random: Add a RNG selection interface and system RNG wrapper.

* random/random-system.c: New.
* random/Makefile.am (librandom_la_SOURCES): Add new module.
* random/random.c (struct rng_types): New.
(_gcry_set_preferred_rng_type, _gcry_get_rng_type): New.
(_gcry_random_initialize, gcry_random_add_bytes, do_randomize)
(_gcry_set_random_seed_file, _gcry_update_random_seed_file)
(_gcry_fast_random_poll): Dispatch to the actual RNG.
* src/gcrypt.h.in (GCRYCTL_SET_PREFERRED_RNG_TYPE): New.
GCRYCTL_GET_CURRENT_RNG_TYPE): New.
(gcry_rng_types): New.
* src/global.c (print_config): Print the TNG type.
(global_init, _gcry_vcontrol): Implement the new control codes.
* doc/gcrypt.texi (Controlling the library): Document the new control
codes.

* tests/benchmark.c (main): Add options to test the RNG types.
* tests/random.c (main): Add new options.
(print_hex): Print to stderr.
(progress_cb, rng_type): New.
(check_rng_type_switching, check_early_rng_type_switching): New.
(run_all_rng_tests): New.
--

The purpose of this change is to allow applications with moderate
random requirements to use the system's RNG (e.g. /dev/urandom).  The
type switching logic makes sure that existing applications won't be
affected by this change.  A library is in almost all cases not able to
degrade the quality of the RNG.  The definition of "degrade" comes
from our own assertion of the quality/trustworthiness of the RNGs:

The most trustworthy RNG is the CSPRNG which dates back to the early
GnuPG days.  It is quite conservative and often requires more seeding
than might be justified.  GCRY_RNG_TYPE_STANDARD is the default unless
the process is in FIPS mode.

The second trustworthy RNG is the FIPS recommended X9.81 AES based
implementation.  It is seeded by the system's RNG.  GCRY_RNG_TYPE_FIPS
is the only available RNG if running in FIPS mode.

The third trustworthy RNG is a mere wrapper around the system's native
RNG.  Thus there is no extra step on top of what, for example,
/dev/random provides.  GCRY_RNG_TYPE_SYSTEM may be used by
applications which would use /dev/random or /dev/urandom instead.

1 files changed, 243 insertions, 0 deletions

diff --git a/random/random-system.c b/random/random-system.c
new file mode 100644
index 00000000..0ef9d247
--- /dev/null
+++ b/random/random-system.c
@@ -0,0 +1,243 @@
+/* random-system.c - wrapper around the system's RNG
+ * Copyright (C) 2012  Free Software Foundation, Inc.
+ *
+ * This file is part of Libgcrypt.
+ *
+ * Libgcrypt is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as
+ * published by the Free Software Foundation; either version 2.1 of
+ * the License, or (at your option) any later version.
+ *
+ * Libgcrypt is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+   This RNG is merely wrapper around the system's native RNG.  For
+   example on Unix systems it directly uses /dev/{u,}random.
+ */
+
+#include <config.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <unistd.h>
+#ifdef HAVE_GETTIMEOFDAY
+#include <sys/time.h>
+#endif
+
+#include "g10lib.h"
+#include "random.h"
+#include "rand-internal.h"
+#include "ath.h"
+
+/* This is the lock we use to serialize access to this RNG.  The extra
+   integer variable is only used to check the locking state; that is,
+   it is not meant to be thread-safe but merely as a failsafe feature
+   to assert proper locking.  */
+static ath_mutex_t system_rng_lock;
+static int system_rng_is_locked;
+
+
+/* --- Local prototypes ---  */
+
+
+
+
+/* --- Functions  --- */
+
+/* Basic initialization is required to initialize mutexes and
+   do a few checks on the implementation.  */
+static void
+basic_initialization (void)
+{
+  static int initialized;
+  int my_errno;
+
+  if (initialized)
+    return;
+  initialized = 1;
+
+  my_errno = ath_mutex_init (&system_rng_lock);
+  if (my_errno)
+    log_fatal ("failed to create the System RNG lock: %s\n",
+               strerror (my_errno));
+  system_rng_is_locked = 0;
+
+  /* Make sure that we are still using the values we traditionally
+     used for the random levels.  */
+  gcry_assert (GCRY_WEAK_RANDOM == 0
+               && GCRY_STRONG_RANDOM == 1
+               && GCRY_VERY_STRONG_RANDOM == 2);
+
+}
+
+
+/* Acquire the system_rng_lock.  */
+static void
+lock_rng (void)
+{
+  int my_errno;
+
+  my_errno = ath_mutex_lock (&system_rng_lock);
+  if (my_errno)
+    log_fatal ("failed to acquire the System RNG lock: %s\n",
+               strerror (my_errno));
+  system_rng_is_locked = 1;
+}
+
+
+/* Release the system_rng_lock.  */
+static void
+unlock_rng (void)
+{
+  int my_errno;
+
+  system_rng_is_locked = 0;
+  my_errno = ath_mutex_unlock (&system_rng_lock);
+  if (my_errno)
+    log_fatal ("failed to release the System RNG lock: %s\n",
+               strerror (my_errno));
+}
+
+
+/* Helper variables for read_cb().
+
+   The _gcry_rnd*_gather_random interface does not allow to provide a
+   data pointer.  Thus we need to use a global variable for
+   communication.  However, the then required locking is anyway a good
+   idea because it does not make sense to have several readers of (say
+   /dev/random).  It is easier to serve them one after the other.  */
+static unsigned char *read_cb_buffer;   /* The buffer.  */
+static size_t         read_cb_size;     /* Size of the buffer.  */
+static size_t         read_cb_len;      /* Used length.  */
+
+
+/* Callback for _gcry_rnd*_gather_random.  */
+static void
+read_cb (const void *buffer, size_t length, enum random_origins origin)
+{
+  const unsigned char *p = buffer;
+
+  (void)origin;
+
+  gcry_assert (system_rng_is_locked);
+  gcry_assert (read_cb_buffer);
+
+  /* Note that we need to protect against gatherers returning more
+     than the requested bytes (e.g. rndw32).  */
+  while (length-- && read_cb_len < read_cb_size)
+    {
+      read_cb_buffer[read_cb_len++] = *p++;
+    }
+}
+
+
+/* Fill BUFFER with LENGTH bytes of random at quality LEVEL.  The
+   function either succeeds or terminates the process in case of a
+   fatal error. */
+static void
+get_random (void *buffer, size_t length, int level)
+{
+  int rc;
+
+  gcry_assert (buffer);
+
+  read_cb_buffer = buffer;
+  read_cb_size   = length;
+  read_cb_len    = 0;
+
+#if USE_RNDLINUX
+  rc = _gcry_rndlinux_gather_random (read_cb, 0, length, level);
+#elif USE_RNDUNIX
+  rc = _gcry_rndunix_gather_random (read_cb, 0, length, level);
+#elif USE_RNDW32
+  do
+    {
+      rc = _gcry_rndw32_gather_random (read_cb, 0, length, level);
+    }
+  while (rc >= 0 && read_cb_len < read_cb_size);
+#else
+  rc = -1;
+#endif
+
+  if (rc < 0 || read_cb_len != read_cb_size)
+    {
+      log_fatal ("error reading random from system RNG (rc=%d)\n", rc);
+    }
+}
+
+
+
+/* --- Public Functions --- */
+
+/* Initialize this random subsystem.  If FULL is false, this function
+   merely calls the basic initialization of the module and does not do
+   anything more.  Doing this is not really required but when running
+   in a threaded environment we might get a race condition
+   otherwise. */
+void
+_gcry_rngsystem_initialize (int full)
+{
+  basic_initialization ();
+  if (!full)
+    return;
+  /* Nothing more to initialize.  */
+  return;
+}
+
+
+/* Print some statistics about the RNG.  */
+void
+_gcry_rngsystem_dump_stats (void)
+{
+  /* Not yet implemented.  */
+}
+
+
+/* This function returns true if no real RNG is available or the
+   quality of the RNG has been degraded for test purposes.  */
+int
+_gcry_rngsystem_is_faked (void)
+{
+  return 0;  /* Faked random is not supported.  */
+}
+
+
+/* Add BUFLEN bytes from BUF to the internal random pool.  QUALITY
+   should be in the range of 0..100 to indicate the goodness of the
+   entropy added, or -1 for goodness not known. */
+gcry_error_t
+_gcry_rngsystem_add_bytes (const void *buf, size_t buflen, int quality)
+{
+  (void)buf;
+  (void)buflen;
+  (void)quality;
+  return 0;  /* Not implemented. */
+}
+
+
+/* Public function to fill the buffer with LENGTH bytes of
+   cryptographically strong random bytes.  Level GCRY_WEAK_RANDOM is
+   here mapped to GCRY_STRONG_RANDOM, GCRY_STRONG_RANDOM is strong
+   enough for most usage, GCRY_VERY_STRONG_RANDOM is good for key
+   generation stuff but may be very slow.  */
+void
+_gcry_rngsystem_randomize (void *buffer, size_t length,
+                           enum gcry_random_level level)
+{
+  _gcry_rngsystem_initialize (1);  /* Auto-initialize if needed.  */
+
+  if (level != GCRY_VERY_STRONG_RANDOM)
+    level = GCRY_STRONG_RANDOM;
+
+  lock_rng ();
+  get_random (buffer, length, level);
+  unlock_rng ();
+}