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/ChangeLog.d/mpi-window-perf b/ChangeLog.d/mpi-window-perf
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index 0000000..0f75d6a
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+++ b/ChangeLog.d/mpi-window-perf
@@ -0,0 +1,7 @@
+Changes
+ * Changed the default MBEDTLS_ECP_WINDOW_SIZE from 6 to 2.
+ As tested in issue 6790, the correlation between this define and
+ RSA decryption performance has changed lately due to security fixes.
+ To fix the performance degradation when using default values the
+ window was reduced from 6 to 2, a value that gives the best or close
+ to best results when tested on Cortex-M4 and Intel i7.