span class="date-display-start" property="dc:date" datatype="xsd:dateTime" content="2017-07-31T16:00:00+05:30">16:00</span> to <span class="date-display-end" property="dc:date" datatype="xsd:dateTime" content="2017-07-31T17:00:00+05:30">17:00</span></span></span></div></div></section><section class="field field-name-field-venue field-type-taxonomy-term-reference field-label-inline clearfix view-mode-rss clearfix">
<h2 class="field-label">Venue: </h2>
<ul class="field-items">
<li class="field-item even">
<a href="/venue/201-stcs-seminar-room" typeof="skos:Concept" property="rdfs:label skos:prefLabel" datatype="">A-201 (STCS Seminar Room)</a> </li>
</ul>
</section>
<section class="field field-name-field-organisers field-type-entityreference field-label-inline clearfix view-mode-rss"><h2 class="field-label">Organisers: </h2><div class="field-items"><div class="field-item even"><a href="/people/kavitha-telikepalli">Kavitha Telikepalli</a></div></div></section><div class="field field-name-body field-type-text-with-summary field-label-hidden view-mode-rss"><div class="field-items"><div class="field-item even" property="content:encoded"><div class="tex2jax">
<p>Information theoretically secure multi-party computation (MPC) has been a central primitive of modern cryptography, in which mutually distrusting parties collaborate to compute a function of their private data without revealing any additional information about their data to the other parties. It is known that information theoretically secure MPC is possible among $n$ parties against the collusion of less than $n/2$ parties in the honest-but-curious model; the threshold is $n/3$ in the malicious model.</p>
<p> Despite the huge success in many frontiers of cryptography, many basic questions in the study of secure MPC have seen a little progress. Two of these questions are the subject of this thesis: communication and randomness complexity of secure MPC; and characterization of which functions are securely computable. We study these questions in two and three party settings against the corruption of a single party in the honest-but-curious model. In the three party setting, we develop new information theoretic tools to obtain tight lower bounds on communication and randomness complexity of secure MPC. We derive lower bounds for both the perfect security case (i.e., zero-error and no leakage of information) and asymptotic security (where the probability of error and information leakage vanish as block-length goes to infinity); and they are shown to be tight for several interesting functions.</p>
<p> In the two party setting, we consider secure computation of randomized functions. When both the parties (Alice and Bob) are required to produce outputs, even the characterization of which <em>randomized</em> functions are securely computable is not known; however, the <em>deterministic</em> counterpart of this problem was resolved by Kushilevitz (FOCS 1989) around three decades ago. We make some progress in this long standing open problem and give a couple of characterizations: for randomized functions that have up to ternary output alphabet, and for randomized functions that are securely computable by up to two-round protocols. The problem becomes easier when only one party is required to produce the output. We study this problem further in four cases: (i) when privacy is required against both the parties; (ii) when privacy is required only against Alice; (iii) when privacy is required only against Bob; and (iv) when there is no privacy requirement. For all the four cases we obtain optimal rate expressions in both perfect and asymptotic security settings.</p>
</div>
</div></div></div><section class="field field-name-field-diplay-profile field-type-list-boolean field-label-above view-mode-rss"><h2 class="field-label">Faculty Candidate: </h2><div class="field-items"><div class="field-item even"></div></div></section>Sat, 22 Jul 2017 06:22:13 +0000John Barretto3777 at https://www.tcs.tifr.res.in