diff --git a/did/didtest/crypto.go b/did/didtest/crypto.go
index 513787a..6999b4e 100644
--- a/did/didtest/crypto.go
+++ b/did/didtest/crypto.go
@@ -5,10 +5,8 @@ package didtest
 
 import (
 	"fmt"
-	"testing"
 
 	"github.com/libp2p/go-libp2p/core/crypto"
-	"github.com/stretchr/testify/require"
 
 	"github.com/ucan-wg/go-ucan/did"
 )
@@ -92,6 +90,14 @@ func (p Persona) PrivKey() crypto.PrivKey {
 	return res
 }
 
+func (p Persona) PrivKeyConfig() string {
+	res, ok := privKeyB64()[p]
+	if !ok {
+		panic(fmt.Sprintf("Unknown persona: %v", p))
+	}
+	return res
+}
+
 // PubKey returns the Ed25519 public key for the Persona.
 func (p Persona) PubKey() crypto.PubKey {
 	return p.PrivKey().GetPublic()
@@ -99,10 +105,11 @@ func (p Persona) PubKey() crypto.PubKey {
 
 // PubKeyConfig returns the marshaled and encoded Ed25519 public key
 // for the Persona.
-func (p Persona) PubKeyConfig(t *testing.T) string {
+func (p Persona) PubKeyConfig() string {
 	pubKeyMar, err := crypto.MarshalPublicKey(p.PrivKey().GetPublic())
-	require.NoError(t, err)
-
+	if err != nil {
+		panic(err)
+	}
 	return crypto.ConfigEncodeKey(pubKeyMar)
 }
 
diff --git a/pkg/args/args.go b/pkg/args/args.go
index a840c6e..305b9af 100644
--- a/pkg/args/args.go
+++ b/pkg/args/args.go
@@ -92,6 +92,11 @@ func (a *Args) Include(other Iterator) {
 	}
 }
 
+// Len return the number of arguments.
+func (a *Args) Len() int {
+	return len(a.Keys)
+}
+
 // Iter iterates over the args key/values
 func (a *Args) Iter() iter.Seq2[string, ipld.Node] {
 	return func(yield func(string, ipld.Node) bool) {
diff --git a/pkg/args/readonly.go b/pkg/args/readonly.go
index 62c6587..0e4e44f 100644
--- a/pkg/args/readonly.go
+++ b/pkg/args/readonly.go
@@ -14,6 +14,10 @@ func (r ReadOnly) GetNode(key string) (ipld.Node, error) {
 	return r.args.GetNode(key)
 }
 
+func (r ReadOnly) Len() int {
+	return r.args.Len()
+}
+
 func (r ReadOnly) Iter() iter.Seq2[string, ipld.Node] {
 	return r.args.Iter()
 }
diff --git a/pkg/meta/meta.go b/pkg/meta/meta.go
index 9b0e79f..9273bbc 100644
--- a/pkg/meta/meta.go
+++ b/pkg/meta/meta.go
@@ -10,8 +10,8 @@ import (
 	"github.com/ipld/go-ipld-prime"
 	"github.com/ipld/go-ipld-prime/printer"
 
-	"github.com/ucan-wg/go-ucan/pkg/meta/internal/crypto"
 	"github.com/ucan-wg/go-ucan/pkg/policy/literal"
+	"github.com/ucan-wg/go-ucan/pkg/secretbox"
 )
 
 var ErrNotFound = errors.New("key not found in meta")
@@ -63,7 +63,7 @@ func (m *Meta) GetEncryptedString(key string, encryptionKey []byte) (string, err
 		return "", err
 	}
 
-	decrypted, err := crypto.DecryptStringWithKey(v, encryptionKey)
+	decrypted, err := secretbox.DecryptStringWithKey(v, encryptionKey)
 	if err != nil {
 		return "", err
 	}
@@ -111,7 +111,7 @@ func (m *Meta) GetEncryptedBytes(key string, encryptionKey []byte) ([]byte, erro
 		return nil, err
 	}
 
-	decrypted, err := crypto.DecryptStringWithKey(v, encryptionKey)
+	decrypted, err := secretbox.DecryptStringWithKey(v, encryptionKey)
 	if err != nil {
 		return nil, err
 	}
@@ -157,12 +157,12 @@ func (m *Meta) AddEncrypted(key string, val any, encryptionKey []byte) error {
 
 	switch val := val.(type) {
 	case string:
-		encrypted, err = crypto.EncryptWithKey([]byte(val), encryptionKey)
+		encrypted, err = secretbox.EncryptWithKey([]byte(val), encryptionKey)
 		if err != nil {
 			return err
 		}
 	case []byte:
-		encrypted, err = crypto.EncryptWithKey(val, encryptionKey)
+		encrypted, err = secretbox.EncryptWithKey(val, encryptionKey)
 		if err != nil {
 			return err
 		}
@@ -192,6 +192,11 @@ func (m *Meta) Include(other Iterator) {
 	}
 }
 
+// Len returns the number of key/values.
+func (m *Meta) Len() int {
+	return len(m.Values)
+}
+
 // Iter iterates over the meta key/values
 func (m *Meta) Iter() iter.Seq2[string, ipld.Node] {
 	return func(yield func(string, ipld.Node) bool) {
diff --git a/pkg/meta/readonly.go b/pkg/meta/readonly.go
index 26d667d..4e6ddfb 100644
--- a/pkg/meta/readonly.go
+++ b/pkg/meta/readonly.go
@@ -43,6 +43,10 @@ func (r ReadOnly) GetNode(key string) (ipld.Node, error) {
 	return r.meta.GetNode(key)
 }
 
+func (r ReadOnly) Len() int {
+	return r.meta.Len()
+}
+
 func (r ReadOnly) Iter() iter.Seq2[string, ipld.Node] {
 	return r.meta.Iter()
 }
diff --git a/pkg/meta/internal/crypto/secretbox.go b/pkg/secretbox/secretbox.go
similarity index 99%
rename from pkg/meta/internal/crypto/secretbox.go
rename to pkg/secretbox/secretbox.go
index 690be7e..227a333 100644
--- a/pkg/meta/internal/crypto/secretbox.go
+++ b/pkg/secretbox/secretbox.go
@@ -1,4 +1,4 @@
-package crypto
+package secretbox
 
 import (
 	"crypto/rand"
diff --git a/pkg/meta/internal/crypto/secretbox_test.go b/pkg/secretbox/secretbox_test.go
similarity index 99%
rename from pkg/meta/internal/crypto/secretbox_test.go
rename to pkg/secretbox/secretbox_test.go
index d87f860..df8ab89 100644
--- a/pkg/meta/internal/crypto/secretbox_test.go
+++ b/pkg/secretbox/secretbox_test.go
@@ -1,4 +1,4 @@
-package crypto
+package secretbox
 
 import (
 	"bytes"