diff --git a/arbo/verifier.go b/arbo/verifier.go
index 83ea4a7..3ffe3f8 100644
--- a/arbo/verifier.go
+++ b/arbo/verifier.go
@@ -8,13 +8,16 @@ import (
 // prevLevel function calculates the previous level of the merkle tree given the
 // current leaf, the current path bit of the leaf, the validity of the sibling
 // and the sibling itself.
-func prevLevel(api frontend.API, leaf, ipath, valid, sibling frontend.Variable) frontend.Variable {
+func prevLevel(api frontend.API, leaf, ipath, valid, sibling frontend.Variable) (frontend.Variable, error) {
 	// l, r = path == 1 ? sibling, current : current, sibling
 	l, r := api.Select(ipath, sibling, leaf), api.Select(ipath, leaf, sibling)
 	// intermediateLeafKey = H(l | r)
-	intermediateLeafKey := poseidon.Hash(api, l, r)
+	intermediateLeafKey, err := poseidon.Hash(api, l, r)
+	if err != nil {
+		return 0, err
+	}
 	// newCurrent = valid == 1 ? current : intermediateLeafKey
-	return api.Select(valid, intermediateLeafKey, leaf)
+	return api.Select(valid, intermediateLeafKey, leaf), nil
 }
 
 // strictCmp function compares a and b and returns:
@@ -41,7 +44,10 @@ func CheckProof(api frontend.API, key, value, root frontend.Variable, siblings [
 	path := api.ToBinary(key, api.Compiler().FieldBitLen())
 	// calculate the value leaf to start with it to rebuild the tree
 	//   leafValue = H(key | value | 1)
-	leafValue := poseidon.Hash(api, key, value, 1)
+	leafValue, err := poseidon.Hash(api, key, value, 1)
+	if err != nil {
+		return err
+	}
 	// calculate the root and compare it with the provided one
 	prevLeaf := leafValue
 	currentLeaf := leafValue
@@ -52,7 +58,10 @@ func CheckProof(api frontend.API, key, value, root frontend.Variable, siblings [
 		prevLeaf = currentLeaf
 		prevSibling = siblings[i]
 		// compute the next leaf value
-		currentLeaf = prevLevel(api, currentLeaf, path[i], valid, siblings[i])
+		currentLeaf, err = prevLevel(api, currentLeaf, path[i], valid, siblings[i])
+		if err != nil {
+			return err
+		}
 	}
 	api.AssertIsEqual(currentLeaf, root)
 	return nil
diff --git a/arbo/verifier_test.go b/arbo/verifier_test.go
index ace9896..eca26c9 100644
--- a/arbo/verifier_test.go
+++ b/arbo/verifier_test.go
@@ -20,10 +20,10 @@ import (
 )
 
 type testVerifierCircuit struct {
-	Root      frontend.Variable
-	Key       frontend.Variable
-	Value     frontend.Variable
-	Siblings  [160]frontend.Variable
+	Root     frontend.Variable
+	Key      frontend.Variable
+	Value    frontend.Variable
+	Siblings [160]frontend.Variable
 }
 
 func (circuit *testVerifierCircuit) Define(api frontend.API) error {
@@ -74,10 +74,10 @@ func successInputs(t *testing.T, n int) testVerifierCircuit {
 	root, err := tree.Root()
 	c.Assert(err, qt.IsNil)
 	return testVerifierCircuit{
-		Root:      arbo.BytesLEToBigInt(root),
-		Key:       arbo.BytesLEToBigInt(key),
-		Value:     value,
-		Siblings:  siblings,
+		Root:     arbo.BytesLEToBigInt(root),
+		Key:      arbo.BytesLEToBigInt(key),
+		Value:    value,
+		Siblings: siblings,
 	}
 }
 
diff --git a/go.mod b/go.mod
index faed557..95efa4a 100644
--- a/go.mod
+++ b/go.mod
@@ -7,7 +7,7 @@ require (
 	github.com/consensys/gnark-crypto v0.14.0
 	github.com/frankban/quicktest v1.14.6
 	github.com/iden3/go-iden3-crypto v0.0.17
-	github.com/vocdoni/vocdoni-z-sandbox v0.0.0-20241111130906-b8e8592696c6
+	github.com/vocdoni/vocdoni-z-sandbox v0.0.0-20241113074257-1a711ad38a6b
 	go.vocdoni.io/dvote v1.10.2-0.20241024102542-c1ce6d744bc5
 )
 
diff --git a/go.sum b/go.sum
index 7054df7..49cd4e6 100644
--- a/go.sum
+++ b/go.sum
@@ -127,6 +127,8 @@ github.com/syndtr/goleveldb v1.0.1-0.20220614013038-64ee5596c38a h1:1ur3QoCqvE5f
 github.com/syndtr/goleveldb v1.0.1-0.20220614013038-64ee5596c38a/go.mod h1:RRCYJbIwD5jmqPI9XoAFR0OcDxqUctll6zUj/+B4S48=
 github.com/vocdoni/vocdoni-z-sandbox v0.0.0-20241111130906-b8e8592696c6 h1:Lnikgc2rZsnxZDwGbPhlsmq0yiLRotKDOGnuOOYU37o=
 github.com/vocdoni/vocdoni-z-sandbox v0.0.0-20241111130906-b8e8592696c6/go.mod h1:B43i83saYhSReG+jNAj0igxWcZYHGjF2AeXunaXnCQE=
+github.com/vocdoni/vocdoni-z-sandbox v0.0.0-20241113074257-1a711ad38a6b h1:Hf7CZnNm8XhGBb0XBYVDUir7iNhIryJSmSUz+wlV7vw=
+github.com/vocdoni/vocdoni-z-sandbox v0.0.0-20241113074257-1a711ad38a6b/go.mod h1:B43i83saYhSReG+jNAj0igxWcZYHGjF2AeXunaXnCQE=
 github.com/x448/float16 v0.8.4 h1:qLwI1I70+NjRFUR3zs1JPUCgaCXSh3SW62uAKT1mSBM=
 github.com/x448/float16 v0.8.4/go.mod h1:14CWIYCyZA/cWjXOioeEpHeN/83MdbZDRQHoFcYsOfg=
 github.com/xdg-go/pbkdf2 v1.0.0 h1:Su7DPu48wXMwC3bs7MCNG+z4FhcyEuz5dlvchbq0B0c=
diff --git a/poseidon/poseidon.go b/poseidon/poseidon.go
index 7b24b3d..51577a3 100644
--- a/poseidon/poseidon.go
+++ b/poseidon/poseidon.go
@@ -1,22 +1,89 @@
 package poseidon
 
 import (
+	"fmt"
 	"math/big"
 
 	"github.com/consensys/gnark/frontend"
 )
 
+// Poseidon struct represents a Poseidon hash function object that can be used
+// to hash inputs. The Poseidon hash function is a cryptographic hash function
+// that is designed to be efficient in terms of both time and space. It is
+// based on the Merkle-Damgård construction and uses a sponge construction
+// with a permutation that is based on the Poseidon permutation. The Poseidon
+// permutation is a round-based permutation that uses a series of operations
+// to mix the input data and produce the output hash. The Poseidon hash
+// function is designed to be resistant to various cryptographic attacks,
+// including differential and linear cryptanalysis, and is suitable for use
+// in a wide range of applications, including blockchain and cryptocurrency
+// systems.
 type Poseidon struct {
 	api  frontend.API
 	data []frontend.Variable
 }
 
-func Hash(api frontend.API, inputs ...frontend.Variable) frontend.Variable {
+// Hash returns the hash of the provided inputs using the Poseidon hash
+// function. This function supports up to 16 inputs. If more than 16 inputs
+// are provided, it will return an error. If the number of inputs is 16 or less,
+// it will return the hash of the inputs. This function is equivalent to calling
+// NewPoseidon and then calling Write and Sum on the returned Poseidon object.
+func Hash(api frontend.API, inputs ...frontend.Variable) (frontend.Variable, error) {
 	h := NewPoseidon(api)
-	h.Write(inputs...)
-	return h.Sum()
+	if err := h.Write(inputs...); err != nil {
+		return 0, err
+	}
+	return h.Sum(), nil
 }
 
+// MultiHash returns the hash of the provided inputs using the Poseidon hash
+// function. This function supports up to 256 inputs. If more than 256 inputs
+// are provided, it will return an error. If the number of inputs is 16 or
+// less, it will return the result of Hash function. If the number of inputs
+// is greater than 16, it will calculate the hash of the inputs by dividing
+// them into chunks of 16 inputs each, hashing each chunk, and then hashing
+// the resulting chunk hashes.
+func MultiHash(api frontend.API, inputs ...frontend.Variable) (frontend.Variable, error) {
+	if l := len(inputs); l < 16 {
+		return Hash(api, inputs...)
+	} else if l > 256 {
+		return 0, fmt.Errorf("the maximum number of inputs supported is 256")
+	}
+	// calculate chunk hashes
+	hashed := []frontend.Variable{}
+	chunk := []frontend.Variable{}
+	hasher := NewPoseidon(api)
+	for _, input := range inputs {
+		if len(chunk) == 16 {
+			if err := hasher.Write(chunk...); err != nil {
+				return 0, err
+			}
+			hashed = append(hashed, hasher.Sum())
+			chunk = []frontend.Variable{}
+			hasher.Reset()
+		}
+		chunk = append(chunk, input)
+	}
+	// if the final chunk is not empty, hash it to get the last chunk hash
+	if len(chunk) > 0 {
+		if err := hasher.Write(chunk...); err != nil {
+			return 0, err
+		}
+		hashed = append(hashed, hasher.Sum())
+		hasher.Reset()
+	}
+	// if there is only one chunk, return its hash
+	if len(hashed) == 1 {
+		return hashed[0], nil
+	}
+	// return the hash of all chunk hashes
+	if err := hasher.Write(hashed...); err != nil {
+		return 0, err
+	}
+	return hasher.Sum(), nil
+}
+
+// NewPoseidon returns a new Poseidon object that can be used to hash inputs.
 func NewPoseidon(api frontend.API) Poseidon {
 	return Poseidon{
 		api:  api,
@@ -24,17 +91,25 @@ func NewPoseidon(api frontend.API) Poseidon {
 	}
 }
 
-func (h *Poseidon) Write(data ...frontend.Variable) {
+// Write adds the provided inputs to the Poseidon object. If the number of 
+// inputs is greater than 16, it will return an error.
+func (h *Poseidon) Write(data ...frontend.Variable) error {
+	if len(h.data)+len(data) > 16 {
+		return fmt.Errorf("poseidon hash only supports up to 16 inputs, use MultiHash instead")
+	}
 	h.data = append(h.data, data...)
+	return nil
 }
 
+// Reset resets the Poseidon object, removing all written inputs.
 func (h *Poseidon) Reset() {
 	h.data = []frontend.Variable{}
 }
 
+// Sum returns the hash of the inputs written to the Poseidon object.
 func (h *Poseidon) Sum() frontend.Variable {
 	nInputs := len(h.data)
-	// And rounded up to nearest integer that divides by t
+	// and rounded up to nearest integer that divides by t
 	nRoundsPC := [16]int{56, 57, 56, 60, 60, 63, 64, 63, 60, 66, 60, 65, 70, 60, 64, 68}
 	t := nInputs + 1
 	nRoundsF := 8
@@ -69,9 +144,7 @@ func (h *Poseidon) Sum() frontend.Variable {
 	state = h.mix(state, p)
 
 	for r := 0; r < nRoundsP; r++ {
-
 		state[0] = h.sigma(state[0])
-
 		state[0] = h.api.Add(state[0], c[(nRoundsF/2+1)*t+r])
 		newState0 := frontend.Variable(0)
 		for j := 0; j < len(state); j++ {
diff --git a/poseidon/poseidon_test.go b/poseidon/poseidon_test.go
index 2eb3612..c884734 100644
--- a/poseidon/poseidon_test.go
+++ b/poseidon/poseidon_test.go
@@ -1,14 +1,20 @@
 package poseidon
 
 import (
+	"crypto/rand"
+	"fmt"
 	"math/big"
 	"testing"
+	"time"
 
 	"github.com/consensys/gnark-crypto/ecc"
 	"github.com/consensys/gnark/backend"
 	"github.com/consensys/gnark/frontend"
+	"github.com/consensys/gnark/frontend/cs/r1cs"
+	"github.com/consensys/gnark/profile"
 	"github.com/consensys/gnark/test"
 	hash "github.com/iden3/go-iden3-crypto/poseidon"
+	"github.com/vocdoni/vocdoni-z-sandbox/hash/poseidon"
 )
 
 type testPoseidonCiruit struct {
@@ -17,7 +23,10 @@ type testPoseidonCiruit struct {
 }
 
 func (circuit *testPoseidonCiruit) Define(api frontend.API) error {
-	h := Hash(api, circuit.Data)
+	h, err := Hash(api, circuit.Data)
+	if err != nil {
+		return err
+	}
 	api.AssertIsEqual(h, circuit.Hash)
 	return nil
 }
@@ -31,5 +40,52 @@ func TestPoseidon(t *testing.T) {
 	assignment.Data = input
 	assignment.Hash, _ = hash.Hash([]*big.Int{input})
 
-	assert.SolvingSucceeded(&circuit, &assignment, test.WithCurves(ecc.BN254), test.WithBackends(backend.PLONK))
+	assert.SolvingSucceeded(&circuit, &assignment, test.WithCurves(ecc.BN254), test.WithBackends(backend.GROTH16))
+}
+
+type testMultiPoseidonCircuit struct {
+	Data [32]frontend.Variable
+	Hash frontend.Variable `gnark:",public"`
+}
+
+func (circuit *testMultiPoseidonCircuit) Define(api frontend.API) error {
+	h, err := MultiHash(api, circuit.Data[:]...)
+	if err != nil {
+		return err
+	}
+	api.AssertIsEqual(h, circuit.Hash)
+	return nil
+}
+
+func TestMultiPoseidon(t *testing.T) {
+	p := profile.Start()
+	now := time.Now()
+	_, _ = frontend.Compile(ecc.BN254.ScalarField(), r1cs.NewBuilder, &testMultiPoseidonCircuit{})
+	fmt.Println("elapsed", time.Since(now))
+	p.Stop()
+	fmt.Println("constrains", p.NbConstraints())
+
+	var (
+		inputs [32]*big.Int
+		data   [32]frontend.Variable
+	)
+	for i := 0; i < 32; i++ {
+		// generate random input
+		r, err := rand.Int(rand.Reader, ecc.BN254.ScalarField())
+		if err != nil {
+			t.Fatal(err)
+		}
+		inputs[i] = r
+		data[i] = r
+	}
+	hash, err := poseidon.MultiPoseidon(inputs[:]...)
+	if err != nil {
+		t.Fatal(err)
+	}
+	witness := &testMultiPoseidonCircuit{
+		Data: data,
+		Hash: hash,
+	}
+	assert := test.NewAssert(t)
+	assert.SolvingSucceeded(&testMultiPoseidonCircuit{}, witness, test.WithCurves(ecc.BN254), test.WithBackends(backend.GROTH16))
 }
diff --git a/smt/utils.go b/smt/utils.go
index d4da178..46e3054 100644
--- a/smt/utils.go
+++ b/smt/utils.go
@@ -10,7 +10,7 @@ import (
 // provided, hashing it with the predefined hashing function 'H':
 //
 //	newLeafValue = H(key | value | 1)
-func endLeafValue(api frontend.API, key, value frontend.Variable) frontend.Variable {
+func endLeafValue(api frontend.API, key, value frontend.Variable) (frontend.Variable, error) {
 	return poseidon.Hash(api, key, value, 1)
 }
 
@@ -18,7 +18,7 @@ func endLeafValue(api frontend.API, key, value frontend.Variable) frontend.Varia
 // key-value pair provided, hashing it with the predefined hashing function 'H':
 //
 //	intermediateLeafValue = H(l | r)
-func intermediateLeafValue(api frontend.API, l, r frontend.Variable) frontend.Variable {
+func intermediateLeafValue(api frontend.API, l, r frontend.Variable) (frontend.Variable, error) {
 	return poseidon.Hash(api, l, r)
 }
 
diff --git a/smt/verifier.go b/smt/verifier.go
index e280b69..4ef173f 100644
--- a/smt/verifier.go
+++ b/smt/verifier.go
@@ -25,9 +25,15 @@ func smtverifier(api frontend.API,
 
 	// [STEP 1]
 	// hash1Old = H(oldKey | oldValue | 1)
-	hash1Old := endLeafValue(api, oldKey, oldValue)
+	hash1Old, err := endLeafValue(api, oldKey, oldValue)
+	if err != nil {
+		return err
+	}
 	// hash1New = H(key | value | 1)
-	hash1New := endLeafValue(api, key, value)
+	hash1New, err := endLeafValue(api, key, value)
+	if err != nil {
+		return err
+	}
 
 	// [STEP 2]
 	// component n2bNew = Num2Bits_strict();
@@ -79,7 +85,7 @@ func smtverifier(api frontend.API,
 			child = levels[i+1]
 		}
 
-		levels[i] = smtVerifierLevel(api,
+		levels[i], err = smtVerifierLevel(api,
 			sm[i][0],    // st_top
 			sm[i][1],    // st_iold
 			sm[i][3],    // st_new
@@ -89,6 +95,9 @@ func smtverifier(api frontend.API,
 			n2bNew[i],   // lrbit
 			child,       // child
 		)
+		if err != nil {
+			return err
+		}
 	}
 
 	// component areKeyEquals = IsEqual();
@@ -170,7 +179,7 @@ func smtVerifierSM(api frontend.API,
 }
 
 func smtVerifierLevel(api frontend.API, stTop, stIold, stInew, sibling,
-	old1leaf, new1leaf, lrbit, child frontend.Variable) frontend.Variable {
+	old1leaf, new1leaf, lrbit, child frontend.Variable) (frontend.Variable, error) {
 	// component switcher = Switcher();
 	// switcher.sel <== lrbit;
 	// switcher.L <== child;
@@ -179,11 +188,14 @@ func smtVerifierLevel(api frontend.API, stTop, stIold, stInew, sibling,
 	// component proofHash = SMTHash2();
 	// proofHash.L <== switcher.outL;
 	// proofHash.R <== switcher.outR;
-	proofHash := intermediateLeafValue(api, l, r)
+	proofHash, err := intermediateLeafValue(api, l, r)
+	if err != nil {
+		return 0, err
+	}
 	// aux[0] <== proofHash.out * st_top;
 	aux0 := api.Mul(proofHash, stTop)
 	// aux[1] <== old1leaf * st_iold;
 	aux1 := api.Mul(old1leaf, stIold)
 	// root <== aux[0] + aux[1] + new1leaf * st_inew;
-	return api.Add(aux0, aux1, api.Mul(new1leaf, stInew))
+	return api.Add(aux0, aux1, api.Mul(new1leaf, stInew)), nil
 }