From bef12c53dd82df2ceebc2a7c18eea8c19fbc38b3 Mon Sep 17 00:00:00 2001
From: Yehonatan Cohen Scaly <scalys7@gmail.com>
Date: Sun, 19 Mar 2023 17:13:02 +0200
Subject: [PATCH] Added sk_to_pk() for Kem trait and implemented for dhkem
 (#40)

---
 src/kem.rs       | 3 +++
 src/kem/dhkem.rs | 7 ++++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/kem.rs b/src/kem.rs
index ffcef3a..3f594d9 100644
--- a/src/kem.rs
+++ b/src/kem.rs
@@ -48,6 +48,9 @@ pub trait Kem: Sized {
     #[cfg(not(feature = "serde_impls"))]
     type PrivateKey: Clone + PartialEq + Eq + Serializable + Deserializable;
 
+    /// Computes the public key of a given private key
+    fn sk_to_pk(sk: &Self::PrivateKey) -> Self::PublicKey;
+
     /// The encapsulated key for this KEM. This is used by the recipient to derive the shared
     /// secret.
     #[cfg(feature = "serde_impls")]
diff --git a/src/kem/dhkem.rs b/src/kem/dhkem.rs
index 1661d78..0ff960e 100644
--- a/src/kem/dhkem.rs
+++ b/src/kem/dhkem.rs
@@ -114,7 +114,7 @@ macro_rules! impl_dhkem {
 
                 // The encapped key is the ephemeral pubkey
                 let encapped_key = {
-                    let pk_eph = <$dhkex as DhKeyExchange>::sk_to_pk(&sk_eph);
+                    let pk_eph = <$kem_name as KemTrait>::sk_to_pk(&sk_eph);
                     EncappedKey(pk_eph)
                 };
 
@@ -212,6 +212,11 @@ macro_rules! impl_dhkem {
                     <$dhkex as DhKeyExchange>::derive_keypair::<$kdf>(&suite_id, ikm)
                 }
 
+                /// Computes the public key of a given private key
+                fn sk_to_pk(sk: &PrivateKey) -> PublicKey {
+                    <$dhkex as DhKeyExchange>::sk_to_pk(sk)
+                }
+
                 // Runs encap_with_eph using a random ephemeral key
                 fn encap<R: CryptoRng + RngCore>(
                     pk_recip: &Self::PublicKey,