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SUMMARY:Bitcoin as a source of verifiable public randomness - Joseph Bonne
 au\, Center For Information Technology Policy\, Princeton
DTSTART:20140930T130000Z
DTEND:20140930T140000Z
UID:TALK53850@talks.cam.ac.uk
CONTACT:Laurent Simon
DESCRIPTION:*Abstract:*\nMany security protocols can be strengthened by a 
 public randomness beacon: a source of randomness which can be sampled by a
 nybody after time t\, but is strongly unpredictable to anybody prior to ti
 me t. Applications include public lotteries\, election auditing\, and mult
 iple cryptographic protocols such as cut-and-choose or fair contract signi
 ng. Until recently\, all proposals for instantiating a beacon either rely 
 on a trusted third party (such as the NIST beacon or random.org) or have d
 ifficult-to-evaluate security properties (such as hashing stock market dat
 a). In this talk we introduce a new construction for building a beacon bas
 ed on Bitcoin's block chain. This beacon outputs 64 bits of min-entropy ev
 ery 10 minutes on average and we can prove strong financial lower bounds o
 n the cost of manipulating the output which are at least in the tens of th
 ousands of dollars. We discuss constructions for building a manipulation-r
 esistant lottery\, a new security construction\, on top of this primitive 
 which can make attacks even more expensive. Finally\, we discuss a number 
 of interesting smart contracts that can be efficiently implemented by exte
 nding Bitcoin script to enable sampling the beacon output\, including secu
 re multi-party lotteries and self-enforcing non-interactive cut and choose
 .\n\n*Bio:* \nJoseph Bonneau is a Postdoctoral Research Fellow at the Cent
 er for Information Technology Policy\, Princeton. His research interests i
 nclude passwords and web authentication\, Bitcoin and cryptocurrencies\, H
 TTPS\, and secure messaging software. He received a PhD from the Universit
 y of Cambridge under the supervision of Ross Anderson and an MS from Stanf
 ord under the supervision of Dan Boneh. He has worked at Google\, Yahoo\, 
 and Cryptography Research Inc.
LOCATION:Lecture Theatre 2\, Computer Laboratory\, William Gates Building
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