WitnetRandomness Contract

The WitnetRandomness contract, also known as the ยซWitnet Randomness Oracleยป, is the easiest and most convenient way to generate EVM-agnostic and realiable randomness for your smart contracts.

The Witnet Foundation sponsors a pre-deployed instance of WitnetRandomness in practically all the EVM-compatible chains supported by the Witnet oracle.

While the WitnetRandomness contract internally uses an instance of the low-level WitnetRequestRandomness formarly explained, this contract implements also the whole request/resolution asynchronous flow involved in the resolution of a data request in the context of the Witnet side-chain.

Moreover, the same instance can be safely and concurrently used by any number of indepent applications running within the same EVM-chain.

Because of this, you may even have the chance to reuse randomness previously requested by others, at no cost (๐ŸŽ‰), while having the certainty that the acquired randmoness was independently generated by the Witnet side-chain strictly after any given block number.

In a nutshell, by using a WitnetRandomness you just need to:

  1. Eventually, care for requesting and paying for new randomness at any given time: see randomize() payable.

  2. Eventually, fetching a randomness value generated by Witnet after any given block number: see isRandomized(uint256) and getRandomnessAfter(uint256).

As simple as that ;-)

API Reference

Best practices

  • The WitnetRandomness contract is not owned, so anyone is actually allowed to either request new randomness (i.e. randomize()), or get previously solved randomness from storage (i.e. isRandomized(uint _blockNumber), getRandomnessAfter(uint _blockNumber)).

  • Besides, you or your contract will be able to request for new randomness (i.e. randomize() payable), even if other previous randomness requests (either coming from you, or other apps) were still pending to be solved.

  • The WitnetRandomnesscontract is Clonable, which means that you, or your contract, may cheaply create your own cloned copy as a means to gain ownership of the self-contained WitnetRequestRandomness contract. Only the owner of a cloned copy will be allowed to change the witnessing parameters of the low-level Randomness Request.

  • The WitnetRandomnesscontract provides the random(uint32 _range, uint256 _nonce, uint256 _block) and random(uint32 _range, uint256 _nonce, bytes32 _seed) helper functions.

These random(..) functions guarantee that different contracts/apps reading from same randomness request will actually get completely different random sequences of uniformly distributed numbers, within a given range, and doing so while keeping complexity under O(1) (๐ŸŽ‰).

  • Most of all, the WitnetRandomness contract guarantees that the received randomness is the one requested for a given block number, or the subsequent randomness request posted after the given block if there was none posted back then, or if the ones posted after that got reverted for whatever reason at the Witnet side-chain level.

Security concerns

Just call on the isRandomized(uint256) method, passing the block number at which the randomize() payable call got mined, as to check for readiness of the requested randomness.

The RAD bytecode of the self-contained WitnetRequestRandomness instance (accesible via the template() method), will foerever remain immutable, though.

The witnessing parameters part of the self-containedWitnetRequestRandomness instance may eventually turn immutable at the time the WitnetRandomness operator decides to renounce its ownership.

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