2 files changed, 43 insertions, 27 deletions

diff --git a/src/lib/libcrypto/mlkem/mlkem768.c b/src/lib/libcrypto/mlkem/mlkem768.c
index b20545defc..82adea7b42 100644
--- a/src/lib/libcrypto/mlkem/mlkem768.c
+++ b/src/lib/libcrypto/mlkem/mlkem768.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: mlkem768.c,v 1.10 2025/05/19 07:40:17 beck Exp $ */
+/* $OpenBSD: mlkem768.c,v 1.11 2025/05/19 07:53:00 beck Exp $ */
 /*
  * Copyright (c) 2024, Google Inc.
  * Copyright (c) 2024, Bob Beck <beck@obtuse.com>
@@ -611,6 +611,19 @@ vector_encode(uint8_t *out, const vector *a, int bits)
         }
 }
 
+/* Encodes an entire vector as above, but adding it to a CBB */
+static int
+vector_encode_cbb(CBB *cbb, const vector *a, int bits)
+{
+        uint8_t *encoded_vector;
+
+        if (!CBB_add_space(cbb, &encoded_vector, kEncodedVectorSize))
+                return 0;
+        vector_encode(encoded_vector, a, bits);
+
+        return 1;
+}
+
 /*
  * scalar_decode parses |DEGREE * bits| bits from |in| into |DEGREE| values in
  * |out|. It returns one on success and zero if any parsed value is >=
@@ -850,16 +863,9 @@ LCRYPTO_ALIAS(MLKEM768_private_key_from_seed);
 static int
 mlkem_marshal_public_key(CBB *out, const struct public_key *pub)
 {
-        uint8_t *vector_output;
-
-        if (!CBB_add_space(out, &vector_output, kEncodedVectorSize)) {
+        if (!vector_encode_cbb(out, &pub->t, kLog2Prime))
                 return 0;
-        }
-        vector_encode(vector_output, &pub->t, kLog2Prime);
-        if (!CBB_add_bytes(out, pub->rho, sizeof(pub->rho))) {
-                return 0;
-        }
-        return 1;
+        return CBB_add_bytes(out, pub->rho, sizeof(pub->rho));
 }
 
 int
@@ -1117,27 +1123,37 @@ MLKEM768_parse_public_key(struct MLKEM768_public_key *public_key,
 LCRYPTO_ALIAS(MLKEM768_parse_public_key);
 
 int
-MLKEM768_marshal_private_key(CBB *out,
-    const struct MLKEM768_private_key *private_key)
+MLKEM768_marshal_private_key(const struct MLKEM768_private_key *private_key,
+    uint8_t **out_private_key, size_t *out_private_key_len)
 {
         const struct private_key *const priv = private_key_768_from_external(
             private_key);
-        uint8_t *s_output;
+        CBB cbb;
+        int ret = 0;
 
-        if (!CBB_add_space(out, &s_output, kEncodedVectorSize)) {
-                return 0;
-        }
-        vector_encode(s_output, &priv->s, kLog2Prime);
-        if (!mlkem_marshal_public_key(out, &priv->pub))
-                return 0;
-        if (!CBB_add_bytes(out, priv->pub.public_key_hash,
+        if (!CBB_init(&cbb, MLKEM768_PRIVATE_KEY_BYTES))
+                goto err;
+
+        if (!vector_encode_cbb(&cbb, &priv->s, kLog2Prime))
+                goto err;
+        if (!mlkem_marshal_public_key(&cbb, &priv->pub))
+                goto err;
+        if (!CBB_add_bytes(&cbb, priv->pub.public_key_hash,
             sizeof(priv->pub.public_key_hash)))
-                return 0;
-        if (!CBB_add_bytes(out, priv->fo_failure_secret,
+                goto err;
+        if (!CBB_add_bytes(&cbb, priv->fo_failure_secret,
             sizeof(priv->fo_failure_secret)))
-                return 0;
+                goto err;
 
-        return 1;
+        if (!CBB_finish(&cbb, out_private_key, out_private_key_len))
+                goto err;
+
+        ret = 1;
+
+ err:
+        CBB_cleanup(&cbb);
+
+        return ret;
 }
 
 int
diff --git a/src/lib/libcrypto/mlkem/mlkem_internal.h b/src/lib/libcrypto/mlkem/mlkem_internal.h
index 7a51197c36..aed051e980 100644
--- a/src/lib/libcrypto/mlkem/mlkem_internal.h
+++ b/src/lib/libcrypto/mlkem/mlkem_internal.h
@@ -1,4 +1,4 @@
-/*      $OpenBSD: mlkem_internal.h,v 1.5 2025/05/19 06:47:40 beck Exp $ */
+/*      $OpenBSD: mlkem_internal.h,v 1.6 2025/05/19 07:53:00 beck Exp $ */
 /*
  * Copyright (c) 2023, Google Inc.
  *
@@ -57,8 +57,8 @@ int MLKEM768_generate_key_external_entropy(
  * format for ML-KEM private keys. It returns one on success or zero on
  * allocation error.
  */
-int MLKEM768_marshal_private_key(CBB *out,
-    const struct MLKEM768_private_key *private_key);
+int MLKEM768_marshal_private_key(const struct MLKEM768_private_key *private_key,
+    uint8_t **out_private_key, size_t *out_private_key_len);
 
 /*
  * MLKEM_encap_external_entropy behaves like |MLKEM_encap|, but uses