Under some circumstances, certain TLS connections are dropped by certain

openssl/ssl/t1_lib.c

 /* ssl/t1_lib.c */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
  * This package is an SSL implementation written
  * by Eric Young (eay@cryptsoft.com).
  * The implementation was written so as to conform with Netscapes SSL.
  * 
  * This library is free for commercial and non-commercial use as long as
  * the following conditions are aheared to.  The following conditions
@@ skipping 184 matching lines @@
                 NID_secp192k1, /* secp192k1 (18) */
                 NID_X9_62_prime192v1, /* secp192r1 (19) */ 
                 NID_secp224k1, /* secp224k1 (20) */ 
                 NID_secp224r1, /* secp224r1 (21) */
                 NID_secp256k1, /* secp256k1 (22) */ 
                 NID_X9_62_prime256v1, /* secp256r1 (23) */ 
                 NID_secp384r1, /* secp384r1 (24) */
                 NID_secp521r1  /* secp521r1 (25) */     
         };
 
+/* We support only the elliptic curves that are also supported by NSS
+ * to improve compatibility with sites that don't accept large ClientHellos.
+ */
 static int pref_list[] =
         {
-                NID_sect571r1, /* sect571r1 (14) */ 
-                NID_sect571k1, /* sect571k1 (13) */ 
                 NID_secp521r1, /* secp521r1 (25) */     
-                NID_sect409k1, /* sect409k1 (11) */ 
-                NID_sect409r1, /* sect409r1 (12) */
                 NID_secp384r1, /* secp384r1 (24) */
-                NID_sect283k1, /* sect283k1 (9) */
-                NID_sect283r1, /* sect283r1 (10) */ 
-                NID_secp256k1, /* secp256k1 (22) */ 
                 NID_X9_62_prime256v1, /* secp256r1 (23) */ 
-                NID_sect239k1, /* sect239k1 (8) */ 
-                NID_sect233k1, /* sect233k1 (6) */
-                NID_sect233r1, /* sect233r1 (7) */ 
-                NID_secp224k1, /* secp224k1 (20) */ 
-                NID_secp224r1, /* secp224r1 (21) */
-                NID_sect193r1, /* sect193r1 (4) */ 
-                NID_sect193r2, /* sect193r2 (5) */ 
-                NID_secp192k1, /* secp192k1 (18) */
-                NID_X9_62_prime192v1, /* secp192r1 (19) */ 
-                NID_sect163k1, /* sect163k1 (1) */
-                NID_sect163r1, /* sect163r1 (2) */
-                NID_sect163r2, /* sect163r2 (3) */
-                NID_secp160k1, /* secp160k1 (15) */
-                NID_secp160r1, /* secp160r1 (16) */ 
-                NID_secp160r2, /* secp160r2 (17) */ 
         };
 
 int tls1_ec_curve_id2nid(int curve_id)
         {
         /* ECC curves from draft-ietf-tls-ecc-12.txt (Oct. 17, 2005) */
         if ((curve_id < 1) || ((unsigned int)curve_id >
                                 sizeof(nid_list)/sizeof(nid_list[0])))
                 return 0;
         return nid_list[curve_id-1];
         }
@@ skipping 1454 matching lines @@
                 if ((alg_k & (SSL_kEECDH|SSL_kECDHr|SSL_kECDHe) || (alg_a & SSL_aECDSA)))
                         {
                         using_ecc = 1;
                         break;
                         }
                 }
         using_ecc = using_ecc && (s->version >= TLS1_VERSION);
         if (using_ecc)
                 {
                 if (s->tlsext_ecpointformatlist != NULL) OPENSSL_free(s->tlsext_ecpointformatlist);
-                if ((s->tlsext_ecpointformatlist = OPENSSL_malloc(3)) == NULL)
+                /* To save an additional 2 bytes in the ClientHello, we only advertise support
+                 * for the only EC Point Format that NSS supports (instead of all 3).
+                 */
+                if ((s->tlsext_ecpointformatlist = OPENSSL_malloc(1)) == NULL)
                         {
                         SSLerr(SSL_F_SSL_PREPARE_CLIENTHELLO_TLSEXT,ERR_R_MALLOC_FAILURE);
                         return -1;
                         }
-                s->tlsext_ecpointformatlist_length = 3;
+                s->tlsext_ecpointformatlist_length = 1;
                 s->tlsext_ecpointformatlist[0] = TLSEXT_ECPOINTFORMAT_uncompressed;
-                s->tlsext_ecpointformatlist[1] = TLSEXT_ECPOINTFORMAT_ansiX962_compressed_prime;
-                s->tlsext_ecpointformatlist[2] = TLSEXT_ECPOINTFORMAT_ansiX962_compressed_char2;
 
-                /* we support all named elliptic curves in draft-ietf-tls-ecc-12 */
+                /* we only support elliptic curves in NSA Suite B */

[wtc, 2013/06/21 22:12:04]

I suggest we change
    we only support ...
to
    we only advertise support for ...

because OpenSSL actually supports all the curves in RFC 4492.

                 if (s->tlsext_ellipticcurvelist != NULL) OPENSSL_free(s->tlsext_ellipticcurvelist);
                 s->tlsext_ellipticcurvelist_length = sizeof(pref_list)/sizeof(pref_list[0]) * 2;
                 if ((s->tlsext_ellipticcurvelist = OPENSSL_malloc(s->tlsext_ellipticcurvelist_length)) == NULL)
                         {
                         s->tlsext_ellipticcurvelist_length = 0;
                         SSLerr(SSL_F_SSL_PREPARE_CLIENTHELLO_TLSEXT,ERR_R_MALLOC_FAILURE);
                         return -1;
                         }
                 for (i = 0, j = s->tlsext_ellipticcurvelist; (unsigned int)i <
                                 sizeof(pref_list)/sizeof(pref_list[0]); i++)
@@ skipping 947 matching lines @@
                         continue;
                 EVP_MD_CTX_copy_ex(&ctx, s->s3->handshake_dgst[i]);
                 EVP_DigestFinal_ex(&ctx, temp_digest, &temp_digest_len);
                 EVP_DigestUpdate(md, temp_digest, temp_digest_len);
                 }
         EVP_MD_CTX_cleanup(&ctx);
 
         return 1;
         }
 #endif