pgp: check encryption keys before sending message

Add check for public keys of all message recipients (to, cc, and bcc)
before sending the message. Adds an OnFocusLost callback to header
editors to facilitate a callback for checking keys whenever a new
recipient is added (OnChange results in too many keyring checks).

Once encryption is initially set, the callbacks are registered. If a
public key is not available for any recipient, encryption is turned off.
However, notably, the callbacks are still registered meaning as s soon
as the user removes the recipients with missing keys, encryption is
turned back on.

Signed-off-by: Tim Culverhouse <tim@timculverhouse.com>
Tested-by: Koni Marti <koni.marti@gmail.com>

commands/compose/encrypt.go

@@ -2,7 +2,6 @@ package compose
 
 import (
 	"errors"
-	"time"
 
 	"git.sr.ht/~rjarry/aerc/widgets"
 )
@@ -29,16 +28,5 @@ func (Encrypt) Execute(aerc *widgets.Aerc, args []string) error {
 	composer, _ := aerc.SelectedTab().(*widgets.Composer)
 
 	composer.SetEncrypt(!composer.Encrypt())
-
-	var statusline string
-
-	if composer.Encrypt() {
-		statusline = "Message will be encrypted."
-	} else {
-		statusline = "Message will not be encrypted."
-	}
-
-	aerc.PushStatus(statusline, 10*time.Second)
-
 	return nil
 }

lib/crypto/crypto.go

@@ -20,6 +20,7 @@ type Provider interface {
 	Init(*log.Logger) error
 	Close()
 	GetSignerKeyId(string) (string, error)
+	GetKeyId(string) (string, error)
 }
 
 func New(s string) Provider {

lib/crypto/gpg/gpg.go

@@ -55,6 +55,10 @@ func (m *Mail) GetSignerKeyId(s string) (string, error) {
 	return gpgbin.GetPrivateKeyId(s)
 }
 
+func (m *Mail) GetKeyId(s string) (string, error) {
+	return gpgbin.GetKeyId(s)
+}
+
 func handleSignatureError(e string) models.SignatureValidity {
 	if e == "gpg: missing public key" {
 		return models.UnknownEntity

lib/crypto/gpg/gpgbin/keys.go

@@ -11,3 +11,13 @@ func GetPrivateKeyId(s string) (string, error) {
 	}
 	return id, nil
 }
+
+// GetKeyId runs gpg --list-keys s
+func GetKeyId(s string) (string, error) {
+	private := false
+	id := getKeyId(s, private)
+	if id == "" {
+		return "", fmt.Errorf("no public key found")
+	}
+	return id, nil
+}

lib/crypto/pgp/pgp.go

@@ -263,6 +263,14 @@ func (m *Mail) GetSignerKeyId(s string) (string, error) {
 	return signerEntity.PrimaryKey.KeyIdString(), nil
 }
 
+func (m *Mail) GetKeyId(s string) (string, error) {
+	entity, err := m.getEntityByEmail(s)
+	if err != nil {
+		return "", err
+	}
+	return entity.PrimaryKey.KeyIdString(), nil
+}
+
 func handleSignatureError(e string) models.SignatureValidity {
 	if e == "openpgp: signature made by unknown entity" {
 		return models.UnknownEntity

lib/ui/textinput.go

@@ -26,6 +26,7 @@ type TextInput struct {
 	scroll            int
 	text              []rune
 	change            []func(ti *TextInput)
+	focusLost         []func(ti *TextInput)
 	tabcomplete       func(s string) ([]string, string)
 	completions       []string
 	prefix            string
@@ -157,6 +158,9 @@ func (ti *TextInput) MouseEvent(localX int, localY int, event tcell.Event) {
 }
 
 func (ti *TextInput) Focus(focus bool) {
+	if ti.focus && !focus {
+		ti.onFocusLost()
+	}
 	ti.focus = focus
 	if focus && ti.ctx != nil {
 		cells := runewidth.StringWidth(string(ti.text[:ti.index]))
@@ -274,6 +278,12 @@ func (ti *TextInput) onChange() {
 	}
 }
 
+func (ti *TextInput) onFocusLost() {
+	for _, focusLost := range ti.focusLost {
+		focusLost(ti)
+	}
+}
+
 func (ti *TextInput) updateCompletions() {
 	if ti.tabcomplete == nil {
 		// no completer
@@ -304,6 +314,10 @@ func (ti *TextInput) OnChange(onChange func(ti *TextInput)) {
 	ti.change = append(ti.change, onChange)
 }
 
+func (ti *TextInput) OnFocusLost(onFocusLost func(ti *TextInput)) {
+	ti.focusLost = append(ti.focusLost, onFocusLost)
+}
+
 func (ti *TextInput) Event(event tcell.Event) bool {
 	switch event := event.(type) {
 	case *tcell.EventKey:

widgets/compose.go

@@ -198,8 +198,21 @@ func (c *Composer) Sign() bool {
 }
 
 func (c *Composer) SetEncrypt(encrypt bool) *Composer {
-	c.encrypt = encrypt
-	c.updateCrypto()
+	if !encrypt {
+		c.encrypt = encrypt
+		c.updateCrypto()
+		return c
+	}
+	// Check on any attempt to encrypt, and any lost focus of "to", "cc", or
+	// "bcc" field. Use OnFocusLost instead of OnChange to limit keyring checks
+	c.encrypt = c.checkEncryptionKeys("")
+	if c.crypto.setEncOneShot {
+		// Prevent registering a lot of callbacks
+		c.OnFocusLost("to", c.checkEncryptionKeys)
+		c.OnFocusLost("cc", c.checkEncryptionKeys)
+		c.OnFocusLost("bcc", c.checkEncryptionKeys)
+		c.crypto.setEncOneShot = false
+	}
 	return c
 }
 
@@ -365,6 +378,15 @@ func (c *Composer) OnHeaderChange(header string, fn func(subject string)) {
 	}
 }
 
+// OnFocusLost registers an OnFocusLost callback for the specified header.
+func (c *Composer) OnFocusLost(header string, fn func(input string) bool) {
+	if editor, ok := c.editors[strings.ToLower(header)]; ok {
+		editor.OnFocusLost(func() {
+			fn(editor.input.String())
+		})
+	}
+}
+
 func (c *Composer) OnClose(fn func(composer *Composer)) {
 	c.onClose = append(c.onClose, fn)
 }
@@ -984,6 +1006,12 @@ func (he *headerEditor) OnChange(fn func()) {
 	})
 }
 
+func (he *headerEditor) OnFocusLost(fn func()) {
+	he.input.OnFocusLost(func(_ *ui.TextInput) {
+		fn()
+	})
+}
+
 type reviewMessage struct {
 	composer *Composer
 	grid     *ui.Grid
@@ -1090,18 +1118,21 @@ func (rm *reviewMessage) Draw(ctx *ui.Context) {
 }
 
 type cryptoStatus struct {
-	title    string
-	status   *ui.Text
-	uiConfig *config.UIConfig
-	signKey  string
+	title         string
+	status        *ui.Text
+	uiConfig      *config.UIConfig
+	signKey       string
+	setEncOneShot bool
 }
 
 func newCryptoStatus(uiConfig *config.UIConfig) *cryptoStatus {
 	defaultStyle := uiConfig.GetStyle(config.STYLE_DEFAULT)
 	return &cryptoStatus{
-		title:    "Security",
-		status:   ui.NewText("", defaultStyle),
-		uiConfig: uiConfig,
+		title:         "Security",
+		status:        ui.NewText("", defaultStyle),
+		uiConfig:      uiConfig,
+		signKey:       "",
+		setEncOneShot: true,
 	}
 }
 
@@ -1124,3 +1155,33 @@ func (cs *cryptoStatus) OnInvalidate(fn func(ui.Drawable)) {
 		fn(cs)
 	})
 }
+
+func (c *Composer) checkEncryptionKeys(_ string) bool {
+	rcpts, err := getRecipientsEmail(c)
+	if err != nil {
+		// checkEncryptionKeys gets registered as a callback and must
+		// explicitly call c.SetEncrypt(false) when encryption is not possible
+		c.SetEncrypt(false)
+		st := fmt.Sprintf("Cannot encrypt: %v", err)
+		c.aerc.statusline.PushError(st)
+		return false
+	}
+	var mk []string
+	for _, rcpt := range rcpts {
+		key, err := c.aerc.Crypto.GetKeyId(rcpt)
+		if err != nil || key == "" {
+			mk = append(mk, rcpt)
+		}
+	}
+	if len(mk) > 0 {
+		c.SetEncrypt(false)
+		st := fmt.Sprintf("Cannot encrypt, missing keys: %s", strings.Join(mk, ", "))
+		c.aerc.statusline.PushError(st)
+		return false
+	}
+	// If callbacks were registered, encrypt will be set when user removes
+	// recipients with missing keys
+	c.encrypt = true
+	c.updateCrypto()
+	return true
+}