Check DKIM Authentication-Results (#3583)

Fix #3507

Note that this is not intended for a release at this point! We first have to test whether it runs stable enough. If we want to make a release while we are not confident enough in authres-checking, then we have to disable it.

BTW, most of the 3000 new lines are in `test_data/messages/dkimchecks...`, not the actual code

da3a4b94 adds the results to the Message info. It currently does this by adding them to `hop_info`. Maybe we should rename `hop_info` to `extra_info` or something; this has the disadvantage that we can't rename the sql column name though.

Follow-ups for this could be:
- In `update_authservid_candidates()`: Implement the rest of the algorithm @hpk42 and me thought about. What's missing is remembering how sure we are that these are the right authserv-ids. Esp., when receiving a message sent from another account at the same domain, we can be quite sure that the authserv-ids in there are the ones of our email server. This will make authres-checking work with buzon.uy, disroot.org, yandex.ru, mailo.com, and riseup.net.
- Think about how we present this to the user - e.g. currently the only change is that we don't accept key changes, which will mean that the small lock on the message is not shown.
- And it will mean that we can fully enable AEAP, after revisiting the security implications of this, and assuming everyone (esp. @link2xt who pointed out the problems in the first place) feels comfortable with it.

src/mimeparser.rs

@@ -15,7 +15,7 @@ use crate::blob::BlobObject;
 use crate::constants::{DC_DESIRED_TEXT_LINES, DC_DESIRED_TEXT_LINE_LEN};
 use crate::contact::{addr_cmp, addr_normalize, ContactId};
 use crate::context::Context;
-use crate::decrypt::{create_decryption_info, try_decrypt};
+use crate::decrypt::{prepare_decryption, try_decrypt};
 use crate::dehtml::dehtml;
 use crate::events::EventType;
 use crate::format_flowed::unformat_flowed;
@@ -178,7 +178,7 @@ impl MimeMessage {
             .get_header_value(HeaderDef::Date)
             .and_then(|v| mailparse::dateparse(&v).ok())
             .unwrap_or_default();
-        let hop_info = parse_receive_headers(&mail.get_headers());
+        let mut hop_info = parse_receive_headers(&mail.get_headers());
 
         let mut headers = Default::default();
         let mut recipients = Default::default();
@@ -220,7 +220,9 @@ impl MimeMessage {
         let mut mail_raw = Vec::new();
         let mut gossiped_addr = Default::default();
         let mut from_is_signed = false;
-        let mut decryption_info = create_decryption_info(context, &mail, message_time).await?;
+        let mut decryption_info = prepare_decryption(context, &mail, &from, message_time).await?;
+        hop_info += "\n\n";
+        hop_info += &decryption_info.dkim_results.to_string();
 
         // `signatures` is non-empty exactly if the message was encrypted and correctly signed.
         let (mail, signatures, warn_empty_signature) =
@@ -369,6 +371,11 @@ impl MimeMessage {
         parser.heuristically_parse_ndn(context).await;
         parser.parse_headers(context).await?;
 
+        if !decryption_info.dkim_results.allow_keychange {
+            for part in parser.parts.iter_mut() {
+                part.error = Some("Seems like DKIM failed, this either is an attack or (more likely) a bug in Authentication-Results checking. Please tell us about this at https://support.delta.chat.".to_string());
+            }
+        }
         if warn_empty_signature && parser.signatures.is_empty() {
             for part in parser.parts.iter_mut() {
                 part.error = Some("No valid signature".to_string());