1 /*
2 * coap_prng.c -- random number generation
3 *
4 * Copyright (C) 2020 Olaf Bergmann <bergmann@tzi.org>
5 *
6 * SPDX-License-Identifier: BSD-2-Clause
7 *
8 * This file is part of the CoAP library libcoap. Please see README
9 * for terms of use.
10 */
11
12 #include "coap3/coap_internal.h"
13
14 #ifdef HAVE_GETRANDOM
15 #include <sys/random.h>
16 #else /* !HAVE_GETRANDOM */
17 #include <stdlib.h>
18 #endif /* !HAVE_GETRANDOM */
19
20 #if defined(_WIN32)
21
22 errno_t __cdecl rand_s( _Out_ unsigned int* _RandomValue );
23 /**
24 * Fills \p buf with \p len random bytes. This is the default implementation for
25 * coap_prng(). You might want to change coap_prng_impl() to use a better
26 * PRNG on your specific platform.
27 */
28 COAP_STATIC_INLINE int
coap_prng_impl(unsigned char * buf,size_t len)29 coap_prng_impl( unsigned char *buf, size_t len ) {
30 while ( len != 0 ) {
31 uint32_t r = 0;
32 size_t i;
33 if ( rand_s( &r ) != 0 )
34 return 0;
35 for ( i = 0; i < len && i < 4; i++ ) {
36 *buf++ = (uint8_t)r;
37 r >>= 8;
38 }
39 len -= i;
40 }
41 return 1;
42 }
43
44 #endif /* _WIN32 */
45
46 static int
coap_prng_default(void * buf,size_t len)47 coap_prng_default(void *buf, size_t len) {
48 #ifdef HAVE_GETRANDOM
49 return getrandom(buf, len, 0);
50 #else /* !HAVE_GETRANDOM */
51 #if defined(_WIN32)
52 return coap_prng_impl(buf,len);
53 #else /* !_WIN32 */
54 unsigned char *dst = (unsigned char *)buf;
55 while (len--)
56 *dst++ = rand() & 0xFF;
57 return 1;
58 #endif /* !_WIN32 */
59 #endif /* !HAVE_GETRANDOM */
60 }
61
62 static coap_rand_func_t rand_func = coap_prng_default;
63
64 #if defined(WITH_CONTIKI)
65
66 #elif defined(WITH_LWIP) && defined(LWIP_RAND)
67
68 #else
69
70 void
coap_set_prng(coap_rand_func_t rng)71 coap_set_prng(coap_rand_func_t rng) {
72 rand_func = rng;
73 }
74
75 void
coap_prng_init(unsigned int seed)76 coap_prng_init(unsigned int seed) {
77 #ifdef HAVE_GETRANDOM
78 /* No seed to seed the random source if getrandom() is used,
79 * see dtls_prng(). */
80 (void)seed;
81 #else /* !HAVE_GETRANDOM */
82 srand(seed);
83 #endif /* !HAVE_GETRANDOM */
84 }
85
86 int
coap_prng(void * buf,size_t len)87 coap_prng(void *buf, size_t len) {
88 if (!rand_func) {
89 return 0;
90 }
91
92 rand_func(buf, len);
93 return 1;
94 }
95
96 #endif
97