ssl/d1_srvr.c

/*
 * DTLS implementation written by Nagendra Modadugu
 * (nagendra@cs.stanford.edu) for the OpenSSL project 2005. 
 */
/* ====================================================================
 * Copyright (c) 1999-2007 The OpenSSL Project.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. All advertising materials mentioning features or use of this
 *    software must display the following acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit. (http://www.OpenSSL.org/)"
 *
 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For written permission, please contact
 *    openssl-core@OpenSSL.org.
 *
 * 5. Products derived from this software may not be called "OpenSSL"
 *    nor may "OpenSSL" appear in their names without prior written
 *    permission of the OpenSSL Project.
 *
 * 6. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit (http://www.OpenSSL.org/)"
 *
 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 * ====================================================================
 *
 * This product includes cryptographic software written by Eric Young
 * (eay@cryptsoft.com).  This product includes software written by Tim
 * Hudson (tjh@cryptsoft.com).
 *
 */
/* 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
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
 *
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young (eay@cryptsoft.com)"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
 *
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */

#include <stdio.h>

#include <openssl/bn.h>
#include <openssl/buf.h>
#include <openssl/dh.h>
#include <openssl/evp.h>
#include <openssl/md5.h>
#include <openssl/obj.h>
#include <openssl/rand.h>
#include <openssl/x509.h>

#include "ssl_locl.h"

static const SSL_METHOD *dtls1_get_server_method(int ver);
static int dtls1_send_hello_verify_request(SSL *s);

static const SSL_METHOD *dtls1_get_server_method(int ver)
	{
	if (ver == DTLS1_VERSION)
		return(DTLSv1_server_method());
	else if (ver == DTLS1_2_VERSION)
		return(DTLSv1_2_server_method());
	else
		return(NULL);
	}

IMPLEMENT_dtls1_meth_func(DTLS1_VERSION,
			DTLSv1_server_method,
			dtls1_accept,
			ssl_undefined_function,
			dtls1_get_server_method,
			DTLSv1_enc_data)

IMPLEMENT_dtls1_meth_func(DTLS1_2_VERSION,
			DTLSv1_2_server_method,
			dtls1_accept,
			ssl_undefined_function,
			dtls1_get_server_method,
			DTLSv1_2_enc_data)

IMPLEMENT_dtls1_meth_func(DTLS_ANY_VERSION,
			DTLS_server_method,
			dtls1_accept,
			ssl_undefined_function,
			dtls1_get_server_method,
			DTLSv1_2_enc_data)

int dtls1_accept(SSL *s)
	{
	BUF_MEM *buf;
	void (*cb)(const SSL *ssl,int type,int val)=NULL;
	unsigned long alg_a;
	int ret= -1;
	int new_state,state,skip=0;
	int listen;

	ERR_clear_error();
	ERR_clear_system_error();

	if (s->info_callback != NULL)
		cb=s->info_callback;
	else if (s->ctx->info_callback != NULL)
		cb=s->ctx->info_callback;
	
	listen = s->d1->listen;

	/* init things to blank */
	s->in_handshake++;
	if (!SSL_in_init(s) || SSL_in_before(s)) SSL_clear(s);

	s->d1->listen = listen;

	if (s->cert == NULL)
		{
		OPENSSL_PUT_ERROR(SSL, dtls1_accept, SSL_R_NO_CERTIFICATE_SET);
		return(-1);
		}

	for (;;)
		{
		state=s->state;

		switch (s->state)
			{
		case SSL_ST_RENEGOTIATE:
			s->renegotiate=1;
			/* s->state=SSL_ST_ACCEPT; */

		case SSL_ST_BEFORE:
		case SSL_ST_ACCEPT:
		case SSL_ST_BEFORE|SSL_ST_ACCEPT:
		case SSL_ST_OK|SSL_ST_ACCEPT:

			s->server=1;
			if (cb != NULL) cb(s,SSL_CB_HANDSHAKE_START,1);

			if ((s->version & 0xff00) != (DTLS1_VERSION & 0xff00))
				{
				OPENSSL_PUT_ERROR(SSL, dtls1_accept, ERR_R_INTERNAL_ERROR);
				return -1;
				}
			s->type=SSL_ST_ACCEPT;

			if (s->init_buf == NULL)
				{
				if ((buf=BUF_MEM_new()) == NULL)
					{
					ret= -1;
					goto end;
					}
				if (!BUF_MEM_grow(buf,SSL3_RT_MAX_PLAIN_LENGTH))
					{
					ret= -1;
					goto end;
					}
				s->init_buf=buf;
				}

			if (!ssl3_setup_buffers(s))
				{
				ret= -1;
				goto end;
				}

			s->init_num=0;

			if (s->state != SSL_ST_RENEGOTIATE)
				{
				/* Ok, we now need to push on a buffering BIO so that
				 * the output is sent in a way that TCP likes :-)
				 * ...but not with SCTP :-)
				 */
					if (!ssl_init_wbio_buffer(s,1)) { ret= -1; goto end; }

				ssl3_init_finished_mac(s);
				s->state=SSL3_ST_SR_CLNT_HELLO_A;
				s->ctx->stats.sess_accept++;
				}
			else
				{
				/* s->state == SSL_ST_RENEGOTIATE,
				 * we will just send a HelloRequest */
				s->ctx->stats.sess_accept_renegotiate++;
				s->state=SSL3_ST_SW_HELLO_REQ_A;
				}

			break;

		case SSL3_ST_SW_HELLO_REQ_A:
		case SSL3_ST_SW_HELLO_REQ_B:

			s->shutdown=0;
			dtls1_clear_record_buffer(s);
			dtls1_start_timer(s);
			ret=ssl3_send_hello_request(s);
			if (ret <= 0) goto end;
			s->s3->tmp.next_state=SSL3_ST_SR_CLNT_HELLO_A;
			s->state=SSL3_ST_SW_FLUSH;
			s->init_num=0;

			ssl3_init_finished_mac(s);
			break;

		case SSL3_ST_SW_HELLO_REQ_C:
			s->state=SSL_ST_OK;
			break;

		case SSL3_ST_SR_CLNT_HELLO_A:
		case SSL3_ST_SR_CLNT_HELLO_B:
		case SSL3_ST_SR_CLNT_HELLO_C:
		case SSL3_ST_SR_CLNT_HELLO_D:

			s->shutdown=0;
			ret=ssl3_get_client_hello(s);
			if (ret <= 0) goto end;
			dtls1_stop_timer(s);

			if (ret == 1 && (SSL_get_options(s) & SSL_OP_COOKIE_EXCHANGE))
				s->state = DTLS1_ST_SW_HELLO_VERIFY_REQUEST_A;
			else
				s->state = SSL3_ST_SW_SRVR_HELLO_A;

			s->init_num=0;

			/* Reflect ClientHello sequence to remain stateless while listening */
			if (listen)
				{
				memcpy(s->s3->write_sequence, s->s3->read_sequence, sizeof(s->s3->write_sequence));
				}

			/* If we're just listening, stop here */
			if (listen && s->state == SSL3_ST_SW_SRVR_HELLO_A)
				{
				ret = 2;
				s->d1->listen = 0;
				/* Set expected sequence numbers
				 * to continue the handshake.
				 */
				s->d1->handshake_read_seq = 2;
				s->d1->handshake_write_seq = 1;
				s->d1->next_handshake_write_seq = 1;
				goto end;
				}
			
			break;
			
		case DTLS1_ST_SW_HELLO_VERIFY_REQUEST_A:
		case DTLS1_ST_SW_HELLO_VERIFY_REQUEST_B:

			ret = dtls1_send_hello_verify_request(s);
			if ( ret <= 0) goto end;
			s->state=SSL3_ST_SW_FLUSH;
			s->s3->tmp.next_state=SSL3_ST_SR_CLNT_HELLO_A;

			/* HelloVerifyRequest resets Finished MAC */
			ssl3_init_finished_mac(s);
			break;
			

		case SSL3_ST_SW_SRVR_HELLO_A:
		case SSL3_ST_SW_SRVR_HELLO_B:
			s->renegotiate = 2;
			dtls1_start_timer(s);
			ret=ssl3_send_server_hello(s);
			if (ret <= 0) goto end;

			if (s->hit)
				{
				if (s->tlsext_ticket_expected)
					s->state=SSL3_ST_SW_SESSION_TICKET_A;
				else
					s->state=SSL3_ST_SW_CHANGE_A;
				}
			else
				s->state=SSL3_ST_SW_CERT_A;
			s->init_num=0;
			break;

		case SSL3_ST_SW_CERT_A:
		case SSL3_ST_SW_CERT_B:
			/* Check if it is anon DH or normal PSK */
			if (!(s->s3->tmp.new_cipher->algorithm_auth & SSL_aNULL)
				&& !(s->s3->tmp.new_cipher->algorithm_mkey & SSL_kPSK))
				{
				dtls1_start_timer(s);
				ret=ssl3_send_server_certificate(s);
				if (ret <= 0) goto end;
				if (s->tlsext_status_expected)
					s->state=SSL3_ST_SW_CERT_STATUS_A;
				else
					s->state=SSL3_ST_SW_KEY_EXCH_A;
				}
			else
				{
				skip = 1;
				s->state=SSL3_ST_SW_KEY_EXCH_A;
				}
			s->init_num=0;
			break;

		case SSL3_ST_SW_KEY_EXCH_A:
		case SSL3_ST_SW_KEY_EXCH_B:
			alg_a = s->s3->tmp.new_cipher->algorithm_auth;

			/* Send a ServerKeyExchange message if:
			 * - The key exchange is ephemeral or anonymous
			 *   Diffie-Hellman.
			 * - There is a PSK identity hint.
			 *
			 * TODO(davidben): This logic is currently duplicated
			 * in s3_srvr.c. Fix this. In the meantime, keep them
			 * in sync.
			 */
			if (ssl_cipher_requires_server_key_exchange(s->s3->tmp.new_cipher) ||
			    ((alg_a & SSL_aPSK) && s->session->psk_identity_hint))
				{
				dtls1_start_timer(s);
				ret=ssl3_send_server_key_exchange(s);
				if (ret <= 0) goto end;
				}
			else
				skip=1;

			s->state=SSL3_ST_SW_CERT_REQ_A;
			s->init_num=0;
			break;

		case SSL3_ST_SW_CERT_REQ_A:
		case SSL3_ST_SW_CERT_REQ_B:
			if (/* don't request cert unless asked for it: */
				!(s->verify_mode & SSL_VERIFY_PEER) ||
				/* if SSL_VERIFY_CLIENT_ONCE is set,
				 * don't request cert during re-negotiation: */
				((s->session->peer != NULL) &&
				 (s->verify_mode & SSL_VERIFY_CLIENT_ONCE)) ||
				/* never request cert in anonymous ciphersuites
				 * (see section "Certificate request" in SSL 3 drafts
				 * and in RFC 2246): */
				((s->s3->tmp.new_cipher->algorithm_auth & SSL_aNULL) &&
				 /* ... except when the application insists on verification
				  * (against the specs, but s3_clnt.c accepts this for SSL 3) */
				 !(s->verify_mode & SSL_VERIFY_FAIL_IF_NO_PEER_CERT)) ||
				/* With normal PSK Certificates and
				 * Certificate Requests are omitted */
				(s->s3->tmp.new_cipher->algorithm_mkey & SSL_kPSK))
				{
				/* no cert request */
				skip=1;
				s->s3->tmp.cert_request=0;
				s->state=SSL3_ST_SW_SRVR_DONE_A;
				}
			else
				{
				s->s3->tmp.cert_request=1;
				dtls1_start_timer(s);
				ret=ssl3_send_certificate_request(s);
				if (ret <= 0) goto end;
#ifndef NETSCAPE_HANG_BUG
				s->state=SSL3_ST_SW_SRVR_DONE_A;
#else
				s->state=SSL3_ST_SW_FLUSH;
				s->s3->tmp.next_state=SSL3_ST_SR_CERT_A;
#endif
				s->init_num=0;
				}
			break;

		case SSL3_ST_SW_SRVR_DONE_A:
		case SSL3_ST_SW_SRVR_DONE_B:
			dtls1_start_timer(s);
			ret=ssl3_send_server_done(s);
			if (ret <= 0) goto end;
			s->s3->tmp.next_state=SSL3_ST_SR_CERT_A;
			s->state=SSL3_ST_SW_FLUSH;
			s->init_num=0;
			break;
		
		case SSL3_ST_SW_FLUSH:
			s->rwstate=SSL_WRITING;
			if (BIO_flush(s->wbio) <= 0)
				{
				/* If the write error was fatal, stop trying */
				if (!BIO_should_retry(s->wbio))
					{
					s->rwstate=SSL_NOTHING;
					s->state=s->s3->tmp.next_state;
					}
				
				ret= -1;
				goto end;
				}
			s->rwstate=SSL_NOTHING;
			s->state=s->s3->tmp.next_state;
			break;

		case SSL3_ST_SR_CERT_A:
		case SSL3_ST_SR_CERT_B:
			if (s->s3->tmp.cert_request)
				{
				ret=ssl3_get_client_certificate(s);
				if (ret <= 0) goto end;
				}
			s->init_num=0;
			s->state=SSL3_ST_SR_KEY_EXCH_A;
			break;

		case SSL3_ST_SR_KEY_EXCH_A:
		case SSL3_ST_SR_KEY_EXCH_B:
			ret=ssl3_get_client_key_exchange(s);
			if (ret <= 0)
				goto end;
			s->state=SSL3_ST_SR_CERT_VRFY_A;
			s->init_num=0;

			/* TODO(davidben): These two blocks are different
			 * between SSL and DTLS. Resolve the difference and code
			 * duplication. */
			if (SSL_USE_SIGALGS(s))
				{
				if (!s->session->peer)
					break;
				/* For sigalgs freeze the handshake buffer
				 * at this point and digest cached records.
				 */
				if (!s->s3->handshake_buffer)
					{
					OPENSSL_PUT_ERROR(SSL, dtls1_accept, ERR_R_INTERNAL_ERROR);
					return -1;
					}
				s->s3->flags |= TLS1_FLAGS_KEEP_HANDSHAKE;
				if (!ssl3_digest_cached_records(s))
					return -1;
				}
			else
				{
				/* We need to get hashes here so if there is
				 * a client cert, it can be verified */ 
				s->method->ssl3_enc->cert_verify_mac(s,
					NID_md5,
					&(s->s3->tmp.cert_verify_md[0]));
				s->method->ssl3_enc->cert_verify_mac(s,
					NID_sha1,
					&(s->s3->tmp.cert_verify_md[MD5_DIGEST_LENGTH]));
				}
			break;

		case SSL3_ST_SR_CERT_VRFY_A:
		case SSL3_ST_SR_CERT_VRFY_B:

			s->d1->change_cipher_spec_ok = 1;
			/* we should decide if we expected this one */
			ret=ssl3_get_cert_verify(s);
			if (ret <= 0) goto end;
				s->state=SSL3_ST_SR_FINISHED_A;
			s->init_num=0;
			break;

		case SSL3_ST_SR_FINISHED_A:
		case SSL3_ST_SR_FINISHED_B:
			s->d1->change_cipher_spec_ok = 1;
			ret=ssl3_get_finished(s,SSL3_ST_SR_FINISHED_A,
				SSL3_ST_SR_FINISHED_B);
			if (ret <= 0) goto end;
			dtls1_stop_timer(s);
			if (s->hit)
				s->state=SSL_ST_OK;
			else if (s->tlsext_ticket_expected)
				s->state=SSL3_ST_SW_SESSION_TICKET_A;
			else
				s->state=SSL3_ST_SW_CHANGE_A;
			s->init_num=0;
			break;

		case SSL3_ST_SW_SESSION_TICKET_A:
		case SSL3_ST_SW_SESSION_TICKET_B:
			ret=ssl3_send_newsession_ticket(s);
			if (ret <= 0) goto end;
			s->state=SSL3_ST_SW_CHANGE_A;
			s->init_num=0;
			break;

		case SSL3_ST_SW_CERT_STATUS_A:
		case SSL3_ST_SW_CERT_STATUS_B:
			ret=ssl3_send_cert_status(s);
			if (ret <= 0) goto end;
			s->state=SSL3_ST_SW_KEY_EXCH_A;
			s->init_num=0;
			break;


		case SSL3_ST_SW_CHANGE_A:
		case SSL3_ST_SW_CHANGE_B:

			s->session->cipher=s->s3->tmp.new_cipher;
			if (!s->method->ssl3_enc->setup_key_block(s))
				{ ret= -1; goto end; }

			ret=dtls1_send_change_cipher_spec(s,
				SSL3_ST_SW_CHANGE_A,SSL3_ST_SW_CHANGE_B);

			if (ret <= 0) goto end;

			s->state=SSL3_ST_SW_FINISHED_A;
			s->init_num=0;

			if (!s->method->ssl3_enc->change_cipher_state(s,
				SSL3_CHANGE_CIPHER_SERVER_WRITE))
				{
				ret= -1;
				goto end;
				}

			dtls1_reset_seq_numbers(s, SSL3_CC_WRITE);
			break;

		case SSL3_ST_SW_FINISHED_A:
		case SSL3_ST_SW_FINISHED_B:
			ret=ssl3_send_finished(s,
				SSL3_ST_SW_FINISHED_A,SSL3_ST_SW_FINISHED_B,
				s->method->ssl3_enc->server_finished_label,
				s->method->ssl3_enc->server_finished_label_len);
			if (ret <= 0) goto end;
			s->state=SSL3_ST_SW_FLUSH;
			if (s->hit)
				{
				s->s3->tmp.next_state=SSL3_ST_SR_FINISHED_A;
				}
			else
				{
				s->s3->tmp.next_state=SSL_ST_OK;
				}
			s->init_num=0;
			break;

		case SSL_ST_OK:
			/* clean a few things up */
			ssl3_cleanup_key_block(s);

#if 0
			BUF_MEM_free(s->init_buf);
			s->init_buf=NULL;
#endif

			/* remove buffering on output */
			ssl_free_wbio_buffer(s);

			s->init_num=0;

			if (s->renegotiate == 2) /* skipped if we just sent a HelloRequest */
				{
				s->renegotiate=0;
				s->new_session=0;
				
				ssl_update_cache(s,SSL_SESS_CACHE_SERVER);
				
				s->ctx->stats.sess_accept_good++;
				/* s->server=1; */
				s->handshake_func=dtls1_accept;

				if (cb != NULL) cb(s,SSL_CB_HANDSHAKE_DONE,1);
				}
			
			ret = 1;

			/* done handshaking, next message is client hello */
			s->d1->handshake_read_seq = 0;
			/* next message is server hello */
			s->d1->handshake_write_seq = 0;
			s->d1->next_handshake_write_seq = 0;
			goto end;
			/* break; */

		default:
			OPENSSL_PUT_ERROR(SSL, dtls1_accept, SSL_R_UNKNOWN_STATE);
			ret= -1;
			goto end;
			/* break; */
			}
		
		if (!s->s3->tmp.reuse_message && !skip)
			{
			if (s->debug)
				{
				if ((ret=BIO_flush(s->wbio)) <= 0)
					goto end;
				}


			if ((cb != NULL) && (s->state != state))
				{
				new_state=s->state;
				s->state=state;
				cb(s,SSL_CB_ACCEPT_LOOP,1);
				s->state=new_state;
				}
			}
		skip=0;
		}
end:
	/* BIO_flush(s->wbio); */

	s->in_handshake--;

	if (cb != NULL)
		cb(s,SSL_CB_ACCEPT_EXIT,ret);
	return(ret);
	}

int dtls1_send_hello_verify_request(SSL *s)
	{
	unsigned int msg_len;
	unsigned char *msg, *buf, *p;

	if (s->state == DTLS1_ST_SW_HELLO_VERIFY_REQUEST_A)
		{
		buf = (unsigned char *)s->init_buf->data;

		msg = p = &(buf[DTLS1_HM_HEADER_LENGTH]);
		/* Always use DTLS 1.0 version: see RFC 6347 */
		*(p++) = DTLS1_VERSION >> 8;
		*(p++) = DTLS1_VERSION & 0xFF;

		if (s->ctx->app_gen_cookie_cb == NULL ||
		     s->ctx->app_gen_cookie_cb(s, s->d1->cookie, &(s->d1->cookie_len)) == 0)
			{
			OPENSSL_PUT_ERROR(SSL, dtls1_send_hello_verify_request, ERR_R_INTERNAL_ERROR);
			return 0;
			}

		*(p++) = (unsigned char) s->d1->cookie_len;
		memcpy(p, s->d1->cookie, s->d1->cookie_len);
		p += s->d1->cookie_len;
		msg_len = p - msg;

		dtls1_set_message_header(s, buf,
			DTLS1_MT_HELLO_VERIFY_REQUEST, msg_len, 0, msg_len);

		s->state=DTLS1_ST_SW_HELLO_VERIFY_REQUEST_B;
		/* number of bytes to write */
		s->init_num=p-buf;
		s->init_off=0;
		}

	/* s->state = DTLS1_ST_SW_HELLO_VERIFY_REQUEST_B */
	return(dtls1_do_write(s,SSL3_RT_HANDSHAKE));
	}