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random_seed.c
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1 /*
2  * Copyright (c) 2009 Baptiste Coudurier <baptiste.coudurier@gmail.com>
3  *
4  * This file is part of FFmpeg.
5  *
6  * FFmpeg 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  * FFmpeg 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 FFmpeg; 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_CRYPTGENRANDOM
27 #include <windows.h>
28 #include <wincrypt.h>
29 #endif
30 #include <fcntl.h>
31 #include <math.h>
32 #include <time.h>
33 #include <string.h>
34 #include "avassert.h"
35 #include "timer.h"
36 #include "random_seed.h"
37 #include "sha.h"
38 #include "intreadwrite.h"
39 
40 #ifndef TEST
41 #define TEST 0
42 #endif
43 
44 static int read_random(uint32_t *dst, const char *file)
45 {
46 #if HAVE_UNISTD_H
47  int fd = open(file, O_RDONLY);
48  int err = -1;
49 
50  if (fd == -1)
51  return -1;
52  err = read(fd, dst, sizeof(*dst));
53  close(fd);
54 
55  return err;
56 #else
57  return -1;
58 #endif
59 }
60 
61 static uint32_t get_generic_seed(void)
62 {
63  uint8_t tmp[120];
64  struct AVSHA *sha = (void*)tmp;
65  clock_t last_t = 0;
66  static uint64_t i = 0;
67  static uint32_t buffer[512] = {0};
68  unsigned char digest[20];
69  uint64_t last_i = i;
70 
71  av_assert0(sizeof(tmp) >= av_sha_size);
72 
73  if(TEST){
74  memset(buffer, 0, sizeof(buffer));
75  last_i = i = 0;
76  }else{
77 #ifdef AV_READ_TIME
78  buffer[13] ^= AV_READ_TIME();
79  buffer[41] ^= AV_READ_TIME()>>32;
80 #endif
81  }
82 
83  for (;;) {
84  clock_t t = clock();
85 
86  if(last_t == t){
87  buffer[i&511]++;
88  }else{
89  buffer[++i&511]+= (t-last_t) % 3294638521U;
90  if(last_i && i-last_i > 4 || i-last_i > 64 || TEST && i-last_i > 8)
91  break;
92  }
93  last_t = t;
94  }
95 
96  if(TEST)
97  buffer[0] = buffer[1] = 0;
98 
99  av_sha_init(sha, 160);
100  av_sha_update(sha, (uint8_t*)buffer, sizeof(buffer));
101  av_sha_final(sha, digest);
102  return AV_RB32(digest) + AV_RB32(digest+16);
103 }
104 
105 uint32_t av_get_random_seed(void)
106 {
107  uint32_t seed;
108 
109 #if HAVE_CRYPTGENRANDOM
110  HCRYPTPROV provider;
111  if (CryptAcquireContext(&provider, NULL, NULL, PROV_RSA_FULL,
112  CRYPT_VERIFYCONTEXT | CRYPT_SILENT)) {
113  BOOL ret = CryptGenRandom(provider, sizeof(seed), (PBYTE) &seed);
114  CryptReleaseContext(provider, 0);
115  if (ret)
116  return seed;
117  }
118 #endif
119 
120  if (read_random(&seed, "/dev/urandom") == sizeof(seed))
121  return seed;
122  if (read_random(&seed, "/dev/random") == sizeof(seed))
123  return seed;
124  return get_generic_seed();
125 }
126 
127 #if TEST
128 #undef printf
129 #define N 256
130 #include <stdio.h>
131 
132 int main(void)
133 {
134  int i, j, retry;
135  uint32_t seeds[N];
136 
137  for (retry=0; retry<3; retry++){
138  for (i=0; i<N; i++){
139  seeds[i] = av_get_random_seed();
140  for (j=0; j<i; j++)
141  if (seeds[j] == seeds[i])
142  goto retry;
143  }
144  printf("seeds OK\n");
145  return 0;
146  retry:;
147  }
148  printf("FAIL at %d with %X\n", j, seeds[j]);
149  return 1;
150 }
151 #endif