feat(noise): deprecate LegacyConfig without replacement (#3265)

As the name implies, `LegacyConfig` allows users to interact with older versions of the noise protocol. These are not interoperable and we've been supporting them for a long time now. Hopefully, users have migrated away from it since. To not directly break them, we officially deprecate now without a replacement.

transports/noise/CHANGELOG.md

@@ -2,6 +2,13 @@
 
 - Update to `libp2p-core` `v0.39.0`.
 
+- Deprecate non-compliant noise implementation. We intend to remove it in a future release without replacement. See [PR 3227].
+
+- Deprecate `LegacyConfig` without replacement. See [PR 3265].
+
+[PR 3227]: https://github.com/libp2p/rust-libp2p/pull/3227
+[PR 3265]: https://github.com/libp2p/rust-libp2p/pull/3265
+
 # 0.41.0
 
 - Remove `prost::Error` from public API. See [PR 3058].

transports/noise/src/io/handshake.rs

@@ -27,6 +27,7 @@ mod payload_proto {
 
 use crate::io::{framed::NoiseFramed, NoiseOutput};
 use crate::protocol::{KeypairIdentity, Protocol, PublicKey};
+#[allow(deprecated)]
 use crate::LegacyConfig;
 use crate::NoiseError;
 use bytes::Bytes;
@@ -77,6 +78,7 @@ pub struct State<T> {
     /// The known or received public identity key of the remote, if any.
     id_remote_pubkey: Option<identity::PublicKey>,
     /// Legacy configuration parameters.
+    #[allow(deprecated)]
     legacy: LegacyConfig,
 }
 
@@ -86,6 +88,7 @@ impl<T> State<T> {
     /// will be sent and received on the given I/O resource and using the
     /// provided session for cryptographic operations according to the chosen
     /// Noise handshake pattern.
+    #[allow(deprecated)]
     pub fn new(
         io: T,
         session: snow::HandshakeState,
@@ -177,6 +180,7 @@ where
 
     let mut pb_result = payload_proto::NoiseHandshakePayload::decode(&msg[..]);
 
+    #[allow(deprecated)]
     if pb_result.is_err() && state.legacy.recv_legacy_handshake {
         // NOTE: This is support for legacy handshake payloads. As long as
         // the frame length is less than 256 bytes, which is the case for
@@ -238,6 +242,7 @@ where
         pb.identity_sig = sig.clone()
     }
 
+    #[allow(deprecated)]
     let mut msg = if state.legacy.send_legacy_handshake {
         let mut msg = Vec::with_capacity(2 + pb.encoded_len());
         msg.extend_from_slice(&(pb.encoded_len() as u16).to_be_bytes());
@@ -264,6 +269,7 @@ where
         pb.identity_sig = sig.clone()
     }
 
+    #[allow(deprecated)]
     let mut msg = if state.legacy.send_legacy_handshake {
         let mut msg = Vec::with_capacity(2 + pb.encoded_len());
         msg.extend_from_slice(&(pb.encoded_len() as u16).to_be_bytes());

transports/noise/src/lib.rs

@@ -79,6 +79,7 @@ use zeroize::Zeroize;
 pub struct NoiseConfig<P, C: Zeroize, R = ()> {
     dh_keys: AuthenticKeypair<C>,
     params: ProtocolParams,
+    #[allow(deprecated)]
     legacy: LegacyConfig,
     remote: R,
     _marker: std::marker::PhantomData<P>,
@@ -105,6 +106,11 @@ impl<H, C: Zeroize, R> NoiseConfig<H, C, R> {
     }
 
     /// Sets the legacy configuration options to use, if any.
+    #[deprecated(
+        since = "0.42.0",
+        note = "`LegacyConfig` will be removed without replacement."
+    )]
+    #[allow(deprecated)]
     pub fn set_legacy_config(&mut self, cfg: LegacyConfig) -> &mut Self {
         self.legacy = cfg;
         self
@@ -150,7 +156,10 @@ where
         NoiseConfig {
             dh_keys,
             params: C::params_ix(),
-            legacy: LegacyConfig::default(),
+            legacy: {
+                #[allow(deprecated)]
+                LegacyConfig::default()
+            },
             remote: (),
             _marker: std::marker::PhantomData,
             prologue: Vec::default(),
@@ -167,7 +176,10 @@ where
         NoiseConfig {
             dh_keys,
             params: C::params_xx(),
-            legacy: LegacyConfig::default(),
+            legacy: {
+                #[allow(deprecated)]
+                LegacyConfig::default()
+            },
             remote: (),
             _marker: std::marker::PhantomData,
             prologue: Vec::default(),
@@ -187,7 +199,10 @@ where
         NoiseConfig {
             dh_keys,
             params: C::params_ik(),
-            legacy: LegacyConfig::default(),
+            legacy: {
+                #[allow(deprecated)]
+                LegacyConfig::default()
+            },
             remote: (),
             _marker: std::marker::PhantomData,
             prologue: Vec::default(),
@@ -211,7 +226,10 @@ where
         NoiseConfig {
             dh_keys,
             params: C::params_ik(),
-            legacy: LegacyConfig::default(),
+            legacy: {
+                #[allow(deprecated)]
+                LegacyConfig::default()
+            },
             remote: (remote_dh, remote_id),
             _marker: std::marker::PhantomData,
             prologue: Vec::default(),
@@ -573,6 +591,10 @@ where
 
 /// Legacy configuration options.
 #[derive(Clone, Copy, Default)]
+#[deprecated(
+    since = "0.42.0",
+    note = "`LegacyConfig` will be removed without replacement."
+)]
 pub struct LegacyConfig {
     /// Whether to continue sending legacy handshake payloads,
     /// i.e. length-prefixed protobuf payloads inside a length-prefixed

transports/noise/src/protocol/x25519.rs

@@ -59,7 +59,7 @@ static PARAMS_XX: Lazy<ProtocolParams> = Lazy::new(|| {
 /// A X25519 key.
 #[derive(Clone)]
 #[deprecated(
-    since = "0.41.1",
+    since = "0.42.0",
     note = "Will be removed because it is not compliant with the official libp2p specification. Use `X25519Spec` instead."
 )]
 pub struct X25519([u8; 32]);