Introduced PRNG based on Hash_DRBG (NIST SP 800-90A)

This pseudo-random number generator solves problem with
platform-independent generation of randomized nonces.
Current implementation uses weak entropy, especially when
kernel.randomize_va_space = 0. But it can be improved by
adding new sources to xmpp_rand_reseed().

New internal API introduced:
  xmpp_rand_new
  xmpp_rand_free
  xmpp_rand
  xmpp_rand_bytes
  xmpp_rand_nonce

src/auth.c

@@ -16,12 +16,12 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <time.h>
 
 #include "strophe.h"
 #include "common.h"
 #include "sasl.h"
 #include "sha1.h"
+#include "rand.h"
 
 #ifdef _MSC_VER
 #define strcasecmp stricmp
@@ -501,46 +501,25 @@ err:
     return 0;
 }
 
-static char *_get_nonce(xmpp_ctx_t *ctx)
-{
-    unsigned char buffer[sizeof(clock_t) + sizeof(time_t)] = {0};
-    clock_t ticks = clock();
-    time_t t;
-
-    if (ticks != (clock_t)-1) {
-        *(clock_t *)buffer = ticks;
-    }
-    t = time((time_t *)(buffer + sizeof(clock_t)));
-    if (t == (time_t)-1) {
-        *(time_t *)(buffer + sizeof(clock_t)) = (time_t)rand();
-    }
-
-    return base64_encode(ctx, buffer, sizeof(buffer));
-}
-
 static char *_make_scram_sha1_init_msg(xmpp_conn_t * const conn)
 {
     size_t message_len;
     char *node;
     char *message;
-    char *nonce;
+    char nonce[32];
 
     node = xmpp_jid_node(conn->ctx, conn->jid);
     if (!node) {
         return NULL;
     }
 
-    nonce = _get_nonce(conn->ctx);
-    if (!nonce) {
-        return NULL;
-    }
+    xmpp_rand_nonce(conn->ctx, nonce, sizeof(nonce));
     message_len = strlen(node) + strlen(nonce) + 8 + 1;
     message = xmpp_alloc(conn->ctx, message_len);
     if (message) {
         xmpp_snprintf(message, message_len, "n,,n=%s,r=%s", node, nonce);
         xmpp_free(conn->ctx, node);
     }
-    xmpp_free(conn->ctx, nonce);
 
     return message;
 }