Add random delay function to platform_utils
Add delay function to platform_utils. The function will delay
program execution by incrementing local variable randomised number of
times.
diff --git a/include/mbedtls/platform_util.h b/include/mbedtls/platform_util.h
index e20f1c3..d6ee886 100644
--- a/include/mbedtls/platform_util.h
+++ b/include/mbedtls/platform_util.h
@@ -239,6 +239,21 @@
uint32_t mbedtls_platform_random_in_range( size_t num );
/**
+ * \brief Random delay function.
+ *
+ * Function implements random delay by incrementing local variable
+ * randomized number of times.
+ *
+ * \note Currently the function is dependent of hardware providing an
+ * rng with MBEDTLS_ENTROPY_HARDWARE_ALT.
+ *
+ * \param num Max-value for the local variable increments.
+ *
+ * \return In success number of increments, -1 in case of errors.
+ */
+int mbedtls_platform_random_delay( size_t num );
+
+/**
* \brief This function does nothing, but can be inserted between
* successive reads to a volatile local variable to prevent
* compilers from optimizing them away.
diff --git a/library/platform_util.c b/library/platform_util.c
index 16867aa..5a6fc20 100644
--- a/library/platform_util.c
+++ b/library/platform_util.c
@@ -165,6 +165,29 @@
#endif
}
+int mbedtls_platform_random_delay( size_t max_rand )
+{
+#if !defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
+ (void) max_rand;
+ return -1;
+#else
+ size_t random_number;
+ volatile size_t i = 0;
+ if( max_rand == 0 || max_rand > INT_MAX )
+ {
+ return -1;
+ }
+
+ random_number = mbedtls_platform_random_in_range( max_rand );
+
+ do {
+ i++;
+ } while ( i < random_number );
+
+ return (int) i;
+#endif /* !MBEDTLS_ENTROPY_HARDWARE_ALT */
+}
+
/* Some compilers (armcc 5 for example) optimize away successive reads from a
* volatile local variable (which we use as a counter-measure to fault
* injection attacks), unless there is a call to an external function between