From ecaa38d1af035beab36818c9da386b851fd39f13 Mon Sep 17 00:00:00 2001
From: Muhamad Azamy <muhamad@incubaid.com>
Date: Mon, 20 Feb 2023 10:43:00 +0100
Subject: [PATCH] Secret key should only use the x coordinate of a point

---
 src/peer/e2e/mod.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/peer/e2e/mod.rs b/src/peer/e2e/mod.rs
index 00b8712..8bcd30d 100644
--- a/src/peer/e2e/mod.rs
+++ b/src/peer/e2e/mod.rs
@@ -71,7 +71,8 @@ impl Pair {
     pub(crate) fn shared<K: AsRef<[u8]>>(&self, pk: K) -> Result<[u8; SHARED_KEY_SIZE], Error> {
         let pk = PublicKey::from_slice(pk.as_ref())?;
 
-        let point = secp256k1::ecdh::shared_secret_point(&pk, &self.0.secret_key());
+        // we take the x coordinate of the secret point.
+        let point = &secp256k1::ecdh::shared_secret_point(&pk, &self.0.secret_key())[..32];
         use sha2::{Digest, Sha256};
 
         let mut sh = Sha256::new();