add FP_GEN_RANDOM logic as in libtommath

src/headers/tfm.h

@@ -252,6 +252,19 @@
    #endif
 #endif
 
+/* platforms that can use a better rand function */
+#if defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__NetBSD__) || defined(__DragonFly__)
+    #define FP_USE_ALT_RAND 1
+#endif
+
+/* use arc4random on platforms that support it */
+#ifdef FP_USE_ALT_RAND
+    #define FP_GEN_RANDOM()    arc4random()
+    #define FP_GEN_RANDOM_MAX  0xffffffff
+#else
+    #define FP_GEN_RANDOM()    rand()
+    #define FP_GEN_RANDOM_MAX  RAND_MAX
+#endif
 
 /* some default configurations.
  */

src/misc/fp_rand.c

@@ -9,7 +9,31 @@
  */
 #include <tfm_private.h>
 
+#if FP_GEN_RANDOM_MAX == 0xffffffff
+  #define FP_GEN_RANDOM_SHIFT  32
+#elif FP_GEN_RANDOM_MAX == 32767
+  /* SHRT_MAX */
+  #define FP_GEN_RANDOM_SHIFT  15
+#elif FP_GEN_RANDOM_MAX == 2147483647
+  /* INT_MAX */
+  #define FP_GEN_RANDOM_SHIFT  31
+#elif !defined(FP_GEN_RANDOM_SHIFT)
+#error Thou shalt define their own valid FP_GEN_RANDOM_SHIFT
+#endif
+
 /* makes a pseudo-random int of a given size */
+static fp_digit fp_gen_random(void)
+{
+  fp_digit d = 0, msk = 0;
+  do {
+    d <<= FP_GEN_RANDOM_SHIFT;
+    d |= ((fp_digit) FP_GEN_RANDOM());
+    msk <<= FP_GEN_RANDOM_SHIFT;
+    msk |= FP_GEN_RANDOM_MAX;
+  } while ((FP_MASK & msk) != FP_MASK);
+  d &= FP_MASK;
+  return d;
+}
 
 void fp_rand(fp_int *a, int digits)
 {
@@ -22,14 +46,14 @@ void fp_rand(fp_int *a, int digits)
 
    /* first place a random non-zero digit */
    do {
-     d = ((fp_digit) abs (rand ())) & FP_MASK;
+     d = fp_gen_random();
    } while (d == 0);
 
    fp_add_d (a, d, a);
 
    while (--digits > 0) {
      fp_lshd (a, 1);
-     fp_add_d (a, ((fp_digit) abs (rand ())), a);
+     fp_add_d (a, fp_gen_random(), a);
    }
 
    return;