+ const char *protected_headers = NULL;
+ const char *forwarded = NULL;
+ const char *subject = NULL;
+
+ if ((! msg_crypto) || (! part))
+ INTERNAL_ERROR ("_notmuch_message_crypto_potential_payload() got NULL for %s\n",
+ msg_crypto? "part" : "msg_crypto");
+
+ /* only fire on the first payload part encountered */
+ if (msg_crypto->payload_encountered)
+ return false;
+
+ /* the first child of multipart/encrypted that matches the
+ * encryption protocol should be "control information" metadata,
+ * not payload. So we skip it. (see
+ * https://tools.ietf.org/html/rfc1847#page-8) */
+ if (parent && GMIME_IS_MULTIPART_ENCRYPTED (parent) && childnum ==
+ GMIME_MULTIPART_ENCRYPTED_VERSION) {
+ const char *enc_type = g_mime_object_get_content_type_parameter (parent, "protocol");
+ GMimeContentType *ct = g_mime_object_get_content_type (part);
+ if (ct && enc_type) {
+ const char *part_type = g_mime_content_type_get_mime_type (ct);
+ if (part_type && strcmp (part_type, enc_type) == 0)
+ return false;
+ }
+ }
+
+ msg_crypto->payload_encountered = true;
+
+ /* don't bother recording anything if there is no cryptographic
+ * envelope: */
+ if ((msg_crypto->decryption_status != NOTMUCH_MESSAGE_DECRYPTED_FULL) &&
+ (msg_crypto->sig_list == NULL))
+ return false;
+
+ /* Verify that this payload has headers that are intended to be
+ * exported to the larger message: */
+
+ /* Consider a payload that uses Alexei Melinkov's forwarded="no" for
+ * message/global or message/rfc822:
+ * https://tools.ietf.org/html/draft-melnikov-smime-header-signing-05#section-4 */
+ forwarded = g_mime_object_get_content_type_parameter (part, "forwarded");
+ if (GMIME_IS_MESSAGE_PART (part) && forwarded && strcmp (forwarded, "no") == 0) {
+ GMimeMessage *message = g_mime_message_part_get_message (GMIME_MESSAGE_PART (part));
+ subject = g_mime_message_get_subject (message);
+ /* FIXME: handle more than just Subject: at some point */
+ } else {
+ /* Consider "memoryhole"-style protected headers as practiced by Enigmail and K-9 */
+ protected_headers = g_mime_object_get_content_type_parameter (part, "protected-headers");
+ if (protected_headers && strcasecmp ("v1", protected_headers) == 0)
+ subject = g_mime_object_get_header (part, "Subject");
+ /* FIXME: handle more than just Subject: at some point */