From c8d0cd6f3cb18f63d99b36293066d6e6a6e1ca7f Mon Sep 17 00:00:00 2001
From: Jack Grigg <thestr4d@gmail.com>
Date: Fri, 24 Apr 2026 07:34:45 +0000
Subject: [PATCH] Add HPKE Hybrid KEM sizes

Implemented per <https://filippo.io/hpke-pq>, which itself derives from
<https://datatracker.ietf.org/doc/html/draft-ietf-hpke-pq-03>. These
sizes correspond to the encoded sizes of the encapsulating keys and
ciphertexts, which are calculated as `KEM.Nek + Group.Nelem` and
`KEM.Nct + Group.Nelem` respectively.

The X-Wing sizes were already present due to being rounder numbers.
---
 src/sizes.rs | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/src/sizes.rs b/src/sizes.rs
index d42ba6d..276afa6 100644
--- a/src/sizes.rs
+++ b/src/sizes.rs
@@ -849,6 +849,13 @@ mod extra_sizes {
     pub type U1530 = uint!(0 1 0 1 1 1 1 1 1 0 1);
     pub type U1658 = uint!(0 1 0 1 1 1 1 0 0 1 1);
 
+    // HPKE Hybrid KEM sizes
+    // - MLKEM768-P256
+    pub type U1153 = uint!(1 0 0 0 0 0 0 1 0 0 1);
+    pub type U1249 = uint!(1 0 0 0 0 1 1 1 0 0 1);
+    // - MLKEM1024-P384
+    pub type U1665 = uint!(1 0 0 0 0 0 0 1 0 1 1);
+
     // LMS sizes
     pub type U2047 = uint!(1 1 1 1 1 1 1 1 1 1 1);
     pub type U2180 = uint!(0 0 1 0 0 0 0 1 0 0 0 1);
@@ -1110,6 +1117,14 @@ mod extra_sizes {
         1658 => U1658,
     }
 
+    // HPKE Hybrid KEM sizes
+    impl_array_sizes! {
+        hpke_hybrid,
+        1153 => U1153,
+        1249 => U1249,
+        1665 => U1665,
+    }
+
     // LMS sizes
     impl_array_sizes! {
         lms,