API encryption (#2254)

esphome/core/helpers.h

@@ -109,6 +109,8 @@ double random_double();
 /// Returns a random float between 0 and 1. Essentially just casts random_double() to a float.
 float random_float();
 
+void fill_random(uint8_t *data, size_t len);
+
 void fast_random_set_seed(uint32_t seed);
 uint32_t fast_random_32();
 uint16_t fast_random_16();