fix(keys): only use keys valid at the time of PDU or transaction, and actually refresh keys

Previously, we only fetched keys once, only requesting them again if we have any missing, allowing for ancient keys to be used to sign PDUs and transactions
Now we refresh keys that either have or are about to expire, preventing attacks that make use of leaked private keys of a homeserver
We also ensure that when validating PDUs or transactions, that they are valid at the origin_server_ts or time of us receiving the transaction respectfully
As to not break event authorization for old rooms, we need to keep old keys around
We move verify_keys which we no longer see in direct requests to the origin to old_verify_keys
We keep old_verify_keys indefinitely as mentioned above, as to not break event authorization (at least until a future MSC addresses this)

src/service/globals/data.rs

@@ -1,13 +1,71 @@
-use std::collections::BTreeMap;
-
-use async_trait::async_trait;
-use ruma::{
-    api::federation::discovery::{ServerSigningKeys, VerifyKey},
-    signatures::Ed25519KeyPair,
-    DeviceId, OwnedServerSigningKeyId, ServerName, UserId,
+use std::{
+    collections::BTreeMap,
+    time::{Duration, SystemTime},
 };
 
-use crate::Result;
+use crate::{services, Result};
+use async_trait::async_trait;
+use ruma::{
+    api::federation::discovery::{OldVerifyKey, ServerSigningKeys, VerifyKey},
+    serde::Base64,
+    signatures::Ed25519KeyPair,
+    DeviceId, MilliSecondsSinceUnixEpoch, ServerName, UserId,
+};
+use serde::Deserialize;
+
+/// Similar to ServerSigningKeys, but drops a few unnecessary fields we don't require post-validation
+#[derive(Deserialize, Debug, Clone)]
+pub struct SigningKeys {
+    pub verify_keys: BTreeMap<String, VerifyKey>,
+    pub old_verify_keys: BTreeMap<String, OldVerifyKey>,
+    pub valid_until_ts: MilliSecondsSinceUnixEpoch,
+}
+
+impl SigningKeys {
+    /// Creates the SigningKeys struct, using the keys of the current server
+    pub fn load_own_keys() -> Self {
+        let mut keys = Self {
+            verify_keys: BTreeMap::new(),
+            old_verify_keys: BTreeMap::new(),
+            valid_until_ts: MilliSecondsSinceUnixEpoch::from_system_time(
+                SystemTime::now() + Duration::from_secs(7 * 86400),
+            )
+            .expect("Should be valid until year 500,000,000"),
+        };
+
+        keys.verify_keys.insert(
+            format!("ed25519:{}", services().globals.keypair().version()),
+            VerifyKey {
+                key: Base64::new(services().globals.keypair.public_key().to_vec()),
+            },
+        );
+
+        keys
+    }
+}
+
+impl From<ServerSigningKeys> for SigningKeys {
+    fn from(value: ServerSigningKeys) -> Self {
+        let ServerSigningKeys {
+            verify_keys,
+            old_verify_keys,
+            valid_until_ts,
+            ..
+        } = value;
+
+        Self {
+            verify_keys: verify_keys
+                .into_iter()
+                .map(|(id, key)| (id.to_string(), key))
+                .collect(),
+            old_verify_keys: old_verify_keys
+                .into_iter()
+                .map(|(id, key)| (id.to_string(), key))
+                .collect(),
+            valid_until_ts,
+        }
+    }
+}
 
 #[async_trait]
 pub trait Data: Send + Sync {
@@ -21,17 +79,23 @@ pub trait Data: Send + Sync {
     fn clear_caches(&self, amount: u32);
     fn load_keypair(&self) -> Result<Ed25519KeyPair>;
     fn remove_keypair(&self) -> Result<()>;
-    fn add_signing_key(
+    /// Only extends the cached keys, not moving any verify_keys to old_verify_keys, as if we suddenly
+    /// recieve requests from the origin server, we want to be able to accept requests from them
+    fn add_signing_key_from_trusted_server(
         &self,
         origin: &ServerName,
         new_keys: ServerSigningKeys,
-    ) -> Result<BTreeMap<OwnedServerSigningKeyId, VerifyKey>>;
-
-    /// This returns an empty `Ok(BTreeMap<..>)` when there are no keys found for the server.
-    fn signing_keys_for(
+    ) -> Result<SigningKeys>;
+    /// Extends cached keys, as well as moving verify_keys that are not present in these new keys to
+    /// old_verify_keys, so that potnetially comprimised keys cannot be used to make requests
+    fn add_signing_key_from_origin(
         &self,
         origin: &ServerName,
-    ) -> Result<BTreeMap<OwnedServerSigningKeyId, VerifyKey>>;
+        new_keys: ServerSigningKeys,
+    ) -> Result<SigningKeys>;
+
+    /// This returns an empty `Ok(BTreeMap<..>)` when there are no keys found for the server.
+    fn signing_keys_for(&self, origin: &ServerName) -> Result<Option<SigningKeys>>;
     fn database_version(&self) -> Result<u64>;
     fn bump_database_version(&self, new_version: u64) -> Result<()>;
 }