zk

Documentation

Overview

Package zk provides utilities around the zkSNARK (Groth16) tooling.

Index

• func BytesToArboStr(input []byte) []string
• func LittleEndianToNBytes(num *big.Int, n int) *big.Int
• func ProtobufZKProofToProverProof(p *models.ProofZkSNARK) (*prover.Proof, error)
• func ProverProofToProtobufZKProof(p *prover.Proof, electionId, censusRoot, nullifier types.HexBytes, ...) (*models.ProofZkSNARK, error)
• type ZkAddress
  • func AddressFromBytes(seed []byte) (*ZkAddress, error)
  • func AddressFromSignKeys(acc *ethereum.SignKeys) (*ZkAddress, error)
  • func AddressFromString(seed string) (*ZkAddress, error)
  • func NewRandAddress() (*ZkAddress, error)
  • func (zk *ZkAddress) Bytes() []byte
  • func (zk *ZkAddress) Nullifier(electionId []byte) (*big.Int, error)
  • func (zk *ZkAddress) String() string

Functions

func BytesToArboStr

func BytesToArboStr(input []byte) []string

BytesToArboStr calculates the sha256 hash (32 bytes) of the slice of bytes provided. Then, splits the hash into a two parts of 16 bytes, swap the endianess of that parts, encodes they into a two big.Ints and return both as strings into a []string.

func LittleEndianToNBytes

func LittleEndianToNBytes(num *big.Int, n int) *big.Int

LittleEndianToNBytes truncate the most significant n bytes of the provided little endian number provided and returns into a new big.Int.

func ProtobufZKProofToProverProof

func ProtobufZKProofToProverProof(p *models.ProofZkSNARK) (*prover.Proof, error)

ProtobufZKProofToProverProof parses the provided protobuf ready proof struct into a prover ready proof struct.

func ProverProofToProtobufZKProof

func ProverProofToProtobufZKProof(p *prover.Proof,
	electionId, censusRoot, nullifier types.HexBytes, weight *big.Int) (*models.ProofZkSNARK, error)

ProverProofToProtobufZKProof encodes the proof provided into a protobuf ready struct using including the index of the circuit used. If the provided proof does not contains a defined public signals, the rest of the arguments are required to calculate that parameter. If the provided proof does not contains a defined public signals and any of the rest of the parameters is nil, the resulting struct will not contains any defined PublicInputs value.

Types

type ZkAddress

type ZkAddress struct {
	// Privkey contains the big.Int version of the BabyJubJub private key
	PrivKey *big.Int
	// PubKey contains the big.Int poseidon hash of the BabyJubJub public key
	// (x and y coordinates of a point of the curve)
	PubKey *big.Int
	// contains filtered or unexported fields
}

ZkAddress struct allow to create and encoding properly the zk-snark compatible address for the vochain. This address is calculated from a BabyJubJub key pair, based on a seed. The address has 20 bytes of size and it is the truncated version of the poseidon hash of the BabyJubJub publicKey.

func AddressFromBytes

func AddressFromBytes(seed []byte) (*ZkAddress, error)

AddressFromBytes returns a new ZkAddress based on the seed provided. The seed has to be at least 32 bytes. Using it, a BabyJubJub key pair is calculated and based on it. The ZkAddress components are:

• ZkAddress.PrivKey: The BabyJubJub private key big.Int value, following the EdDSA standard, and using blake-512 hash.
• ZkAddress.PublicKey: The poseidon hash of the BabyJubJub public key components (X and Y coordinates as big.Int).
• ZkAddress.addr: The last 20 bytes of the ZkAddress.PublicKey. This is calculated by truncating PublicKey (a little endian number) to the defaultZkAddrLen.

func AddressFromSignKeys

func AddressFromSignKeys(acc *ethereum.SignKeys) (*ZkAddress, error)

AddressFromSignKeys gets the private key from the ethereum.SignKeys provided and pass its string representation as []byte to AddressFromBytes function.

func AddressFromString

func AddressFromString(seed string) (*ZkAddress, error)

AddressFromString wraps AddressFromBytes function transforming the seed from string to []byte.

func NewRandAddress

func NewRandAddress() (*ZkAddress, error)

NewRandAddress returns a ZkAddress based on a random BabyJubJub private key.

func (*ZkAddress) Bytes

func (zk *ZkAddress) Bytes() []byte

Bytes returns the current ZkAddress.addr transformed to types.HexBytes using the arbo.BigIntToBytes() function.

func (*ZkAddress) Nullifier

func (zk *ZkAddress) Nullifier(electionId []byte) (*big.Int, error)

Nullifier returns ZkSnark ready vote nullifier based on the current ZkAddress.PrivKey and the electionId provided. The nullifier is calculated following this definition:

nullifier = poseidon(jubjubPrivKey, sha256(electionId))

func (*ZkAddress) String

func (zk *ZkAddress) String() string

String function returns the current ZkAddress.Bytes() result transformed to string using the types.HexBytes.String() function.