0x3bfc / veedo

VeeDo

VeeDo is a STARK-based Verifiable Delay Function (VDF) service. It is used for periodically generating a secure random number every 820 blocks (~ 3 hours). The randomness is generated from a block hash according to what is explained in Computing the Randomness section below. A proof attesting to the validity of the computation is generated and sent to the STARK Verifier for a verification process (see the Verifier contract). The Beacon contract registers the new randomness if the Verifier accepts the corresponding proof.

API

The Beacon contract serves as the interface and has the following API:

1. getRandomness(uint256 blockNumber)
2. getLatestRandomness().

For full documentation of its API check the Beacon contract.

Computing the Randomness

Denote the delay function by f. The randomness is computed as follows:

1. Given a block, compute b:=keccak256(block_hash, ‘veedo’).
2. Compute the delay function seed s=<x,y> by taking the lowest 250 bits of b and split them to a pair of 125-bit elements each:
   • x: = b & ((1<<125)-1)
   • y: = b >> 125 & ((1<<125)-1)
3. Compute f on s=<x,y> for n iterations.
4. Denote f(s,n):=<x_out, y_out>. Randomness:= keccak256(x_out, y_out, ‘veedo’).

Proof Statement

The proof is for the following statement: "<x_out, y_out> is the result of calculating f on s=<x,y> for n iterations".

Deployed Contract

Verifier contract

Beacon contract