VRF-WASM

A WASM-compatible Verifiable Random Function (VRF) implementation based on FastCrypto.

FastCrypto has C dependencies (secp256k1-sys, blst) that prevent WASM compilation even when compiling with wasm feature flags. This library extracts only the VRF module which uses pure Rust dependencies.

ECVRF implementation following draft-irtf-cfrg-vrf-15.

Installation

To use vrf-wasm, you must explicitly enable a feature flag for your target environment.

Browser/Web Applications

[dependencies]
vrf-wasm = { version = "0.9.1", features = ["browser"] }

NEAR Smart Contracts

[dependencies]
vrf-wasm = { version = "0.9.1", default-features = false, features = ["near"] }

If no feature is selected, you will get a compile-time error with instructions.

Usage

Basic VRF Operations

use vrf_wasm::ecvrf::ECVRFKeyPair;
use vrf_wasm::vrf::{VRFKeyPair, VRFProof};
use vrf_wasm::rng::WasmRng;

// Generate a keypair
let mut rng = WasmRng::default();
let keypair = ECVRFKeyPair::generate(&mut rng);

// Create VRF proof for input
let input = b"Hello, VRF!";
let (hash, proof) = keypair.output(input);

// Verify the proof
assert!(proof.verify(input, &keypair.pk).is_ok());

// The hash is deterministic for the same key and input
let (hash2, _) = keypair.output(input);
assert_eq!(hash, hash2);

println!("VRF Hash: {}", hex::encode(hash));

Deterministic KeyPair Generation

use vrf_wasm::ecvrf::ECVRFKeyPair;
use vrf_wasm::vrf::VRFKeyPair;
use vrf_wasm::rng::WasmRngFromSeed;
use rand_core::SeedableRng;

// Generate deterministic keypair from seed
let seed = [42u8; 32];
let mut rng = WasmRngFromSeed::from_seed(seed);
let keypair = ECVRFKeyPair::generate(&mut rng);

// Same seed always generates same keypair
let mut rng2 = WasmRngFromSeed::from_seed(seed);
let keypair2 = ECVRFKeyPair::generate(&mut rng2);

// Prove this by generating same VRF output
let input = b"test";
let (hash1, _) = keypair.output(input);
let (hash2, _) = keypair2.output(input);
assert_eq!(hash1, hash2);

Serialization

use vrf_wasm::ecvrf::{ECVRFKeyPair, ECVRFProof, ECVRFPublicKey};
use vrf_wasm::vrf::VRFKeyPair;

// All types implement Serialize/Deserialize
let mut rng = vrf_wasm::rng::WasmRng::default();
let keypair = ECVRFKeyPair::generate(&mut rng);
let input = b"data";
let proof = keypair.prove(input);

// Serialize to bytes
let public_key_bytes = bincode::serialize(&keypair.pk).unwrap();
let proof_bytes = bincode::serialize(&proof).unwrap();

// Deserialize
let public_key: ECVRFPublicKey = bincode::deserialize(&public_key_bytes).unwrap();
let deserialized_proof: ECVRFProof = bincode::deserialize(&proof_bytes).unwrap();

// Verify still works
assert!(deserialized_proof.verify(input, &public_key).is_ok());

VRF Component Extraction

For cross-verification scenarios where you need to inspect or reconstruct VRF proofs:

use vrf_wasm::ecvrf::{ECVRFKeyPair, ECVRFProof};
use vrf_wasm::vrf::VRFKeyPair;
use vrf_wasm::rng::WasmRng;

let mut rng = WasmRng::default();
let keypair = ECVRFKeyPair::generate(&mut rng);
let proof = keypair.prove(b"input");

// Extract individual components
let gamma_bytes = proof.gamma_bytes();     // [u8; 32] - compressed point
let challenge_bytes = proof.challenge_bytes(); // [u8; 16] - challenge
let scalar_bytes = proof.scalar_bytes();   // [u8; 32] - scalar

// Extract all at once
let (gamma, challenge, scalar) = proof.to_components();

// Reconstruct proof from components (for cross-verification)
let reconstructed = ECVRFProof::from_components(&gamma, &challenge, &scalar).unwrap();
assert!(reconstructed.verify(b"input", &keypair.pk).is_ok());

Conditional Compilation & Feature Flags

VRF-WASM uses conditional compilation to provide optimized RNG implementations for different target environments:

Available Features

Note: you would only ever use the near vrf-wasm in a contract for verifying VRF output and proofs generated by vrf-wasm on the client, there is no point generating VRF outputs onchain as keypairs would be exposed.

• Alternatively, use the vrf-contract-verifier for a lightweight VRF proof/output verifier you can use to verify vrf-wasm generated outputs and proofs, onchain.
• If you want onchain randomness, use env:random_seed() in NEAR contracts (it is itself a VRF based RNG).

Building for Different Targets

Browser/JavaScript (Default)

# Default build - includes browser RNG
cargo build

# WASM for web
wasm-pack build --target web

NEAR Smart Contracts

# NEAR-specific build (NEAR features only)
cargo build --no-default-features --features near --target wasm32-unknown-unknown

# With cargo-near (recommended for NEAR contracts)
cargo install cargo-near
cargo near build

Environment-Specific RNG Usage

// Generic usage (works with any feature configuration)
use vrf_wasm::rng::WasmRng;
let mut rng = WasmRng::default();

// Browser-specific (when browser feature is enabled)
use vrf_wasm::rng::BrowserWasmRng;
let mut rng = BrowserWasmRng::default();

// NEAR-specific (when near feature is enabled)
use vrf_wasm::rng::NearWasmRng;
let mut rng = NearWasmRng::default();

Binary Size

Attribution

This project is derived from FastCrypto by Mysten Labs, Inc.

Original Copyright: Copyright (c) 2022, Mysten Labs, Inc. License: Apache License 2.0 Original Repository: https://github.com/MystenLabs/fastcrypto/

Advanced: Using with NEAR Smart Contracts

When building a project that uses vrf-wasm for both on-chain (NEAR) and off-chain (testing) purposes, you need to handle Cargo's feature unification.

The Problem: Feature Unification

If your Cargo.toml has this:

# In [dependencies]
vrf-wasm = { version = "0.9.1", default-features = false, features = ["near"] }

# In [dev-dependencies]
vrf-wasm = { version = "0.9.1", features = ["browser"] }

Cargo will enable both near and browser features for all builds, which can cause conflicts.

The Solution: Target-Specific Dev-Dependencies

To solve this, use a [target] configuration in your project's Cargo.toml to specify that the browser version of vrf-wasm should only be used for native testing environments, not for the wasm32 smart contract build.

# In your project's Cargo.toml

[dependencies]
# This will be used for your smart contract build
vrf-wasm = { version = "0.9.1", default-features = false, features = ["near"] }

[target.'cfg(not(target_arch = "wasm32"))'.dev-dependencies]
# This will be used for your native tests (`cargo test`)
vrf-wasm = { version = "0.9.1", features = ["browser"] }

This configuration ensures:

• cargo build --target wasm32-unknown-unknown: Compiles vrf-wasm with only the near feature.
• cargo test: Compiles vrf-wasm with the browser feature for your test suite.

This approach prevents feature conflicts and allows you to test your NEAR smart contracts with a browser-compatible version of the VRF library.