add encrypting for save files

add libhydrogen for encrypting and decrypting

#9

libs/libhydrogen/impl/random/particle.h

@@ -0,0 +1,26 @@
+// Note: All particle platforms except for the Spark Core have a HW RNG.  Only allow building on
+// supported platforms for now. PLATFORM_ID definitions:
+// https://github.com/particle-iot/device-os/blob/mesh-develop/hal/shared/platforms.h
+
+#include <Particle.h>
+
+static int
+hydro_random_init(void)
+{
+    const char       ctx[hydro_hash_CONTEXTBYTES] = { 'h', 'y', 'd', 'r', 'o', 'P', 'R', 'G' };
+    hydro_hash_state st;
+    uint16_t         ebits = 0;
+
+    hydro_hash_init(&st, ctx, NULL);
+
+    while (ebits < 256) {
+        uint32_t r = HAL_RNG_GetRandomNumber();
+        hydro_hash_update(&st, (const uint32_t *) &r, sizeof r);
+        ebits += 32;
+    }
+
+    hydro_hash_final(&st, hydro_random_context.state, sizeof hydro_random_context.state);
+    hydro_random_context.counter = ~LOAD64_LE(hydro_random_context.state);
+
+    return 0;
+}