报告题目: Traitor Deterring Schemes: Using Bitcoin as Collateral for Digital Contents

报告人：Qiang Tang（Assistant Professor）

主持人：曹珍富（教授）

报告时间：7月8日（周五）10:00-12:00

报告地点：中北校区数学馆201室

报告摘要:

We put forth a new cryptographic primitive called a {/em Traitor Deterring Scheme} (TDS). A TDS is a multi-recipient public-key encryption scheme where an authority issues decryption keys to a set of users. The distinguishing feature of a TDS is that secret-keys are issued only after the users provide some private information as a form of {/em collateral}. The traitor deterring property ensures that if a malicious coalition of users (aka ``traitors'') produces an unauthorized (aka ``pirate'') decryption device, any recipient of the device will be able to recover at least one of the traitors' collaterals with only black-box access to the device. On the other hand, honest users' collaterals are guaranteed to remain hidden. In this fashion a TDS de-incentivizes malicious behavior among users.

We will present how to model, construct and analyze TDS's based on various cryptographic assumptions and we will show how bitcoin can be used as collateral for real world deployment of TDS's for the distribution of digital content. Along the way, we will present cryptographic building blocks that may be of independent interest, namely fuzzy lockers, and comparison predicate encryption schemes for exponentially large domains.

We will also compare TDS with previous primitives specifically traitor tracing schemes (TTS) introduced by Chor et al. /cite{CFN}

and digital signets for self enforcement introduced by Dwork et al. /cite{DLN96}. A TDS constitutes a strict strengthening of a TTS 

and, when modeled in what we call the ``known ciphertext model'', it is a reformulation of digital signets in the public-key, black-box secure setting. In digital signets the adversary attempts to transmit a pirate copy at a favorable ``space rate'', i.e., without having to send the whole plaintext (and without revealing the traitor collaterals). It is an open question from /cite{DLN96} to construct $o(1)$ space rate schemes under a falsifiable assumption. With our TDS constructions we resolve this open question showing feasibility for space rates $O(/log /lambda / /lambda)$ and infeasibility for space rates $/Omega(/log^2/lambda/ /lambda)$.

报告人简介:

Dr Qiang Tang is currently a postdoctoral researcher at Cornell University, he is also affiliated with the Initiative of cryptocurrency and contract (IC3). He will be joining New Jersey Institute of Technology (NJIT) as an assistant professor this fall. Qiang obtained his Ph.D. from the University of Connecticut on August 2015, under the supervision of Aggelos Kiayias and Alexander Russell. He was awarded the Taylor Booth Graduate Scholarship and several pre-doctoral fellowships from UCONN. He worked as a research intern at NTT research lab, Tokyo with Tatsuaki Okamoto, and the University of Wisconsin, Madison with Thomas Ristenpart, and he was also a visiting researcher at the University of Athens, Greece. His research interests lie in the combination of accountability, post-Snowden cryptography, and crypto-currency.