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util: add function to generate random bytes

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Add a function to fill a buffer with random bytes which uses a better
PRNG than random(). Use arc4random() if it's available on the system.
Fall back to reading from /dev/urandom, which should be available on
all currently supported systems.
This commit is contained in:
Miroslav Lichvar
2015-11-10 16:46:40 +01:00
parent cbd77c9752
commit 6199a89170
3 changed files with 27 additions and 0 deletions
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20
util.c
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@@ -1070,3 +1070,23 @@ UTI_CheckDirPermissions(const char *path, mode_t perm, uid_t uid, gid_t gid)
return 1;
}
/* ================================================== */
#define DEV_URANDOM "/dev/urandom"
void
UTI_GetRandomBytes(void *buf, unsigned int len)
{
#ifdef HAVE_ARC4RANDOM
arc4random_buf(buf, len);
#else
static FILE *f = NULL;
if (!f)
f = fopen(DEV_URANDOM, "r");
if (!f)
LOG_FATAL(LOGF_Util, "Can't open %s : %s", DEV_URANDOM, strerror(errno));
if (fread(buf, 1, len, f) != len)
LOG_FATAL(LOGF_Util, "Can't read from %s", DEV_URANDOM);
#endif
}