A Trust Framework For Blockchain Apps Design

Level of Trust. For each business case, there is an “intrinsic” level of trust between the players and a “desirable” level of trust (needed for the transaction to occur). “On-chain activity” bridges the two levels of trust.

On-chain activity. Blockchain can be used in various ways, but two of them correspond to 99% of existing use cases:
— “Currency ownership”: the user has the custody and has control over the “digital money” owned. “Store-of-value” and “payments” are different applications leveraged by currency ownership.
— “State notarisation”: the certification that a certain state occurred in a specific moment of time.

Table 1 : Existing “level of trust” between players (rent-a-car example)
Table 2 — “desirable level of trust”; in green changes related with payments and in blue related with information registry.
Currency ownsership scenarios.
State notorisation scenarios.
Relation of Levels of Trust and On-chain activity.

Approach 1: Proper use of blockchain
Driver pays upfront the renting fee to the website using Ether. The payment is done through a smart contract that: 1) stores the money until the rent is finished 2) stores a security deposit to support possible damages 3) registers in the blockchain all the information (date, car model, driver, …) about the reservation 4) when the renting is over, implements the revenue share between the website and the rent-a-car and returns the security deposit to the driver 5) registers a record that the car has been successfully returned.

Table 3 — “Intrinsic” trust level Vs “desirable” level

Approach 2: Adapted use of the blockchain

Driver pays upfront the renting fee / security deposit to the website using Ether. The payment is done through a smart contract that: 1) stores the renting fee / security deposit 2) registers in the blockchain a digest of all the reservation information (date, car model, driver, …) and sends an email with the information, plus the block of the blockchain where the digest is stored 4) when the renting is over, returns the pledge to the driver 5) once a month, the revenue share to be paid to the website and rent-a-car is distributed 6) once a hour, registers a “root hash” of the “merkle tree” of all cars returned and send email information to the drivers with the block of the blockchain where the digest is stored.

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