Reduce the default MBEDTLS_ECP_WINDOW_SIZE value to 2
As tested in https://github.com/Mbed-TLS/mbedtls/issues/6790,
after introducing side-channel counter-measures to bignum,
the performance of RSA decryption in correlation to the
MBEDTLS_ECP_WINDOW_SIZE has changed.
The default value of 2 has been chosen as it provides best
or close-to-best results for tests on Cortex-M4 and Intel i7.
Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>
diff --git a/include/mbedtls/bignum.h b/include/mbedtls/bignum.h
index e8fb2de..b1d4b88 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -63,7 +63,7 @@
#if !defined(MBEDTLS_MPI_WINDOW_SIZE)
/*
- * Maximum window size used for modular exponentiation. Default: 6
+ * Maximum window size used for modular exponentiation. Default: 2
* Minimum value: 1. Maximum value: 6.
*
* Result is an array of ( 2 ** MBEDTLS_MPI_WINDOW_SIZE ) MPIs used
@@ -71,7 +71,7 @@
*
* Reduction in size, reduces speed.
*/
-#define MBEDTLS_MPI_WINDOW_SIZE 6 /**< Maximum window size used. */
+#define MBEDTLS_MPI_WINDOW_SIZE 2 /**< Maximum window size used. */
#endif /* !MBEDTLS_MPI_WINDOW_SIZE */
#if !defined(MBEDTLS_MPI_MAX_SIZE)
diff --git a/include/mbedtls/mbedtls_config.h b/include/mbedtls/mbedtls_config.h
index 9ae51c9..b874995 100644
--- a/include/mbedtls/mbedtls_config.h
+++ b/include/mbedtls/mbedtls_config.h
@@ -3559,7 +3559,7 @@
* comment in the specific module. */
/* MPI / BIGNUM options */
-//#define MBEDTLS_MPI_WINDOW_SIZE 6 /**< Maximum window size used. */
+//#define MBEDTLS_MPI_WINDOW_SIZE 2 /**< Maximum window size used. */
//#define MBEDTLS_MPI_MAX_SIZE 1024 /**< Maximum number of bytes for usable MPIs. */
/* CTR_DRBG options */