Update, following David's comments.

xaptum · Sep 21, 2017 · 6705bcc · 6705bcc
1 parent 3f036c8
commit 6705bcc
Show file tree

Hide file tree

Showing 3 changed files with 41 additions and 52 deletions.
diff --git a/include/ecdaa/prng.h b/include/ecdaa/prng.h
@@ -70,29 +70,20 @@ int ecdaa_prng_init(struct ecdaa_prng *prng_in);
 
 #endif  // DISABLE_LIBSODIUM_RNG_SEED_FUNCTION
 
-/*
- * Type of function used to obtain a cryptographically-secure seed.
- *
- * Must be able to provide AMCL_SEED_SIZE crpytographically-strong bytes in a single call.
- *
- * Returns:
- * 0 on success
- * non-zero on failure
- */
-typedef int (*ecdaa_prng_custom_seed_function_type)(void * const buf, const size_t size);
-
 /*
  * Properly seed a `ecdaa_prng`.
  *
  * MUST be called on a `ecdaa_prng` before first use.
  *
  * No dynamic memory allocation is performed.
  *
+ * `seed_size` MUST be at least AMCL_SEED_SIZE.
+ *
  * Returns:
  * 0 on success
- * return value of `custom_func`, if non-zero
+ * -1 if seed_size < AMCL_SEED_SIZE
  */
-int ecdaa_prng_init_custom(struct ecdaa_prng *prng_in, ecdaa_prng_custom_seed_function_type custom_func);
+int ecdaa_prng_init_custom(struct ecdaa_prng *prng_in, char *seed, size_t seed_size);
 
 #ifdef __cplusplus
 }

diff --git a/src/prng.c b/src/prng.c
@@ -29,39 +29,32 @@
 #include <linux/random.h>
 #endif  // defined(__linux__)
 
+static int check_entropy();
+
 int ecdaa_prng_init(struct ecdaa_prng *prng_in)
 {
     int ret = 0;
 
     prng_in->initialized = ECDAA_PRNG_INITIALIZED_NO;
 
     do {
+        ret = check_entropy();
+        if (0 != ret)
+            break;
+
         // Note: We don't have to worry about the race-condition here.
         // `sodium_init` can be called multiple times, and from multiple threads.
         if (-1 == sodium_init()) {
             ret = -1;
             break;
         }
-#if defined(__linux__) && defined(RNDGETENTCNT)
-        int fd;
-        if ((fd = open("/dev/random", O_RDONLY)) != -1) {
-            int c;
-            if (ioctl(fd, RNDGETENTCNT, &c) == 0 && c < 160) {
-                ret = -2;
-            }
-            (void) close(fd);
-            if (0 != ret)
-                break;
-        }
-#endif
-
-        RAND_clean(&prng_in->impl);
 
         char seed[AMCL_SEED_SIZE];
+        randombytes_buf(seed, sizeof(seed));
 
-        randombytes_buf(seed, AMCL_SEED_SIZE);
-
-        RAND_seed(&prng_in->impl, AMCL_SEED_SIZE, seed);
+        ret = ecdaa_prng_init_custom(prng_in, seed, sizeof(seed));
+        if (0 != ret)
+            break;
     } while(0);
 
     if (0 == ret)
@@ -70,21 +63,35 @@ int ecdaa_prng_init(struct ecdaa_prng *prng_in)
     return ret;
 }
 
+static int check_entropy()
+{
+    int ret = 0;
+#if defined(__linux__) && defined(RNDGETENTCNT)
+    int fd;
+    if ((fd = open("/dev/random", O_RDONLY)) != -1) {
+        int c;
+        if (ioctl(fd, RNDGETENTCNT, &c) == 0 && c < 160) {
+            ret = -2;
+        }
+        (void) close(fd);
+    }
+#endif
+
+    return ret;
+}
+
 #endif  // DISABLE_LIBSODIUM_RNG_SEED_FUNCTION
 
-int ecdaa_prng_init_custom(struct ecdaa_prng *prng_in, ecdaa_prng_custom_seed_function_type custom_func)
+int ecdaa_prng_init_custom(struct ecdaa_prng *prng_in, char *seed, size_t seed_size)
 {
     prng_in->initialized = ECDAA_PRNG_INITIALIZED_NO;
 
-    RAND_clean(&prng_in->impl);
+    if (AMCL_SEED_SIZE > seed_size)
+        return -1;
 
-    char seed[AMCL_SEED_SIZE];
-
-    int ret = custom_func(seed, AMCL_SEED_SIZE);
-    if (0 != ret)
-        return ret;
+    RAND_clean(&prng_in->impl);
 
-    RAND_seed(&prng_in->impl, AMCL_SEED_SIZE, seed);
+    RAND_seed(&prng_in->impl, seed_size, seed);
 
     prng_in->initialized = ECDAA_PRNG_INITIALIZED_YES;
 

diff --git a/test/prng-tests.c b/test/prng-tests.c
@@ -22,8 +22,6 @@
 
 #include <amcl/amcl.h>
 
-static int deterministic_seed_func(void * const buf, const size_t size);
-
 static void different_rngs_are_different();
 static void deterministic_seed_makes_same_rngs();
 
@@ -56,8 +54,11 @@ static void different_rngs_are_different()
 static void deterministic_seed_makes_same_rngs()
 {
     struct ecdaa_prng rng1, rng2;
-    ecdaa_prng_init_custom(&rng1, &deterministic_seed_func);
-    ecdaa_prng_init_custom(&rng2, &deterministic_seed_func);
+    char seed[AMCL_SEED_SIZE];
+    for (size_t i = 0; i < sizeof(seed); i++)
+        seed[i] = 5;
+    ecdaa_prng_init_custom(&rng1, seed, sizeof(seed));
+    ecdaa_prng_init_custom(&rng2, seed, sizeof(seed));
 
     int bytes1[5];
     int bytes2[5];
@@ -72,13 +73,3 @@ static void deterministic_seed_makes_same_rngs()
                 && bytes1[4] == bytes2[4]
                 );
 }
-
-static int deterministic_seed_func(void * const buf, const size_t size)
-{
-    uint8_t *buf_ = (uint8_t*)buf;
-
-    for (size_t i = 0; i < size; i++)
-        buf_[i] = 5;
-
-    return 0;
-}