1. Duke University and NBER
Innovation and Cryptoventures
Logger
Campbell R. Harvey*
Duke University and NBER
*Prepared with the help of Joey Santoro

3. Overview You are interacting with Ethereum (Testnet)
Manually check in each day via tx
Contract knows who you are
Campbell R. Harvey 2019

4. Overview Data are stored variables with important info
Public functions can either update data or view data
Owner functions are only for admin use
Campbell R. Harvey 2019

5. Logger Data owner_ : the address who can access owned functions
Currently set to Joey’s address: “0x25Cb ”
addressToName : a map of your addresses to names
wasInClass : a list of 12 attendance sheets, one/class
Live : True if contract is open (during class) and False if not
Class : number representing which class day it is
Campbell R. Harvey 2019

6. Logger Data studentAddresses : list of addresses
registered : checklist for who has registered
Notice no owner_ below: it is inherited other contract
Campbell R. Harvey 2019

7. Link to Website
Contract is called every time you push “Register” or “Check In”
Web data is formatted into Ethereum transaction by MetaMask
Website reflects contract data and updates
Campbell R. Harvey 2019

8. Logger Public Functions : Register
Input a string called “name”
Student is the message sender
If not registered, add student and register
Update name
Campbell R. Harvey 2019

9. Logger Public Functions : CheckIn
Logger must be “live”
Student must be registered
Set wasInClass for today to “true”
Campbell R. Harvey 2019

10. Logger View Functions Can view all data publicly
Chart uses getAttendanceDay function
Campbell R. Harvey 2019

11. Logger Owner Functions
Only the owner can:
Change the day
Open/close the contract
Check in another student manually
Contract enforces this via “onlyOwner”
Requires message sender to equal owner_
Campbell R. Harvey 2019

12. Etherscan.io Block explorer Nothing is hidden
Shows transactions, accounts, data, times, etc.
Nothing is hidden
Trying to game the system works against you...
Campbell R. Harvey 2019

13. Etherscan.io Top box: people checking in on Friday Middle box: Joey
Bottom box...
Campbell R. Harvey 2019

14. Sample Check In Success Friday - 12:30pm Call to CheckIn
Data = hash of function name
0xe8e...
Campbell R. Harvey 2019

15. Joey’s Calls Open contract Change day (to day 4) 0xf18… Func: 0x827…
Input:
Campbell R. Harvey 2019

16. Epic Fail Check in attempt 7:30 pm on Thurs We know who you are
0xe8e...
Failed
7:30 pm on Thurs
We know who you are
Campbell R. Harvey 2019

17. Takeaways Smart contracts are robust databases
Complex financial and business logic
Can’t break the rules
All attempts are recorded
Campbell R. Harvey 2019

18. Development plan Mobile app development over the summer
Harvest GPS information
Proof of Attendance (PoAT) or Proof of Presence (PoP)
Potentially, a more general idea. Store offers you $10 if you go to the store and spend at least five minutes in the store.
Campbell R. Harvey 2019