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Speed up initialization by preferring /dev/urandom to GnuTLS

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* src/sysdep.c (init_random): Try /dev/urandom before GnuTLS.
This commit is contained in:
Daniel Colascione 2016-10-06 12:46:36 -07:00
parent 27443df092
commit a37eba849e
1 changed files with 27 additions and 19 deletions
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46
src/sysdep.c
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@ -2188,27 +2188,35 @@ void
init_random (void)
{
random_seed v;
if (! (EQ (emacs_gnutls_global_init (), Qt)
&& gnutls_rnd (GNUTLS_RND_NONCE, &v, sizeof v) == 0))
{
bool success = false;
#ifndef WINDOWSNT
int fd = emacs_open ("/dev/urandom", O_RDONLY, 0);
if (0 <= fd)
{
success = emacs_read (fd, &v, sizeof v) == sizeof v;
emacs_close (fd);
}
bool success = false;
/* First, try seeding the PRNG from the operating system's entropy
source. This approach is both fast and secure. */
#ifdef WINDOWSNT
success = w32_init_random (&v, sizeof v) == 0;
#else
success = w32_init_random (&v, sizeof v) == 0;
#endif
if (! success)
{
/* Fall back to current time value + PID. */
struct timespec t = current_timespec ();
v = getpid () ^ t.tv_sec ^ t.tv_nsec;
}
int fd = emacs_open ("/dev/urandom", O_RDONLY, 0);
if (0 <= fd)
{
success = emacs_read (fd, &v, sizeof v) == sizeof v;
close (fd);
}
#endif
/* If that didn't work, try using GnuTLS, which is secure, but on
some systems, can be somewhat slow. */
if (!success)
success = EQ (emacs_gnutls_global_init (), Qt)
&& gnutls_rnd (GNUTLS_RND_NONCE, &v, sizeof v) == 0;
/* If _that_ didn't work, just use the current time value and PID.
It's at least better than XKCD 221. */
if (!success)
{
struct timespec t = current_timespec ();
v = getpid () ^ t.tv_sec ^ t.tv_nsec;
}
set_random_seed (v);
}