3 files changed, 40 insertions, 0 deletions
diff --git a/lib/crypto/gpg/gpg.go b/lib/crypto/gpg/gpg.go
index 66cd372..457788d 100644
--- a/lib/crypto/gpg/gpg.go
+++ b/lib/crypto/gpg/gpg.go
@@ -51,6 +51,10 @@ func (m *Mail) Sign(buf *bytes.Buffer, signer string, decryptKeys openpgp.Prompt
 
 func (m *Mail) Close() {}
 
+func (m *Mail) GetSignerKeyId(s string) (string, error) {
+	return gpgbin.GetPrivateKeyId(s)
+}
+
 func handleSignatureError(e string) models.SignatureValidity {
 	if e == "gpg: missing public key" {
 		return models.UnknownEntity
diff --git a/lib/crypto/gpg/gpgbin/gpgbin.go b/lib/crypto/gpg/gpgbin/gpgbin.go
index da046f4..3ee8139 100644
--- a/lib/crypto/gpg/gpgbin/gpgbin.go
+++ b/lib/crypto/gpg/gpgbin/gpgbin.go
@@ -77,6 +77,29 @@ func getIdentity(key uint64) string {
 	return ""
 }
 
+// getKeyId returns the 16 digit key id, if key exists
+func getKeyId(s string, private bool) string {
+	cmd := exec.Command("gpg", "--with-colons", "--batch")
+	listArg := "--list-keys"
+	if private {
+		listArg = "--list-secret-keys"
+	}
+	cmd.Args = append(cmd.Args, listArg, s)
+
+	var outbuf strings.Builder
+	cmd.Stdout = &outbuf
+	cmd.Run()
+	out := strings.Split(outbuf.String(), "\n")
+	for _, line := range out {
+		if strings.HasPrefix(line, "fpr") {
+			flds := strings.Split(line, ":")
+			id := flds[9]
+			return id[len(id)-16:]
+		}
+	}
+	return ""
+}
+
 // longKeyToUint64 returns a uint64 version of the given key
 func longKeyToUint64(key string) (uint64, error) {
 	fpr := string(key[len(key)-16:])
diff --git a/lib/crypto/gpg/gpgbin/keys.go b/lib/crypto/gpg/gpgbin/keys.go
new file mode 100644
index 0000000..660ce82
--- /dev/null
+++ b/lib/crypto/gpg/gpgbin/keys.go
@@ -0,0 +1,13 @@
+package gpgbin
+
+import "fmt"
+
+// GetPrivateKeyId runs gpg --list-secret-keys s
+func GetPrivateKeyId(s string) (string, error) {
+	private := true
+	id := getKeyId(s, private)
+	if id == "" {
+		return "", fmt.Errorf("no private key found")
+	}
+	return id, nil
+}