Override default `ffdhe_group()` for all kx impls

This prevents these impls linking in `FfdheGroup::from_named_group`,
which is a ~60KB function.

3 files changed, 27 insertions, 1 deletions

diff --git a/provider-example/src/kx.rs b/provider-example/src/kx.rs
index 93e1540d..80fb235b 100644
--- a/provider-example/src/kx.rs
+++ b/provider-example/src/kx.rs
@@ -2,6 +2,7 @@ use alloc::boxed::Box;
 
 use crypto::SupportedKxGroup;
 use rustls::crypto;
+use rustls::ffdhe_groups::FfdheGroup;
 
 pub struct KeyExchange {
     priv_key: x25519_dalek::EphemeralSecret,
@@ -25,6 +26,10 @@ impl crypto::ActiveKeyExchange for KeyExchange {
         self.pub_key.as_bytes()
     }
 
+    fn ffdhe_group(&self) -> Option<FfdheGroup<'static>> {
+        None
+    }
+
     fn group(&self) -> rustls::NamedGroup {
         X25519.name()
     }
@@ -44,6 +49,10 @@ impl crypto::SupportedKxGroup for X25519 {
         }))
     }
 
+    fn ffdhe_group(&self) -> Option<FfdheGroup<'static>> {
+        None
+    }
+
     fn name(&self) -> rustls::NamedGroup {
         rustls::NamedGroup::X25519
     }
diff --git a/rustls-post-quantum/src/lib.rs b/rustls-post-quantum/src/lib.rs
index 9816bc1a..d1a1717c 100644
--- a/rustls-post-quantum/src/lib.rs
+++ b/rustls-post-quantum/src/lib.rs
@@ -55,6 +55,7 @@ use rustls::crypto::aws_lc_rs::{default_provider, kx_group};
 use rustls::crypto::{
     ActiveKeyExchange, CompletedKeyExchange, CryptoProvider, SharedSecret, SupportedKxGroup,
 };
+use rustls::ffdhe_groups::FfdheGroup;
 use rustls::{Error, NamedGroup, PeerMisbehaved};
 
 /// A `CryptoProvider` which includes `X25519Kyber768Draft00` key exchange.
@@ -119,6 +120,10 @@ impl SupportedKxGroup for X25519Kyber768Draft00 {
         })
     }
 
+    fn ffdhe_group(&self) -> Option<FfdheGroup<'static>> {
+        None
+    }
+
     fn name(&self) -> NamedGroup {
         NAMED_GROUP
     }
@@ -153,6 +158,10 @@ impl ActiveKeyExchange for Active {
         &self.combined_pub_key
     }
 
+    fn ffdhe_group(&self) -> Option<FfdheGroup<'static>> {
+        None
+    }
+
     fn group(&self) -> NamedGroup {
         NAMED_GROUP
     }
diff --git a/rustls/src/crypto/ring/kx.rs b/rustls/src/crypto/ring/kx.rs
index 55dcd2c0..8c267e9e 100644
--- a/rustls/src/crypto/ring/kx.rs
+++ b/rustls/src/crypto/ring/kx.rs
@@ -5,7 +5,7 @@ use core::fmt;
 
 use super::ring_like::agreement;
 use super::ring_like::rand::SystemRandom;
-use crate::crypto::{ActiveKeyExchange, SharedSecret, SupportedKxGroup};
+use crate::crypto::{ActiveKeyExchange, FfdheGroup, SharedSecret, SupportedKxGroup};
 use crate::error::{Error, PeerMisbehaved};
 use crate::msgs::enums::NamedGroup;
 use crate::rand::GetRandomFailed;
@@ -46,6 +46,10 @@ impl SupportedKxGroup for KxGroup {
         }))
     }
 
+    fn ffdhe_group(&self) -> Option<FfdheGroup<'static>> {
+        None
+    }
+
     fn name(&self) -> NamedGroup {
         self.name
     }
@@ -108,6 +112,10 @@ impl ActiveKeyExchange for KeyExchange {
             .map_err(|_| PeerMisbehaved::InvalidKeyShare.into())
     }
 
+    fn ffdhe_group(&self) -> Option<FfdheGroup<'static>> {
+        None
+    }
+
     /// Return the group being used.
     fn group(&self) -> NamedGroup {
         self.name