Added a configuration option to enable prediction resistance in the P…

…olarSSL random number generator. Signed-off-by: Eelse-jan Stutvoet <[email protected]> Signed-off-by: Adriaan de Jong <[email protected]> Acked-by: James Yonan <[email protected]> Message-Id: [email protected] URL: http://article.gmane.org/gmane.network.openvpn.devel/6213 Signed-off-by: David Sommerseth <[email protected]>
zhengweisk · Apr 27, 2012 · 0f25d29 · 0f25d29
1 parent 6efeaa2
commit 0f25d29
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diff --git a/doc/openvpn.8 b/doc/openvpn.8
@@ -3846,6 +3846,20 @@ space-saving optimization that uses the unique identifier for
 datagram replay protection as the IV.
 .\"*********************************************************
 .TP
+.B \-\-use-prediction-resistance
+Enable prediction resistance on PolarSSL's RNG.
+
+Enabling prediction resistance causes the RNG to reseed in each
+call for random. Reseeding this often can quickly deplete the kernel
+entropy pool.
+
+If you need this option, please consider running a daemon that adds
+entropy to the kernel pool.
+
+Note that this option only works with PolarSSL versions greater
+than 1.1.
+.\"*********************************************************
+.TP
 .B \-\-test-crypto
 Do a self-test of OpenVPN's crypto options by encrypting and
 decrypting test packets using the data channel encryption options

diff --git a/src/openvpn/crypto_polarssl.c b/src/openvpn/crypto_polarssl.c
@@ -219,6 +219,15 @@ havege_state * rand_ctx_get()
 
 #endif /* (POLARSSL_VERSION_NUMBER >= 0x01010000) */
 
+#ifdef ENABLE_PREDICTION_RESISTANCE
+void rand_ctx_enable_prediction_resistance()
+{
+  ctr_drbg_context *cd_ctx = rand_ctx_get();
+
+  ctr_drbg_set_prediction_resistance(cd_ctx, 1);
+}
+#endif /* ENABLE_PREDICTION_RESISTANCE */
+
 int
 rand_bytes (uint8_t *output, int len)
 {

diff --git a/src/openvpn/crypto_polarssl.h b/src/openvpn/crypto_polarssl.h
@@ -96,4 +96,11 @@ ctr_drbg_context * rand_ctx_get();
 havege_state * rand_ctx_get();
 #endif
 
+#ifdef ENABLE_PREDICTION_RESISTANCE
+/**
+ * Enable prediction resistance on the random number generator.
+ */
+void rand_ctx_enable_prediction_resistance();
+#endif
+
 #endif /* CRYPTO_POLARSSL_H_ */
diff --git a/src/openvpn/init.c b/src/openvpn/init.c
@@ -2008,6 +2008,12 @@ init_crypto_pre (struct context *c, const unsigned int flags)
 
   if (c->options.mute_replay_warnings)
     c->c2.crypto_options.flags |= CO_MUTE_REPLAY_WARNINGS;
+
+#ifdef ENABLE_PREDICTION_RESISTANCE
+  if (c->options.use_prediction_resistance)
+    rand_ctx_enable_prediction_resistance();
+#endif
+
 }
 
 /*

diff --git a/src/openvpn/options.c b/src/openvpn/options.c
@@ -545,6 +545,10 @@ static const char usage_message[] =
   "                  using file.\n"
   "--test-crypto   : Run a self-test of crypto features enabled.\n"
   "                  For debugging only.\n"
+#ifdef ENABLE_PREDICTION_RESISTANCE
+  "--use-prediction-resistance: Enable prediction resistance on the random\n"
+  "                             number generator.\n"
+#endif
 #ifdef ENABLE_SSL
   "\n"
   "TLS Key Negotiation Options:\n"
@@ -837,6 +841,9 @@ init_options (struct options *o, const bool init_gc)
   o->replay_time = DEFAULT_TIME_BACKTRACK;
   o->use_iv = true;
   o->key_direction = KEY_DIRECTION_BIDIRECTIONAL;
+#ifdef ENABLE_PREDICTION_RESISTANCE
+  o->use_prediction_resistance = false;
+#endif
 #ifdef ENABLE_SSL
   o->key_method = 2;
   o->tls_timeout = 2;
@@ -1581,6 +1588,9 @@ show_settings (const struct options *o)
   SHOW_STR (packet_id_file);
   SHOW_BOOL (use_iv);
   SHOW_BOOL (test_crypto);
+#ifdef ENABLE_PREDICTION_RESISTANCE
+  SHOW_BOOL (use_prediction_resistance);
+#endif
 
 #ifdef ENABLE_SSL
   SHOW_BOOL (tls_server);
@@ -3018,6 +3028,11 @@ options_string (const struct options *o,
 	  buf_printf (&out, ",no-replay");
 	if (!o->use_iv)
 	  buf_printf (&out, ",no-iv");
+
+#ifdef ENABLE_PREDICTION_RESISTANCE
+        if (o->use_prediction_resistance)
+          buf_printf (&out, ",use-prediction-resistance");
+#endif
       }
 
 #ifdef ENABLE_SSL
@@ -6416,6 +6431,13 @@ add_option (struct options *options,
       options->keysize = keysize;
     }
 #endif
+#ifdef ENABLE_PREDICTION_RESISTANCE
+  else if (streq (p[0], "use-prediction-resistance"))
+    {
+      VERIFY_PERMISSION (OPT_P_GENERAL);
+      options->use_prediction_resistance = true;
+    }
+#endif
 #ifdef ENABLE_SSL
   else if (streq (p[0], "show-tls"))
     {

diff --git a/src/openvpn/options.h b/src/openvpn/options.h
@@ -520,6 +520,9 @@ struct options
   const char *packet_id_file;
   bool use_iv;
   bool test_crypto;
+#ifdef ENABLE_PREDICTION_RESISTANCE
+  bool use_prediction_resistance;
+#endif
 
 #ifdef ENABLE_SSL
   /* TLS (control channel) parms */

diff --git a/src/openvpn/syshead.h b/src/openvpn/syshead.h
@@ -538,6 +538,14 @@ socket_defined (const socket_descriptor_t sd)
 #define MANAGMENT_EXTERNAL_KEY
 #endif
 
+/* Enable PolarSSL RNG prediction resistance support */
+#ifdef ENABLE_CRYPTO_POLARSSL
+#include <polarssl/version.h>
+#if POLARSSL_VERSION_NUMBER >= 0x01010000
+#define ENABLE_PREDICTION_RESISTANCE
+#endif
+#endif /* ENABLE_CRYPTO_POLARSSL */
+
 /*
  * MANAGEMENT_IN_EXTRA allows the management interface to
  * read multi-line inputs from clients.