Feat: GKR-Hashers

internal/generator/backend/template/gkr/gkr.go.tmpl

@@ -771,13 +771,13 @@ func (gateAPI) Println(a ...frontend.Variable) {
 
 	for i, v := range a {
 		if _, err := x.SetInterface(v); err != nil {
-			toPrint[i] = x.String()
-		} else {
 			if s, ok := v.(string); ok {
 				toPrint[i] = s
 				continue
 			}
 			panic(fmt.Errorf("not numeric or string: %w", err))
+		} else {
+			toPrint[i] = x.String()
 		}
 	}
 	fmt.Println(toPrint...)

std/hash/hash.go

@@ -5,6 +5,8 @@
 package hash
 
 import (
+	"fmt"
+
 	"github.com/consensys/gnark/frontend"
 	"github.com/consensys/gnark/std/math/uints"
 )
@@ -114,7 +116,7 @@ type merkleDamgardHasher struct {
 
 // NewMerkleDamgardHasher transforms a 2-1 one-way function into a hash
 // initialState is a value whose preimage is not known
-func NewMerkleDamgardHasher(api frontend.API, f Compressor, initialState frontend.Variable) FieldHasher {
+func NewMerkleDamgardHasher(api frontend.API, f Compressor, initialState frontend.Variable) StateStorer {
 	return &merkleDamgardHasher{
 		state: initialState,
 		iv:    initialState,
@@ -136,3 +138,18 @@ func (h *merkleDamgardHasher) Write(data ...frontend.Variable) {
 func (h *merkleDamgardHasher) Sum() frontend.Variable {
 	return h.state
 }
+
+func (h *merkleDamgardHasher) State() []frontend.Variable {
+	return []frontend.Variable{h.state}
+}
+
+func (h *merkleDamgardHasher) SetState(state []frontend.Variable) error {
+	if h.state != h.iv {
+		return fmt.Errorf("the hasher is not in an initial state; reset before attempting to set the state")
+	}
+	if len(state) != 1 {
+		return fmt.Errorf("expected one state variable, got %d", len(state))
+	}
+	h.state = state[0]
+	return nil
+}

std/hash/mimc/gkr-mimc/gkr-mimc.go

@@ -0,0 +1,17 @@
+package gkr_mimc
+
+import (
+	"fmt"
+
+	"github.com/consensys/gnark/frontend"
+	"github.com/consensys/gnark/std/hash"
+	gkr_mimc "github.com/consensys/gnark/std/permutation/gkr-mimc"
+)
+
+func New(api frontend.API) (hash.StateStorer, error) {
+	f, err := gkr_mimc.NewCompressor(api)
+	if err != nil {
+		return nil, fmt.Errorf("could not create mimc hasher: %w", err)
+	}
+	return hash.NewMerkleDamgardHasher(api, f, 0), nil
+}

std/hash/mimc/gkr-mimc/gkr-mimc_test.go

@@ -0,0 +1,172 @@
+package gkr_mimc
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"slices"
+	"testing"
+
+	"github.com/consensys/gnark-crypto/ecc"
+	"github.com/consensys/gnark/backend/plonk"
+	"github.com/consensys/gnark/constraint"
+	"github.com/consensys/gnark/frontend"
+	"github.com/consensys/gnark/frontend/cs/scs"
+	"github.com/consensys/gnark/std/hash/mimc"
+	"github.com/consensys/gnark/test"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGkrMiMC(t *testing.T) {
+	lengths := []int{1, 2, 3}
+	vals := make([]frontend.Variable, len(lengths)*2)
+	for i := range vals {
+		vals[i] = i + 1
+	}
+
+	for _, length := range lengths {
+		circuit := &testGkrMiMCCircuit{
+			In: make([]frontend.Variable, length*2),
+		}
+		assignment := &testGkrMiMCCircuit{
+			In: slices.Clone(vals[:length*2]),
+		}
+
+		test.NewAssert(t).CheckCircuit(circuit, test.WithValidAssignment(assignment))
+	}
+}
+
+type testGkrMiMCCircuit struct {
+	In        []frontend.Variable
+	skipCheck bool
+}
+
+func (c *testGkrMiMCCircuit) Define(api frontend.API) error {
+	gkrmimc, err := New(api)
+	if err != nil {
+		return err
+	}
+
+	plainMiMC, err := mimc.New(api)
+	if err != nil {
+		return err
+	}
+
+	// first check that empty input is handled correctly
+	api.AssertIsEqual(gkrmimc.Sum(), plainMiMC.Sum())
+
+	ins := [][]frontend.Variable{c.In[:len(c.In)/2], c.In[len(c.In)/2:]}
+	for _, in := range ins {
+		gkrmimc.Reset()
+		gkrmimc.Write(in...)
+		res := gkrmimc.Sum()
+
+		if !c.skipCheck {
+			plainMiMC.Reset()
+			plainMiMC.Write(in...)
+			expected := plainMiMC.Sum()
+			api.AssertIsEqual(expected, res)
+		}
+	}
+
+	return nil
+}
+
+func TestGkrMiMCCompiles(t *testing.T) {
+	const n = 52000
+	circuit := testGkrMiMCCircuit{
+		In: make([]frontend.Variable, n),
+	}
+	cs, err := frontend.Compile(ecc.BLS12_377.ScalarField(), scs.NewBuilder, &circuit, frontend.WithCapacity(27_000_000))
+	require.NoError(t, err)
+	fmt.Println(cs.GetNbConstraints(), "constraints")
+}
+
+type hashTreeCircuit struct {
+	Leaves []frontend.Variable
+}
+
+func (c hashTreeCircuit) Define(api frontend.API) error {
+	if len(c.Leaves) == 0 {
+		return errors.New("no hashing to do")
+	}
+
+	hsh, err := New(api)
+	if err != nil {
+		return err
+	}
+
+	layer := slices.Clone(c.Leaves)
+
+	for len(layer) > 1 {
+		if len(layer)%2 == 1 {
+			layer = append(layer, 0) // pad with zero
+		}
+
+		for i := range len(layer) / 2 {
+			hsh.Reset()
+			hsh.Write(layer[2*i], layer[2*i+1])
+			layer[i] = hsh.Sum()
+		}
+
+		layer = layer[:len(layer)/2]
+	}
+
+	api.AssertIsDifferent(layer[0], 0)
+	return nil
+}
+
+func loadCs(t require.TestingT, fileTitle string, circuit frontend.Circuit) constraint.ConstraintSystem {
+	filename := filepath.Join(os.TempDir(), fileTitle)
+	_, err := os.Stat(filename)
+
+	if os.IsNotExist(err) {
+		// actually compile
+		cs, err := frontend.Compile(ecc.BLS12_377.ScalarField(), scs.NewBuilder, circuit)
+		require.NoError(t, err)
+		f, err := os.Create(filename)
+		require.NoError(t, err)
+		defer func() {
+			require.NoError(t, f.Close())
+		}()
+		_, err = cs.WriteTo(f)
+		require.NoError(t, err)
+		return cs
+	}
+
+	f, err := os.Open(filename)
+	require.NoError(t, err)
+	defer func() {
+		require.NoError(t, f.Close())
+	}()
+
+	cs := plonk.NewCS(ecc.BLS12_377)
+
+	_, err = cs.ReadFrom(f)
+	require.NoError(t, err)
+
+	return cs
+}
+
+func BenchmarkHashTree(b *testing.B) {
+	const size = 1 << 15 // about 2 ^ 16 total hashes
+
+	circuit := hashTreeCircuit{
+		Leaves: make([]frontend.Variable, size),
+	}
+	assignment := hashTreeCircuit{
+		Leaves: make([]frontend.Variable, size),
+	}
+
+	for i := range assignment.Leaves {
+		assignment.Leaves[i] = i
+	}
+
+	cs := loadCs(b, "gkrmimc_hashtree.cs", &circuit)
+
+	w, err := frontend.NewWitness(&assignment, ecc.BLS12_377.ScalarField())
+	require.NoError(b, err)
+
+	require.NoError(b, cs.IsSolved(w))
+}

std/hash/mimc/mimc.go

@@ -34,7 +34,7 @@ func NewMiMC(api frontend.API) (MiMC, error) {
 // NB! See the package documentation for length extension attack consideration.
 //
 // [gnark-crypto]: https://pkg.go.dev/github.com/consensys/gnark-crypto/hash
-func New(api frontend.API) (hash.FieldHasher, error) {
+func New(api frontend.API) (hash.StateStorer, error) {
 	h, err := NewMiMC(api)
 	if err != nil {
 		return nil, err
@@ -43,5 +43,7 @@ func New(api frontend.API) (hash.FieldHasher, error) {
 }
 
 func init() {
-	hash.Register(hash.MIMC, New)
+	hash.Register(hash.MIMC, func(api frontend.API) (hash.FieldHasher, error) {
+		return New(api)
+	})
 }