fix: replaced empty tuple error types with Infallible

dhkem/src/ecdh_kem.rs

@@ -1,7 +1,7 @@
 //! Generic Elliptic Curve Diffie-Hellman KEM adapter.
 
 use crate::{DhDecapsulator, DhEncapsulator, DhKem};
-use core::marker::PhantomData;
+use core::{convert::Infallible, marker::PhantomData};
 use elliptic_curve::{
     ecdh::{EphemeralSecret, SharedSecret},
     CurveArithmetic, PublicKey,
@@ -19,7 +19,7 @@ impl<C> Encapsulate<PublicKey<C>, SharedSecret<C>> for DhEncapsulator<PublicKey<
 where
     C: CurveArithmetic,
 {
-    type Error = ();
+    type Error = Infallible;
 
     fn encapsulate(
         &self,
@@ -38,7 +38,7 @@ impl<C> Decapsulate<PublicKey<C>, SharedSecret<C>> for DhDecapsulator<EphemeralS
 where
     C: CurveArithmetic,
 {
-    type Error = ();
+    type Error = Infallible;
 
     fn decapsulate(&self, encapsulated_key: &PublicKey<C>) -> Result<SharedSecret<C>, Self::Error> {
         let ss = self.0.diffie_hellman(encapsulated_key);

dhkem/src/x25519_kem.rs

@@ -1,4 +1,5 @@
 use crate::{DhDecapsulator, DhEncapsulator, DhKem};
+use core::convert::Infallible;
 use kem::{Decapsulate, Encapsulate};
 use rand_core::CryptoRngCore;
 use x25519::{PublicKey, ReusableSecret, SharedSecret};
@@ -9,7 +10,7 @@ use x25519::{PublicKey, ReusableSecret, SharedSecret};
 pub struct X25519Kem;
 
 impl Encapsulate<PublicKey, SharedSecret> for DhEncapsulator<PublicKey> {
-    type Error = ();
+    type Error = Infallible;
 
     fn encapsulate(
         &self,
@@ -25,7 +26,7 @@ impl Encapsulate<PublicKey, SharedSecret> for DhEncapsulator<PublicKey> {
 }
 
 impl Decapsulate<PublicKey, SharedSecret> for DhDecapsulator<ReusableSecret> {
-    type Error = ();
+    type Error = Infallible;
 
     fn decapsulate(&self, encapsulated_key: &PublicKey) -> Result<SharedSecret, Self::Error> {
         let ss = self.0.diffie_hellman(encapsulated_key);

ml-kem/src/kem.rs

@@ -1,3 +1,4 @@
+use core::convert::Infallible;
 use core::marker::PhantomData;
 use hybrid_array::typenum::U32;
 use rand_core::CryptoRngCore;
@@ -85,12 +86,12 @@ impl<P> ::kem::Decapsulate<EncodedCiphertext<P>, SharedKey> for DecapsulationKey
 where
     P: KemParams,
 {
-    // Decapsulation is infallible
-    // XXX(RLB): Maybe we should reflect decryption failure as an error?
-    // TODO(RLB) Make Infallible
-    type Error = ();
+    type Error = Infallible;
 
-    fn decapsulate(&self, encapsulated_key: &EncodedCiphertext<P>) -> Result<SharedKey, ()> {
+    fn decapsulate(
+        &self,
+        encapsulated_key: &EncodedCiphertext<P>,
+    ) -> Result<SharedKey, Self::Error> {
         let mp = self.dk_pke.decrypt(encapsulated_key);
         let (Kp, rp) = G(&[&mp, &self.ek.h]);
         let Kbar = J(&[self.z.as_slice(), encapsulated_key.as_ref()]);
@@ -187,9 +188,7 @@ impl<P> ::kem::Encapsulate<EncodedCiphertext<P>, SharedKey> for EncapsulationKey
 where
     P: KemParams,
 {
-    // TODO(RLB) Make Infallible
-    // TODO(RLB) Swap the order of the
-    type Error = ();
+    type Error = Infallible;
 
     fn encapsulate(
         &self,
@@ -205,8 +204,7 @@ impl<P> crate::EncapsulateDeterministic<EncodedCiphertext<P>, SharedKey> for Enc
 where
     P: KemParams,
 {
-    // TODO(RLB) Make Infallible
-    type Error = ();
+    type Error = Infallible;
 
     fn encapsulate_deterministic(
         &self,

x-wing/src/lib.rs

@@ -27,6 +27,8 @@
 //! assert_eq!(ss_sender, ss_receiver);
 //! ```
 
+use core::convert::Infallible;
+
 use kem::{Decapsulate, Encapsulate};
 use ml_kem::array::ArrayN;
 use ml_kem::{kem, EncodedSizeUser, KemCore, MlKem768, MlKem768Params, B32};
@@ -73,7 +75,7 @@ pub struct EncapsulationKey {
 }
 
 impl Encapsulate<Ciphertext, SharedSecret> for EncapsulationKey {
-    type Error = ();
+    type Error = Infallible;
 
     fn encapsulate(
         &self,
@@ -133,7 +135,7 @@ pub struct DecapsulationKey {
 }
 
 impl Decapsulate<Ciphertext, SharedSecret> for DecapsulationKey {
-    type Error = ();
+    type Error = Infallible;
 
     fn decapsulate(&self, ct: &Ciphertext) -> Result<SharedSecret, Self::Error> {
         let (sk_m, sk_x, _pk_m, pk_x) = self.expand_key();
@@ -346,34 +348,30 @@ mod tests {
 
     /// Test with test vectors from: https://github.com/dconnolly/draft-connolly-cfrg-xwing-kem/blob/main/spec/test-vectors.json
     #[test]
-    fn rfc_test_vectors() -> Result<(), ()> {
+    fn rfc_test_vectors() {
         let test_vectors =
             serde_json::from_str::<Vec<TestVector>>(include_str!("test-vectors.json")).unwrap();
 
         for test_vector in test_vectors {
-            run_test(test_vector)?;
+            run_test(test_vector);
         }
-
-        Ok(())
     }
 
-    fn run_test(test_vector: TestVector) -> Result<(), ()> {
+    fn run_test(test_vector: TestVector) {
         let mut seed = SeedRng::new(test_vector.seed);
         let (sk, pk) = generate_key_pair(&mut seed);
 
         assert_eq!(sk.as_bytes().to_vec(), test_vector.sk);
         assert_eq!(pk.as_bytes().to_vec(), test_vector.pk);
 
         let mut eseed = SeedRng::new(test_vector.eseed);
-        let (ct, ss) = pk.encapsulate(&mut eseed)?;
+        let (ct, ss) = pk.encapsulate(&mut eseed).unwrap();
 
         assert_eq!(ss, test_vector.ss);
         assert_eq!(ct.as_bytes().to_vec(), test_vector.ct);
 
-        let ss = sk.decapsulate(&ct)?;
+        let ss = sk.decapsulate(&ct).unwrap();
         assert_eq!(ss, test_vector.ss);
-
-        Ok(())
     }
 
     #[test]