From 7a62361cafeb0e346793ef8d8f88024296b36c4e Mon Sep 17 00:00:00 2001
From: Andy Balaam <andy.balaam@matrix.org>
Date: Mon, 29 Jul 2024 13:20:21 +0100
Subject: [PATCH] crypto: Extract a new error type: MismatchedIdentityKeysError

---
 crates/matrix-sdk-crypto/src/error.rs         | 38 ++++++++++++++-----
 .../src/identities/device.rs                  | 16 ++++----
 2 files changed, 37 insertions(+), 17 deletions(-)

diff --git a/crates/matrix-sdk-crypto/src/error.rs b/crates/matrix-sdk-crypto/src/error.rs
index c73a8ed27e9..72297e82f22 100644
--- a/crates/matrix-sdk-crypto/src/error.rs
+++ b/crates/matrix-sdk-crypto/src/error.rs
@@ -13,6 +13,7 @@
 // limitations under the License.
 
 use ruma::{CanonicalJsonError, IdParseError, OwnedDeviceId, OwnedRoomId, OwnedUserId};
+use serde::{ser::SerializeMap, Serializer};
 use serde_json::Error as SerdeError;
 use thiserror::Error;
 use vodozemac::{Curve25519PublicKey, Ed25519PublicKey};
@@ -93,16 +94,7 @@ pub enum MegolmError {
     #[error(
         "decryption failed because of mismatched identity keys of the sending device and those recorded in the to-device message"
     )]
-    MismatchedIdentityKeys {
-        /// The Ed25519 key recorded in the room key's to-device message.
-        key_ed25519: Box<Ed25519PublicKey>,
-        /// The Ed25519 identity key of the device sending the room key.
-        device_ed25519: Option<Box<Ed25519PublicKey>>,
-        /// The Curve25519 key recorded in the room key's to-device message.
-        key_curve25519: Box<Curve25519PublicKey>,
-        /// The Curve25519 identity key of the device sending the room key.
-        device_curve25519: Option<Box<Curve25519PublicKey>>,
-    },
+    MismatchedIdentityKeys(MismatchedIdentityKeysError),
 
     /// The encrypted megolm message couldn't be decoded.
     #[error(transparent)]
@@ -117,6 +109,32 @@ pub enum MegolmError {
     Store(#[from] CryptoStoreError),
 }
 
+/// Decryption failed because of a mismatch between the identity keys of the
+/// device we received the room key from and the identity keys recorded in
+/// the plaintext of the room key to-device message.
+#[derive(Error, Debug)]
+pub struct MismatchedIdentityKeysError {
+    /// The Ed25519 key recorded in the room key's to-device message.
+    pub key_ed25519: Box<Ed25519PublicKey>,
+    /// The Ed25519 identity key of the device sending the room key.
+    pub device_ed25519: Option<Box<Ed25519PublicKey>>,
+    /// The Curve25519 key recorded in the room key's to-device message.
+    pub key_curve25519: Box<Curve25519PublicKey>,
+    /// The Curve25519 identity key of the device sending the room key.
+    pub device_curve25519: Option<Box<Curve25519PublicKey>>,
+}
+
+impl std::fmt::Display for MismatchedIdentityKeysError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let mut ser = f.serialize_struct("MismatchedIdentityKeysError", 4)?;
+        ser.serialize_entry("key_ed25519", &self.key_ed25519)?;
+        ser.serialize_entry("device_ed25519", &self.device_ed25519)?;
+        ser.serialize_entry("key_curve25519", &self.key_curve25519)?;
+        ser.serialize_entry("device_curve25519", &self.device_curve25519)?;
+        ser.end()
+    }
+}
+
 /// Error that occurs when decrypting an event that is malformed.
 #[derive(Error, Debug)]
 pub enum EventError {
diff --git a/crates/matrix-sdk-crypto/src/identities/device.rs b/crates/matrix-sdk-crypto/src/identities/device.rs
index eaeb24bc979..ef4be5e5711 100644
--- a/crates/matrix-sdk-crypto/src/identities/device.rs
+++ b/crates/matrix-sdk-crypto/src/identities/device.rs
@@ -38,7 +38,7 @@ use super::{atomic_bool_deserializer, atomic_bool_serializer};
 #[cfg(any(test, feature = "testing", doc))]
 use crate::OlmMachine;
 use crate::{
-    error::{EventError, OlmError, OlmResult, SignatureError},
+    error::{EventError, MismatchedIdentityKeysError, OlmError, OlmResult, SignatureError},
     identities::{OwnUserIdentityData, UserIdentityData},
     olm::{
         InboundGroupSession, OutboundGroupSession, Session, ShareInfo, SignedJsonObject, VerifyJson,
@@ -261,12 +261,14 @@ impl Device {
             match (ed25519_comparison, curve25519_comparison) {
                 // If we have any of the keys but they don't turn out to match, refuse to decrypt
                 // instead.
-                (_, Some(false)) | (Some(false), _) => Err(MegolmError::MismatchedIdentityKeys {
-                    key_ed25519: key.into(),
-                    device_ed25519: self.ed25519_key().map(Into::into),
-                    key_curve25519: session.sender_key().into(),
-                    device_curve25519: self.curve25519_key().map(Into::into),
-                }),
+                (_, Some(false)) | (Some(false), _) => {
+                    Err(MegolmError::MismatchedIdentityKeys(MismatchedIdentityKeysError {
+                        key_ed25519: key.into(),
+                        device_ed25519: self.ed25519_key().map(Into::into),
+                        key_curve25519: session.sender_key().into(),
+                        device_curve25519: self.curve25519_key().map(Into::into),
+                    }))
+                }
                 // If both keys match, we have ourselves an owner.
                 (Some(true), Some(true)) => Ok(true),
                 // In the remaining cases, the device is missing at least one of the required