Introduction to Fin Tech Dr Meng Han A

Introduction to Fin. Tech Dr. Meng Han

A Change of Perspective • • Blockchains traditionally considered a “cryptographic goal” Way to decentralized digital currency Blockchains as a “cryptographic primitive” Way to bypass impossibility results Thanks for: Overcoming Cryptographic Impossibility Results using Blockchains • Rishab Goyal Vipul Goyal

Results • Non-Interactive Zero Knowledge (NIZK) w/o CRS • One-Time Programs (OTPs) w/o hardware assumptions • Pay-Per-Use Services • General Framework for using Blockchains

NIZKs [Goldwasser. Micali. Rackoff 89, Goldreich. Oren 94] Common Reference String I know w such that (x, w) RL Statement x ϵ L e g led w r Ze o- o Kn I don’t want to reveal w Generated by Trusted Party Using Blockchains Sou ndn Statement must be true ess

NIZKs [Goldwasser. Micali. Rackoff 89, Goldreich. Oren 94] • Impossible in the standard model • Constructed in ROM and CRS • Our Result • NIZKs from NIWIs using blockchain

One-Time Programs [Goldwasser. Kalai. Rothblum 08] • Can only be executed on single input • Input chosen at run-time x x y f f(x) + x f � + f

OTPs: Prior Work f One-Time Compiler f • Prior constructions based on “tamper-proof hardware tokens” • Tokens useless after single execution • Our Result • OTPs from extractable-WE using blockchain

Outline • Part I: Blockchain Review • Part II: Framework • Part III: Applications

Part I: Blockchain 101

What are Blockchains? ……… …… …… Distributed Consensus …… …… ……

What are Blockchains?

What are Blockchains? …… …… “Header” to connect to previous block “Records”

Applications: Cryptocurrencies • Decentralized, no trusted server Central Trusted Authority Public Ledger

Applications: Cryptocurrencies “Stake” “A transfers 2 coins to B. ” …… “Records” SKA

How to Generate New Blocks? • Block generation is like election/ puzzle-solving race • Different ideologies • Proof-Of-Work (POW) • Proof-Of-Stake (POS) • … Solve moderately hard “puzzles”

How to Generate New Blocks? • Block generation is like election/ puzzle-solving race • Different ideologies • Proof-Of-Work (POW) • Proof-Of-Stake (POS) • …

Part II: Our Abstractions and Definitions

Existing Properties [Garay. Kiayias. Leonardos 15, Pass. Seeman. Shelat 16] • …… ……

Existing Properties [Garay. Kiayias. Leonardos 15, Pass. Seeman. Shelat 16] • New POS Specific Abstractions

Defining Stake Fraction • Measure of combined difficulty of POS puzzles solved …… Mined by A Mined by C Mined by A Mined by B Proved 10% stake Proved 5% stake Proved 10% stake Proved 15% stake

Defining Stake Fraction • Measure of combined difficulty of POS puzzles solved …… Mined by A Mined by C Mined by A Mined by B Proved 10% stake Proved 5% stake Proved 10% stake Proved 15% stake Stake Fraction = 30%

• Honest chain of blocks can be distinguished from adversarial fork ……

Connecting to Existing Notions With suitable parameters And minimal assumptions

25 http: //ksuweb. kennesaw. edu/~mhan 9/