Prefer encryption for the peer if the message is encrypted or signed with the known key (#3844)

Note that if the message is encrypted, we don't check whether it's signed with an attached key
currently, otherwise a massive refactoring of the code is needed because for encrypted messages a
signature is checked and discarded first now.

Author: iequidoo

.gitattributes

@@ -4,7 +4,7 @@
 
 # This directory contains email messages verbatim, and changing CRLF to
 # LF will corrupt them.
-test-data/* text=false
+test-data/** text=false
 
 # binary files should be detected by git, however, to be sure, you can add them here explicitly
 *.png  binary

CHANGELOG.md

@@ -19,6 +19,7 @@
 - Fix cargo clippy and doc errors after Rust update to 1.66 #3850
 - Don't send GroupNameChanged message if the group name doesn't change in terms of
   improve_single_line_input() #3852
+- Prefer encryption for the peer if the message is encrypted or signed with the known key #3849
 
 
 ## 1.103.0

src/decrypt.rs

@@ -31,7 +31,7 @@ pub async fn try_decrypt(
     decryption_info: &DecryptionInfo,
 ) -> Result<Option<(Vec<u8>, HashSet<Fingerprint>)>> {
     // Possibly perform decryption
-    let public_keyring_for_validate = keyring_from_peerstate(&decryption_info.peerstate);
+    let public_keyring_for_validate = keyring_from_peerstate(decryption_info.peerstate.as_ref());
 
     let encrypted_data_part = match get_autocrypt_mime(mail)
         .or_else(|| get_mixed_up_mime(mail))
@@ -251,7 +251,7 @@ fn has_decrypted_pgp_armor(input: &[u8]) -> bool {
 ///
 /// Returns `None` if the part is not a Multipart/Signed part, otherwise retruns the set of key
 /// fingerprints for which there is a valid signature.
-fn validate_detached_signature(
+pub(crate) fn validate_detached_signature(
     mail: &ParsedMail<'_>,
     public_keyring_for_validate: &Keyring<SignedPublicKey>,
 ) -> Result<Option<(Vec<u8>, HashSet<Fingerprint>)>> {
@@ -272,9 +272,9 @@ fn validate_detached_signature(
     }
 }
 
-fn keyring_from_peerstate(peerstate: &Option<Peerstate>) -> Keyring<SignedPublicKey> {
+pub(crate) fn keyring_from_peerstate(peerstate: Option<&Peerstate>) -> Keyring<SignedPublicKey> {
     let mut public_keyring_for_validate: Keyring<SignedPublicKey> = Keyring::new();
-    if let Some(ref peerstate) = *peerstate {
+    if let Some(peerstate) = peerstate {
         if let Some(key) = &peerstate.public_key {
             public_keyring_for_validate.add(key.clone());
         } else if let Some(key) = &peerstate.gossip_key {

src/mimeparser.rs

@@ -806,7 +806,6 @@ mod tests {
             verified_key_fingerprint: None,
             fingerprint_changed: false,
         };
-        assert_eq!(peerstate.prefer_encrypt, EncryptPreference::NoPreference);
 
         peerstate.apply_header(&header, 100);
         assert_eq!(peerstate.prefer_encrypt, EncryptPreference::Mutual);

src/peerstate.rs

@@ -5359,7 +5359,13 @@ Reply from different address
 
         let raw = include_bytes!("../test-data/message/thunderbird_with_autocrypt_unencrypted.eml");
         receive_imf(&t, raw, false).await?;
+        let peerstate = Peerstate::from_addr(&t, "[email protected]")
+            .await?
+            .unwrap();
+        assert_eq!(peerstate.prefer_encrypt, EncryptPreference::Mutual);
 
+        let raw = include_bytes!("../test-data/message/thunderbird_signed_unencrypted.eml");
+        receive_imf(&t, raw, false).await?;
         let peerstate = Peerstate::from_addr(&t, "[email protected]")
             .await?
             .unwrap();

src/receive_imf.rs

@@ -0,0 +1,56 @@
+From - Thu, 15 Dec 2022 14:45:17 GMT
+X-Mozilla-Status: 0801
+X-Mozilla-Status2: 00000000
+Message-ID: <[email protected]>
+Date: Thu, 15 Dec 2022 11:45:16 -0300
+MIME-Version: 1.0
+User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
+ Thunderbird/102.5.1
+Content-Language: en-US
+To: [email protected]
+From: Alice <[email protected]>
+Subject: test message 15:53
+X-Mozilla-Draft-Info: internal/draft; vcard=0; receipt=0; DSN=0; uuencode=0;
+ attachmentreminder=0; deliveryformat=0
+X-Identity-Key: id3
+Fcc: imap://alice%[email protected]/Sent
+Content-Type: multipart/signed; micalg=pgp-sha256;
+ protocol="application/pgp-signature";
+ boundary="------------iX39J1p7DOgblwacjo0e7jX7"
+
+This is an OpenPGP/MIME signed message (RFC 4880 and 3156)
+--------------iX39J1p7DOgblwacjo0e7jX7
+Content-Type: multipart/mixed; boundary="------------WD4DG7TcI4p4lbzyM4toRaDw";
+ protected-headers="v1"
+From: Alice <[email protected]>
+To: [email protected]
+Message-ID: <[email protected]>
+Subject: test message 15:53
+
+--------------WD4DG7TcI4p4lbzyM4toRaDw
+Content-Type: text/plain; charset=UTF-8; format=flowed
+Content-Transfer-Encoding: base64
+
+DQo=
+
+--------------WD4DG7TcI4p4lbzyM4toRaDw--
+
+--------------iX39J1p7DOgblwacjo0e7jX7
+Content-Type: application/pgp-signature; name="OpenPGP_signature.asc"
+Content-Description: OpenPGP digital signature
+Content-Disposition: attachment; filename="OpenPGP_signature"
+
+-----BEGIN PGP SIGNATURE-----
+
+wsD5BAABCAAjFiEEFKs/ZfwnS721+naMJfAHJFnkeuIFAmObMvwFAwAAAAAACgkQJfAHJFnkeuLM
+TgwAnAADX93HE5vXmuBcAbRN2HKIwMzBtRtUF4FNPKchffUvvhSNpHkW2jW7A4hOHNgVSDQdqIUn
++62NgkaKrT1bZqozOZNHXMECHtKBwXWTkIAVqcBdvscCztVIgGby56OPnzZ5y09BsRaqqE5AhDgN
+wGCLa6ipu5FYSF6+KzdO0GIPMY5aGRgVhtl4N01v4S3+r/Yu60MkN87nd15Eaqsrs60P9RmKJTt4
+hDie35kKvHnPzLNs8+xLfqPuO/P7ZbPQgkgCwMAMsMDRUYOv+k5c/bL3PKiOENuDpQ7dkKJ2OzSn
+nTcg8qhDf17vWe26C/QBhFiGEsrHNBQ1KW5by+cqjIUBJgXElFnPl35S5L3fn6JHZLcz6q+wQuJu
+vGT1mJuP//jLFkMHSexukFIVXzn41rWPLd05rBqMgwRcOHMIyzE9zaO1aa8MF2TirPaZ5lH9rx/y
+9DCU/d2sqbbYt8TGqj4hM3pqg5K22eq4KT1W7y8+28I5QfjZumLLrHBdYTnR
+=6JTB
+-----END PGP SIGNATURE-----
+
+--------------iX39J1p7DOgblwacjo0e7jX7--