feat: merkle damgard and poseidon2

go.mod

@@ -9,7 +9,7 @@ require (
 	github.com/blang/semver/v4 v4.0.0
 	github.com/consensys/bavard v0.1.27
 	github.com/consensys/compress v0.2.5
-	github.com/consensys/gnark-crypto v0.15.0
+	github.com/consensys/gnark-crypto v0.16.1-0.20250205153847-10a243d332ca
 	github.com/fxamacker/cbor/v2 v2.7.0
 	github.com/google/go-cmp v0.6.0
 	github.com/google/pprof v0.0.0-20240727154555-813a5fbdbec8

go.sum

@@ -61,8 +61,8 @@ github.com/consensys/bavard v0.1.27 h1:j6hKUrGAy/H+gpNrpLU3I26n1yc+VMGmd6ID5+gAh
 github.com/consensys/bavard v0.1.27/go.mod h1:k/zVjHHC4B+PQy1Pg7fgvG3ALicQw540Crag8qx+dZs=
 github.com/consensys/compress v0.2.5 h1:gJr1hKzbOD36JFsF1AN8lfXz1yevnJi1YolffY19Ntk=
 github.com/consensys/compress v0.2.5/go.mod h1:pyM+ZXiNUh7/0+AUjUf9RKUM6vSH7T/fsn5LLS0j1Tk=
-github.com/consensys/gnark-crypto v0.15.0 h1:OXsWnhheHV59eXIzhL5OIexa/vqTK8wtRYQCtwfMDtY=
-github.com/consensys/gnark-crypto v0.15.0/go.mod h1:Ke3j06ndtPTVvo++PhGNgvm+lgpLvzbcE2MqljY7diU=
+github.com/consensys/gnark-crypto v0.16.1-0.20250205153847-10a243d332ca h1:u6iXwMBfbXODF+hDSwKSTBg6yfD3+eMX6o3PILAK474=
+github.com/consensys/gnark-crypto v0.16.1-0.20250205153847-10a243d332ca/go.mod h1:Ke3j06ndtPTVvo++PhGNgvm+lgpLvzbcE2MqljY7diU=
 github.com/coreos/go-semver v0.3.0/go.mod h1:nnelYz7RCh+5ahJtPPxZlU+153eP4D4r3EedlOD2RNk=
 github.com/coreos/go-systemd/v22 v22.3.2/go.mod h1:Y58oyj3AT4RCenI/lSvhwexgC+NSVTIJ3seZv2GcEnc=
 github.com/coreos/go-systemd/v22 v22.5.0/go.mod h1:Y58oyj3AT4RCenI/lSvhwexgC+NSVTIJ3seZv2GcEnc=

std/hash/hash.go

@@ -5,7 +5,7 @@
 package hash
 
 import (
-	"errors"
+	"fmt"
 	"sync"
 
 	"github.com/consensys/gnark/frontend"
@@ -58,7 +58,7 @@ func GetFieldHasher(name string, api frontend.API) (FieldHasher, error) {
 	defer lock.RUnlock()
 	builder, ok := builderRegistry[name]
 	if !ok {
-		return nil, errors.New("hash function not found")
+		return nil, fmt.Errorf("hash function \"%s\" not registered", name)
 	}
 	return builder(api)
 }
@@ -87,3 +87,48 @@ type BinaryFixedLengthHasher interface {
 	// FixedLengthSum returns digest of the first length bytes.
 	FixedLengthSum(length frontend.Variable) []uints.U8
 }
+
+// Compressor is a 2-1 one-way function. It takes two inputs and compresses
+// them into one output.
+//
+// NB! This is lossy compression, meaning that the output is not guaranteed to
+// be unique for different inputs. The output is guaranteed to be the same for
+// the same inputs.
+//
+// The Compressor is used in the Merkle-Damgard construction to build a hash
+// function.
+type Compressor interface {
+	Compress(frontend.Variable, frontend.Variable) frontend.Variable
+}
+
+type merkleDamgardHasher struct {
+	state frontend.Variable
+	iv    frontend.Variable
+	f     Compressor
+	api   frontend.API
+}
+
+// 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 {
+	return &merkleDamgardHasher{
+		state: initialState,
+		iv:    initialState,
+		f:     f,
+		api:   api,
+	}
+}
+
+func (h *merkleDamgardHasher) Reset() {
+	h.state = h.iv
+}
+
+func (h *merkleDamgardHasher) Write(data ...frontend.Variable) {
+	for _, d := range data {
+		h.state = h.f.Compress(h.state, d)
+	}
+}
+
+func (h *merkleDamgardHasher) Sum() frontend.Variable {
+	return h.state
+}

std/hash/poseidon2/poseidon2.go

@@ -0,0 +1,19 @@
+package poseidon2
+
+import (
+	"fmt"
+
+	"github.com/consensys/gnark/frontend"
+	"github.com/consensys/gnark/std/hash"
+	poseidon2 "github.com/consensys/gnark/std/permutation/poseidon2"
+)
+
+// NewMerkleDamgardHasher returns a Poseidon2 hasher using the Merkle-Damgard
+// construction with the default parameters.
+func NewMerkleDamgardHasher(api frontend.API) (hash.FieldHasher, error) {
+	f, err := poseidon2.NewPoseidon2(api)
+	if err != nil {
+		return nil, fmt.Errorf("could not create poseidon2 hasher: %w", err)
+	}
+	return hash.NewMerkleDamgardHasher(api, f, 0), nil
+}

std/hash/poseidon2/poseidon2_test.go

@@ -0,0 +1,41 @@
+package poseidon2
+
+import (
+	"testing"
+
+	"github.com/consensys/gnark-crypto/ecc"
+	"github.com/consensys/gnark-crypto/ecc/bls12-377/fr/poseidon2"
+	"github.com/consensys/gnark/frontend"
+	"github.com/consensys/gnark/test"
+)
+
+type Poseidon2Circuit struct {
+	Input    []frontend.Variable
+	Expected frontend.Variable `gnark:",public"`
+}
+
+func (c *Poseidon2Circuit) Define(api frontend.API) error {
+	hsh, err := NewMerkleDamgardHasher(api)
+	if err != nil {
+		return err
+	}
+	hsh.Write(c.Input...)
+	api.AssertIsEqual(hsh.Sum(), c.Expected)
+	return nil
+}
+
+func TestPoseidon2Hash(t *testing.T) {
+	assert := test.NewAssert(t)
+
+	const nbInputs = 5
+	// prepare expected output
+	h := poseidon2.NewMerkleDamgardHasher()
+	circInput := make([]frontend.Variable, nbInputs)
+	for i := range nbInputs {
+		_, err := h.Write([]byte{byte(i)})
+		assert.NoError(err)
+		circInput[i] = i
+	}
+	res := h.Sum(nil)
+	assert.CheckCircuit(&Poseidon2Circuit{Input: make([]frontend.Variable, nbInputs)}, test.WithValidAssignment(&Poseidon2Circuit{Input: circInput, Expected: res}), test.WithCurves(ecc.BLS12_377)) // we have parametrized currently only for BLS12-377
+}