Adds pm keyring sign

keyring/keyring.go

@@ -183,6 +183,27 @@ func Import(root string, w io.Reader) error {
 	return nil
 }
 
+// Sign takes an id and a reader and writes the signature for that id to sig.
+func Sign(root, id string, in io.Reader, sig io.Writer) error {
+	if err := ensureDir(root); err != nil {
+		return errors.Wrap(err, "can't find or create pgp dir")
+	}
+	srn, prn := getNames(root)
+	secs, _, err := getELs(srn, prn)
+	if err != nil {
+		return errors.Wrap(err, "getting existing keyrings")
+	}
+	e, err := findKey(secs, id)
+	if err != nil {
+		return errors.Wrapf(err, "finding key %q", id)
+	}
+	if err := openpgp.ArmoredDetachSign(sig, e, in, nil); err != nil {
+		return errors.Wrap(err, "armored detach sign")
+	}
+	fmt.Fprintf(sig, "\n")
+	return nil
+}
+
 func pGPDir(root string) string {
 	return filepath.Join(root, "var", "lib", "pm", "pgp")
 }