Nucypher Ethereum Contracts

Contract Listing

  • NuCypherToken ERC20 token contract

  • StakingEscrow Holds Ursula’s stake, stores information about Ursula’s activity, and assigns a reward for participating in the NuCypher network. (The Issuer contract is part of the StakingEscrow)

  • PolicyManager Holds a policy’s fee and distributes fee by periods

  • Adjudicator Manages the slashing protocol

  • Upgradeable Base contract for upgrading

  • Dispatcher Proxy to other contracts and provides upgrading of the StakingEscrow, PolicyManager and Adjudicator contracts

  • UserEscrow Locks tokens for predetermined time. Tokens will be unlocked after specified time and all tokens can be used as stake in the StakingEscrow contract

Deployment Procedure

  1. Deploy NuCypherToken with all future supply tokens

  2. Deploy StakingEscrow with a dispatcher targeting it

  3. Deploy PolicyManager with its own dispatcher, also targeting it

  4. Deploy Adjudicator with a dispatcher

  5. Transfer reward tokens to the StakingEscrow contract. These tokens are future mining rewards and initial allocations

  6. Run the initialize() method to initialize the StakingEscrow contract

  7. Set the address of the PolicyManager contract in the StakingEscrow by using the setPolicyManager(address)

  8. Pre-deposit tokens to the StakingEscrow if necessary:

    • Approve the transfer tokens for the StakingEscrow contract using the approve(address, uint) method. The parameters are the address of StakingEscrow and the amount of tokens for a staker or group of stakers;

    • Deposit tokens to the StakingEscrow contract using the preDeposit(address[], uint[], uint[]) method. The parameters are the addresses of the stakers, the amount of tokens for each staker, and the number of periods during which tokens will be locked for each staker

  9. Deploy UserEscrowProxy with UserEscrowLibraryLinker targeting it

  10. Pre-deposit tokens to the UserEscrow and, if necessary:

    • Create new instance of the UserEscrow contract

    • Transfer ownership of the instance of the UserEscrow contract to the user

    • Approve the transfer of tokens for the UserEscrow

    • Deposit tokens by the initialDeposit(uint256, uint256) method

Alice’s Contract Interaction

Alice Authors a Blockchain Policy

Alice uses a network of Ursula stakers to deploy policies. In order to take advantage of the network, Alice chooses stakers and deploys policies with fees for those stakers. Alice can choose stakers by herself (“handpicked”) or by using StakingEscrow.sample(uint256[], uint16) - This is known as (“sampling”). sample parameters are:

  • The array of absolute values

  • Minimum number of periods during which tokens are locked This method will return only active stakers.

In order to place the fee for a policy, Alice calls the method PolicyManager.createPolicy(bytes16, uint16, uint256, address[]), specifying the staker’s addresses, the policy ID (off-chain generation), the policy duration in periods, and the first period’s reward. Payment should be added to the transaction in ETH and the amount is firstReward * stakers.length + rewardRate * periods * stakers.length. The reward rate must be greater than or equal to the minimum reward for each staker in the list. The first period’s reward is not refundable, and can be zero.

Alice Revokes a Blockchain Policy

When Alice wants to revoke a policy, she calls the PolicyManager.revokePolicy(bytes16) or PolicyManager.revokeArrangement(bytes16, address). Execution of these methods results in Alice recovering all fees for future periods, and also for periods when the stakers were inactive. Alice can refund ETH for any inactive periods without revoking the policy by using the method PolicyManager.refund(bytes16) or PolicyManager.refund(bytes16, address).

Ursula’s Contract Interaction

Ursula Locks Tokens

In order to become a participant of the network, a staker stakes tokens in the StakingEscrow contract. The staker allows the (staking) contract to perform a transaction using the NuCypherToken.approve(address, uint256) method (ERC20 contracts allow access delegation to another address).

After that, the staker transfers some quantity of tokens (StakingEscrow.deposit(uint256, uint16)), locking them at the same time. Alternately the NucypherToken.approveAndCall(address, uint256, bytes) method can be used. The parameters are:

  • The address of the StakingEscrow contract

  • The amount of staked tokens

  • The periods for locking (which are serialized into an array of bytes)

When staking tokens, the staker sets the number of periods the tokens will be locked, which must be no less than some minimal locking time (30 periods). In order to unlock tokens, the staker must be active during the time of locking (and confirm activity each period). Each stake is represented by the amount of tokens locked, and the stake’s duration in periods. The staker can add a new stake using StakingEscrow.deposit(uint256, uint16) or StakingEscrow.lock(uint256, uint16) methods. The staker can split stake into two parts: one with the same duration and another with an extended duration. For this purpose, the StakingEscrow.divideStake(uint256, uint256, uint16) method is used. The first parameter is used to identify the stake to divide and the last two for the extended part of the stake. When calculating locked tokens using the StakingEscrow.getLockedTokens(address, uint16) method, all stakes that are active during the specified period are summed.

Ursula Confirms Activity

In order to confirm activity every period, stakers call StakingEscrow.confirmActivity() wherein activities for the next period are registered. The staker gets a reward for every confirmed period.

Ursula Generates Staking Rewards

After the period of activity has passed, the staker may call StakingEscrow.mint() method which computes and transfers tokens to the staker’s account. Also note that calls to StakingEscrow.confirmActivity() are included the StakingEscrow.mint() method.

The reward value depends on the fraction of locked tokens for the period (only those who confirmed activity are accounted for). Also, the reward depends on the number of periods during which the tokens will be locked: if the tokens will be locked for half a year, the coefficient is 1.5. The minimum coefficient is 1 (when tokens will get unlocked in the next period), and the maximum is 2 (when the time is 1 year or more). The reward is calculated separately for each stake that is active during the mining period and all rewards are summed up. The order of calling StakingEscrow.mint() by stakers (e.g. who calls first, second etc) doesn’t matter. Stakers can claim their rewards by using the StakingEscrow.withdraw(uint256) method. Only non-locked tokens can be withdrawn.

Ursula Generates Policy Rewards

Also the staker gets rewards for policies deployed. Computation of a policy reward happens every time StakingEscrow.mint() is called by the PolicyManager.updateReward(address, uint16) method. In order to take the reward, the staker needs to call method withdraw() of the contract PolicyManager. The staker can set a minimum reward rate for a policy. For that, the staker should call the PolicyManager.setMinRewardRate(uint256) method.

NuCypher Partner Ursula Staking

Some users will have locked but not staked tokens. In that case, an instance of the UserEscrow contract will hold their tokens (method UserEscrow.initialDeposit(uint256, uint256)). All tokens will be unlocked after a specified time and the user can retrieve them using the UserEscrow.withdraw(uint256) method. When the user wants to become a staker - he uses the UserEscrow contract as a proxy for the StakingEscrow and PolicyManager contracts.

Ursula’s Worker

The staker must specify a worker who will confirm the activity and sign on behalf of this staker by calling the StakingEscrow.setWorker(address) method. Changing a worker is allowed no more than 1 time in StakingEscrow.minWorkerPeriods(). Only the worker can confirm activity.