go-ecvrf

Zero-dependency Golang implementation of Elliptic Curve Verifiable Random Function (VRF) follows draft-irtf-cfrg-vrf-06 and RFC 6979.

What's VRF

A Verifiable Random Function (VRF) is the public-key version of a keyed cryptographic hash. Only the holder of the private key can compute the hash, but anyone with public key can verify the correctness of the hash.

A key application of the VRF is to provide privacy against offline enumeration (e.g. dictionary attacks) on data stored in a hash-based data structure. In this application, a Prover holds the VRF private key and uses the VRF hashing to construct a hash-based data structure on the input data. Due to the nature of the VRF, only the Prover can answer queries about whether or not some data is stored in the data structure. Anyone who knows the public VRF key can verify that the Prover has answered the queries correctly. However no offline inferences (i.e. inferences without querying the Prover) can be made about the data stored in the data strucuture.

Installation

go get -u github.com/vechain/go-ecvrf

Examples

Using SECP256K1_SHA256_TAI cipher suite:

• VRF Proving

  // the private key
  var sk *ecdsa.PrivateKey
  // code to load sk
  // ... 
  
  // the input to be hashed by the VRF
  alpha := "Hello VeChain"
  
  // `beta`: the VRF hash output
  // `pi`: the VRF proof
  beta, pi, err := ecvrf.NewSecp256k1Sha256Tai().Prove(sk, []byte(alpha))
  if err != nil {
      // something wrong.
      // most likely sk is not properly loaded.
      return
  }

• VRF Verifying

  // the public key
  var pk *ecdsa.PublicKey
  // code to load pk
  // ...
  
  // the input to be hashed by the VRF
  alpha := "Hello VeChain"
  
  // `pi` is the VRF proof
  beta, err := ecvrf.NewSecp256k1Sha256Tai().Verify(pk, []byte(alpha), pi)
  if err != nil {
      // invalid proof
      return
  }
  
  // got correct beta

Supported Cipher Suites

• P256_SHA256_TAI
• SECP256K1_SHA256_TAI

It's easy to extends this library to use different Weierstrass curves and Hash algorithms, by providing cooked Config like:

// the following codes build a new P256_SHA256_TAI VRF object.
vrf := ecvrf.New(&ecvrf.Config{
    SuiteString: 0x01,
    Cofactor:    0x01,
    NewHasher:   sha256.New,
    Y2: func(c elliptic.Curve, x *big.Int) *big.Int {
        // y² = x³ - 3x + b
        x3 := new(big.Int).Mul(x, x)
        x3.Mul(x3, x)

        threeX := new(big.Int).Lsh(x, 1)
        threeX.Add(threeX, x)

        x3.Sub(x3, threeX)
        x3.Add(x3, c.Params().B)
        x3.Mod(x3, c.Params().P)
        return x3
    },
    Sqrt: ecvrf.DefaultSqrt,
})

Benchmark

On quad-core i5 13" macbook pro 2018

goos: darwin
goarch: amd64
pkg: github.com/vechain/go-ecvrf/tests
BenchmarkVRF
BenchmarkVRF/secp256k1sha256tai-proving
BenchmarkVRF/secp256k1sha256tai-proving-8         	    2198	    598180 ns/op	   16680 B/op	     604 allocs/op
BenchmarkVRF/secp256k1sha256tai-verifying
BenchmarkVRF/secp256k1sha256tai-verifying-8       	    1587	    739716 ns/op	   14214 B/op	     406 allocs/op
BenchmarkVRF/p256sha256tai-proving
BenchmarkVRF/p256sha256tai-proving-8              	    4887	    263843 ns/op	    9509 B/op	     243 allocs/op
BenchmarkVRF/p256sha256tai-verifying
BenchmarkVRF/p256sha256tai-verifying-8            	    3172	    507240 ns/op	   17636 B/op	     428 allocs/op
PASS
ok  	github.com/vechain/go-ecvrf/tests	5.668s
Success: Benchmarks passed.

References

• draft-irtf-cfrg-vrf-06
• RFC 6979
• witnet/vrf-rs
• google/keytransparency

License

Copyright (c) 2020 vechain.org. Licensed under the MIT license.