Secure and Practical lottery protocol Sep. 13, C&IS lab. Ham Woo Seok ICE 615 Network Security Term project Progressive Report

by Charlie Ham Lottery -2- Contents 1.Overview 2.Threats 3.Requirement 4.Pervious Work – KMHN00,GS98 5.Proposed scheme 6.Further Works 7.Reference

by Charlie Ham Lottery Overview  Sports TOTO  Nationwide issue of tickets was launched Oct. 6  England (Football Pools,1923), France (Loto Foot), Italia (TotoCalcio, TotoGoal), Japan(TOTO) etc. TargetSoccer (K-league) PublisherSeoul Olympic Sports Promotion Foundation(SOSPF) ConsigneeTigerpools Korea Game typeResult-based (1X2) Rate1,000 won per an unit (maximum 96 units) AvailableUp to 10 minutes before game RestrictionLess then 100,000 won a person Over 19 years old Annual IssueLess than 90 times Prize50% of the amount of sold tickets If no winner, winning pool is rolled over to the next lottery Current operationFill out the ticket  present ticket with money to vender  receive a receipt

by Charlie Ham Lottery Threats  Ticket Information manipulation  Altering, Insertion, Deletion  Promoter’s misbehaviors  Wrong winning computation, No payment of prize, etc  Collusion of lottery components  User, Lottery organizer, Financial facility, Vendor, Audit authorities etc.  Phantom vendors  Receive claims and disappear  Denial of service  Hindrance of normal operation, penalization of server, etc  Disputes  Winner arguments, refund etc

by Charlie Ham Lottery Requirement  Basic requirement  Reduction of Computational complexity & communication data  Security requirement  R1: Privacy Prize-winner’s privacy should be maintained  R2: Fairness Every ticket has the same probability to win  R3: Publicly verifiability Valid winnings could be verified publicly  R4: Reliability Anyone can detect injustice of lottery components  R5: Integrity Lottery ticket cannot tampered  R6: Timeliness A lottery should be terminated in the pre-defined period

by Charlie Ham Lottery Previous Work – KMHN00  K.Kobayashi, H.Morita, M.Hakuta, T.Nakanowatari, IEICE 2000 Bit commitment & Hash function  Soccer lottery protocol Based on Bit commitment & Hash function  Notation  h: hash function  h*: partial information of hash value  TLP: Target Lottery Pattern (=mark sheet)  PID: Personal Identification information  SID: Shop Identification  n: total ticket number sold by a shop  SLI: Concatenation of SID, Lottery number, n)  || : concatenation  Sig: Digital signature  $M: Electronic money

by Charlie Ham Lottery -7-  Lottery Protocol 4. Previous Work – KMHN00 User Promoter Shop SIDh1h2TLP User Shop Soccer Lottery Protocol Payment Protocol (Off-line)

by Charlie Ham Lottery Previous Work – KMHN00  Details  Purchase protocol 1) User computes hash value h1 with the concatenation of hashed PID and TLP –Hashed PID: If original PID used, an malicious insider in bank can impersonate prize winners. Also, PID includes a random number to hide PID itself. –TLP: it is generated by User according to specific rules 2) User sends TLP, h1, and fee (electronic money) for her betting 3) User receives SID as a receipt and Shop transfer TLP, h1, $M and SID as well 4) Promoter yields h2 using SID and h1 and store TLP, h2, h1, SID  Inquiry protocol (To verify her betting information is registered) 5) User calculates h2 –h2: protect information difference between Promotor & Shop 6) User sends TLP and partial value of h2 (=h2*) to Promoter 7) Promoter searches and extracts matching values with TLP & partial hash value from database and send them to User  After closing (To detect the promoter’s injustice to update the database illegally) 8) Promoter notifies Shop the number of lottery tickets which are from the Shop 9) Shop confirms the number, if right, she generates signature with SID, lottery number and n. And Promoter generates digital signature on all TLPs and h2s  Payment protocol (Off-line operation) 1) Winner sends her hash value of PID 2) She visits the Bank(financial facility) and presents her real ID in person 3) If correct, Bank delivers a prize to her

by Charlie Ham Lottery Previous Work – KMHN00  Problems  Prize-payment by off-line In case of small prize, User feel inconvenience  PID can not be secret information Even though using a random number with original PID, assumed that there are a number of winners, we can get more probability of hash collision  Promoter can find possible partial combination of summation of TLP and h2. she can alter some information which does not match to one from shop after closing the period  Collusion of Promoter and Shop might be occurred to get manipulate total lottery number and information

by Charlie Ham Lottery Previous Work – GS98  David M. Goldschlag, Stuart G. Stubblebine, IFCA 98 delaying function  Drawing number type lottery based on delaying function  Delaying function Function F is moderately hard to compute given a minimum operation time P, and probability that function is computable is arbitrarily small F preserves the information of its inputs. No information leakage e.g) large number of rounds of DES in OFB mode  Notation  L, C : Lottery server, Client respectively  : Keyed one way hash function  : Certification of client C  Seq : Sequence number of lottery ticket  Time: Time stamp  Seed: betting information  P : critical purchase period  L : the total number of sold tickets

by Charlie Ham Lottery -11-  Phases  Registration To make A certain collusion which can control lottery impossible, identification is needed Mapping between client and client agent by certification For anonymous, use bind certificate or lottery service own certificate  Purchase Sequence number: to supervise server’s injustice(double issue, non-registration, etc) by audit query Time Stamp: To verify that Critical purchase period and time is correct and registration was processed within the time  Critical Purchase period It is published before a lottery game Delaying function cannot yield result within this period  Winning Entry Calculation 4. Previous Work – GS98 Client Server All seed values within P Winning Number

by Charlie Ham Lottery Previous Work – GS98  Problems  Only applicable to simple lottery such as number based one  Winning verification time is too long Needed the same time as total game period  Insider in server can forge or alter betting information  Attacking method computationally, information-theoretically on current cryptosystem is rapidly improving

by Charlie Ham Lottery Proposed scheme (tentative)  Notation

by Charlie Ham Lottery Proposed scheme (tentative) U U LO B B MHUHU SS 2

by Charlie Ham Lottery Proposed scheme (tentative)  Assumption  Lottery ticket is generated by Users themselves along with pre-defined rules  Lottery Organizer allows only allied Banks  Operation period is chosen considering transaction time in every components  Some details  Additional Information is depend on Bank’s requirement with which Bank can identify User  Payment is only paid when H U & Coupon are harmonized with stored data  Winning prize is given the account comes from secret sharing computation  Properties  User can trace all processes  Every process is handled in on-line  Amount of Communication data is low  It doesn’t need additional inquiry protocol User can naturally check through his bank note  Requirement R1 is strongly guaranteed  The other requirements are efficiently satisfied

by Charlie Ham Lottery Further Work  More communication data & computational complexity reduction  How to prevent Integrity of Message during transferring  Public key cryptosystem is necessary?  How to detect the total sold ticket number cheating by LO  Secret sharing is needed? Other methods?  Comparison with previous scheme

by Charlie Ham Lottery Reference  Tigerpools Korea,  Korea online lottery system co.ltd.,  K.Kobayashi, H.Morita, M.Hakuta, and T.Nakanowatari, An Electronic Soccer Lottery System that Uses Bit Commitment, IEICE00, Vol.E83-D, pp ,2000.  D.M.goldschlag, S.G.Stubblebine, Publicly Verifiable Lotteries: Applications of Delaying Functions, Proc.of Financial Cryptography 98, LNCS 1465, pp ,  Ross Anderson, How to cheat at the lottery, Proc. of Computer Security Applications Conference,  Ronal L.Rivest, Electronic Lottery Tickets as Micropayments, Proc.of Financial Cryptography 97, LNCS 1318, pp ,  A.Shamir, How to share a secret, CACM 22, pp , 1979.