feat: use AWS-LC crypto provider and support PQ key-exchange (#6568)

## Description

go-libp2p's tls implementation advertises hybrid X25519MLKEM768 key exchange in client hello enabling quantum resistance against "harvest now, decrypt later" attacks. This PR brings the same functionality to rust-libp2p by introducing the following changes:

* Use rustls's AWS-LC crypto provider instead of ring for TLS configurations to enable hybrid X25519MLKEM768 key-exchange while keeping interoperability with X25519.

## AI Assistance Disclosure



**Tools used** OpenCode

**Attestation** _(required)_:

- [x] I have read every line of this diff, understand what it does, and can explain it in review.

## Notes & open questions

Note, that `prefer-post-quantum` for rustls was enabled, to put X25519MLKEM768 in the first place of key exchanges advertised in client hello, which mimics go-libp2p's tls implementation and enable hybrid key exchange by default when both peers support it

## Change checklist



- [x] I have performed a self-review of my own code
- [x] I have made corresponding changes to the documentation
- [x] I have added tests that prove my fix is effective or that my feature works
- [x] A changelog entry has been made in the appropriate crates


Approved-by: jxs <1204690+jxs@users.noreply.github.com>

Author: kamilsa

Cargo.lock

@@ -1,5 +1,8 @@
 ## 0.14.0
 
+- Prefer and advertise the X25519MLKEM768 key exchange group for QUIC.
+  See [PR 6568](https://github.com/libp2p/rust-libp2p/pull/6568).
+
 - Raise MSRV to 1.88.0.
   See [PR 6273](https://github.com/libp2p/rust-libp2p/pull/6273).
 

transports/quic/CHANGELOG.md

@@ -15,10 +15,9 @@ if-watch = { workspace = true }
 libp2p-core = { workspace = true }
 libp2p-tls = { workspace = true }
 libp2p-identity = { workspace = true }
-quinn = { version = "0.11", default-features = false, features = ["rustls", "futures-io"] }
-quinn-proto = { version = "0.11" }
+quinn = { version = "0.11", default-features = false, features = ["rustls-aws-lc-rs", "futures-io"] }
+quinn-proto = { version = "0.11", default-features = false, features = ["bloom", "log", "ring"] }
 rand = { workspace = true }
-rustls = { version = "0.23", default-features = false }
 thiserror = { workspace = true }
 tokio = { workspace = true, default-features = false, features = ["net", "rt", "time"], optional = true }
 tracing = { workspace = true }

transports/quic/Cargo.toml

@@ -1,5 +1,8 @@
 ## 0.7.0
 
+- Use the AWS-LC crypto provider and prefer the X25519MLKEM768 key exchange group for TLS configurations.
+  See [PR 6568](https://github.com/libp2p/rust-libp2p/pull/6568).
+
 - Replace deprecated `webpki::Error` variants with their new context-based equivalents.
   See [PR 6355](https://github.com/libp2p/rust-libp2p/pull/6355).
 

transports/tls/CHANGELOG.md

@@ -24,8 +24,7 @@ yasna = "0.6"
 [dependencies.rustls]
 version = "0.23"
 default-features = false
-features = ["ring", "std"] # Must enable this to allow for custom verification code.
-
+features = ["aws-lc-rs", "prefer-post-quantum", "std"] # Must enable this to allow for custom verification code.
 
 [dev-dependencies]
 hex-literal = { workspace = true }

transports/tls/Cargo.toml

@@ -54,7 +54,7 @@ impl AlwaysResolvesCert {
     ) -> Result<Self, rustls::Error> {
         let certified_key = rustls::sign::CertifiedKey::new(
             vec![cert],
-            rustls::crypto::ring::sign::any_ecdsa_type(key)?,
+            rustls::crypto::aws_lc_rs::sign::any_ecdsa_type(key)?,
         );
         Ok(Self(Arc::new(certified_key)))
     }

transports/tls/src/certificate.rs

@@ -45,7 +45,7 @@ pub fn make_client_config(
 ) -> Result<rustls::ClientConfig, certificate::GenError> {
     let (certificate, private_key) = certificate::generate(keypair)?;
 
-    let mut provider = rustls::crypto::ring::default_provider();
+    let mut provider = rustls::crypto::aws_lc_rs::default_provider();
     provider.cipher_suites = verifier::CIPHERSUITES.to_vec();
 
     let cert_resolver = Arc::new(
@@ -73,7 +73,7 @@ pub fn make_server_config(
 ) -> Result<rustls::ServerConfig, certificate::GenError> {
     let (certificate, private_key) = certificate::generate(keypair)?;
 
-    let mut provider = rustls::crypto::ring::default_provider();
+    let mut provider = rustls::crypto::aws_lc_rs::default_provider();
     provider.cipher_suites = verifier::CIPHERSUITES.to_vec();
 
     let cert_resolver = Arc::new(
@@ -91,3 +91,21 @@ pub fn make_server_config(
 
     Ok(crypto)
 }
+
+#[cfg(test)]
+mod tests {
+    use rustls::NamedGroup;
+
+    use super::*;
+
+    #[test]
+    fn prefers_x25519_mlkem768() {
+        let keypair = Keypair::generate_ed25519();
+        let config = make_client_config(&keypair, None).unwrap();
+
+        assert_eq!(
+            config.crypto_provider().kx_groups[0].name(),
+            NamedGroup::X25519MLKEM768
+        );
+    }
+}

transports/tls/src/lib.rs

@@ -30,7 +30,7 @@ use rustls::{
     CertificateError, DigitallySignedStruct, DistinguishedName, OtherError, SignatureScheme,
     SupportedCipherSuite, SupportedProtocolVersion,
     client::danger::{HandshakeSignatureValid, ServerCertVerified, ServerCertVerifier},
-    crypto::ring::cipher_suite::{
+    crypto::aws_lc_rs::cipher_suite::{
         TLS13_AES_128_GCM_SHA256, TLS13_AES_256_GCM_SHA384, TLS13_CHACHA20_POLY1305_SHA256,
     },
     pki_types::CertificateDer,