random: more unit tests to check entropy injection

soft/lib/random.c

@@ -33,7 +33,11 @@
 #define RANDOM_POLY1 0x4E   /**< x^14+x^11+x^10+x^9 */
 #define RANDOM_POLY0 0x63   /**< x^6+x^5+x^1+1 */
 
-#define STATIC static
+#ifdef TEST
+# define STATIC /* extern */
+#else
+# define STATIC static
+#endif
 
 /** @note LFSR must never be zero or it will get stuck there */
 STATIC uint8_t random_lfsr[4] = { 0, 0, 0, 0x80 };
@@ -100,6 +104,7 @@ uint8_t random_get(uint8_t maximum)
         for(mask = 0xFF; maximum <= (mask>>1); mask >>= 1);
     }
 
+#if 1
     /* Pump LFSR until a number in range is returned. On average this
      * should not take more than 2 iterations. */
     for(;;)
@@ -112,4 +117,9 @@ uint8_t random_get(uint8_t maximum)
             return value;
         }
     }
+#else
+    /* Test the unit test :-) */
+    random_pump();
+    return (uint8_t)(random_lfsr[0] % (1+(unsigned)maximum));
+#endif
 }

soft/test/unittest/test_random.c

@@ -18,8 +18,13 @@
 
 #include "random.h"    /* Module under test */
 
+#include <stdbool.h>
 #include <stdlib.h>    /* calloc, free */
 
+/* Private access into module under test */
+extern uint8_t random_lfsr[4];
+extern void random_pump(void);
+
 void do_distribution(uint8_t maximum, unsigned iterations, float tolerance)
 {
 	unsigned* histogram = calloc((maximum+1), sizeof(unsigned));
@@ -72,3 +77,73 @@ void test_coin(void)
 {
 	do_distribution(1, 1000000, 0.001);
 }
+
+void test_pump(void)
+{
+    /* Without carry */
+    random_lfsr[0] = 1;
+    random_lfsr[1] = 2;
+    random_lfsr[2] = 3;
+    random_lfsr[3] = 4;
+    random_pump();
+    TEST_ASSERT_EQUAL(2, random_lfsr[0]);
+    TEST_ASSERT_EQUAL(4, random_lfsr[1]);
+    TEST_ASSERT_EQUAL(6, random_lfsr[2]);
+    TEST_ASSERT_EQUAL(8, random_lfsr[3]);
+
+    /* With carry */
+    random_lfsr[0] = 1;
+    random_lfsr[1] = 2;
+    random_lfsr[2] = 3;
+    random_lfsr[3] = 0x84;
+    random_pump();
+    TEST_ASSERT_NOT_EQUAL(2, random_lfsr[0]);
+    TEST_ASSERT_NOT_EQUAL(4, random_lfsr[1]);
+    TEST_ASSERT_NOT_EQUAL(6, random_lfsr[2]);
+    TEST_ASSERT_NOT_EQUAL(8, random_lfsr[3]);
+}
+
+void test_add_entropy(void)
+{
+    /* Clear entropy */
+    random_lfsr[0] = 0;
+    random_lfsr[1] = 0;
+    random_lfsr[2] = 0;
+    random_lfsr[3] = 0;
+
+    /* Add 1 bit of entropy */
+    random_add(0x1);
+
+    /* Look for some entropy */
+    bool entropic = false;
+    for (unsigned i = 0; i < 4; i++)
+    {
+        /* Not 0 (initial), 1 (seed) or 1<<1 (pumped seed) */
+        if (random_lfsr[i] > 2)
+        {
+            entropic = true;
+        }
+    }
+    TEST_ASSERT_TRUE(entropic);
+}
+
+void test_clear_entropy(void)
+{
+    /* Try to clear entropy with add */
+    random_lfsr[0] = 0;
+    random_lfsr[1] = 0;
+    random_lfsr[2] = 0;
+    random_lfsr[3] = 0;
+    random_add(0);
+
+    /* Look for some entropy */
+    bool entropic = false;
+    for (unsigned i = 0; i < 4; i++)
+    {
+        if (random_lfsr[i] != 0)
+        {
+            entropic = true;
+        }
+    }
+    TEST_ASSERT_TRUE(entropic);
+}