2

•  ENGG5383AppliedCryptography– Fall2018– Research-oriented– Assumenopriorbackground

•  CSCI5590AdvancesinBlockchain– Spring2019– co-teachwithEricLoofCSE– Lessresearch-oriented

3

•  Yourdataisanywherebutnotinyourcontrol•  Securitybreachesarerecurrent– Weakestlink:hardware,software,technicians,…

•  Youmaytrustthescienceofcryptography

4

•  Storage/bandwidthofyourdeviceislimited.•  Youwanttodownloadencryptedfilesmarkedwiththekeyword“urgent”fromtheserver.

•  Youdon’twanttheservertoknowwhatarethekeywordsassociatedwitheachfile.

5

= Enc( )

= “Urgent! blah blah …”

Keyword( ) = [“urgent”]

= Enc(“Urgent!…”)

Encrypted Database

search token for “urgent”

6

•  ElectronicPayments/Cash– Doyouwanttoleakyourspendingpattern?–  Ifyouareanonymous,willyoudo“badthings”?– Merchants&Bankalsohavetheirconcerns•  Double-spending,moneylaundry,etc.

•  Aclassicalresearchtopicincryptography

7

•  Along-livedandactiveresearchtopicinacademia–  Near4000citationsto-date

•  Butwasnotsosuccessfulinreality/industry–  DavidChaumestablishedthecompanyDigiCash–  Only~5000customerssignedup–  DigiCashwentbankruptin1998

•  Nosuccessfuldeploymentofsuchsystems•  UntilBitcoin’sbirthin2009

8

•  Industry:•  Academic:

9

•  Enhancingsecurity/privacy

–  Zerocoin,Zerocash,Monero(2.0),…•  Applicationsofblockchaintechnologies

–  Smart-contract,digitalidentitymanagement,e-voting,...•  Increasingthroughput

–  Bitcoin:~10transactions/s;Ethereum:~15transactions/s–  Visa:>1500transactions/s;Paypal:~200transactions/s

•  Consensusmechanismsdesign–  ProofofWork(PoW),ProofofStake(PoS),hybridconsensus,…

•  Attacks–  Selfishmining,stubbornmining,doublespendingattack

10

11

12

•  Balancingbetweensecurityandfunctionality•  Diversespectrumofresearchflavor– Crypto/TheoreticCS– Security/Privacy– AmixofSystemandTheory

•  http://crypto.ie.cuhk.edu.hk•  sherman@ie.cuhk.edu.hk