erc20-demurrage-token/README.md

RedistributedDemurrageToken

Use Case

• Network / Basic Income Token
  • 100 Sarafu is distributed to anyone in Kenya after user validation by the owner of a faucet which mints new Sarafu.
    • Validated users are those that validate their phone number in Kenya.
  • A Sarafu holding tax aka (demurrage) of 0.000050105908373373% is charged from users per minute - such that over 1 month to total tax would be 2%.
  • After 1 week the total amount tax is distributed evenly out to active users.
    • any single transaction by a user within that week is considered active (heartbeat)
  • This is meant to result in a disincentivization to hold (hodl) the Sarafu token and increase its usage as a medium of exchange rather than a store of value.
  • This token can be added to liquidity pools with other ERC20 tokens and or Community Inclusion Currencies (CICs) - and thereby act as a central network token and connect various tokens and CICs together.
  • Example
    • With a demurrage of 2% (net per month) and a reward period of 1 month - If there are 10 users all with balances of 1000 Sarafu and only 2 of them trade that month (assume they trade back and forth with no net balance change).
    • Then the resulting balances after one tax period of those two trading would be 1080 Sarafu while the remaining non-active users would be 980 Sarafu. If this behaviour continued in the next tax period, with the same two users only trading (with no net balance changes), they would have 1158.39999968 Sarafu and those users that are not trading would have their balances further reduced to 960.40 Sarafu. If this continued on ~forever those two active trading users would have the entire token supply and the non-trading users would eventually reach a zero balance.
    • this example calculation for 3 tax periods can be found here: https://gitlab.com/grassrootseconomics/cic-docs/-/blob/master/demurrage-redist-sarafu.ods

Variables

• Inputs to Constructor (Set only once during contract deployment can't be changed )
  • Demurrage aka Decay amount: A percentage of token supply that will be charged once per minute and evenly redistributed to active users every Demurrage Period (minutes)
  • Demurrage Period (minutes)- aka period: The number of minutes over which a user must be active to receive tax-redistibution.
  • Inflated Balance: The inflated balance of each user is stored for bookkeeping.
  • Number of Decimals: Resolution on token (TODO) (Default 6)
  • Minimum Activity Volume: (TODO) the minimum transaction amount to be considered active
  • Sink Token Address: Rounding errors and if no one trades the tax goes to this address

Ownership

• Contract creator is owner
• Ownership can be transferred (also to ownership void contract "no more changes can be made")

Mint

• Owner can add minters
  • A faucet contract would be a minter and choose the amount of tokens to mint and distribute to new validated users.
  • The interface says the amount and is at the caller's discretion per contract call. validation is outside of this contract.
• Minters can mint any amount

Demurrage

• Holding Tax (demurrage) is applied when a mint or transfer; (it can also be triggered explicitly)
  • Note that the token supply stays the same but a virtual balance output is created.
  • Updates demurrageModifier which represents the accumulated tax value and is an exponential decay step (of size demurrage) for each minute that has passed.
    • demurrageModifier = (1-demurrage)^(minute_passed)
      • e.g. a demurrage of 2% after the 1st minute would be give a demurrageModifier = (1-0.02)^1 = 0.98.
      • e.g. a demurrage after the 2nd minute would be give a demurrageModifier = (1-0.02)^2 = 0.9604.
• All client-facing values (balance output , transfer inputs) are adjusted with demurrageModifier.
  • e.g. _balance output_ = user_balance - user_balance * demurrageModifier
• Edge case: approve call, which may be called on either side of a period.

Redistribution

• One redistribution entry is added to storage for each period;
  • When mint is triggered, the new totalsupply is stored to the entry
  • When transfer is triggered, and the account did not yet participate in the period, the entry's participant count is incremented.
• Account must have "participated" in a period to be redistribution beneficiary.
• Redistribution is applied when an account triggers a transfer for the first time in a new period;
  • Check if user has participated in period. (active user heartbeat)
  • Each active user balance in the period is increased by (total supply at end of period * demurrageModifier ) / number_of_active_participants via minting
  • Participation field is zeroed out for that user.
• Fractions must be rounded down (TODO)
  • Remainder is "dust" and should be sent to a dedicated "sink" token address (TODO)
  • If no one is active all taxes go to the same sink address

Data structures

• One word per account:
  • bits 000-159: value
  • bits 160-255: period
  • (we have more room here in case we want to cram something else in)
• One word per redistribution period:
  • bits 000-055: period
  • bits 056-215: supply
  • bits 216-253: participant count
  • bits 254: Set if individual redistribution amounts are fractions (TODO)
  • bits 255: Set if "dust" has been transferred to sink (TODO)

QA

• Basic python tests in place
• How to determine and generate test vectors, and how to adapt them to scripts.
• Audit sources?