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package babyjub
import (
"crypto/rand"
"github.com/iden3/go-iden3-crypto/mimc7"
"github.com/iden3/go-iden3-crypto/poseidon"
"github.com/iden3/go-iden3-crypto/utils"
"math/big"
)
// pruneBuffer prunes the buffer during key generation according to RFC 8032.
// https://tools.ietf.org/html/rfc8032#page-13
func pruneBuffer(buf *[32]byte) *[32]byte {
buf[0] = buf[0] & 0xF8
buf[31] = buf[31] & 0x7F
buf[31] = buf[31] | 0x40
return buf
}
// PrivateKey is an EdDSA private key, which is a 32byte buffer.
type PrivateKey [32]byte
// NewRandPrivKey generates a new random private key (using cryptographically
// secure randomness).
func NewRandPrivKey() PrivateKey {
var k PrivateKey
_, err := rand.Read(k[:])
if err != nil {
panic(err)
}
return k
}
// Scalar converts a private key into the scalar value s following the EdDSA
// standard, and using blake-512 hash.
func (k *PrivateKey) Scalar() *PrivKeyScalar {
sBuf := Blake512(k[:])
sBuf32 := [32]byte{}
copy(sBuf32[:], sBuf[:32])
pruneBuffer(&sBuf32)
s := new(big.Int)
utils.SetBigIntFromLEBytes(s, sBuf32[:])
s.Rsh(s, 3)
return NewPrivKeyScalar(s)
}
// Pub returns the public key corresponding to a private key.
func (k *PrivateKey) Public() *PublicKey {
return k.Scalar().Public()
}
// PrivKeyScalar represents the scalar s output of a private key
type PrivKeyScalar big.Int
// NewPrivKeyScalar creates a new PrivKeyScalar from a big.Int
func NewPrivKeyScalar(s *big.Int) *PrivKeyScalar {
sk := PrivKeyScalar(*s)
return &sk
}
// Pub returns the public key corresponding to the scalar value s of a private
// key.
func (s *PrivKeyScalar) Public() *PublicKey {
p := NewPoint().Mul((*big.Int)(s), B8)
pk := PublicKey(*p)
return &pk
}
// BigInt returns the big.Int corresponding to a PrivKeyScalar.
func (s *PrivKeyScalar) BigInt() *big.Int {
return (*big.Int)(s)
}
// PublicKey represents an EdDSA public key, which is a curve point.
type PublicKey Point
func (pk PublicKey) MarshalText() ([]byte, error) {
pkc := pk.Compress()
return utils.Hex(pkc[:]).MarshalText()
}
func (pk PublicKey) String() string {
pkc := pk.Compress()
return utils.Hex(pkc[:]).String()
}
func (pk *PublicKey) UnmarshalText(h []byte) error {
var pkc PublicKeyComp
if err := utils.HexDecodeInto(pkc[:], h); err != nil {
return err
}
pkd, err := pkc.Decompress()
if err != nil {
return err
}
*pk = *pkd
return nil
}
// Point returns the Point corresponding to a PublicKey.
func (p *PublicKey) Point() *Point {
return (*Point)(p)
}
// PublicKeyComp represents a compressed EdDSA Public key; it's a compressed curve
// point.
type PublicKeyComp [32]byte
func (buf PublicKeyComp) MarshalText() ([]byte, error) { return utils.Hex(buf[:]).MarshalText() }
func (buf PublicKeyComp) String() string { return utils.Hex(buf[:]).String() }
func (buf *PublicKeyComp) UnmarshalText(h []byte) error { return utils.HexDecodeInto(buf[:], h) }
func (p *PublicKey) Compress() PublicKeyComp {
return PublicKeyComp((*Point)(p).Compress())
}
func (p *PublicKeyComp) Decompress() (*PublicKey, error) {
point, err := NewPoint().Decompress(*p)
if err != nil {
return nil, err
}
pk := PublicKey(*point)
return &pk, nil
}
// Signature represents an EdDSA uncompressed signature.
type Signature struct {
R8 *Point
S *big.Int
}
// SignatureComp represents a compressed EdDSA signature.
type SignatureComp [64]byte
func (buf SignatureComp) MarshalText() ([]byte, error) { return utils.Hex(buf[:]).MarshalText() }
func (buf SignatureComp) String() string { return utils.Hex(buf[:]).String() }
func (buf *SignatureComp) UnmarshalText(h []byte) error { return utils.HexDecodeInto(buf[:], h) }
// Compress an EdDSA signature by concatenating the compression of
// the point R8 and the Little-Endian encoding of S.
func (s *Signature) Compress() SignatureComp {
R8p := s.R8.Compress()
Sp := utils.BigIntLEBytes(s.S)
buf := [64]byte{}
copy(buf[:32], R8p[:])
copy(buf[32:], Sp[:])
return SignatureComp(buf)
}
// Decompress a compressed signature into s, and also returns the decompressed
// signature. Returns error if the Point decompression fails.
func (s *Signature) Decompress(buf [64]byte) (*Signature, error) {
R8p := [32]byte{}
copy(R8p[:], buf[:32])
var err error
if s.R8, err = NewPoint().Decompress(R8p); err != nil {
return nil, err
}
s.S = utils.SetBigIntFromLEBytes(new(big.Int), buf[32:])
return s, nil
}
// Decompress a compressed signature. Returns error if the Point decompression
// fails.
func (s *SignatureComp) Decompress() (*Signature, error) {
return new(Signature).Decompress(*s)
}
// SignMimc7 signs a message encoded as a big.Int in Zq using blake-512 hash
// for buffer hashing and mimc7 for big.Int hashing.
func (k *PrivateKey) SignMimc7(msg *big.Int) *Signature {
h1 := Blake512(k[:])
msgBuf := utils.BigIntLEBytes(msg)
msgBuf32 := [32]byte{}
copy(msgBuf32[:], msgBuf[:])
rBuf := Blake512(append(h1[32:], msgBuf32[:]...))
r := utils.SetBigIntFromLEBytes(new(big.Int), rBuf) // r = H(H_{32..63}(k), msg)
r.Mod(r, SubOrder)
R8 := NewPoint().Mul(r, B8) // R8 = r * 8 * B
A := k.Public().Point()
hmInput := []*big.Int{R8.X, R8.Y, A.X, A.Y, msg}
hm, err := mimc7.Hash(hmInput, nil) // hm = H1(8*R.x, 8*R.y, A.x, A.y, msg)
if err != nil {
panic(err)
}
S := new(big.Int).Lsh(k.Scalar().BigInt(), 3)
S = S.Mul(hm, S)
S.Add(r, S)
S.Mod(S, SubOrder) // S = r + hm * 8 * s
return &Signature{R8: R8, S: S}
}
// VerifyMimc7 verifies the signature of a message encoded as a big.Int in Zq
// using blake-512 hash for buffer hashing and mimc7 for big.Int hashing.
func (p *PublicKey) VerifyMimc7(msg *big.Int, sig *Signature) bool {
hmInput := []*big.Int{sig.R8.X, sig.R8.Y, p.X, p.Y, msg}
hm, err := mimc7.Hash(hmInput, nil) // hm = H1(8*R.x, 8*R.y, A.x, A.y, msg)
if err != nil {
panic(err)
}
left := NewPoint().Mul(sig.S, B8) // left = s * 8 * B
r1 := big.NewInt(8)
r1.Mul(r1, hm)
right := NewPoint().Mul(r1, p.Point())
right.Add(sig.R8, right) // right = 8 * R + 8 * hm * A
return (left.X.Cmp(right.X) == 0) && (left.Y.Cmp(right.Y) == 0)
}
// SignPoseidon signs a message encoded as a big.Int in Zq using blake-512 hash
// for buffer hashing and Poseidon for big.Int hashing.
func (k *PrivateKey) SignPoseidon(msg *big.Int) *Signature {
h1 := Blake512(k[:])
msgBuf := utils.BigIntLEBytes(msg)
msgBuf32 := [32]byte{}
copy(msgBuf32[:], msgBuf[:])
rBuf := Blake512(append(h1[32:], msgBuf32[:]...))
r := utils.SetBigIntFromLEBytes(new(big.Int), rBuf) // r = H(H_{32..63}(k), msg)
r.Mod(r, SubOrder)
R8 := NewPoint().Mul(r, B8) // R8 = r * 8 * B
A := k.Public().Point()
hmInput := [poseidon.T]*big.Int{R8.X, R8.Y, A.X, A.Y, msg, big.NewInt(int64(0))}
hm, err := poseidon.PoseidonHash(hmInput) // hm = H1(8*R.x, 8*R.y, A.x, A.y, msg)
if err != nil {
panic(err)
}
S := new(big.Int).Lsh(k.Scalar().BigInt(), 3)
S = S.Mul(hm, S)
S.Add(r, S)
S.Mod(S, SubOrder) // S = r + hm * 8 * s
return &Signature{R8: R8, S: S}
}
// VerifyPoseidon verifies the signature of a message encoded as a big.Int in Zq
// using blake-512 hash for buffer hashing and Poseidon for big.Int hashing.
func (p *PublicKey) VerifyPoseidon(msg *big.Int, sig *Signature) bool {
hmInput := [poseidon.T]*big.Int{sig.R8.X, sig.R8.Y, p.X, p.Y, msg, big.NewInt(int64(0))}
hm, err := poseidon.PoseidonHash(hmInput) // hm = H1(8*R.x, 8*R.y, A.x, A.y, msg)
if err != nil {
panic(err)
}
left := NewPoint().Mul(sig.S, B8) // left = s * 8 * B
r1 := big.NewInt(8)
r1.Mul(r1, hm)
right := NewPoint().Mul(r1, p.Point())
right.Add(sig.R8, right) // right = 8 * R + 8 * hm * A
return (left.X.Cmp(right.X) == 0) && (left.Y.Cmp(right.Y) == 0)
}