unsigned char *ssl_add_clienthello_tlsext(SSL *s, unsigned char *p, unsigned char *limit)
	{
	int extdatalen=0;
	unsigned char *ret = p;
#ifndef OPENSSL_NO_EC
	/* See if we support any ECC ciphersuites */
	int using_ecc = 0;
	if (s->version != DTLS1_VERSION && s->version >= TLS1_VERSION)
		{
		int i;
		unsigned long alg_k, alg_a;
		STACK_OF(SSL_CIPHER) *cipher_stack = SSL_get_ciphers(s);

		for (i = 0; i < sk_SSL_CIPHER_num(cipher_stack); i++)
			{
			SSL_CIPHER *c = sk_SSL_CIPHER_value(cipher_stack, i);

			alg_k = c->algorithm_mkey;
			alg_a = c->algorithm_auth;
			if ((alg_k & (SSL_kEECDH|SSL_kECDHr|SSL_kECDHe)
				|| (alg_a & SSL_aECDSA)))
				{
				using_ecc = 1;
				break;
				}
			}
		}
#endif

	/* don't add extensions for SSLv3 unless doing secure renegotiation */
	if (s->client_version == SSL3_VERSION
					&& !s->s3->send_connection_binding)
		return p;

	ret+=2;

	if (ret>=limit) return NULL; /* this really never occurs, but ... */

 	if (s->tlsext_hostname != NULL)
		{ 
		/* Add TLS extension servername to the Client Hello message */
		unsigned long size_str;
		long lenmax; 

		/* check for enough space.
		   4 for the servername type and entension length
		   2 for servernamelist length
		   1 for the hostname type
		   2 for hostname length
		   + hostname length 
		*/
		   
		if ((lenmax = limit - ret - 9) < 0 
		    || (size_str = strlen(s->tlsext_hostname)) > (unsigned long)lenmax) 
			return NULL;
			
		/* extension type and length */
		s2n(TLSEXT_TYPE_server_name,ret); 
		s2n(size_str+5,ret);
		
		/* length of servername list */
		s2n(size_str+3,ret);
	
		/* hostname type, length and hostname */
		*(ret++) = (unsigned char) TLSEXT_NAMETYPE_host_name;
		s2n(size_str,ret);
		memcpy(ret, s->tlsext_hostname, size_str);
		ret+=size_str;
		}

        /* Add RI if renegotiating */
        if (s->renegotiate)
          {
          int el;
          
          if(!ssl_add_clienthello_renegotiate_ext(s, 0, &el, 0))
              {
              SSLerr(SSL_F_SSL_ADD_CLIENTHELLO_TLSEXT, ERR_R_INTERNAL_ERROR);
              return NULL;
              }

          if((limit - p - 4 - el) < 0) return NULL;
          
          s2n(TLSEXT_TYPE_renegotiate,ret);
          s2n(el,ret);

          if(!ssl_add_clienthello_renegotiate_ext(s, ret, &el, el))
              {
              SSLerr(SSL_F_SSL_ADD_CLIENTHELLO_TLSEXT, ERR_R_INTERNAL_ERROR);
              return NULL;
              }

          ret += el;
        }

#ifndef OPENSSL_NO_SRP
	/* Add SRP username if there is one */
	if (s->srp_ctx.login != NULL)
		{ /* Add TLS extension SRP username to the Client Hello message */

		int login_len = strlen(s->srp_ctx.login);	
		if (login_len > 255 || login_len == 0)
			{
			SSLerr(SSL_F_SSL_ADD_CLIENTHELLO_TLSEXT, ERR_R_INTERNAL_ERROR);
			return NULL;
			} 

		/* check for enough space.
		   4 for the srp type type and entension length
		   1 for the srp user identity
		   + srp user identity length 
		*/
		if ((limit - ret - 5 - login_len) < 0) return NULL; 

		/* fill in the extension */
		s2n(TLSEXT_TYPE_srp,ret);
		s2n(login_len+1,ret);
		(*ret++) = (unsigned char) login_len;
		memcpy(ret, s->srp_ctx.login, login_len);
		ret+=login_len;
		}
#endif

#ifndef OPENSSL_NO_EC
	if (using_ecc)
		{
		/* Add TLS extension ECPointFormats to the ClientHello message */
		long lenmax; 
		const unsigned char *plist;
		size_t plistlen;
		/* If we have a custom point format list use it otherwise
		 * use default */
		plist = s->tlsext_ecpointformatlist;
		if (plist)
			plistlen = s->tlsext_ecpointformatlist_length;
		else
			{
			plist = ecformats_default;
			plistlen = sizeof(ecformats_default);
			}

		if ((lenmax = limit - ret - 5) < 0) return NULL; 
		if (plistlen > (size_t)lenmax) return NULL;
		if (plistlen > 255)
			{
			SSLerr(SSL_F_SSL_ADD_CLIENTHELLO_TLSEXT, ERR_R_INTERNAL_ERROR);
			return NULL;
			}
		
		s2n(TLSEXT_TYPE_ec_point_formats,ret);
		s2n(plistlen + 1,ret);
		*(ret++) = (unsigned char)plistlen ;
		memcpy(ret, plist, plistlen);
		ret+=plistlen;

		/* Add TLS extension EllipticCurves to the ClientHello message */
		plist = s->tlsext_ellipticcurvelist;
		tls1_get_curvelist(s, 0, &plist, &plistlen);

		if ((lenmax = limit - ret - 6) < 0) return NULL; 
		if (plistlen > (size_t)lenmax) return NULL;
		if (plistlen > 65532)
			{
			SSLerr(SSL_F_SSL_ADD_CLIENTHELLO_TLSEXT, ERR_R_INTERNAL_ERROR);
			return NULL;
			}
		
		s2n(TLSEXT_TYPE_elliptic_curves,ret);
		s2n(plistlen + 2, ret);

		/* NB: draft-ietf-tls-ecc-12.txt uses a one-byte prefix for
		 * elliptic_curve_list, but the examples use two bytes.
		 * http://www1.ietf.org/mail-archive/web/tls/current/msg00538.html
		 * resolves this to two bytes.
		 */
		s2n(plistlen, ret);
		memcpy(ret, plist, plistlen);
		ret+=plistlen;
		}
#endif /* OPENSSL_NO_EC */

	if (!(SSL_get_options(s) & SSL_OP_NO_TICKET))
		{
		int ticklen;
		if (!s->new_session && s->session && s->session->tlsext_tick)
			ticklen = s->session->tlsext_ticklen;
		else if (s->session && s->tlsext_session_ticket &&
			 s->tlsext_session_ticket->data)
			{
			ticklen = s->tlsext_session_ticket->length;
			s->session->tlsext_tick = OPENSSL_malloc(ticklen);
			if (!s->session->tlsext_tick)
				return NULL;
			memcpy(s->session->tlsext_tick,
			       s->tlsext_session_ticket->data,
			       ticklen);
			s->session->tlsext_ticklen = ticklen;
			}
		else
			ticklen = 0;
		if (ticklen == 0 && s->tlsext_session_ticket &&
		    s->tlsext_session_ticket->data == NULL)
			goto skip_ext;
		/* Check for enough room 2 for extension type, 2 for len
 		 * rest for ticket
  		 */
		if ((long)(limit - ret - 4 - ticklen) < 0) return NULL;
		s2n(TLSEXT_TYPE_session_ticket,ret); 
		s2n(ticklen,ret);
		if (ticklen)
			{
			memcpy(ret, s->session->tlsext_tick, ticklen);
			ret += ticklen;
			}
		}
		skip_ext:

	if (TLS1_get_client_version(s) >= TLS1_2_VERSION)
		{
		size_t salglen;
		salglen = tls12_get_sig_algs(s, NULL);
		if ((size_t)(limit - ret) < salglen + 6)
			return NULL; 
		s2n(TLSEXT_TYPE_signature_algorithms,ret);
		s2n(salglen + 2, ret);
		s2n(salglen, ret);
		tls12_get_sig_algs(s, ret);
		ret += salglen;
		}

#ifdef TLSEXT_TYPE_opaque_prf_input
	if (s->s3->client_opaque_prf_input != NULL &&
	    s->version != DTLS1_VERSION)
		{
		size_t col = s->s3->client_opaque_prf_input_len;
		
		if ((long)(limit - ret - 6 - col < 0))
			return NULL;
		if (col > 0xFFFD) /* can't happen */
			return NULL;

		s2n(TLSEXT_TYPE_opaque_prf_input, ret); 
		s2n(col + 2, ret);
		s2n(col, ret);
		memcpy(ret, s->s3->client_opaque_prf_input, col);
		ret += col;
		}
#endif

	if (s->tlsext_status_type == TLSEXT_STATUSTYPE_ocsp &&
	    s->version != DTLS1_VERSION)
		{
		int i;
		long extlen, idlen, itmp;
		OCSP_RESPID *id;

		idlen = 0;
		for (i = 0; i < sk_OCSP_RESPID_num(s->tlsext_ocsp_ids); i++)
			{
			id = sk_OCSP_RESPID_value(s->tlsext_ocsp_ids, i);
			itmp = i2d_OCSP_RESPID(id, NULL);
			if (itmp <= 0)
				return NULL;
			idlen += itmp + 2;
			}

		if (s->tlsext_ocsp_exts)
			{
			extlen = i2d_X509_EXTENSIONS(s->tlsext_ocsp_exts, NULL);
			if (extlen < 0)
				return NULL;
			}
		else
			extlen = 0;
			
		if ((long)(limit - ret - 7 - extlen - idlen) < 0) return NULL;
		s2n(TLSEXT_TYPE_status_request, ret);
		if (extlen + idlen > 0xFFF0)
			return NULL;
		s2n(extlen + idlen + 5, ret);
		*(ret++) = TLSEXT_STATUSTYPE_ocsp;
		s2n(idlen, ret);
		for (i = 0; i < sk_OCSP_RESPID_num(s->tlsext_ocsp_ids); i++)
			{
			/* save position of id len */
			unsigned char *q = ret;
			id = sk_OCSP_RESPID_value(s->tlsext_ocsp_ids, i);
			/* skip over id len */
			ret += 2;
			itmp = i2d_OCSP_RESPID(id, &ret);
			/* write id len */
			s2n(itmp, q);
			}
		s2n(extlen, ret);
		if (extlen > 0)
			i2d_X509_EXTENSIONS(s->tlsext_ocsp_exts, &ret);
		}

#ifndef OPENSSL_NO_HEARTBEATS
	/* Add Heartbeat extension */
	s2n(TLSEXT_TYPE_heartbeat,ret);
	s2n(1,ret);
	/* Set mode:
	 * 1: peer may send requests
	 * 2: peer not allowed to send requests
	 */
	if (s->tlsext_heartbeat & SSL_TLSEXT_HB_DONT_RECV_REQUESTS)
		*(ret++) = SSL_TLSEXT_HB_DONT_SEND_REQUESTS;
	else
		*(ret++) = SSL_TLSEXT_HB_ENABLED;
#endif

#ifndef OPENSSL_NO_NEXTPROTONEG
	if (s->ctx->next_proto_select_cb && !s->s3->tmp.finish_md_len)
		{
		/* The client advertises an emtpy extension to indicate its
		 * support for Next Protocol Negotiation */
		if (limit - ret - 4 < 0)
			return NULL;
		s2n(TLSEXT_TYPE_next_proto_neg,ret);
		s2n(0,ret);
		}
#endif

        if(SSL_get_srtp_profiles(s))
                {
                int el;

                ssl_add_clienthello_use_srtp_ext(s, 0, &el, 0);
                
                if((limit - p - 4 - el) < 0) return NULL;

                s2n(TLSEXT_TYPE_use_srtp,ret);
                s2n(el,ret);

                if(ssl_add_clienthello_use_srtp_ext(s, ret, &el, el))
			{
			SSLerr(SSL_F_SSL_ADD_CLIENTHELLO_TLSEXT, ERR_R_INTERNAL_ERROR);
			return NULL;
			}
                ret += el;
                }

	/* Add TLS extension Server_Authz_DataFormats to the ClientHello */
	/* 2 bytes for extension type */
	/* 2 bytes for extension length */
	/* 1 byte for the list length */
	/* 1 byte for the list (we only support audit proofs) */
	if (s->ctx->tlsext_authz_server_audit_proof_cb != NULL)
		{
		size_t lenmax;
                const unsigned short ext_len = 2;
                const unsigned char list_len = 1;

		if ((lenmax = limit - ret - 6) < 0) return NULL;

		s2n(TLSEXT_TYPE_server_authz, ret);
                /* Extension length: 2 bytes */
		s2n(ext_len, ret);
		*(ret++) = list_len;
		*(ret++) = TLSEXT_AUTHZDATAFORMAT_audit_proof;
		}

	if ((extdatalen = ret-p-2) == 0)
		return p;

	s2n(extdatalen,p);
	return ret;
	}
unsigned char *ssl_add_clienthello_tlsext(SSL *s, unsigned char *p, unsigned char *limit)
	{
	int extdatalen=0;
	unsigned char *ret = p;
#ifndef OPENSSL_NO_EC
	 
	int using_ecc = 0;
	if (s->version != DTLS1_VERSION && s->version >= TLS1_VERSION)
		{
		int i;
		unsigned long alg_k, alg_a;
		STACK_OF(SSL_CIPHER) *cipher_stack = SSL_get_ciphers(s);

		for (i = 0; i < sk_SSL_CIPHER_num(cipher_stack); i++)
			{
			SSL_CIPHER *c = sk_SSL_CIPHER_value(cipher_stack, i);

			alg_k = c->algorithm_mkey;
			alg_a = c->algorithm_auth;
			if ((alg_k & (SSL_kEECDH|SSL_kECDHr|SSL_kECDHe)
				|| (alg_a & SSL_aECDSA)))
				{
				using_ecc = 1;
				break;
				}
			}
		}
#endif

	 
	if (s->client_version == SSL3_VERSION
					&& !s->s3->send_connection_binding)
		return p;

	ret+=2;

	if (ret>=limit) return NULL;  

 	if (s->tlsext_hostname != NULL)
		{ 
		 
		unsigned long size_str;
		long lenmax; 

		 
		   
		if ((lenmax = limit - ret - 9) < 0 
		    || (size_str = strlen(s->tlsext_hostname)) > (unsigned long)lenmax) 
			return NULL;
			
		 
		s2n(TLSEXT_TYPE_server_name,ret); 
		s2n(size_str+5,ret);
		
		 
		s2n(size_str+3,ret);
	
		 
		*(ret++) = (unsigned char) TLSEXT_NAMETYPE_host_name;
		s2n(size_str,ret);
		memcpy(ret, s->tlsext_hostname, size_str);
		ret+=size_str;
		}

         
        if (s->renegotiate)
          {
          int el;
          
          if(!ssl_add_clienthello_renegotiate_ext(s, 0, &el, 0))
              {
              SSLerr(SSL_F_SSL_ADD_CLIENTHELLO_TLSEXT, ERR_R_INTERNAL_ERROR);
              return NULL;
              }

          if((limit - p - 4 - el) < 0) return NULL;
          
          s2n(TLSEXT_TYPE_renegotiate,ret);
          s2n(el,ret);

          if(!ssl_add_clienthello_renegotiate_ext(s, ret, &el, el))
              {
              SSLerr(SSL_F_SSL_ADD_CLIENTHELLO_TLSEXT, ERR_R_INTERNAL_ERROR);
              return NULL;
              }

          ret += el;
        }

#ifndef OPENSSL_NO_SRP
	 
	if (s->srp_ctx.login != NULL)
		{  

		int login_len = strlen(s->srp_ctx.login);	
		if (login_len > 255 || login_len == 0)
			{
			SSLerr(SSL_F_SSL_ADD_CLIENTHELLO_TLSEXT, ERR_R_INTERNAL_ERROR);
			return NULL;
			} 

		 
		if ((limit - ret - 5 - login_len) < 0) return NULL; 

		 
		s2n(TLSEXT_TYPE_srp,ret);
		s2n(login_len+1,ret);
		(*ret++) = (unsigned char) login_len;
		memcpy(ret, s->srp_ctx.login, login_len);
		ret+=login_len;
		}
#endif

#ifndef OPENSSL_NO_EC
	if (using_ecc)
		{
		 
		long lenmax; 
		const unsigned char *plist;
		size_t plistlen;
		 
		plist = s->tlsext_ecpointformatlist;
		if (plist)
			plistlen = s->tlsext_ecpointformatlist_length;
		else
			{
			plist = ecformats_default;
			plistlen = sizeof(ecformats_default);
			}

		if ((lenmax = limit - ret - 5) < 0) return NULL; 
		if (plistlen > (size_t)lenmax) return NULL;
		if (plistlen > 255)
			{
			SSLerr(SSL_F_SSL_ADD_CLIENTHELLO_TLSEXT, ERR_R_INTERNAL_ERROR);
			return NULL;
			}
		
		s2n(TLSEXT_TYPE_ec_point_formats,ret);
		s2n(plistlen + 1,ret);
		*(ret++) = (unsigned char)plistlen ;
		memcpy(ret, plist, plistlen);
		ret+=plistlen;

		 
		plist = s->tlsext_ellipticcurvelist;
		tls1_get_curvelist(s, 0, &plist, &plistlen);

		if ((lenmax = limit - ret - 6) < 0) return NULL; 
		if (plistlen > (size_t)lenmax) return NULL;
		if (plistlen > 65532)
			{
			SSLerr(SSL_F_SSL_ADD_CLIENTHELLO_TLSEXT, ERR_R_INTERNAL_ERROR);
			return NULL;
			}
		
		s2n(TLSEXT_TYPE_elliptic_curves,ret);
		s2n(plistlen + 2, ret);

		 
		s2n(plistlen, ret);
		memcpy(ret, plist, plistlen);
		ret+=plistlen;
		}
#endif  

	if (!(SSL_get_options(s) & SSL_OP_NO_TICKET))
		{
		int ticklen;
		if (!s->new_session && s->session && s->session->tlsext_tick)
			ticklen = s->session->tlsext_ticklen;
		else if (s->session && s->tlsext_session_ticket &&
			 s->tlsext_session_ticket->data)
			{
			ticklen = s->tlsext_session_ticket->length;
			s->session->tlsext_tick = OPENSSL_malloc(ticklen);
			if (!s->session->tlsext_tick)
				return NULL;
			memcpy(s->session->tlsext_tick,
			       s->tlsext_session_ticket->data,
			       ticklen);
			s->session->tlsext_ticklen = ticklen;
			}
		else
			ticklen = 0;
		if (ticklen == 0 && s->tlsext_session_ticket &&
		    s->tlsext_session_ticket->data == NULL)
			goto skip_ext;
		 
		if ((long)(limit - ret - 4 - ticklen) < 0) return NULL;
		s2n(TLSEXT_TYPE_session_ticket,ret); 
		s2n(ticklen,ret);
		if (ticklen)
			{
			memcpy(ret, s->session->tlsext_tick, ticklen);
			ret += ticklen;
			}
		}
		skip_ext:

	if (TLS1_get_client_version(s) >= TLS1_2_VERSION)
		{
		size_t salglen;
		salglen = tls12_get_sig_algs(s, NULL);
		if ((size_t)(limit - ret) < salglen + 6)
			return NULL; 
		s2n(TLSEXT_TYPE_signature_algorithms,ret);
		s2n(salglen + 2, ret);
		s2n(salglen, ret);
		tls12_get_sig_algs(s, ret);
		ret += salglen;
		}

#ifdef TLSEXT_TYPE_opaque_prf_input
	if (s->s3->client_opaque_prf_input != NULL &&
	    s->version != DTLS1_VERSION)
		{
		size_t col = s->s3->client_opaque_prf_input_len;
		
		if ((long)(limit - ret - 6 - col < 0))
			return NULL;
		if (col > 0xFFFD)  
			return NULL;

		s2n(TLSEXT_TYPE_opaque_prf_input, ret); 
		s2n(col + 2, ret);
		s2n(col, ret);
		memcpy(ret, s->s3->client_opaque_prf_input, col);
		ret += col;
		}
#endif

	if (s->tlsext_status_type == TLSEXT_STATUSTYPE_ocsp &&
	    s->version != DTLS1_VERSION)
		{
		int i;
		long extlen, idlen, itmp;
		OCSP_RESPID *id;

		idlen = 0;
		for (i = 0; i < sk_OCSP_RESPID_num(s->tlsext_ocsp_ids); i++)
			{
			id = sk_OCSP_RESPID_value(s->tlsext_ocsp_ids, i);
			itmp = i2d_OCSP_RESPID(id, NULL);
			if (itmp <= 0)
				return NULL;
			idlen += itmp + 2;
			}

		if (s->tlsext_ocsp_exts)
			{
			extlen = i2d_X509_EXTENSIONS(s->tlsext_ocsp_exts, NULL);
			if (extlen < 0)
				return NULL;
			}
		else
			extlen = 0;
			
		if ((long)(limit - ret - 7 - extlen - idlen) < 0) return NULL;
		s2n(TLSEXT_TYPE_status_request, ret);
		if (extlen + idlen > 0xFFF0)
			return NULL;
		s2n(extlen + idlen + 5, ret);
		*(ret++) = TLSEXT_STATUSTYPE_ocsp;
		s2n(idlen, ret);
		for (i = 0; i < sk_OCSP_RESPID_num(s->tlsext_ocsp_ids); i++)
			{
			 
			unsigned char *q = ret;
			id = sk_OCSP_RESPID_value(s->tlsext_ocsp_ids, i);
			 
			ret += 2;
			itmp = i2d_OCSP_RESPID(id, &ret);
			 
			s2n(itmp, q);
			}
		s2n(extlen, ret);
		if (extlen > 0)
			i2d_X509_EXTENSIONS(s->tlsext_ocsp_exts, &ret);
		}

#ifndef OPENSSL_NO_HEARTBEATS
	 
	s2n(TLSEXT_TYPE_heartbeat,ret);
	s2n(1,ret);
	 
	if (s->tlsext_heartbeat & SSL_TLSEXT_HB_DONT_RECV_REQUESTS)
		*(ret++) = SSL_TLSEXT_HB_DONT_SEND_REQUESTS;
	else
		*(ret++) = SSL_TLSEXT_HB_ENABLED;
#endif

#ifndef OPENSSL_NO_NEXTPROTONEG
	if (s->ctx->next_proto_select_cb && !s->s3->tmp.finish_md_len)
		{
		 
		if (limit - ret - 4 < 0)
			return NULL;
		s2n(TLSEXT_TYPE_next_proto_neg,ret);
		s2n(0,ret);
		}
#endif

        if(SSL_get_srtp_profiles(s))
                {
                int el;

                ssl_add_clienthello_use_srtp_ext(s, 0, &el, 0);
                
                if((limit - p - 4 - el) < 0) return NULL;

                s2n(TLSEXT_TYPE_use_srtp,ret);
                s2n(el,ret);

                if(ssl_add_clienthello_use_srtp_ext(s, ret, &el, el))
			{
			SSLerr(SSL_F_SSL_ADD_CLIENTHELLO_TLSEXT, ERR_R_INTERNAL_ERROR);
			return NULL;
			}
                ret += el;
                }

	 
	 
	 
	 
	 
	if (s->ctx->tlsext_authz_server_audit_proof_cb != NULL)
		{
		size_t lenmax;
                const unsigned short ext_len = 2;
                const unsigned char list_len = 1;

		if ((lenmax = limit - ret - 6) < 0) return NULL;

		s2n(TLSEXT_TYPE_server_authz, ret);
                 
		s2n(ext_len, ret);
		*(ret++) = list_len;
		*(ret++) = TLSEXT_AUTHZDATAFORMAT_audit_proof;
		}

	if ((extdatalen = ret-p-2) == 0)
		return p;

	s2n(extdatalen,p);
	return ret;
	}