Reduce the default ECP window size
MBEDTLS_ECP_WINDOW_SIZE is a compromise between memory usage (growing based
on the value) and performance (faster with larger values). There are
disminishing returns as the value grows larger. Based on Manuel's benchmarks
recorded in https://github.com/ARMmbed/mbedtls/issues/4127, 4 is a good
compromise point, with larger values bringing little advantage. So reduce
the default from 6 to 4.
Document the default value as in optimized for performance mostly, but don't
document the specific value, so we may change it later or make it
platform-dependent.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index d0e61c5..1ae5125 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -3617,7 +3617,7 @@
/* ECP options */
//#define MBEDTLS_ECP_MAX_BITS 521 /**< Maximum bit size of groups */
-//#define MBEDTLS_ECP_WINDOW_SIZE 6 /**< Maximum window size used */
+//#define MBEDTLS_ECP_WINDOW_SIZE 4 /**< Maximum window size used */
//#define MBEDTLS_ECP_FIXED_POINT_OPTIM 1 /**< Enable fixed-point speed-up */
/* Entropy options */