From 7d75c1ac83dd9bc5fc237248d821e6cb1780673f Mon Sep 17 00:00:00 2001
From: Hugo Rosenkranz-Costa <hugo.rosenkranz@cosmian.com>
Date: Mon, 20 Nov 2023 17:07:58 +0100
Subject: [PATCH] feat: iterate through subkeys using BFS for decaps

---
 src/core/primitives.rs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/core/primitives.rs b/src/core/primitives.rs
index 541ffdf8..10f528f6 100644
--- a/src/core/primitives.rs
+++ b/src/core/primitives.rs
@@ -231,7 +231,9 @@ pub fn decaps(
 ) -> Result<SymmetricKey<SYM_KEY_LENGTH>, Error> {
     let precomp = &(&encapsulation.c1 * &usk.a) + &(&encapsulation.c2 * &usk.b);
     for encapsulation_i in &encapsulation.encs {
-        for (_, (sk_j, x_j)) in usk.subkeys.iter() {
+        // BFS search user subkeys to first try the most recent rotations of each
+        // partitions.
+        for (_, (sk_j, x_j)) in usk.subkeys.bfs() {
             let e_j = match encapsulation_i {
                 KeyEncapsulation::HybridEncapsulation(epq_i) => {
                     if let Some(sk_j) = sk_j {