fix: fetch_root_key refuses to play along if called on the mainnet

CHANGELOG.md

@@ -23,6 +23,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 * Function `Agent::fetch_api_boundary_nodes()` is split into two functions: `fetch_api_boundary_nodes_by_canister_id()` and `fetch_api_boundary_nodes_by_subnet_id()`.
 * `ReqwestTransport` and `HyperTransport` structures storing the trait object `route_provider: Box<dyn RouteProvider>` have been modified to allow for shared ownership via `Arc<dyn RouteProvider>`.
 * Added `wasm_memory_limit` to canister creation and canister setting update options.
+* Agent::fetch_root_key() now returns an error, and sets its root key to an empty vector, if got the same root key as the mainnet. This reduce the potentiality of MITM attack.
 
 ## [0.34.0] - 2024-03-18
 

ic-agent/src/agent/agent_error.rs

@@ -205,6 +205,11 @@ pub enum AgentError {
     /// Route provider failed to generate a url for some reason.
     #[error("Route provider failed to generate url: {0}")]
     RouteProviderError(String),
+
+    /// It's an error to fetch the root key on the mainnet.
+    /// Doing so would enable a man-in-the-middle attack.
+    #[error("Never fetch the root key on the mainnet")]
+    NeverFetchRootKeyOnMainNet(),
 }
 
 impl PartialEq for AgentError {

ic-agent/src/agent/agent_test.rs

@@ -45,6 +45,20 @@ fn make_certifying_agent(url: &str) -> Agent {
         .unwrap()
 }
 
+#[cfg_attr(not(target_family = "wasm"), tokio::test)]
+async fn refuse_to_install_mainnet_root_key() -> Result<(), AgentError> {
+    let url = "https://icp0.io";
+
+    let agent = make_agent(url);
+    let result = agent.fetch_root_key().await;
+    assert!(matches!(
+        result,
+        Err(AgentError::NeverFetchRootKeyOnMainNet())
+    ));
+    assert_eq!(agent.read_root_key(), Vec::<u8>::new());
+    Ok(())
+}
+
 #[cfg_attr(not(target_family = "wasm"), tokio::test)]
 #[cfg_attr(target_family = "wasm", wasm_bindgen_test)]
 async fn query() -> Result<(), AgentError> {

ic-agent/src/agent/mod.rs

@@ -333,6 +333,11 @@ impl Agent {
         }
         let status = self.status().await?;
         let root_key = match status.root_key {
+            Some(key) if key[..] == IC_ROOT_KEY[..] => {
+                // even if the caller ignores this error, we're done here.
+                self.set_root_key(vec![]);
+                return Err(AgentError::NeverFetchRootKeyOnMainNet());
+            }
             Some(key) => key,
             None => return Err(AgentError::NoRootKeyInStatus(status)),
         };
@@ -343,7 +348,7 @@ impl Agent {
     /// By default, the agent is configured to talk to the main Internet Computer, and verifies
     /// responses using a hard-coded public key.
     ///
-    /// Using this function you can set the root key to a known one if you know if beforehand.
+    /// Using this function you can set the root key to a known one if you know it beforehand.
     pub fn set_root_key(&self, root_key: Vec<u8>) {
         *self.root_key.write().unwrap() = root_key;
     }