x-wing: Reject non-contributory behaviour in X25519 component

Cargo.toml

@@ -95,3 +95,6 @@ required-features = ["getrandom"]
 
 [lib]
 bench = false
+
+[patch.crates-io]
+x-wing = { git = "https://github.com/str4d/RustCrypto-KEMs.git", rev = "faabbc960470b38a51f4aec07ce7f1d1c381d401" }

src/kem/xwing.rs

@@ -14,7 +14,7 @@ use hybrid_array::typenum::{Prod, Sum, U3, U32, U64, U1024, Unsigned};
 use rand_core::CryptoRng;
 use shake::Shake256;
 use subtle::{Choice, ConstantTimeEq};
-use x_wing::{Decapsulator, KeyExport, TryKeyInit, kem::Decapsulate};
+use x_wing::{Decapsulator, KeyExport, TryKeyInit, kem::TryDecapsulate};
 use zeroize::Zeroize;
 
 // Type-level size constants for X-Wing
@@ -48,7 +48,9 @@ impl Deserializable for PrivateKey {
         let mut arr = [0u8; Self::OutputSize::USIZE];
         arr.copy_from_slice(encoded);
 
-        let sk = PrivateKey(arr.into());
+        let sk = PrivateKey(
+            x_wing::DecapsulationKey::from(arr).reject_x25519_non_contributory_behaviour(),
+        );
         arr.zeroize();
 
         Ok(sk)
@@ -178,7 +180,10 @@ impl KemTrait for XWing {
             "X-Wing doesn't support authenticated encapsulation. Use Base or Psk operation mode."
         );
 
-        let ss = sk_recip.0.decapsulate(&encapped_key.0);
+        let ss = sk_recip
+            .0
+            .try_decapsulate(&encapped_key.0)
+            .map_err(|_| HpkeError::DecapError)?;
         Ok(SharedSecret(ss))
     }