Add babyjub from go-iden3/crypto/babyjub

2026-02-07 11:36:41 +01:00 · 2019-06-25 14:53:16 +02:00
parent eea757956c
commit 0f93c8ce38
5 changed files with 811 additions and 0 deletions
--- a/babyjub/babyjub.go
+++ b/babyjub/babyjub.go
@@ -0,0 +1,240 @@
+package babyjub
+
+import (
+	"fmt"
+	"math/big"
+)
+
+// Q is the order of the integer field where the curve point coordinates are (Zq).
+var Q *big.Int
+
+// A is one of the babyjub constants.
+var A *big.Int
+
+// D is one of the babyjub constants.
+var D *big.Int
+
+// Zero is 0.
+var Zero *big.Int
+
+// One is 1.
+var One *big.Int
+
+// MinusOne is -1.
+var MinusOne *big.Int
+
+// Order of the babyjub curve.
+var Order *big.Int
+
+// SubOrder is the order of the subgroup of the babyjub curve that contains the
+// points that we use.
+var SubOrder *big.Int
+
+// B8 is a base point of the babyjub multiplied by 8 to make it a base point of
+// the subgroup in the curve.
+var B8 *Point
+
+// NewIntFromString creates a new big.Int from a decimal integer encoded as a
+// string.  It will panic if the string is not a decimal integer.
+func NewIntFromString(s string) *big.Int {
+	v, ok := new(big.Int).SetString(s, 10)
+	if !ok {
+		panic(fmt.Sprintf("Bad base 10 string %s", s))
+	}
+	return v
+}
+
+// init initializes global numbers and the subgroup base.
+func init() {
+	Zero = big.NewInt(0)
+	One = big.NewInt(1)
+	MinusOne = big.NewInt(-1)
+	Q = NewIntFromString(
+		"21888242871839275222246405745257275088548364400416034343698204186575808495617")
+	A = NewIntFromString("168700")
+	D = NewIntFromString("168696")
+
+	Order = NewIntFromString(
+		"21888242871839275222246405745257275088614511777268538073601725287587578984328")
+	SubOrder = new(big.Int).Rsh(Order, 3)
+
+	B8 = NewPoint()
+	B8.X = NewIntFromString(
+		"17777552123799933955779906779655732241715742912184938656739573121738514868268")
+	B8.Y = NewIntFromString(
+		"2626589144620713026669568689430873010625803728049924121243784502389097019475")
+}
+
+// Point represents a point of the babyjub curve.
+type Point struct {
+	X *big.Int
+	Y *big.Int
+}
+
+// NewPoint creates a new Point.
+func NewPoint() *Point {
+	return &Point{X: big.NewInt(0), Y: big.NewInt(1)}
+}
+
+// Set copies a Point c into the Point p
+func (p *Point) Set(c *Point) *Point {
+	p.X.Set(c.X)
+	p.Y.Set(c.Y)
+	return p
+}
+
+// Add adds Point a and b into res
+func (res *Point) Add(a *Point, b *Point) *Point {
+	// x = (a.x * b.y + b.x * a.y) * (1 + D * a.x * b.x * a.y * b.y)^-1 mod q
+	x1a := new(big.Int).Mul(a.X, b.Y)
+	x1b := new(big.Int).Mul(b.X, a.Y)
+	x1a.Add(x1a, x1b) // x1a = a.x * b.y + b.x * a.y
+
+	x2 := new(big.Int).Set(D)
+	x2.Mul(x2, a.X)
+	x2.Mul(x2, b.X)
+	x2.Mul(x2, a.Y)
+	x2.Mul(x2, b.Y)
+	x2.Add(One, x2)
+	x2.Mod(x2, Q)
+	x2.ModInverse(x2, Q) // x2 = (1 + D * a.x * b.x * a.y * b.y)^-1
+
+	// y = (a.y * b.y + A * a.x * a.x) * (1 - D * a.x * b.x * a.y * b.y)^-1 mod q
+	y1a := new(big.Int).Mul(a.Y, b.Y)
+	y1b := new(big.Int).Set(A)
+	y1b.Mul(y1b, a.X)
+	y1b.Mul(y1b, b.X)
+
+	y1a.Sub(y1a, y1b) // y1a = a.y * b.y - A * a.x * b.x
+
+	y2 := new(big.Int).Set(D)
+	y2.Mul(y2, a.X)
+	y2.Mul(y2, b.X)
+	y2.Mul(y2, a.Y)
+	y2.Mul(y2, b.Y)
+	y2.Sub(One, y2)
+	y2.Mod(y2, Q)
+	y2.ModInverse(y2, Q) // y2 = (1 - D * a.x * b.x * a.y * b.y)^-1
+
+	res.X = x1a.Mul(x1a, x2)
+	res.X = res.X.Mod(res.X, Q)
+
+	res.Y = y1a.Mul(y1a, y2)
+	res.Y = res.Y.Mod(res.Y, Q)
+
+	return res
+}
+
+// Mul multiplies the Point p by the scalar s and stores the result in res,
+// which is also returned.
+func (res *Point) Mul(s *big.Int, p *Point) *Point {
+	res.X = big.NewInt(0)
+	res.Y = big.NewInt(1)
+	exp := NewPoint().Set(p)
+
+	for i := 0; i < s.BitLen(); i++ {
+		if s.Bit(i) == 1 {
+			res.Add(res, exp)
+		}
+		exp.Add(exp, exp)
+	}
+
+	return res
+}
+
+// InCurve returns true when the Point p is in the babyjub curve.
+func (p *Point) InCurve() bool {
+	x2 := new(big.Int).Set(p.X)
+	x2.Mul(x2, x2)
+	x2.Mod(x2, Q)
+
+	y2 := new(big.Int).Set(p.Y)
+	y2.Mul(y2, y2)
+	y2.Mod(y2, Q)
+
+	a := new(big.Int).Mul(A, x2)
+	a.Add(a, y2)
+	a.Mod(a, Q)
+
+	b := new(big.Int).Set(D)
+	b.Mul(b, x2)
+	b.Mul(b, y2)
+	b.Add(One, b)
+	b.Mod(b, Q)
+
+	return a.Cmp(b) == 0
+}
+
+// InSubGroup returns true when the Point p is in the subgroup of the babyjub
+// curve.
+func (p *Point) InSubGroup() bool {
+	if !p.InCurve() {
+		return false
+	}
+	res := NewPoint().Mul(SubOrder, p)
+	return (res.X.Cmp(Zero) == 0) && (res.Y.Cmp(One) == 0)
+}
+
+// PointCoordSign returns the sign of the curve point coordinate.  It returns
+// false if the sign is positive and false if the sign is negative.
+func PointCoordSign(c *big.Int) bool {
+	if c.Cmp(new(big.Int).Rsh(Q, 1)) == 1 {
+		return true
+	}
+	return false
+}
+
+func PackPoint(ay *big.Int, sign bool) [32]byte {
+	leBuf := BigIntLEBytes(ay)
+	if sign {
+		leBuf[31] = leBuf[31] | 0x80
+	}
+	return leBuf
+}
+
+// Compress the point into a 32 byte array that contains the y coordinate in
+// little endian and the sign of the x coordinate.
+func (p *Point) Compress() [32]byte {
+	sign := false
+	if PointCoordSign(p.X) {
+		sign = true
+	}
+	return PackPoint(p.Y, sign)
+}
+
+// Decompress a compressed Point into p, and also returns the decompressed
+// Point.  Returns error if the compressed Point is invalid.
+func (p *Point) Decompress(leBuf [32]byte) (*Point, error) {
+	sign := false
+	if (leBuf[31] & 0x80) != 0x00 {
+		sign = true
+		leBuf[31] = leBuf[31] & 0x7F
+	}
+	SetBigIntFromLEBytes(p.Y, leBuf[:])
+	if p.Y.Cmp(Q) >= 0 {
+		return nil, fmt.Errorf("p.y >= Q")
+	}
+
+	y2 := new(big.Int).Mul(p.Y, p.Y)
+	y2.Mod(y2, Q)
+	xa := big.NewInt(1)
+	xa.Sub(xa, y2) // xa == 1 - y^2
+
+	xb := new(big.Int).Mul(D, y2)
+	xb.Mod(xb, Q)
+	xb.Sub(A, xb) // xb = A - d * y^2
+
+	if xb.Cmp(big.NewInt(0)) == 0 {
+		return nil, fmt.Errorf("division by 0")
+	}
+	xb.ModInverse(xb, Q)
+	p.X.Mul(xa, xb) // xa / xb
+	p.X.Mod(p.X, Q)
+	p.X.ModSqrt(p.X, Q)
+	if (sign && !PointCoordSign(p.X)) || (!sign && PointCoordSign(p.X)) {
+		p.X.Mul(p.X, MinusOne)
+	}
+	p.X.Mod(p.X, Q)
+
+	return p, nil
+}
--- a/babyjub/babyjub_test.go
+++ b/babyjub/babyjub_test.go
@@ -0,0 +1,232 @@
+package babyjub
+
+import (
+	// "fmt"
+	"encoding/hex"
+	"github.com/stretchr/testify/assert"
+	"math/big"
+	"testing"
+)
+
+func TestAdd1(t *testing.T) {
+	a := &Point{X: big.NewInt(0), Y: big.NewInt(1)}
+	b := &Point{X: big.NewInt(0), Y: big.NewInt(1)}
+
+	c := NewPoint().Add(a, b)
+	// fmt.Printf("%v = 2 * %v", *c, *a)
+	assert.Equal(t, "0", c.X.String())
+	assert.Equal(t, "1", c.Y.String())
+}
+
+func TestAdd2(t *testing.T) {
+	aX := NewIntFromString(
+		"17777552123799933955779906779655732241715742912184938656739573121738514868268")
+	aY := NewIntFromString(
+		"2626589144620713026669568689430873010625803728049924121243784502389097019475")
+	a := &Point{X: aX, Y: aY}
+
+	bX := NewIntFromString(
+		"17777552123799933955779906779655732241715742912184938656739573121738514868268")
+	bY := NewIntFromString(
+		"2626589144620713026669568689430873010625803728049924121243784502389097019475")
+	b := &Point{X: bX, Y: bY}
+
+	c := NewPoint().Add(a, b)
+	// fmt.Printf("%v = 2 * %v", *c, *a)
+	assert.Equal(t,
+		"6890855772600357754907169075114257697580319025794532037257385534741338397365",
+		c.X.String())
+	assert.Equal(t,
+		"4338620300185947561074059802482547481416142213883829469920100239455078257889",
+		c.Y.String())
+}
+
+func TestAdd3(t *testing.T) {
+	aX := NewIntFromString(
+		"17777552123799933955779906779655732241715742912184938656739573121738514868268")
+	aY := NewIntFromString(
+		"2626589144620713026669568689430873010625803728049924121243784502389097019475")
+	a := &Point{X: aX, Y: aY}
+
+	bX := NewIntFromString(
+		"16540640123574156134436876038791482806971768689494387082833631921987005038935")
+	bY := NewIntFromString(
+		"20819045374670962167435360035096875258406992893633759881276124905556507972311")
+	b := &Point{X: bX, Y: bY}
+
+	c := NewPoint().Add(a, b)
+	// fmt.Printf("%v = 2 * %v", *c, *a)
+	assert.Equal(t,
+		"7916061937171219682591368294088513039687205273691143098332585753343424131937",
+		c.X.String())
+	assert.Equal(t,
+		"14035240266687799601661095864649209771790948434046947201833777492504781204499",
+		c.Y.String())
+}
+
+func TestAdd4(t *testing.T) {
+	aX := NewIntFromString(
+		"0")
+	aY := NewIntFromString(
+		"1")
+	a := &Point{X: aX, Y: aY}
+
+	bX := NewIntFromString(
+		"16540640123574156134436876038791482806971768689494387082833631921987005038935")
+	bY := NewIntFromString(
+		"20819045374670962167435360035096875258406992893633759881276124905556507972311")
+	b := &Point{X: bX, Y: bY}
+
+	c := NewPoint().Add(a, b)
+	// fmt.Printf("%v = 2 * %v", *c, *a)
+	assert.Equal(t,
+		"16540640123574156134436876038791482806971768689494387082833631921987005038935",
+		c.X.String())
+	assert.Equal(t,
+		"20819045374670962167435360035096875258406992893633759881276124905556507972311",
+		c.Y.String())
+}
+
+func TestInCurve1(t *testing.T) {
+	p := &Point{X: big.NewInt(0), Y: big.NewInt(1)}
+	assert.Equal(t, true, p.InCurve())
+}
+
+func TestInCurve2(t *testing.T) {
+	p := &Point{X: big.NewInt(1), Y: big.NewInt(0)}
+	assert.Equal(t, false, p.InCurve())
+}
+
+func TestMul0(t *testing.T) {
+	x := NewIntFromString(
+		"17777552123799933955779906779655732241715742912184938656739573121738514868268")
+	y := NewIntFromString(
+		"2626589144620713026669568689430873010625803728049924121243784502389097019475")
+	p := &Point{X: x, Y: y}
+	s := NewIntFromString("3")
+
+	r2 := NewPoint().Add(p, p)
+	r2 = NewPoint().Add(r2, p)
+	r := NewPoint().Mul(s, p)
+	assert.Equal(t, r2.X.String(), r.X.String())
+	assert.Equal(t, r2.Y.String(), r.Y.String())
+
+	assert.Equal(t,
+		"19372461775513343691590086534037741906533799473648040012278229434133483800898",
+		r.X.String())
+	assert.Equal(t,
+		"9458658722007214007257525444427903161243386465067105737478306991484593958249",
+		r.Y.String())
+}
+
+func TestMul1(t *testing.T) {
+	x := NewIntFromString(
+		"17777552123799933955779906779655732241715742912184938656739573121738514868268")
+	y := NewIntFromString(
+		"2626589144620713026669568689430873010625803728049924121243784502389097019475")
+	p := &Point{X: x, Y: y}
+	s := NewIntFromString(
+		"14035240266687799601661095864649209771790948434046947201833777492504781204499")
+	r := NewPoint().Mul(s, p)
+	assert.Equal(t,
+		"17070357974431721403481313912716834497662307308519659060910483826664480189605",
+		r.X.String())
+	assert.Equal(t,
+		"4014745322800118607127020275658861516666525056516280575712425373174125159339",
+		r.Y.String())
+}
+
+func TestMul2(t *testing.T) {
+	x := NewIntFromString(
+		"6890855772600357754907169075114257697580319025794532037257385534741338397365")
+	y := NewIntFromString(
+		"4338620300185947561074059802482547481416142213883829469920100239455078257889")
+	p := &Point{X: x, Y: y}
+	s := NewIntFromString(
+		"20819045374670962167435360035096875258406992893633759881276124905556507972311")
+	r := NewPoint().Mul(s, p)
+	assert.Equal(t,
+		"13563888653650925984868671744672725781658357821216877865297235725727006259983",
+		r.X.String())
+	assert.Equal(t,
+		"8442587202676550862664528699803615547505326611544120184665036919364004251662",
+		r.Y.String())
+}
+
+func TestInCurve3(t *testing.T) {
+	x := NewIntFromString(
+		"17777552123799933955779906779655732241715742912184938656739573121738514868268")
+	y := NewIntFromString(
+		"2626589144620713026669568689430873010625803728049924121243784502389097019475")
+	p := &Point{X: x, Y: y}
+	assert.Equal(t, true, p.InCurve())
+}
+
+func TestInCurve4(t *testing.T) {
+	x := NewIntFromString(
+		"6890855772600357754907169075114257697580319025794532037257385534741338397365")
+	y := NewIntFromString(
+		"4338620300185947561074059802482547481416142213883829469920100239455078257889")
+	p := &Point{X: x, Y: y}
+	assert.Equal(t, true, p.InCurve())
+}
+
+func TestInSubGroup1(t *testing.T) {
+	x := NewIntFromString(
+		"17777552123799933955779906779655732241715742912184938656739573121738514868268")
+	y := NewIntFromString(
+		"2626589144620713026669568689430873010625803728049924121243784502389097019475")
+	p := &Point{X: x, Y: y}
+	assert.Equal(t, true, p.InSubGroup())
+}
+
+func TestInSubGroup2(t *testing.T) {
+	x := NewIntFromString(
+		"6890855772600357754907169075114257697580319025794532037257385534741338397365")
+	y := NewIntFromString(
+		"4338620300185947561074059802482547481416142213883829469920100239455078257889")
+	p := &Point{X: x, Y: y}
+	assert.Equal(t, true, p.InSubGroup())
+}
+
+func TestCompressDecompress1(t *testing.T) {
+	x := NewIntFromString(
+		"17777552123799933955779906779655732241715742912184938656739573121738514868268")
+	y := NewIntFromString(
+		"2626589144620713026669568689430873010625803728049924121243784502389097019475")
+	p := &Point{X: x, Y: y}
+
+	buf := p.Compress()
+	assert.Equal(t, "53b81ed5bffe9545b54016234682e7b2f699bd42a5e9eae27ff4051bc698ce85", hex.EncodeToString(buf[:]))
+
+	p2, err := NewPoint().Decompress(buf)
+	assert.Equal(t, nil, err)
+	assert.Equal(t, p.X.String(), p2.X.String())
+	assert.Equal(t, p.Y.String(), p2.Y.String())
+}
+
+func TestCompressDecompress2(t *testing.T) {
+	x := NewIntFromString(
+		"6890855772600357754907169075114257697580319025794532037257385534741338397365")
+	y := NewIntFromString(
+		"4338620300185947561074059802482547481416142213883829469920100239455078257889")
+	p := &Point{X: x, Y: y}
+
+	buf := p.Compress()
+	assert.Equal(t, "e114eb17eddf794f063a68fecac515e3620e131976108555735c8b0773929709", hex.EncodeToString(buf[:]))
+
+	p2, err := NewPoint().Decompress(buf)
+	assert.Equal(t, nil, err)
+	assert.Equal(t, p.X.String(), p2.X.String())
+	assert.Equal(t, p.Y.String(), p2.Y.String())
+}
+
+func TestCompressDecompressRnd(t *testing.T) {
+	for i := 0; i < 64; i++ {
+		p1 := NewPoint().Mul(big.NewInt(int64(i)), B8)
+		buf := p1.Compress()
+		p2, err := NewPoint().Decompress(buf)
+		assert.Equal(t, nil, err)
+		assert.Equal(t, p1, p2)
+	}
+}
--- a/babyjub/eddsa.go
+++ b/babyjub/eddsa.go
@@ -0,0 +1,211 @@
+package babyjub
+
+import (
+	"crypto/rand"
+	// "encoding/hex"
+	// "fmt"
+	common3 "github.com/iden3/go-iden3/common"
+	"github.com/iden3/go-iden3/crypto/mimc7"
+	// "golang.org/x/crypto/blake2b"
+	"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)
+	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 common3.Hex(pkc[:]).MarshalText()
+}
+
+func (pk PublicKey) String() string {
+	pkc := pk.Compress()
+	return common3.Hex(pkc[:]).String()
+}
+
+func (pk *PublicKey) UnmarshalText(h []byte) error {
+	var pkc PublicKeyComp
+	if err := common3.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 common3.Hex(buf[:]).MarshalText() }
+func (buf PublicKeyComp) String() string                { return common3.Hex(buf[:]).String() }
+func (buf *PublicKeyComp) UnmarshalText(h []byte) error { return common3.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 common3.Hex(buf[:]).MarshalText() }
+func (buf SignatureComp) String() string                { return common3.Hex(buf[:]).String() }
+func (buf *SignatureComp) UnmarshalText(h []byte) error { return common3.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 := 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 = 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 := BigIntLEBytes(msg)
+	msgBuf32 := [32]byte{}
+	copy(msgBuf32[:], msgBuf[:])
+	rBuf := Blake512(append(h1[32:], msgBuf32[:]...))
+	r := 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, err := mimc7.BigIntsToRElems([]*big.Int{R8.X, R8.Y, A.X, A.Y, msg})
+	if err != nil {
+		panic(err)
+	}
+	hm := mimc7.Hash(hmInput, nil) // hm = H1(8*R.x, 8*R.y, A.x, A.y, msg)
+	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, err := mimc7.BigIntsToRElems([]*big.Int{sig.R8.X, sig.R8.Y, p.X, p.Y, msg})
+	if err != nil {
+		panic(err)
+	}
+	hm := mimc7.Hash(hmInput, nil) // hm = H1(8*R.x, 8*R.y, A.x, A.y, msg)
+
+	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)
+}
--- a/babyjub/eddsa_test.go
+++ b/babyjub/eddsa_test.go
@@ -0,0 +1,89 @@
+package babyjub
+
+import (
+	"crypto/rand"
+	"encoding/hex"
+	"fmt"
+
+	"github.com/stretchr/testify/assert"
+
+	// "golang.org/x/crypto/blake2b"
+	"math/big"
+	"testing"
+)
+
+func genInputs() (*PrivateKey, *big.Int) {
+	k := NewRandPrivKey()
+	fmt.Println("k", hex.EncodeToString(k[:]))
+
+	msgBuf := [32]byte{}
+	rand.Read(msgBuf[:])
+	msg := SetBigIntFromLEBytes(new(big.Int), msgBuf[:])
+	msg.Mod(msg, Q)
+	fmt.Println("msg", msg)
+
+	return &k, msg
+}
+
+func TestSignVerify1(t *testing.T) {
+	var k PrivateKey
+	hex.Decode(k[:], []byte("0001020304050607080900010203040506070809000102030405060708090001"))
+	msgBuf, err := hex.DecodeString("00010203040506070809")
+	if err != nil {
+		panic(err)
+	}
+	msg := SetBigIntFromLEBytes(new(big.Int), msgBuf)
+
+	pk := k.Public()
+	assert.Equal(t,
+		"2610057752638682202795145288373380503107623443963127956230801721756904484787",
+		pk.X.String())
+	assert.Equal(t,
+		"16617171478497210597712478520507818259149717466230047843969353176573634386897",
+		pk.Y.String())
+
+	sig := k.SignMimc7(msg)
+	assert.Equal(t,
+		"4974729414807584049518234760796200867685098748448054182902488636762478901554",
+		sig.R8.X.String())
+	assert.Equal(t,
+		"18714049394522540751536514815950425694461287643205706667341348804546050128733",
+		sig.R8.Y.String())
+	assert.Equal(t,
+		"2171284143457722024136077617757713039502332290425057126942676527240038689549",
+		sig.S.String())
+
+	ok := pk.VerifyMimc7(msg, sig)
+	assert.Equal(t, true, ok)
+
+	sigBuf := sig.Compress()
+	sig2, err := new(Signature).Decompress(sigBuf)
+	assert.Equal(t, nil, err)
+
+	assert.Equal(t, ""+
+		"5dfb6f843c023fe3e52548ccf22e55c81b426f7af81b4f51f7152f2fcfc65f29"+
+		"0dab19c5a0a75973cd75a54780de0c3a41ede6f57396fe99b5307fff3ce7cc04",
+		hex.EncodeToString(sigBuf[:]))
+
+	ok = pk.VerifyMimc7(msg, sig2)
+	assert.Equal(t, true, ok)
+}
+
+func TestCompressDecompress(t *testing.T) {
+	var k PrivateKey
+	hex.Decode(k[:], []byte("0001020304050607080900010203040506070809000102030405060708090001"))
+	pk := k.Public()
+	for i := 0; i < 64; i++ {
+		msgBuf, err := hex.DecodeString(fmt.Sprintf("000102030405060708%02d", i))
+		if err != nil {
+			panic(err)
+		}
+		msg := SetBigIntFromLEBytes(new(big.Int), msgBuf)
+		sig := k.SignMimc7(msg)
+		sigBuf := sig.Compress()
+		sig2, err := new(Signature).Decompress(sigBuf)
+		assert.Equal(t, nil, err)
+		ok := pk.VerifyMimc7(msg, sig2)
+		assert.Equal(t, true, ok)
+	}
+}
--- a/babyjub/helpers.go
+++ b/babyjub/helpers.go
@@ -0,0 +1,39 @@
+package babyjub
+
+import (
+	"github.com/dchest/blake512" // I have personally reviewed that this module doesn't do anything suspicious
+	"math/big"
+)
+
+// SwapEndianness swaps the endianness of the value encoded in xs.  If xs is
+// Big-Endian, the result will be Little-Endian and viceversa.
+func SwapEndianness(xs []byte) []byte {
+	ys := make([]byte, len(xs))
+	for i, b := range xs {
+		ys[len(xs)-1-i] = b
+	}
+	return ys
+}
+
+// BigIntLEBytes encodes a big.Int into an array in Little-Endian.
+func BigIntLEBytes(v *big.Int) [32]byte {
+	le := SwapEndianness(v.Bytes())
+	res := [32]byte{}
+	copy(res[:], le)
+	return res
+}
+
+// SetBigIntFromLEBytes sets the value of a big.Int from a Little-Endian
+// encoded value.
+func SetBigIntFromLEBytes(v *big.Int, leBuf []byte) *big.Int {
+	beBuf := SwapEndianness(leBuf)
+	return v.SetBytes(beBuf)
+}
+
+// Blake512 performs the blake-512 hash over the buffer m.  Note that this is
+// the original blake from the SHA3 competition and not the new blake2 version.
+func Blake512(m []byte) []byte {
+	h := blake512.New()
+	h.Write(m[:])
+	return h.Sum(nil)
+}