Introduction to KCC VRF

KCC VRF (Verifiable Random Function) is a provably fair and verifiable random number generator (RNG) that enables smart contracts to access random values without compromising security or usability. For each request, KCC VRF generates one or more random values and cryptographic proof of how those values were determined. The proof is published and verified on-chain before any consuming applications can use it. This process ensures that results cannot be tampered with or manipulated by any single entity including oracle operators, miners, users, or smart contract developers.
Two methods to request randomness
KCC VRF  offers two methods for requesting randomness:
​Subscription: Create a subscription account and fund its balance with WKCS tokens. Users can then connect multiple consuming contracts to the subscription account. When the consuming contracts request randomness, the transaction costs are calculated after the randomness requests are fulfilled and the subscription balance is deducted accordingly. This method allows you to fund requests for multiple consumer contracts from a single subscription.
​Direct funding: Consuming contracts directly pay with WKCS when they request random values. You must directly fund your consumer contracts and ensure that there are enough WKCS tokens to pay for randomness requests.
Choosing the correct method
Depending on your use case, one method might be more suitable than another. Consider the following characteristics when you choose a method:
Suitable for regular requests
Suitable for infrequent one-off requests
Supports multiple VRF consuming contracts connected to one subscription account
Each VRF consuming contract directly pays for its requests
VRF costs are calculated after requests are fulfilled and then deducted from the subscription balance. 
VRF costs are estimated and charged at request time, which may make it easier to transfer the cost of VRF to the end user. 
Reduced gas overhead and more control over the maximum gas price for requests
Higher gas overhead than the subscription method
More random values returned per single request. See the maximum random values per request for the Subscription supported networks.
Fewer random values returned per single request than the subscription method, due to higher overhead. See the maximum random values per request and gas overhead for the Direct funding supported networks.
You don’t have to estimate costs precisely for each request. Ensure that the subscription account has enough funds.
You must estimate transaction costs carefully for each request to ensure the consuming contract has enough funds to pay for the request.
Requires a subscription account
No subscription account required
VRF costs are billed to your subscription account. 
No refunds for overpayment after requests are completed
Supported networks
The contract addresses and gas price limits are different depending on which method you use to get randomness. You can find the configuration, addresses, and limits for each method on the following pages:
​Subscription Supported networks​
​Direct Funding Supported networks​

Last modified 28d ago

Suitable for regular requests	Suitable for infrequent one-off requests
Supports multiple VRF consuming contracts connected to one subscription account	Each VRF consuming contract directly pays for its requests
VRF costs are calculated after requests are fulfilled and then deducted from the subscription balance.	VRF costs are estimated and charged at request time, which may make it easier to transfer the cost of VRF to the end user.
Reduced gas overhead and more control over the maximum gas price for requests	Higher gas overhead than the subscription method
More random values returned per single request. See the maximum random values per request for the Subscription supported networks.	Fewer random values returned per single request than the subscription method, due to higher overhead. See the maximum random values per request and gas overhead for the Direct funding supported networks.
You don’t have to estimate costs precisely for each request. Ensure that the subscription account has enough funds.	You must estimate transaction costs carefully for each request to ensure the consuming contract has enough funds to pay for the request.
Requires a subscription account	No subscription account required
VRF costs are billed to your subscription account.	No refunds for overpayment after requests are completed