Add proof parsers to string (decimal & hex)

Also adds ProofToSmartContractFormat, which returns a ProofString as the
proof.B elements swap is not a valid point for the bn256.G2 format.

Also unexports internal structs and methods of the prover package.
Also apply golint.

parsers/parsers.go

@@ -467,8 +467,35 @@ func stringToG2(h [][]string) (*bn256.G2, error) {
 	return p, err
 }
 
-// ProofToJson outputs the Proof i Json format
+// ProofStringToSmartContractFormat converts the ProofString to a ProofString in the SmartContract format in a ProofString structure
-func ProofToJson(p *types.Proof) ([]byte, error) {
+func ProofStringToSmartContractFormat(s ProofString) ProofString {
+	var rs ProofString
+	rs.A = make([]string, 2)
+	rs.B = make([][]string, 2)
+	rs.B[0] = make([]string, 2)
+	rs.B[1] = make([]string, 2)
+	rs.C = make([]string, 2)
+
+	rs.A[0] = s.A[0]
+	rs.A[1] = s.A[1]
+	rs.B[0][0] = s.B[0][1]
+	rs.B[0][1] = s.B[0][0]
+	rs.B[1][0] = s.B[1][1]
+	rs.B[1][1] = s.B[1][0]
+	rs.C[0] = s.C[0]
+	rs.C[1] = s.C[1]
+	rs.Protocol = s.Protocol
+	return rs
+}
+
+// ProofToSmartContractFormat converts the *types.Proof to a ProofString in the SmartContract format in a ProofString structure
+func ProofToSmartContractFormat(p *types.Proof) ProofString {
+	s := ProofToString(p)
+	return ProofStringToSmartContractFormat(s)
+}
+
+// ProofToString converts the Proof to ProofString
+func ProofToString(p *types.Proof) ProofString {
 	var ps ProofString
 	ps.A = make([]string, 3)
 	ps.B = make([][]string, 3)
@@ -497,10 +524,55 @@ func ProofToJson(p *types.Proof) ([]byte, error) {
 
 	ps.Protocol = "groth"
 
+	return ps
+}
+
+// ProofToJson outputs the Proof i Json format
+func ProofToJson(p *types.Proof) ([]byte, error) {
+	ps := ProofToString(p)
 	return json.Marshal(ps)
 }
 
-// ParseWitness parses binary file representation of the Witness into the Witness struct
+// ProofToHex converts the Proof to ProofString with hexadecimal strings
+func ProofToHex(p *types.Proof) ProofString {
+	var ps ProofString
+	ps.A = make([]string, 3)
+	ps.B = make([][]string, 3)
+	ps.B[0] = make([]string, 2)
+	ps.B[1] = make([]string, 2)
+	ps.B[2] = make([]string, 2)
+	ps.C = make([]string, 3)
+
+	a := p.A.Marshal()
+	ps.A[0] = "0x" + hex.EncodeToString(new(big.Int).SetBytes(a[:32]).Bytes())
+	ps.A[1] = "0x" + hex.EncodeToString(new(big.Int).SetBytes(a[32:64]).Bytes())
+	ps.A[2] = "1"
+
+	b := p.B.Marshal()
+	ps.B[0][1] = "0x" + hex.EncodeToString(new(big.Int).SetBytes(b[:32]).Bytes())
+	ps.B[0][0] = "0x" + hex.EncodeToString(new(big.Int).SetBytes(b[32:64]).Bytes())
+	ps.B[1][1] = "0x" + hex.EncodeToString(new(big.Int).SetBytes(b[64:96]).Bytes())
+	ps.B[1][0] = "0x" + hex.EncodeToString(new(big.Int).SetBytes(b[96:128]).Bytes())
+	ps.B[2][0] = "1"
+	ps.B[2][1] = "0"
+
+	c := p.C.Marshal()
+	ps.C[0] = "0x" + hex.EncodeToString(new(big.Int).SetBytes(c[:32]).Bytes())
+	ps.C[1] = "0x" + hex.EncodeToString(new(big.Int).SetBytes(c[32:64]).Bytes())
+	ps.C[2] = "1"
+
+	ps.Protocol = "groth"
+
+	return ps
+}
+
+// ProofToJsonHex outputs the Proof i Json format with hexadecimal strings
+func ProofToJsonHex(p *types.Proof) ([]byte, error) {
+	ps := ProofToHex(p)
+	return json.Marshal(ps)
+}
+
+// ParseWitnessBin parses binary file representation of the Witness into the Witness struct
 func ParseWitnessBin(f *os.File) (types.Witness, error) {
 	var w types.Witness
 	r := bufio.NewReader(f)

parsers/parsers_test.go

@@ -172,3 +172,27 @@ func TestParseWitnessBin(t *testing.T) {
 	testCircuitParseWitnessBin(t, "circuit1k")
 	testCircuitParseWitnessBin(t, "circuit5k")
 }
+
+func TestProofSmartContractFormat(t *testing.T) {
+	proofJson, err := ioutil.ReadFile("../testdata/circuit1k/proof.json")
+	require.Nil(t, err)
+	proof, err := ParseProof(proofJson)
+	require.Nil(t, err)
+	pS := ProofToString(proof)
+
+	pSC := ProofToSmartContractFormat(proof)
+	assert.Nil(t, err)
+	assert.Equal(t, pS.A[0], pSC.A[0])
+	assert.Equal(t, pS.A[1], pSC.A[1])
+	assert.Equal(t, pS.B[0][0], pSC.B[0][1])
+	assert.Equal(t, pS.B[0][1], pSC.B[0][0])
+	assert.Equal(t, pS.B[1][0], pSC.B[1][1])
+	assert.Equal(t, pS.B[1][1], pSC.B[1][0])
+	assert.Equal(t, pS.C[0], pSC.C[0])
+	assert.Equal(t, pS.C[1], pSC.C[1])
+	assert.Equal(t, pS.Protocol, pSC.Protocol)
+
+	pSC2 := ProofStringToSmartContractFormat(pS)
+	assert.Equal(t, pSC, pSC2)
+
+}

prover/gextra.go

@@ -0,0 +1,463 @@
+package prover
+
+import (
+	"math/big"
+
+	bn256 "github.com/ethereum/go-ethereum/crypto/bn256/cloudflare"
+	cryptoConstants "github.com/iden3/go-iden3-crypto/constants"
+)
+
+type tableG1 struct {
+	data []*bn256.G1
+}
+
+func (t tableG1) getData() []*bn256.G1 {
+	return t.data
+}
+
+// Compute table of gsize elements as ::
+//  Table[0] = Inf
+//  Table[1] = a[0]
+//  Table[2] = a[1]
+//  Table[3] = a[0]+a[1]
+//  .....
+//  Table[(1<<gsize)-1] = a[0]+a[1]+...+a[gsize-1]
+func (t *tableG1) newTableG1(a []*bn256.G1, gsize int, toaffine bool) {
+	// EC table
+	table := make([]*bn256.G1, 0)
+
+	// We need at least gsize elements. If not enough, fill with 0
+	aExt := make([]*bn256.G1, 0)
+	aExt = append(aExt, a...)
+
+	for i := len(a); i < gsize; i++ {
+		aExt = append(aExt, new(bn256.G1).ScalarBaseMult(big.NewInt(0)))
+	}
+
+	elG1 := new(bn256.G1).ScalarBaseMult(big.NewInt(0))
+	table = append(table, elG1)
+	lastPow2 := 1
+	nelems := 0
+	for i := 1; i < 1<<gsize; i++ {
+		elG1 := new(bn256.G1)
+		// if power of 2
+		if i&(i-1) == 0 {
+			lastPow2 = i
+			elG1.Set(aExt[nelems])
+			nelems++
+		} else {
+			elG1.Add(table[lastPow2], table[i-lastPow2])
+			// TODO bn256 doesn't export MakeAffine function. We need to fork repo
+			//table[i].MakeAffine()
+		}
+		table = append(table, elG1)
+	}
+	if toaffine {
+		for i := 0; i < len(table); i++ {
+			info := table[i].Marshal()
+			table[i].Unmarshal(info)
+		}
+	}
+	t.data = table
+}
+
+func (t tableG1) Marshal() []byte {
+	info := make([]byte, 0)
+	for _, el := range t.data {
+		info = append(info, el.Marshal()...)
+	}
+
+	return info
+}
+
+// Multiply scalar by precomputed table of G1 elements
+func (t *tableG1) mulTableG1(k []*big.Int, qPrev *bn256.G1, gsize int) *bn256.G1 {
+	// We need at least gsize elements. If not enough, fill with 0
+	kExt := make([]*big.Int, 0)
+	kExt = append(kExt, k...)
+
+	for i := len(k); i < gsize; i++ {
+		kExt = append(kExt, new(big.Int).SetUint64(0))
+	}
+
+	Q := new(bn256.G1).ScalarBaseMult(big.NewInt(0))
+
+	msb := getMsb(kExt)
+
+	for i := msb - 1; i >= 0; i-- {
+		// TODO. bn256 doesn't export double operation. We will need to fork repo and export it
+		Q = new(bn256.G1).Add(Q, Q)
+		b := getBit(kExt, i)
+		if b != 0 {
+			// TODO. bn256 doesn't export mixed addition (Jacobian + Affine), which is more efficient.
+			Q.Add(Q, t.data[b])
+		}
+	}
+	if qPrev != nil {
+		return Q.Add(Q, qPrev)
+	}
+	return Q
+}
+
+// Multiply scalar by precomputed table of G1 elements without intermediate doubling
+func mulTableNoDoubleG1(t []tableG1, k []*big.Int, qPrev *bn256.G1, gsize int) *bn256.G1 {
+	// We need at least gsize elements. If not enough, fill with 0
+	minNElems := len(t) * gsize
+	kExt := make([]*big.Int, 0)
+	kExt = append(kExt, k...)
+	for i := len(k); i < minNElems; i++ {
+		kExt = append(kExt, new(big.Int).SetUint64(0))
+	}
+	// Init Adders
+	nbitsQ := cryptoConstants.Q.BitLen()
+	Q := make([]*bn256.G1, nbitsQ)
+
+	for i := 0; i < nbitsQ; i++ {
+		Q[i] = new(bn256.G1).ScalarBaseMult(big.NewInt(0))
+	}
+
+	// Perform bitwise addition
+	for j := 0; j < len(t); j++ {
+		msb := getMsb(kExt[j*gsize : (j+1)*gsize])
+
+		for i := msb - 1; i >= 0; i-- {
+			b := getBit(kExt[j*gsize:(j+1)*gsize], i)
+			if b != 0 {
+				// TODO. bn256 doesn't export mixed addition (Jacobian + Affine), which is more efficient.
+				Q[i].Add(Q[i], t[j].data[b])
+			}
+		}
+	}
+
+	// Consolidate Addition
+	R := new(bn256.G1).Set(Q[nbitsQ-1])
+	for i := nbitsQ - 1; i > 0; i-- {
+		// TODO. bn256 doesn't export double operation. We will need to fork repo and export it
+		R = new(bn256.G1).Add(R, R)
+		R.Add(R, Q[i-1])
+	}
+
+	if qPrev != nil {
+		return R.Add(R, qPrev)
+	}
+	return R
+}
+
+// Compute tables within function. This solution should still be faster than std  multiplication
+// for gsize = 7
+func scalarMultG1(a []*bn256.G1, k []*big.Int, qPrev *bn256.G1, gsize int) *bn256.G1 {
+	ntables := int((len(a) + gsize - 1) / gsize)
+	table := tableG1{}
+	Q := new(bn256.G1).ScalarBaseMult(new(big.Int))
+
+	for i := 0; i < ntables-1; i++ {
+		table.newTableG1(a[i*gsize:(i+1)*gsize], gsize, false)
+		Q = table.mulTableG1(k[i*gsize:(i+1)*gsize], Q, gsize)
+	}
+	table.newTableG1(a[(ntables-1)*gsize:], gsize, false)
+	Q = table.mulTableG1(k[(ntables-1)*gsize:], Q, gsize)
+
+	if qPrev != nil {
+		return Q.Add(Q, qPrev)
+	}
+	return Q
+}
+
+// Multiply scalar by precomputed table of G1 elements without intermediate doubling
+func scalarMultNoDoubleG1(a []*bn256.G1, k []*big.Int, qPrev *bn256.G1, gsize int) *bn256.G1 {
+	ntables := int((len(a) + gsize - 1) / gsize)
+	table := tableG1{}
+
+	// We need at least gsize elements. If not enough, fill with 0
+	minNElems := ntables * gsize
+	kExt := make([]*big.Int, 0)
+	kExt = append(kExt, k...)
+	for i := len(k); i < minNElems; i++ {
+		kExt = append(kExt, new(big.Int).SetUint64(0))
+	}
+	// Init Adders
+	nbitsQ := cryptoConstants.Q.BitLen()
+	Q := make([]*bn256.G1, nbitsQ)
+
+	for i := 0; i < nbitsQ; i++ {
+		Q[i] = new(bn256.G1).ScalarBaseMult(big.NewInt(0))
+	}
+
+	// Perform bitwise addition
+	for j := 0; j < ntables-1; j++ {
+		table.newTableG1(a[j*gsize:(j+1)*gsize], gsize, false)
+		msb := getMsb(kExt[j*gsize : (j+1)*gsize])
+
+		for i := msb - 1; i >= 0; i-- {
+			b := getBit(kExt[j*gsize:(j+1)*gsize], i)
+			if b != 0 {
+				// TODO. bn256 doesn't export mixed addition (Jacobian + Affine), which is more efficient.
+				Q[i].Add(Q[i], table.data[b])
+			}
+		}
+	}
+	table.newTableG1(a[(ntables-1)*gsize:], gsize, false)
+	msb := getMsb(kExt[(ntables-1)*gsize:])
+
+	for i := msb - 1; i >= 0; i-- {
+		b := getBit(kExt[(ntables-1)*gsize:], i)
+		if b != 0 {
+			// TODO. bn256 doesn't export mixed addition (Jacobian + Affine), which is more efficient.
+			Q[i].Add(Q[i], table.data[b])
+		}
+	}
+
+	// Consolidate Addition
+	R := new(bn256.G1).Set(Q[nbitsQ-1])
+	for i := nbitsQ - 1; i > 0; i-- {
+		// TODO. bn256 doesn't export double operation. We will need to fork repo and export it
+		R = new(bn256.G1).Add(R, R)
+		R.Add(R, Q[i-1])
+	}
+	if qPrev != nil {
+		return R.Add(R, qPrev)
+	}
+	return R
+}
+
+/////
+
+// TODO - How can avoid replicating code in G2?
+//G2
+
+type tableG2 struct {
+	data []*bn256.G2
+}
+
+func (t tableG2) getData() []*bn256.G2 {
+	return t.data
+}
+
+// Compute table of gsize elements as ::
+//  Table[0] = Inf
+//  Table[1] = a[0]
+//  Table[2] = a[1]
+//  Table[3] = a[0]+a[1]
+//  .....
+//  Table[(1<<gsize)-1] = a[0]+a[1]+...+a[gsize-1]
+// TODO -> toaffine = True doesnt work. Problem with Marshal/Unmarshal
+func (t *tableG2) newTableG2(a []*bn256.G2, gsize int, toaffine bool) {
+	// EC table
+	table := make([]*bn256.G2, 0)
+
+	// We need at least gsize elements. If not enough, fill with 0
+	aExt := make([]*bn256.G2, 0)
+	aExt = append(aExt, a...)
+
+	for i := len(a); i < gsize; i++ {
+		aExt = append(aExt, new(bn256.G2).ScalarBaseMult(big.NewInt(0)))
+	}
+
+	elG2 := new(bn256.G2).ScalarBaseMult(big.NewInt(0))
+	table = append(table, elG2)
+	lastPow2 := 1
+	nelems := 0
+	for i := 1; i < 1<<gsize; i++ {
+		elG2 := new(bn256.G2)
+		// if power of 2
+		if i&(i-1) == 0 {
+			lastPow2 = i
+			elG2.Set(aExt[nelems])
+			nelems++
+		} else {
+			elG2.Add(table[lastPow2], table[i-lastPow2])
+			// TODO bn256 doesn't export MakeAffine function. We need to fork repo
+			//table[i].MakeAffine()
+		}
+		table = append(table, elG2)
+	}
+	if toaffine {
+		for i := 0; i < len(table); i++ {
+			info := table[i].Marshal()
+			table[i].Unmarshal(info)
+		}
+	}
+	t.data = table
+}
+
+func (t tableG2) Marshal() []byte {
+	info := make([]byte, 0)
+	for _, el := range t.data {
+		info = append(info, el.Marshal()...)
+	}
+
+	return info
+}
+
+// Multiply scalar by precomputed table of G2 elements
+func (t *tableG2) mulTableG2(k []*big.Int, qPrev *bn256.G2, gsize int) *bn256.G2 {
+	// We need at least gsize elements. If not enough, fill with 0
+	kExt := make([]*big.Int, 0)
+	kExt = append(kExt, k...)
+
+	for i := len(k); i < gsize; i++ {
+		kExt = append(kExt, new(big.Int).SetUint64(0))
+	}
+
+	Q := new(bn256.G2).ScalarBaseMult(big.NewInt(0))
+
+	msb := getMsb(kExt)
+
+	for i := msb - 1; i >= 0; i-- {
+		// TODO. bn256 doesn't export double operation. We will need to fork repo and export it
+		Q = new(bn256.G2).Add(Q, Q)
+		b := getBit(kExt, i)
+		if b != 0 {
+			// TODO. bn256 doesn't export mixed addition (Jacobian + Affine), which is more efficient.
+			Q.Add(Q, t.data[b])
+		}
+	}
+	if qPrev != nil {
+		return Q.Add(Q, qPrev)
+	}
+	return Q
+}
+
+// Multiply scalar by precomputed table of G2 elements without intermediate doubling
+func mulTableNoDoubleG2(t []tableG2, k []*big.Int, qPrev *bn256.G2, gsize int) *bn256.G2 {
+	// We need at least gsize elements. If not enough, fill with 0
+	minNElems := len(t) * gsize
+	kExt := make([]*big.Int, 0)
+	kExt = append(kExt, k...)
+	for i := len(k); i < minNElems; i++ {
+		kExt = append(kExt, new(big.Int).SetUint64(0))
+	}
+	// Init Adders
+	nbitsQ := cryptoConstants.Q.BitLen()
+	Q := make([]*bn256.G2, nbitsQ)
+
+	for i := 0; i < nbitsQ; i++ {
+		Q[i] = new(bn256.G2).ScalarBaseMult(big.NewInt(0))
+	}
+
+	// Perform bitwise addition
+	for j := 0; j < len(t); j++ {
+		msb := getMsb(kExt[j*gsize : (j+1)*gsize])
+
+		for i := msb - 1; i >= 0; i-- {
+			b := getBit(kExt[j*gsize:(j+1)*gsize], i)
+			if b != 0 {
+				// TODO. bn256 doesn't export mixed addition (Jacobian + Affine), which is more efficient.
+				Q[i].Add(Q[i], t[j].data[b])
+			}
+		}
+	}
+
+	// Consolidate Addition
+	R := new(bn256.G2).Set(Q[nbitsQ-1])
+	for i := nbitsQ - 1; i > 0; i-- {
+		// TODO. bn256 doesn't export double operation. We will need to fork repo and export it
+		R = new(bn256.G2).Add(R, R)
+		R.Add(R, Q[i-1])
+	}
+	if qPrev != nil {
+		return R.Add(R, qPrev)
+	}
+	return R
+}
+
+// Compute tables within function. This solution should still be faster than std  multiplication
+// for gsize = 7
+func scalarMultG2(a []*bn256.G2, k []*big.Int, qPrev *bn256.G2, gsize int) *bn256.G2 {
+	ntables := int((len(a) + gsize - 1) / gsize)
+	table := tableG2{}
+	Q := new(bn256.G2).ScalarBaseMult(new(big.Int))
+
+	for i := 0; i < ntables-1; i++ {
+		table.newTableG2(a[i*gsize:(i+1)*gsize], gsize, false)
+		Q = table.mulTableG2(k[i*gsize:(i+1)*gsize], Q, gsize)
+	}
+	table.newTableG2(a[(ntables-1)*gsize:], gsize, false)
+	Q = table.mulTableG2(k[(ntables-1)*gsize:], Q, gsize)
+
+	if qPrev != nil {
+		return Q.Add(Q, qPrev)
+	}
+	return Q
+}
+
+// Multiply scalar by precomputed table of G2 elements without intermediate doubling
+func scalarMultNoDoubleG2(a []*bn256.G2, k []*big.Int, qPrev *bn256.G2, gsize int) *bn256.G2 {
+	ntables := int((len(a) + gsize - 1) / gsize)
+	table := tableG2{}
+
+	// We need at least gsize elements. If not enough, fill with 0
+	minNElems := ntables * gsize
+	kExt := make([]*big.Int, 0)
+	kExt = append(kExt, k...)
+	for i := len(k); i < minNElems; i++ {
+		kExt = append(kExt, new(big.Int).SetUint64(0))
+	}
+	// Init Adders
+	nbitsQ := cryptoConstants.Q.BitLen()
+	Q := make([]*bn256.G2, nbitsQ)
+
+	for i := 0; i < nbitsQ; i++ {
+		Q[i] = new(bn256.G2).ScalarBaseMult(big.NewInt(0))
+	}
+
+	// Perform bitwise addition
+	for j := 0; j < ntables-1; j++ {
+		table.newTableG2(a[j*gsize:(j+1)*gsize], gsize, false)
+		msb := getMsb(kExt[j*gsize : (j+1)*gsize])
+
+		for i := msb - 1; i >= 0; i-- {
+			b := getBit(kExt[j*gsize:(j+1)*gsize], i)
+			if b != 0 {
+				// TODO. bn256 doesn't export mixed addition (Jacobian + Affine), which is more efficient.
+				Q[i].Add(Q[i], table.data[b])
+			}
+		}
+	}
+	table.newTableG2(a[(ntables-1)*gsize:], gsize, false)
+	msb := getMsb(kExt[(ntables-1)*gsize:])
+
+	for i := msb - 1; i >= 0; i-- {
+		b := getBit(kExt[(ntables-1)*gsize:], i)
+		if b != 0 {
+			// TODO. bn256 doesn't export mixed addition (Jacobian + Affine), which is more efficient.
+			Q[i].Add(Q[i], table.data[b])
+		}
+	}
+
+	// Consolidate Addition
+	R := new(bn256.G2).Set(Q[nbitsQ-1])
+	for i := nbitsQ - 1; i > 0; i-- {
+		// TODO. bn256 doesn't export double operation. We will need to fork repo and export it
+		R = new(bn256.G2).Add(R, R)
+		R.Add(R, Q[i-1])
+	}
+	if qPrev != nil {
+		return R.Add(R, qPrev)
+	}
+	return R
+}
+
+// Return most significant bit position in a group of Big Integers
+func getMsb(k []*big.Int) int {
+	msb := 0
+
+	for _, el := range k {
+		tmpMsb := el.BitLen()
+		if tmpMsb > msb {
+			msb = tmpMsb
+		}
+	}
+	return msb
+}
+
+// Return ith bit in group of Big Integers
+func getBit(k []*big.Int, i int) uint {
+	tableIdx := uint(0)
+
+	for idx, el := range k {
+		b := el.Bit(i)
+		tableIdx += (b << idx)
+	}
+	return tableIdx
+}

prover/gextra_test.go

@@ -0,0 +1,163 @@
+package prover
+
+import (
+	"bytes"
+	"crypto/rand"
+	"fmt"
+	"math/big"
+	"testing"
+	"time"
+
+	bn256 "github.com/ethereum/go-ethereum/crypto/bn256/cloudflare"
+)
+
+const (
+	N1 = 5000
+	N2 = 5000
+)
+
+func randomBigIntArray(n int) []*big.Int {
+	var p []*big.Int
+	for i := 0; i < n; i++ {
+		pi := randBI()
+		p = append(p, pi)
+	}
+
+	return p
+}
+
+func randomG1Array(n int) []*bn256.G1 {
+	arrayG1 := make([]*bn256.G1, n)
+
+	for i := 0; i < n; i++ {
+		_, arrayG1[i], _ = bn256.RandomG1(rand.Reader)
+	}
+	return arrayG1
+}
+
+func randomG2Array(n int) []*bn256.G2 {
+	arrayG2 := make([]*bn256.G2, n)
+
+	for i := 0; i < n; i++ {
+		_, arrayG2[i], _ = bn256.RandomG2(rand.Reader)
+	}
+	return arrayG2
+}
+
+func TestTableG1(t *testing.T) {
+	n := N1
+
+	// init scalar
+	var arrayW = randomBigIntArray(n)
+	// init G1 array
+	var arrayG1 = randomG1Array(n)
+
+	beforeT := time.Now()
+	Q1 := new(bn256.G1).ScalarBaseMult(new(big.Int))
+	for i := 0; i < n; i++ {
+		Q1.Add(Q1, new(bn256.G1).ScalarMult(arrayG1[i], arrayW[i]))
+	}
+	fmt.Println("Std. Mult. time elapsed:", time.Since(beforeT))
+
+	for gsize := 2; gsize < 10; gsize++ {
+		ntables := int((n + gsize - 1) / gsize)
+		table := make([]tableG1, ntables)
+
+		for i := 0; i < ntables-1; i++ {
+			table[i].newTableG1(arrayG1[i*gsize:(i+1)*gsize], gsize, true)
+		}
+		table[ntables-1].newTableG1(arrayG1[(ntables-1)*gsize:], gsize, true)
+
+		beforeT = time.Now()
+		Q2 := new(bn256.G1).ScalarBaseMult(new(big.Int))
+		for i := 0; i < ntables-1; i++ {
+			Q2 = table[i].mulTableG1(arrayW[i*gsize:(i+1)*gsize], Q2, gsize)
+		}
+		Q2 = table[ntables-1].mulTableG1(arrayW[(ntables-1)*gsize:], Q2, gsize)
+		fmt.Printf("Gsize : %d, TMult time elapsed: %s\n", gsize, time.Since(beforeT))
+
+		beforeT = time.Now()
+		Q3 := scalarMultG1(arrayG1, arrayW, nil, gsize)
+		fmt.Printf("Gsize : %d, TMult time elapsed (inc table comp): %s\n", gsize, time.Since(beforeT))
+
+		beforeT = time.Now()
+		Q4 := mulTableNoDoubleG1(table, arrayW, nil, gsize)
+		fmt.Printf("Gsize : %d, TMultNoDouble time elapsed: %s\n", gsize, time.Since(beforeT))
+
+		beforeT = time.Now()
+		Q5 := scalarMultNoDoubleG1(arrayG1, arrayW, nil, gsize)
+		fmt.Printf("Gsize : %d, TMultNoDouble time elapsed (inc table comp): %s\n", gsize, time.Since(beforeT))
+
+		if bytes.Compare(Q1.Marshal(), Q2.Marshal()) != 0 {
+			t.Error("Error in TMult")
+		}
+		if bytes.Compare(Q1.Marshal(), Q3.Marshal()) != 0 {
+			t.Error("Error in  TMult with table comp")
+		}
+		if bytes.Compare(Q1.Marshal(), Q4.Marshal()) != 0 {
+			t.Error("Error in  TMultNoDouble")
+		}
+		if bytes.Compare(Q1.Marshal(), Q5.Marshal()) != 0 {
+			t.Error("Error in  TMultNoDoublee with table comp")
+		}
+	}
+}
+
+func TestTableG2(t *testing.T) {
+	n := N2
+
+	// init scalar
+	var arrayW = randomBigIntArray(n)
+	// init G2 array
+	var arrayG2 = randomG2Array(n)
+
+	beforeT := time.Now()
+	Q1 := new(bn256.G2).ScalarBaseMult(new(big.Int))
+	for i := 0; i < n; i++ {
+		Q1.Add(Q1, new(bn256.G2).ScalarMult(arrayG2[i], arrayW[i]))
+	}
+	fmt.Println("Std. Mult. time elapsed:", time.Since(beforeT))
+
+	for gsize := 2; gsize < 10; gsize++ {
+		ntables := int((n + gsize - 1) / gsize)
+		table := make([]tableG2, ntables)
+
+		for i := 0; i < ntables-1; i++ {
+			table[i].newTableG2(arrayG2[i*gsize:(i+1)*gsize], gsize, false)
+		}
+		table[ntables-1].newTableG2(arrayG2[(ntables-1)*gsize:], gsize, false)
+
+		beforeT = time.Now()
+		Q2 := new(bn256.G2).ScalarBaseMult(new(big.Int))
+		for i := 0; i < ntables-1; i++ {
+			Q2 = table[i].mulTableG2(arrayW[i*gsize:(i+1)*gsize], Q2, gsize)
+		}
+		Q2 = table[ntables-1].mulTableG2(arrayW[(ntables-1)*gsize:], Q2, gsize)
+		fmt.Printf("Gsize : %d, TMult time elapsed: %s\n", gsize, time.Since(beforeT))
+
+		beforeT = time.Now()
+		Q3 := scalarMultG2(arrayG2, arrayW, nil, gsize)
+		fmt.Printf("Gsize : %d, TMult time elapsed (inc table comp): %s\n", gsize, time.Since(beforeT))
+
+		beforeT = time.Now()
+		Q4 := mulTableNoDoubleG2(table, arrayW, nil, gsize)
+		fmt.Printf("Gsize : %d, TMultNoDouble time elapsed: %s\n", gsize, time.Since(beforeT))
+
+		beforeT = time.Now()
+		Q5 := scalarMultNoDoubleG2(arrayG2, arrayW, nil, gsize)
+		fmt.Printf("Gsize : %d, TMultNoDouble time elapsed (inc table comp): %s\n", gsize, time.Since(beforeT))
+
+		if bytes.Compare(Q1.Marshal(), Q2.Marshal()) != 0 {
+			t.Error("Error in TMult")
+		}
+		if bytes.Compare(Q1.Marshal(), Q3.Marshal()) != 0 {
+			t.Error("Error in  TMult with table comp")
+		}
+		if bytes.Compare(Q1.Marshal(), Q4.Marshal()) != 0 {
+			t.Error("Error in  TMultNoDouble")
+		}
+		if bytes.Compare(Q1.Marshal(), Q5.Marshal()) != 0 {
+			t.Error("Error in  TMultNoDoublee with table comp")
+		}
+	}
+}

prover/prover.go

@@ -10,6 +10,7 @@ import (
 	bn256 "github.com/ethereum/go-ethereum/crypto/bn256/cloudflare"
 	"github.com/iden3/go-circom-prover-verifier/types"
 	"github.com/iden3/go-iden3-crypto/utils"
+	//"fmt"
 )
 
 // Proof is the data structure of the Groth16 zkSNARK proof
@@ -42,6 +43,11 @@ type Pk struct {
 // Witness contains the witness
 type Witness []*big.Int
 
+// Group Size
+const (
+	GSIZE = 6
+)
+
 func randBigInt() (*big.Int, error) {
 	maxbits := types.R.BitLen()
 	b := make([]byte, (maxbits/8)-1)
@@ -75,18 +81,33 @@ func GenerateProof(pk *types.Pk, w types.Witness) (*types.Proof, []*big.Int, err
 	proofB := arrayOfZeroesG2(numcpu)
 	proofC := arrayOfZeroesG1(numcpu)
 	proofBG1 := arrayOfZeroesG1(numcpu)
+	gsize := GSIZE
 	var wg1 sync.WaitGroup
 	wg1.Add(numcpu)
 	for _cpu, _ranges := range ranges(pk.NVars, numcpu) {
 		// split 1
 		go func(cpu int, ranges [2]int) {
-			for i := ranges[0]; i < ranges[1]; i++ {
+			proofA[cpu] = scalarMultNoDoubleG1(pk.A[ranges[0]:ranges[1]],
-				proofA[cpu].Add(proofA[cpu], new(bn256.G1).ScalarMult(pk.A[i], w[i]))
+				w[ranges[0]:ranges[1]],
-				proofB[cpu].Add(proofB[cpu], new(bn256.G2).ScalarMult(pk.B2[i], w[i]))
+				proofA[cpu],
-				proofBG1[cpu].Add(proofBG1[cpu], new(bn256.G1).ScalarMult(pk.B1[i], w[i]))
+				gsize)
-				if i >= pk.NPublic+1 {
+			proofB[cpu] = scalarMultNoDoubleG2(pk.B2[ranges[0]:ranges[1]],
-					proofC[cpu].Add(proofC[cpu], new(bn256.G1).ScalarMult(pk.C[i], w[i]))
+				w[ranges[0]:ranges[1]],
+				proofB[cpu],
+				gsize)
+			proofBG1[cpu] = scalarMultNoDoubleG1(pk.B1[ranges[0]:ranges[1]],
+				w[ranges[0]:ranges[1]],
+				proofBG1[cpu],
+				gsize)
+			minLim := pk.NPublic + 1
+			if ranges[0] > pk.NPublic+1 {
+				minLim = ranges[0]
 			}
+			if ranges[1] > pk.NPublic+1 {
+				proofC[cpu] = scalarMultNoDoubleG1(pk.C[minLim:ranges[1]],
+					w[minLim:ranges[1]],
+					proofC[cpu],
+					gsize)
 			}
 			wg1.Done()
 		}(_cpu, _ranges)
@@ -121,9 +142,10 @@ func GenerateProof(pk *types.Pk, w types.Witness) (*types.Proof, []*big.Int, err
 	for _cpu, _ranges := range ranges(len(h), numcpu) {
 		// split 2
 		go func(cpu int, ranges [2]int) {
-			for i := ranges[0]; i < ranges[1]; i++ {
+			proofC[cpu] = scalarMultNoDoubleG1(pk.HExps[ranges[0]:ranges[1]],
-				proofC[cpu].Add(proofC[cpu], new(bn256.G1).ScalarMult(pk.HExps[i], h[i]))
+				h[ranges[0]:ranges[1]],
-			}
+				proofC[cpu],
+				gsize)
 			wg2.Done()
 		}(_cpu, _ranges)
 	}

prover/tables.md

@@ -0,0 +1,49 @@
+# Tables Pre-calculation
+The most time consuming part of a ZKSnark proof calculation is the scalar multiplication of elliptic curve points. Direct mechanism accumulates each multiplication. However, prover only needs the total accumulation.
+
+There are two potential improvements to the naive approach:
+
+1. Apply Strauss-Shamir method (https://stackoverflow.com/questions/50993471/ec-scalar-multiplication-with-strauss-shamir-method).
+2. Leave the doubling operation for the last step
+
+Both options can be combined. 
+
+In the following table, we show the results of using the naive method, Srauss-Shamir and Strauss-Shamir + No doubling. These last two options are repeated for different table grouping order.
+
+There are 50000 G1 Elliptical Curve Points, and the scalars are 254 bits (BN256 curve). 
+
+There may be some concern on the additional size of the tables since they need to be loaded into a smartphone during the proof, and the time required to load these tables may exceed the benefits. If this is a problem, another althernative is to compute the tables during the proof itself. Depending on the Group Size, timing may be better than the naive approach.
+
+
+| Algorithm (G1) | GS 2 | GS 3 | GS 4 | GS 5 | GS 6 | GS 7 | GS 8 | GS 9 | 
+|---|---|---|--|---|---|---|---|---|
+| Naive | 6.63s | - | - | - | - | - |  - | - |
+| Strauss |  13.16s | 9.03s | 6.95s | 5.61s | 4.91s | 4.26s | 3.88s | 3.54 s |
+| Strauss + Table Computation | 16.13s | 11.32s | 8.47s | 7.10s | 6.2s | 5.94s | 6.01s | 6.69s |
+| No Doubling | 3.74s | 3.00s | 2.38s | 1.96s | 1.79s | 1.54s | 1.50s | 1.44s|
+| No Doubling + Table Computation  | 6.83s | 5.1s | 4.16s | 3.52s| 3.22s | 3.21s | 3.57s | 4.56s |
+
+There are 5000 G2 Elliptical Curve Points, and the scalars are 254 bits (BN256 curve). 
+
+| Algorithm (G2) | GS 2 | GS 3 | GS 4 | GS 5 | GS 6 | GS 7 | GS 8 | GS 9 | 
+|---|---|---|--|---|---|---|---|---|
+| Naive | 3.55s | | | | | | | |
+| Strauss |  3.55s | 2.54s | 1.96s | 1.58s |  1.38s | 1.20s | 1.03s | 937ms |
+| Strauss + Table Computation | 3.59s | 2.58s | 2.04s | 1.71s | 1.51s | 1.46s | 1.51s | 1.82s |
+| No Doubling | 1.49s | 1.16s | 952ms | 719ms | 661ms | 548ms | 506ms| 444ms |
+| No Doubling + Table Computation  | 1.55s |  1.21s | 984ms | 841ms | 826ms | 847ms | 1.03s | 1.39s |
+
+| GS | Extra Disk Space per Constraint (G1)|
+|----|--------|
+| 2  |  64 B  |
+| 3  |  106 B |
+| 4  |  192 B |
+| 5  |  346 B |
+| 6  |  618 B |
+| 7  |  1106 B |
+| 8  |  1984 B |
+| 9  |  3577 B |
+| N  |  2^(N+6)/N - 64 B |
+
+Extra disk space per constraint in G2 is twice the requirements for G1
+