Make ML-KEM optional

boring-sys/build/main.rs

@@ -741,12 +741,13 @@ fn generate_bindings(config: &Config) {
     ];
     for header in &headers {
         let header_path = include_path.join("openssl").join(header);
-        assert!(
-            header_path.exists(),
-            "{} is missing. Is {} correct? run `cargo clean`",
-            header_path.display(),
-            include_path.display()
-        );
+        if !header_path.exists() {
+            println!(
+                "cargo::warning={} is missing. Is {} correct?",
+                header_path.display(),
+                include_path.display()
+            );
+        }
         builder = builder.header(header_path.to_str().unwrap());
     }
 

boring/Cargo.toml

@@ -29,6 +29,9 @@ legacy-compat-deprecated = []
 # PQ is always enabled. This feature is a no-op, only for backwards compatibility.
 pq-experimental = []
 
+# Interface for ML-KEM (FIPS 203) post-quantum key encapsulation. Does not affect ciphers used in TLS.
+mlkem = []
+
 # Enables Raw public key API (https://datatracker.ietf.org/doc/html/rfc7250)
 # This feature is necessary in order to compile the bindings for the
 # default branch of boringSSL. Alternatively, a version of boringSSL that

boring/src/lib.rs

@@ -137,6 +137,7 @@ pub mod hash;
 pub mod hmac;
 pub mod hpke;
 pub mod memcmp;
+#[cfg(feature = "mlkem")]
 pub mod mlkem;
 pub mod nid;
 pub mod pkcs12;