pgp: PGP/MIME signing for outgoing emails

implements PGP/MIME signing with go-pgpmail. The Sign() function of
go-pgpmail requires a private (signing) key. The signing key which matches
the senders email address (from field in email header) is looked up
in aerc's copy of the keyring.

Private keys can be exported from gpg into aerc as follows:
$ gpg --export-secret-keys  >> ~/.local/share/aerc/keyring.asc

A message is signed with the ":sign" command. The sign command sets
a bool flag in the Composer struct. Using the command repeatedly will
toggle the flag.

References: https://todo.sr.ht/~rjarry/aerc/6
Signed-off-by: Koni Marti <koni.marti@gmail.com>

1 files changed, 44 insertions, 0 deletions

diff --git a/commands/compose/sign.go b/commands/compose/sign.go
new file mode 100644
index 00000000..eb985e99
--- /dev/null
+++ b/commands/compose/sign.go
@@ -0,0 +1,44 @@
+package compose
+
+import (
+	"errors"
+	"time"
+
+	"git.sr.ht/~rjarry/aerc/widgets"
+)
+
+type Sign struct{}
+
+func init() {
+	register(Sign{})
+}
+
+func (Sign) Aliases() []string {
+	return []string{"sign"}
+}
+
+func (Sign) Complete(aerc *widgets.Aerc, args []string) []string {
+	return nil
+}
+
+func (Sign) Execute(aerc *widgets.Aerc, args []string) error {
+	if len(args) != 1 {
+		return errors.New("Usage: sign")
+	}
+
+	composer, _ := aerc.SelectedTab().(*widgets.Composer)
+
+	composer.SetSign(!composer.Sign())
+
+	var statusline string
+
+	if composer.Sign() {
+		statusline = "Message will be signed."
+	} else {
+		statusline = "Message will not be signed."
+	}
+
+	aerc.PushStatus(statusline, 10*time.Second)
+
+	return nil
+}