Make the DH parameter we use for TLS match the one from Apache's mod_ssl

Our regular DH parameters that we use for circuit and rendezvous
crypto are unchanged.  This is yet another small step on the path of
protocol fingerprinting resistance.

(Backport from 0.2.2's 5ed73e3807d90dd0a3)

diff --git a/changes/dhparam b/changes/dhparam
new file mode 100644 (file)
index 0000000..cb31243
--- /dev/null
+++ b/changes/dhparam
@@ -0,0 +1,3 @@
+  o Minor features
+    - Adjust our TLS Diffie-Hellman parameters to match those used by
+      Apache's mod_ssl.

diff --git a/src/common/crypto.c b/src/common/crypto.c
index 29137a834dd2c9a5918d24b5cfb19303193c961c..48c8dea08fd5732df5d5f1081f35d8df43f3ee7e 100644 (file)
--- a/src/common/crypto.c
+++ b/src/common/crypto.c
@@ -1505,8 +1505,10 @@ crypto_hmac_sha1(char *hmac_out,
 
 /* DH */
 
-/** Shared P parameter for our DH key exchanged. */
+/** Shared P parameter for our circuit-crypto DH key exchanges. */
 static BIGNUM *dh_param_p = NULL;
+/** Shared P parameter for our TLS DH key exchanges. */
+static BIGNUM *dh_param_p_tls = NULL;
 /** Shared G parameter for our DH key exchanges. */
 static BIGNUM *dh_param_g = NULL;
 
@@ -1515,14 +1517,16 @@ static BIGNUM *dh_param_g = NULL;
 static void
 init_dh_param(void)
 {
-  BIGNUM *p, *g;
+  BIGNUM *p, *p2, *g;
   int r;
-  if (dh_param_p && dh_param_g)
+  if (dh_param_p && dh_param_g && dh_param_p_tls)
     return;
 
   p = BN_new();
+  p2 = BN_new();
   g = BN_new();
   tor_assert(p);
+  tor_assert(p2);
   tor_assert(g);
 
   /* This is from rfc2409, section 6.2.  It's a safe prime, and
@@ -1536,10 +1540,20 @@ init_dh_param(void)
                 "A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE6"
                 "49286651ECE65381FFFFFFFFFFFFFFFF");
   tor_assert(r);
+  /* This is the 1024-bit safe prime that Apache uses for its DH stuff; see
+   * modules/ssl/ssl_engine_dh.c */
+  r = BN_hex2bn(&p2,
+                  "D67DE440CBBBDC1936D693D34AFD0AD50C84D239A45F520BB88174CB98"
+                "BCE951849F912E639C72FB13B4B4D7177E16D55AC179BA420B2A29FE324A"
+                "467A635E81FF5901377BEDDCFD33168A461AAD3B72DAE8860078045B07A7"
+                "DBCA7874087D1510EA9FCC9DDD330507DD62DB88AEAA747DE0F4D6E2BD68"
+                "B0E7393E0F24218EB3");
+  tor_assert(r);
 
   r = BN_set_word(g, 2);
   tor_assert(r);
   dh_param_p = p;
+  dh_param_p_tls = p2;
   dh_param_g = g;
 }
 
@@ -1548,18 +1562,26 @@ init_dh_param(void)
 /** Allocate and return a new DH object for a key exchange.
  */
 crypto_dh_env_t *
-crypto_dh_new(void)
+crypto_dh_new(int dh_type)
 {
   crypto_dh_env_t *res = tor_malloc_zero(sizeof(crypto_dh_env_t));
 
+  tor_assert(dh_type == DH_TYPE_CIRCUIT || dh_type == DH_TYPE_TLS ||
+             dh_type == DH_TYPE_REND);
+
   if (!dh_param_p)
     init_dh_param();
 
   if (!(res->dh = DH_new()))
     goto err;
 
-  if (!(res->dh->p = BN_dup(dh_param_p)))
-    goto err;
+  if (dh_type == DH_TYPE_TLS) {
+    if (!(res->dh->p = BN_dup(dh_param_p_tls)))
+      goto err;
+  } else {
+    if (!(res->dh->p = BN_dup(dh_param_p)))
+      goto err;
+  }
 
   if (!(res->dh->g = BN_dup(dh_param_g)))
     goto err;

diff --git a/src/common/crypto.h b/src/common/crypto.h
index d6f5555379a11e2a7ce1c4479169caae5ca3b81a..576c03dc30fda2f91d6715a8d65c1444dbca773e 100644 (file)
--- a/src/common/crypto.h
+++ b/src/common/crypto.h
@@ -159,7 +159,10 @@ void crypto_hmac_sha1(char *hmac_out,
                       const char *msg, size_t msg_len);
 
 /* Key negotiation */
-crypto_dh_env_t *crypto_dh_new(void);
+#define DH_TYPE_CIRCUIT 1
+#define DH_TYPE_REND 2
+#define DH_TYPE_TLS 3
+crypto_dh_env_t *crypto_dh_new(int dh_type);
 int crypto_dh_get_bytes(crypto_dh_env_t *dh);
 int crypto_dh_generate_public(crypto_dh_env_t *dh);
 int crypto_dh_get_public(crypto_dh_env_t *dh, char *pubkey_out,

diff --git a/src/common/tortls.c b/src/common/tortls.c
index 1d597e295288503dc9590ff03968e16a599ef86d..7735618ea2b1216e290d7ec4724dfc34be4ac37f 100644 (file)
--- a/src/common/tortls.c
+++ b/src/common/tortls.c
@@ -684,7 +684,7 @@ tor_tls_context_new(crypto_pk_env_t *identity, unsigned int key_lifetime)
   if (!SSL_CTX_check_private_key(result->ctx))
     goto error;
   {
-    crypto_dh_env_t *dh = crypto_dh_new();
+    crypto_dh_env_t *dh = crypto_dh_new(DH_TYPE_TLS);
     SSL_CTX_set_tmp_dh(result->ctx, _crypto_dh_env_get_dh(dh));
     crypto_dh_free(dh);
   }

diff --git a/src/or/onion.c b/src/or/onion.c
index bf72b4cab1c4bf90def10bc04b22ac3d127afb38..e455a526372c42f64828f13e7fb4a36412ab2543 100644 (file)
--- a/src/or/onion.c
+++ b/src/or/onion.c
@@ -173,7 +173,7 @@ onion_skin_create(crypto_pk_env_t *dest_router_key,
   *handshake_state_out = NULL;
   memset(onion_skin_out, 0, ONIONSKIN_CHALLENGE_LEN);
 
-  if (!(dh = crypto_dh_new()))
+  if (!(dh = crypto_dh_new(DH_TYPE_CIRCUIT)))
     goto err;
 
   dhbytes = crypto_dh_get_bytes(dh);
@@ -247,7 +247,7 @@ onion_skin_server_handshake(const char *onion_skin, /*ONIONSKIN_CHALLENGE_LEN*/
     goto err;
   }
 
-  dh = crypto_dh_new();
+  dh = crypto_dh_new(DH_TYPE_CIRCUIT);
   if (crypto_dh_get_public(dh, handshake_reply_out, DH_KEY_LEN)) {
     log_info(LD_GENERAL, "crypto_dh_get_public failed.");
     goto err;

diff --git a/src/or/rendclient.c b/src/or/rendclient.c
index 95875465cbffe4310c0198a178e2ff20102a38c2..783a66150ed838d95950f08ffb7726923d600cac 100644 (file)
--- a/src/or/rendclient.c
+++ b/src/or/rendclient.c
@@ -130,7 +130,7 @@ rend_client_send_introduction(origin_circuit_t *introcirc,
     cpath = rendcirc->build_state->pending_final_cpath =
       tor_malloc_zero(sizeof(crypt_path_t));
     cpath->magic = CRYPT_PATH_MAGIC;
-    if (!(cpath->dh_handshake_state = crypto_dh_new())) {
+    if (!(cpath->dh_handshake_state = crypto_dh_new(DH_TYPE_REND))) {
       log_warn(LD_BUG, "Internal error: couldn't allocate DH.");
       goto err;
     }

diff --git a/src/or/rendservice.c b/src/or/rendservice.c
index a650eda405336dabaaf4c280e1db42634dc72d9b..33e8d3e7e9da3aec91189f866411a0854d530863 100644 (file)
--- a/src/or/rendservice.c
+++ b/src/or/rendservice.c
@@ -1151,7 +1151,7 @@ rend_service_introduce(origin_circuit_t *circuit, const uint8_t *request,
   }
 
   /* Try DH handshake... */
-  dh = crypto_dh_new();
+  dh = crypto_dh_new(DH_TYPE_REND);
   if (!dh || crypto_dh_generate_public(dh)<0) {
     log_warn(LD_BUG,"Internal error: couldn't build DH state "
              "or generate public key.");

diff --git a/src/or/test.c b/src/or/test.c
index 904ca69db1ff07959b3701a39ebfdb9271fe2ae4..b08f202c20eaa91970bc2ea9c7252c0019755268 100644 (file)
--- a/src/or/test.c
+++ b/src/or/test.c
@@ -404,8 +404,8 @@ test_buffers(void)
 static void
 test_crypto_dh(void)
 {
-  crypto_dh_env_t *dh1 = crypto_dh_new();
-  crypto_dh_env_t *dh2 = crypto_dh_new();
+  crypto_dh_env_t *dh1 = crypto_dh_new(DH_TYPE_CIRCUIT);
+  crypto_dh_env_t *dh2 = crypto_dh_new(DH_TYPE_CIRCUIT);
   char p1[DH_BYTES];
   char p2[DH_BYTES];
   char s1[DH_BYTES];