libavutil/random_seed.c

   1 /*
   2  * Copyright (c) 2009 Baptiste Coudurier <baptiste.coudurier@gmail.com>
   3  *
   4  * This file is part of Libav.
   5  *
   6  * Libav is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Lesser General Public
   8  * License as published by the Free Software Foundation; either
   9  * version 2.1 of the License, or (at your option) any later version.
  10  *
  11  * Libav is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public
  17  * License along with Libav; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  19  */
  20
  21 #include "config.h"
  22
  23 #if HAVE_UNISTD_H
  24 #include <unistd.h>
  25 #endif
  26 #if HAVE_BCRYPT
  27 #include <windows.h>
  28 #include <bcrypt.h>
  29 #endif
  30 #include <fcntl.h>
  31 #include <math.h>
  32 #include <time.h>
  33 #include "internal.h"
  34 #include "intreadwrite.h"
  35 #include "mem.h"
  36 #include "timer.h"
  37 #include "random_seed.h"
  38 #include "sha.h"
  39
  40 static int read_random(uint32_t *dst, const char *file)
  41 {
  42 #if HAVE_UNISTD_H
  43     int fd = avpriv_open(file, O_RDONLY);
  44     int err = -1;
  45
  46     if (fd == -1)
  47         return -1;
  48     err = read(fd, dst, sizeof(*dst));
  49     close(fd);
  50
  51     return err;
  52 #else
  53     return -1;
  54 #endif
  55 }
  56
  57 static uint32_t get_generic_seed(void)
  58 {
  59     struct AVSHA *sha = av_sha_alloc();
  60     clock_t last_t  = 0;
  61     static uint64_t i = 0;
  62     static uint32_t buffer[512] = { 0 };
  63     unsigned char digest[20];
  64     uint64_t last_i = i;
  65
  66     for (;;) {
  67         clock_t t = clock();
  68
  69         if (last_t == t) {
  70             buffer[i & 511]++;
  71         } else {
  72             buffer[++i & 511] += (t - last_t) % 3294638521U;
  73             if (last_i && i - last_i > 4 || i - last_i > 64)
  74                 break;
  75         }
  76         last_t = t;
  77     }
  78
  79     if (!sha) {
  80         uint32_t seed = 0;
  81         int j;
  82         // Unable to allocate an SHA context, just XOR the buffer together
  83         // to create something hopefully unique.
  84         for (j = 0; j < 512; j++)
  85             seed ^= buffer[j];
  86         return seed;
  87     }
  88     av_sha_init(sha, 160);
  89     av_sha_update(sha, (const uint8_t *) buffer, sizeof(buffer));
  90     av_sha_final(sha, digest);
  91     av_free(sha);
  92     return AV_RB32(digest) + AV_RB32(digest + 16);
  93 }
  94
  95 uint32_t av_get_random_seed(void)
  96 {
  97     uint32_t seed;
  98
  99 #if HAVE_BCRYPT
 100     BCRYPT_ALG_HANDLE algo_handle;
 101     NTSTATUS ret = BCryptOpenAlgorithmProvider(&algo_handle, BCRYPT_RNG_ALGORITHM,
 102                                                MS_PRIMITIVE_PROVIDER, 0);
 103     if (BCRYPT_SUCCESS(ret)) {
 104         NTSTATUS ret = BCryptGenRandom(algo_handle, (UCHAR*)&seed, sizeof(seed), 0);
 105         BCryptCloseAlgorithmProvider(algo_handle, 0);
 106         if (BCRYPT_SUCCESS(ret))
 107             return seed;
 108     }
 109 #endif
 110
 111     if (read_random(&seed, "/dev/urandom") == sizeof(seed))
 112         return seed;
 113     if (read_random(&seed, "/dev/random")  == sizeof(seed))
 114         return seed;
 115     return get_generic_seed();
 116 }