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 d706a2c..788ea21 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -66,7 +66,7 @@
#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
@@ -74,7 +74,7 @@
*
* 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)