Add documentation notes about the required size of the signature buffers
diff --git a/include/mbedtls/pk.h b/include/mbedtls/pk.h
index 91950f9..1364275 100644
--- a/include/mbedtls/pk.h
+++ b/include/mbedtls/pk.h
@@ -416,6 +416,10 @@
*
* \note For RSA, md_alg may be MBEDTLS_MD_NONE if hash_len != 0.
* For ECDSA, md_alg may never be MBEDTLS_MD_NONE.
+ *
+ * \note In order to ensure enough space for the signature, the
+ * \p sig buffer size must be of at least
+ * `max(MBEDTLS_ECDSA_MAX_LEN, MBEDTLS_MPI_MAX_SIZE)` bytes.
*/
int mbedtls_pk_sign( mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
const unsigned char *hash, size_t hash_len,
@@ -430,6 +434,10 @@
* \c mbedtls_ecp_set_max_ops() to reduce blocking for ECC
* operations. For RSA, same as \c mbedtls_pk_sign().
*
+ * \note In order to ensure enough space for the signature, the
+ * \p sig buffer size must be of at least
+ * `max(MBEDTLS_ECDSA_MAX_LEN, MBEDTLS_MPI_MAX_SIZE)` bytes.
+ *
* \param ctx The PK context to use. It must have been set up
* with a private key.
* \param md_alg Hash algorithm used (see notes)