Merge pull request #51 from ucan-wg/v1-meta-encryption

feat(meta): values symmetric encryption

pkg/meta/internal/crypto/aes.go

@@ -0,0 +1,132 @@
+package crypto
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"errors"
+	"fmt"
+	"io"
+)
+
+// KeySize represents valid AES key sizes
+type KeySize int
+
+const (
+	KeySize128 KeySize = 16 // AES-128
+	KeySize192 KeySize = 24 // AES-192
+	KeySize256 KeySize = 32 // AES-256 (recommended)
+)
+
+// IsValid returns true if the key size is valid for AES
+func (ks KeySize) IsValid() bool {
+	switch ks {
+	case KeySize128, KeySize192, KeySize256:
+		return true
+	default:
+		return false
+	}
+}
+
+var ErrShortCipherText = errors.New("ciphertext too short")
+var ErrNoEncryptionKey = errors.New("encryption key is required")
+var ErrInvalidKeySize = errors.New("invalid key size: must be 16, 24, or 32 bytes")
+var ErrZeroKey = errors.New("encryption key cannot be all zeros")
+
+// GenerateKey generates a random AES key of default size KeySize256 (32 bytes).
+// Returns an error if the specified size is invalid or if key generation fails.
+func GenerateKey() ([]byte, error) {
+	return GenerateKeyWithSize(KeySize256)
+}
+
+// GenerateKeyWithSize generates a random AES key of the specified size.
+// Returns an error if the specified size is invalid or if key generation fails.
+func GenerateKeyWithSize(size KeySize) ([]byte, error) {
+	if !size.IsValid() {
+		return nil, ErrInvalidKeySize
+	}
+
+	key := make([]byte, size)
+	if _, err := io.ReadFull(rand.Reader, key); err != nil {
+		return nil, fmt.Errorf("failed to generate AES key: %w", err)
+	}
+
+	return key, nil
+}
+
+// EncryptWithAESKey encrypts data using AES-GCM with the provided key.
+// The key must be 16, 24, or 32 bytes long (for AES-128, AES-192, or AES-256).
+// Returns the encrypted data with the nonce prepended, or an error if encryption fails.
+func EncryptWithAESKey(data, key []byte) ([]byte, error) {
+	if err := validateAESKey(key); err != nil {
+		return nil, err
+	}
+
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+
+	nonce := make([]byte, gcm.NonceSize())
+	if _, err = io.ReadFull(rand.Reader, nonce); err != nil {
+		return nil, err
+	}
+
+	return gcm.Seal(nonce, nonce, data, nil), nil
+}
+
+// DecryptStringWithAESKey decrypts data that was encrypted with EncryptWithAESKey.
+// The key must match the one used for encryption.
+// Expects the input to have a prepended nonce.
+// Returns the decrypted data or an error if decryption fails.
+func DecryptStringWithAESKey(data, key []byte) ([]byte, error) {
+	if err := validateAESKey(key); err != nil {
+		return nil, err
+	}
+
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(data) < gcm.NonceSize() {
+		return nil, ErrShortCipherText
+	}
+
+	nonce, ciphertext := data[:gcm.NonceSize()], data[gcm.NonceSize():]
+	decrypted, err := gcm.Open(nil, nonce, ciphertext, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	return decrypted, nil
+}
+
+func validateAESKey(key []byte) error {
+	if key == nil {
+		return ErrNoEncryptionKey
+	}
+
+	if !KeySize(len(key)).IsValid() {
+		return ErrInvalidKeySize
+	}
+
+	// check if key is all zeros
+	for _, b := range key {
+		if b != 0 {
+			return nil
+		}
+	}
+
+	return ErrZeroKey
+}

pkg/meta/internal/crypto/aes_test.go

@@ -0,0 +1,124 @@
+package crypto
+
+import (
+	"bytes"
+	"crypto/rand"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestAESEncryption(t *testing.T) {
+	t.Parallel()
+
+	key := make([]byte, 32) // generated random 32-byte key
+	_, errKey := rand.Read(key)
+	require.NoError(t, errKey)
+
+	tests := []struct {
+		name    string
+		data    []byte
+		key     []byte
+		wantErr error
+	}{
+		{
+			name: "valid encryption/decryption",
+			data: []byte("hello world"),
+			key:  key,
+		},
+		{
+			name:    "nil key returns error",
+			data:    []byte("hello world"),
+			key:     nil,
+			wantErr: ErrNoEncryptionKey,
+		},
+		{
+			name: "empty data",
+			data: []byte{},
+			key:  key,
+		},
+		{
+			name:    "invalid key size",
+			data:    []byte("hello world"),
+			key:     make([]byte, 31),
+			wantErr: ErrInvalidKeySize,
+		},
+		{
+			name:    "zero key returns error",
+			data:    []byte("hello world"),
+			key:     make([]byte, 32),
+			wantErr: ErrZeroKey,
+		},
+	}
+
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			encrypted, err := EncryptWithAESKey(tt.data, tt.key)
+			if tt.wantErr != nil {
+				require.ErrorIs(t, err, tt.wantErr)
+
+				return
+			}
+			require.NoError(t, err)
+
+			decrypted, err := DecryptStringWithAESKey(encrypted, tt.key)
+			require.NoError(t, err)
+
+			if tt.key == nil {
+				require.Equal(t, tt.data, encrypted)
+				require.Equal(t, tt.data, decrypted)
+			} else {
+				require.NotEqual(t, tt.data, encrypted)
+				require.True(t, bytes.Equal(tt.data, decrypted))
+			}
+		})
+	}
+}
+
+func TestDecryptionErrors(t *testing.T) {
+	t.Parallel()
+
+	key := make([]byte, 32)
+	_, err := rand.Read(key)
+	require.NoError(t, err)
+
+	tests := []struct {
+		name   string
+		data   []byte
+		key    []byte
+		errMsg string
+	}{
+		{
+			name:   "short ciphertext",
+			data:   []byte("short"),
+			key:    key,
+			errMsg: "ciphertext too short",
+		},
+		{
+			name:   "invalid ciphertext",
+			data:   make([]byte, 16), // just nonce size
+			key:    key,
+			errMsg: "message authentication failed",
+		},
+		{
+			name:   "missing key",
+			data:   []byte("�`M���l\u001AIF�\u0012���=h�?�c� ��\u0012����\u001C�\u0018Ƽ(g"),
+			key:    nil,
+			errMsg: "encryption key is required",
+		},
+	}
+
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			_, err := DecryptStringWithAESKey(tt.data, tt.key)
+			require.Error(t, err)
+			require.Contains(t, err.Error(), tt.errMsg)
+		})
+	}
+}

pkg/meta/meta.go

@@ -1,16 +1,22 @@
 package meta
 
 import (
+	"errors"
 	"fmt"
 	"strings"
 
 	"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"
 )
 
-var ErrNotFound = fmt.Errorf("key-value not found in meta")
+var ErrUnsupported = errors.New("failure adding unsupported type to meta")
+
+var ErrNotFound = errors.New("key-value not found in meta")
+
+var ErrNotEncryptable = errors.New("value of this type cannot be encrypted")
 
 // Meta is a container for meta key-value pairs in a UCAN token.
 // This also serves as a way to construct the underlying IPLD data with minimum allocations
@@ -50,6 +56,21 @@ func (m *Meta) GetString(key string) (string, error) {
 	return v.AsString()
 }
 
+// GetEncryptedString decorates GetString and decrypt its output with the given symmetric encryption key.
+func (m *Meta) GetEncryptedString(key string, encryptionKey []byte) (string, error) {
+	v, err := m.GetBytes(key)
+	if err != nil {
+		return "", err
+	}
+
+	decrypted, err := crypto.DecryptStringWithAESKey(v, encryptionKey)
+	if err != nil {
+		return "", err
+	}
+
+	return string(decrypted), nil
+}
+
 // GetInt64 retrieves a value as an int64.
 // Returns ErrNotFound if the given key is missing.
 // Returns datamodel.ErrWrongKind if the value has the wrong type.
@@ -83,6 +104,21 @@ func (m *Meta) GetBytes(key string) ([]byte, error) {
 	return v.AsBytes()
 }
 
+// GetEncryptedBytes decorates GetBytes and decrypt its output with the given symmetric encryption key.
+func (m *Meta) GetEncryptedBytes(key string, encryptionKey []byte) ([]byte, error) {
+	v, err := m.GetBytes(key)
+	if err != nil {
+		return nil, err
+	}
+
+	decrypted, err := crypto.DecryptStringWithAESKey(v, encryptionKey)
+	if err != nil {
+		return nil, err
+	}
+
+	return decrypted, nil
+}
+
 // GetNode retrieves a value as a raw IPLD node.
 // Returns ErrNotFound if the given key is missing.
 // Returns datamodel.ErrWrongKind if the value has the wrong type.
@@ -112,6 +148,31 @@ func (m *Meta) Add(key string, val any) error {
 	return nil
 }
 
+// AddEncrypted adds a key/value pair in the meta set.
+// The value is encrypted with the given encryptionKey.
+// Accepted types for the value are: string, []byte.
+func (m *Meta) AddEncrypted(key string, val any, encryptionKey []byte) error {
+	var encrypted []byte
+	var err error
+
+	switch val := val.(type) {
+	case string:
+		encrypted, err = crypto.EncryptWithAESKey([]byte(val), encryptionKey)
+		if err != nil {
+			return err
+		}
+	case []byte:
+		encrypted, err = crypto.EncryptWithAESKey(val, encryptionKey)
+		if err != nil {
+			return err
+		}
+	default:
+		return ErrNotEncryptable
+	}
+
+	return m.Add(key, encrypted)
+}
+
 // Equals tells if two Meta hold the same key/values.
 func (m *Meta) Equals(other *Meta) bool {
 	if len(m.Keys) != len(other.Keys) {