age: return better errors from Decrypt for scrypt identities

age.go

@@ -209,7 +209,10 @@ type NoIdentityMatchError struct {
 	StanzaTypes []string
 }
 
-func (*NoIdentityMatchError) Error() string {
+func (e *NoIdentityMatchError) Error() string {
+	if len(e.Errors) == 1 {
+		return "identity did not match any of the recipients: " + e.Errors[0].Error()
+	}
 	return "no identity matched any of the recipients"
 }
 

age_test.go

@@ -379,6 +379,71 @@ func TestNoIdentityMatchErrorStanzaTypes(t *testing.T) {
 	}
 }
 
+func TestScryptIdentityErrors(t *testing.T) {
+	t.Run("not passphrase-encrypted", func(t *testing.T) {
+		i, err := age.GenerateX25519Identity()
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		buf := &bytes.Buffer{}
+		w, err := age.Encrypt(buf, i.Recipient())
+		if err != nil {
+			t.Fatal(err)
+		}
+		if err := w.Close(); err != nil {
+			t.Fatal(err)
+		}
+
+		scryptID, err := age.NewScryptIdentity("password")
+		if err != nil {
+			t.Fatal(err)
+		}
+		_, err = age.Decrypt(bytes.NewReader(buf.Bytes()), scryptID)
+		if err == nil {
+			t.Fatal("expected decryption to fail")
+		}
+		if !errors.Is(err, age.ErrIncorrectIdentity) {
+			t.Errorf("expected ErrIncorrectIdentity, got %v", err)
+		}
+		if !strings.Contains(err.Error(), "not passphrase-encrypted") {
+			t.Errorf("expected error to mention 'not passphrase-encrypted', got %v", err)
+		}
+	})
+
+	t.Run("incorrect passphrase", func(t *testing.T) {
+		r, err := age.NewScryptRecipient("correct-password")
+		if err != nil {
+			t.Fatal(err)
+		}
+		r.SetWorkFactor(10) // Low for fast test
+
+		buf := &bytes.Buffer{}
+		w, err := age.Encrypt(buf, r)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if err := w.Close(); err != nil {
+			t.Fatal(err)
+		}
+
+		scryptID, err := age.NewScryptIdentity("wrong-password")
+		if err != nil {
+			t.Fatal(err)
+		}
+		_, err = age.Decrypt(bytes.NewReader(buf.Bytes()), scryptID)
+		if err == nil {
+			t.Fatal("expected decryption to fail")
+		}
+		if !errors.Is(err, age.ErrIncorrectIdentity) {
+			t.Errorf("expected ErrIncorrectIdentity, got %v", err)
+		}
+		if !strings.Contains(err.Error(), "incorrect passphrase") {
+			t.Errorf("expected error to mention 'incorrect passphrase', got %v", err)
+		}
+	})
+}
+
 func TestDetachedHeader(t *testing.T) {
 	i, err := age.GenerateX25519Identity()
 	if err != nil {

scrypt.go

@@ -150,14 +150,20 @@ func (i *ScryptIdentity) Unwrap(stanzas []*Stanza) ([]byte, error) {
 			return nil, errors.New("an scrypt recipient must be the only one")
 		}
 	}
-	return multiUnwrap(i.unwrap, stanzas)
+	for _, s := range stanzas {
+		if s.Type != "scrypt" {
+			continue
+		}
+		return i.unwrap(s)
+	}
+	return nil, fmt.Errorf("%w: file is not passphrase-encrypted", ErrIncorrectIdentity)
 }
 
 var digitsRe = regexp.MustCompile(`^[1-9][0-9]*$`)
 
 func (i *ScryptIdentity) unwrap(block *Stanza) ([]byte, error) {
 	if block.Type != "scrypt" {
-		return nil, ErrIncorrectIdentity
+		return nil, errors.New("internal error: unwrap called on non-scrypt stanza")
 	}
 	if len(block.Args) != 2 {
 		return nil, errors.New("invalid scrypt recipient block")
@@ -200,7 +206,9 @@ func (i *ScryptIdentity) unwrap(block *Stanza) ([]byte, error) {
 	if err == errIncorrectCiphertextSize {
 		return nil, errors.New("invalid scrypt recipient block: incorrect file key size")
 	} else if err != nil {
-		return nil, ErrIncorrectIdentity
+		// Wrap [ErrIncorrectIdentity] so that multiple passphrases can be tried
+		// in sequence by passing multiple [ScryptIdentity] values to [Decrypt].
+		return nil, fmt.Errorf("%w: incorrect passphrase", ErrIncorrectIdentity)
 	}
 	return fileKey, nil
 }