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

  • WorkLock Manages token distribution

  • Upgradeable Base contract for upgrading

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

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

Deployment Procedure

This section provides a step-by-step guide of how NuCypher contracts are deployed. For a guide of how to deploy these contracts automatically, see the Deployment guide.

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

  5. Deploy Adjudicator with a dispatcher

  6. Set the address of the Adjudicator contract in the StakingEscrow by using the setAdjudicator(address)

  7. Deploy StakingInterface with StakingInterfaceRouter targeting it

  8. Deploy WorkLock contract

  9. Set the address of the WorkLock contract in the StakingEscrow by using the setWorkLock(address)

  10. Approve tokens transfer to the StakingEscrow contract. These tokens are future staking rewards

  11. Run the initialize(uint256) method to initialize the StakingEscrow contract

  12. Approve tokens transfer for distribution to the WorkLock contract and call tokenDeposit(uint256) method

  13. Pre-deposit tokens to the PreallocationEscrow:

    • Create new instance of the PreallocationEscrow contract

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

    • Approve the transfer of tokens for the PreallocationEscrow

    • 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 select from the result of StakingEscrow.getActiveStakers(uint16, uint256, uint256) method - This is known as (“sampling”). getActiveStakers parameters are:

  • Minimum number of periods during which tokens are locked

  • Start index in stakers array

  • Maximum number of stakers This method will return only active stakers.

In order to place the fee for a policy, Alice calls the method PolicyManager.createPolicy(bytes16, address, uint64, address[]), specifying the policy ID (off-chain generation), the policy owner (could be zero address), the end timestamp of the policy and the stakers’ addresses. Payment should be added to the transaction in ETH and the amount is rewardRate * periods * stakers.length, where periods is endTimestampPeriod - currentPeriod + 1. The reward rate must be greater than or equal to the minimum reward for each staker in the list.

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). If Alice can’t execute an on-chain transaction or wants to share the ability to revoke, then she can sign revocation parameters. Anyone who has this signature will be able to revoke policy using PolicyManager.revoke(bytes16, address, bytes)

Staker’s Contract Interaction

Staker 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.

The Staker Bonds to a Worker (“Ursula”)

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 once within StakingEscrow.minWorkerPeriods(). Only the worker can confirm activity.

Ursula Confirms Activity

In order to confirm activity every period, workers 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 PreallocationEscrow contract will hold their tokens (method PreallocationEscrow.initialDeposit(uint256, uint256)). All tokens will be unlocked after a specified time and the user can retrieve them using the PreallocationEscrow.withdrawTokens(uint256) method. When the user wants to become a staker - they use the PreallocationEscrow contract as a proxy for the StakingEscrow and PolicyManager contracts.

Contracts Versioning

Upgradeable contracts, such as Adjudicator, StakingEscrow, PolicyManager and StakingInterface, have their version specified in contract doc inside @dev.
Version format is |vi.j.k|, where i - major version, j - minor version, k - patch, for example |v1.2.3|:

  • Different major versions mean different forks and they are not upgradeable

  • Minor versions relate to any signatures or state changes inside contract, contracts are upgradeable between minor versions, but have different ABI and follows different agent layers

  • Patches involve changes inside function(s) with signature(s) untouched. All patches with a common minor version can be upgraded from one to another without other changes