SSL/TLS建立連接之狀態切換

本文基於OpenSSL 1.0.2u學習OpenSSL中對SSL/TLS協商過程的實現

協商過程的狀態切換

OpenSSL中服務端ssl3_accept接口實現對協商過程數據包的解析，解析完不同的數據包之後，切換到下一個狀態：

上圖是ssl3_accept中狀態切換的大概流程，其中根據s->hit判斷是否進入會話恢復流程，在SessionID和SessionTicket會話恢復流程中，會有一些狀態差異，因爲恢復過程中，比如重新計算密鑰等過程就不需要了，會複用之前會話的密鑰等信息。

ssl3_accept接口註釋

int ssl3_accept(SSL *s)
{
    BUF_MEM *buf;
    unsigned long alg_k, Time = (unsigned long)time(NULL);
    void (*cb) (const SSL *ssl, int type, int val) = NULL;
    int ret = -1;
    int new_state, state, skip = 0;

    //設置隨機種子
    RAND_add(&Time, sizeof(Time), 0);
    ERR_clear_error();
    clear_sys_error();

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

    /* init things to blank */
    //in_handshake標識協商過程是否完成，剛開始是1，協商完成後設置爲0
    s->in_handshake++;
    if (!SSL_in_init(s) || SSL_in_before(s))
        SSL_clear(s);

    if (s->cert == NULL) {
        SSLerr(SSL_F_SSL3_ACCEPT, SSL_R_NO_CERTIFICATE_SET);
        return (-1);
    }
#ifndef OPENSSL_NO_HEARTBEATS
    /*
     * If we're awaiting a HeartbeatResponse, pretend we already got and
     * don't await it anymore, because Heartbeats don't make sense during
     * handshakes anyway.
     */
    if (s->tlsext_hb_pending) {
        s->tlsext_hb_pending = 0;
        s->tlsext_hb_seq++;
    }
#endif

    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:  //初始化狀態
        case SSL_ST_OK | SSL_ST_ACCEPT:
            //這是服務端程序，設爲1
            s->server = 1;
            if (cb != NULL)
                cb(s, SSL_CB_HANDSHAKE_START, 1);

            if ((s->version >> 8) != 3) {
                SSLerr(SSL_F_SSL3_ACCEPT, ERR_R_INTERNAL_ERROR);
                s->state = SSL_ST_ERR;
                return -1;
            }
            s->type = SSL_ST_ACCEPT;

            if (s->init_buf == NULL) {
                if ((buf = BUF_MEM_new()) == NULL) {
                    ret = -1;
                    s->state = SSL_ST_ERR;
                    goto end;
                }
                if (!BUF_MEM_grow(buf, SSL3_RT_MAX_PLAIN_LENGTH)) {
                    BUF_MEM_free(buf);
                    ret = -1;
                    s->state = SSL_ST_ERR;
                    goto end;
                }
                s->init_buf = buf;
            }
            //申請TLS緩衝區，rbuff和wbuff
            if (!ssl3_setup_buffers(s)) {
                ret = -1;
                s->state = SSL_ST_ERR;
                goto end;
            }

            s->init_num = 0;
            s->s3->flags &= ~TLS1_FLAGS_SKIP_CERT_VERIFY;
            s->s3->flags &= ~SSL3_FLAGS_CCS_OK;
            /*
             * Should have been reset by ssl3_get_finished, too.
             */
            s->s3->change_cipher_spec = 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 :-)
                 */
                if (!ssl_init_wbio_buffer(s, 1)) {
                    ret = -1;
                    s->state = SSL_ST_ERR;
                    goto end;
                }
                //初始化消息摘要驗證
                if (!ssl3_init_finished_mac(s)) {
                    ret = -1;
                    s->state = SSL_ST_ERR;
                    goto end;
                }

                s->state = SSL3_ST_SR_CLNT_HELLO_A;
                s->ctx->stats.sess_accept++;
            } else if (!s->s3->send_connection_binding &&
                       !(s->options &
                         SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION)) {
                /*
                 * Server attempting to renegotiate with client that doesn't
                 * support secure renegotiation.
                 */
                SSLerr(SSL_F_SSL3_ACCEPT,
                       SSL_R_UNSAFE_LEGACY_RENEGOTIATION_DISABLED);
                ssl3_send_alert(s, SSL3_AL_FATAL, SSL_AD_HANDSHAKE_FAILURE);
                ret = -1;
                s->state = SSL_ST_ERR;
                goto end;
            } 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;
            ret = ssl3_send_hello_request(s);
            if (ret <= 0)
                goto end;
            s->s3->tmp.next_state = SSL3_ST_SW_HELLO_REQ_C;
            s->state = SSL3_ST_SW_FLUSH;
            s->init_num = 0;

            if (!ssl3_init_finished_mac(s)) {
                ret = -1;
                s->state = SSL_ST_ERR;
                goto end;
            }
            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:
            //SSL3_ST_SR_CLNT_HELLO_A狀態解析客戶端第一個請求數據包ClientHello
            //獲取客戶端支持的密碼套件和擴展字段等信息
            s->shutdown = 0;
            ret = ssl3_get_client_hello(s);
            if (ret <= 0)
                goto end;
#ifndef OPENSSL_NO_SRP
            s->state = SSL3_ST_SR_CLNT_HELLO_D;
        case SSL3_ST_SR_CLNT_HELLO_D:
            {
                int al;
                if ((ret = ssl_check_srp_ext_ClientHello(s, &al)) < 0) {
                    /*
                     * callback indicates firther work to be done
                     */
                    s->rwstate = SSL_X509_LOOKUP;
                    goto end;
                }
                if (ret != SSL_ERROR_NONE) {
                    ssl3_send_alert(s, SSL3_AL_FATAL, al);
                    /*
                     * This is not really an error but the only means to for
                     * a client to detect whether srp is supported.
                     */
                    if (al != TLS1_AD_UNKNOWN_PSK_IDENTITY)
                        SSLerr(SSL_F_SSL3_ACCEPT, SSL_R_CLIENTHELLO_TLSEXT);
                    ret = -1;
                    s->state = SSL_ST_ERR;
                    goto end;
                }
            }
#endif

            s->renegotiate = 2;
            s->state = SSL3_ST_SW_SRVR_HELLO_A;
            s->init_num = 0;
            break;

        case SSL3_ST_SW_SRVR_HELLO_A:
        case SSL3_ST_SW_SRVR_HELLO_B:
        //SSL3_ST_SW_SRVR_HELLO_A此狀態是服務端響應ClientHello的消息
        //根據客戶端支持的密碼套件和擴展字段信息，把最終確定後續要使用的密碼套件和服務端選定的擴展字段發送給客戶端
        //如果
            ret = ssl3_send_server_hello(s);
            if (ret <= 0)
                goto end;
#ifndef OPENSSL_NO_TLSEXT
            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
            //通過在服務端判斷ClientHello中的SessionId是否存在，確定是否走會話恢復流程
            if (s->hit)
                s->state = SSL3_ST_SW_CHANGE_A;
#endif
            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:
        //這個狀態是服務端把自己的證書發送給客戶端，讓客戶端進行驗證，確認服務端的身份
            /* Check if it is anon DH or anon ECDH, */
            /* normal PSK or KRB5 or SRP */
            if (!
                (s->s3->tmp.
                 new_cipher->algorithm_auth & (SSL_aNULL | SSL_aKRB5 |
                                               SSL_aSRP))
&& !(s->s3->tmp.new_cipher->algorithm_mkey & SSL_kPSK)) {
                ret = ssl3_send_server_certificate(s);
                if (ret <= 0)
                    goto end;
#ifndef OPENSSL_NO_TLSEXT
                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;
            }
#else
            } else
                skip = 1;

            s->state = SSL3_ST_SW_KEY_EXCH_A;
#endif
            s->init_num = 0;
            break;

        case SSL3_ST_SW_KEY_EXCH_A:
        case SSL3_ST_SW_KEY_EXCH_B:
        //此狀態是服務端發送Server Key Exchange子消息，這個子消息是否發送，是根據不同密碼套件有關，比如是DH、ECDHE密鑰協商算法，則會發送此消息
            alg_k = s->s3->tmp.new_cipher->algorithm_mkey;

            /*
             * clear this, it may get reset by
             * send_server_key_exchange
             */
            s->s3->tmp.use_rsa_tmp = 0;

            /*
             * only send if a DH key exchange, fortezza or RSA but we have a
             * sign only certificate PSK: may send PSK identity hints For
             * ECC ciphersuites, we send a serverKeyExchange message only if
             * the cipher suite is either ECDH-anon or ECDHE. In other cases,
             * the server certificate contains the server's public key for
             * key exchange.
             */
            if (0
                /*
                 * PSK: send ServerKeyExchange if PSK identity hint if
                 * provided
                 */
#ifndef OPENSSL_NO_PSK
                || ((alg_k & SSL_kPSK) && s->ctx->psk_identity_hint)
#endif
#ifndef OPENSSL_NO_SRP
                /* SRP: send ServerKeyExchange */
                || (alg_k & SSL_kSRP)
#endif
                || (alg_k & SSL_kEDH)
                || (alg_k & SSL_kEECDH)
                || ((alg_k & SSL_kRSA)
                    && (s->cert->pkeys[SSL_PKEY_RSA_ENC].privatekey == NULL
                        || (SSL_C_IS_EXPORT(s->s3->tmp.new_cipher)
                            && EVP_PKEY_size(s->cert->pkeys
                                             [SSL_PKEY_RSA_ENC].privatekey) *
                            8 > SSL_C_EXPORT_PKEYLENGTH(s->s3->tmp.new_cipher)
                        )
                    )
                )
                ) {
                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->s3->tmp.finish_md_len != 0 &&
                    (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)) ||
                   /*
                    * never request cert in Kerberos ciphersuites
                    */
                   (s->s3->tmp.new_cipher->algorithm_auth & SSL_aKRB5) ||
                   /* don't request certificate for SRP auth */
                   (s->s3->tmp.new_cipher->algorithm_auth & SSL_aSRP)
                   /*
                    * 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;
                if (s->s3->handshake_buffer) {
                    if (!ssl3_digest_cached_records(s)) {
                        s->state = SSL_ST_ERR;
                        return -1;
                    }
                }
            } else {
                s->s3->tmp.cert_request = 1;
                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:
        //此消息是服務端響應，說明服務端消息已發送完畢
            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:
            //清空wbio緩衝區
            /*
             * This code originally checked to see if any data was pending
             * using BIO_CTRL_INFO and then flushed. This caused problems as
             * documented in PR#1939. The proposed fix doesn't completely
             * resolve this issue as buggy implementations of
             * BIO_CTRL_PENDING still exist. So instead we just flush
             * unconditionally.
             */

            s->rwstate = SSL_WRITING;
            if (BIO_flush(s->wbio) <= 0) {
                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:
        //此狀態是讀取客戶端的證書信息，在需要驗證客戶端身份信息（雙向認證）中用到
            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:
        //解析客戶端的Client Key Exchange子消息，客戶端在發送此消息時，客戶端實際已經計算出後續加密通信需要的密鑰等信息，此消息中包含preMaster key信息，服務端通過preMaster key計算主密鑰等信息
            ret = ssl3_get_client_key_exchange(s);
            if (ret <= 0)
                goto end;
            if (ret == 2) {
                /*
                 * For the ECDH ciphersuites when the client sends its ECDH
                 * pub key in a certificate, the CertificateVerify message is
                 * not sent. Also for GOST ciphersuites when the client uses
                 * its key from the certificate for key exchange.
                 */
#if defined(OPENSSL_NO_TLSEXT) || defined(OPENSSL_NO_NEXTPROTONEG)
                s->state = SSL3_ST_SR_FINISHED_A;
#else
                if (s->s3->next_proto_neg_seen)
                    s->state = SSL3_ST_SR_NEXT_PROTO_A;
                else
                    s->state = SSL3_ST_SR_FINISHED_A;
#endif
                s->init_num = 0;
            } else if (SSL_USE_SIGALGS(s)) {
                s->state = SSL3_ST_SR_CERT_VRFY_A;
                s->init_num = 0;
                if (!s->session->peer)
                    break;
                /*
                 * For sigalgs freeze the handshake buffer at this point and
                 * digest cached records.
                 */
                if (!s->s3->handshake_buffer) {
                    SSLerr(SSL_F_SSL3_ACCEPT, ERR_R_INTERNAL_ERROR);
                    s->state = SSL_ST_ERR;
                    return -1;
                }
                s->s3->flags |= TLS1_FLAGS_KEEP_HANDSHAKE;
                if (!ssl3_digest_cached_records(s)) {
                    s->state = SSL_ST_ERR;
                    return -1;
                }
            } else {
                int offset = 0;
                int dgst_num;

                s->state = SSL3_ST_SR_CERT_VRFY_A;
                s->init_num = 0;

                /*
                 * We need to get hashes here so if there is a client cert,
                 * it can be verified FIXME - digest processing for
                 * CertificateVerify should be generalized. But it is next
                 * step
                 */
                if (s->s3->handshake_buffer) {
                    if (!ssl3_digest_cached_records(s)) {
                        s->state = SSL_ST_ERR;
                        return -1;
                    }
                }
                for (dgst_num = 0; dgst_num < SSL_MAX_DIGEST; dgst_num++)
                    if (s->s3->handshake_dgst[dgst_num]) {
                        int dgst_size;

                        s->method->ssl3_enc->cert_verify_mac(s,
                                                             EVP_MD_CTX_type
                                                             (s->
                                                              s3->handshake_dgst
                                                              [dgst_num]),
                                                             &(s->s3->
                                                               tmp.cert_verify_md
                                                               [offset]));
                        dgst_size =
                            EVP_MD_CTX_size(s->s3->handshake_dgst[dgst_num]);
                        if (dgst_size < 0) {
                            s->state = SSL_ST_ERR;
                            ret = -1;
                            goto end;
                        }
                        offset += dgst_size;
                    }
            }
            break;

        case SSL3_ST_SR_CERT_VRFY_A:
        case SSL3_ST_SR_CERT_VRFY_B:
            ret = ssl3_get_cert_verify(s);
            if (ret <= 0)
                goto end;

#if defined(OPENSSL_NO_TLSEXT) || defined(OPENSSL_NO_NEXTPROTONEG)
            s->state = SSL3_ST_SR_FINISHED_A;
#else
            if (s->s3->next_proto_neg_seen)
                s->state = SSL3_ST_SR_NEXT_PROTO_A;
            else
                s->state = SSL3_ST_SR_FINISHED_A;
#endif
            s->init_num = 0;
            break;

#if !defined(OPENSSL_NO_TLSEXT) && !defined(OPENSSL_NO_NEXTPROTONEG)
        case SSL3_ST_SR_NEXT_PROTO_A:
        case SSL3_ST_SR_NEXT_PROTO_B:
            /*
             * Enable CCS for NPN. Receiving a CCS clears the flag, so make
             * sure not to re-enable it to ban duplicates. This *should* be the
             * first time we have received one - but we check anyway to be
             * cautious.
             * s->s3->change_cipher_spec is set when a CCS is
             * processed in s3_pkt.c, and remains set until
             * the client's Finished message is read.
             */
            if (!s->s3->change_cipher_spec)
                s->s3->flags |= SSL3_FLAGS_CCS_OK;

            ret = ssl3_get_next_proto(s);
            if (ret <= 0)
                goto end;
            s->init_num = 0;
            s->state = SSL3_ST_SR_FINISHED_A;
            break;
#endif

        case SSL3_ST_SR_FINISHED_A:
        case SSL3_ST_SR_FINISHED_B:
        //此狀態解析客戶端發送的Change Cipher Spec和Finished子消息
        //在Change Cipher Spec子消息過程中，服務端調用計算主密鑰等接口，計算後續解密通信中使用的密鑰信息
        //Finished子消息中是客戶端把從開始協商到發送此數據包爲止的所有數據計算摘要值，並使用計算出的密鑰進行加密後的數據，服務端使用解密的密鑰解密數據，然後做摘要驗證，防止協商數據中間被篡改
            /*
             * Enable CCS for handshakes without NPN. In NPN the CCS flag has
             * already been set. Receiving a CCS clears the flag, so make
             * sure not to re-enable it to ban duplicates.
             * s->s3->change_cipher_spec is set when a CCS is
             * processed in s3_pkt.c, and remains set until
             * the client's Finished message is read.
             */
            if (!s->s3->change_cipher_spec)
                s->s3->flags |= SSL3_FLAGS_CCS_OK;
            ret = ssl3_get_finished(s, SSL3_ST_SR_FINISHED_A,
                                    SSL3_ST_SR_FINISHED_B);
            if (ret <= 0)
                goto end;
            if (s->hit)
                s->state = SSL_ST_OK;
#ifndef OPENSSL_NO_TLSEXT
            else if (s->tlsext_ticket_expected)
                s->state = SSL3_ST_SW_SESSION_TICKET_A;
#endif
            else
                s->state = SSL3_ST_SW_CHANGE_A;
            s->init_num = 0;
            break;

#ifndef OPENSSL_NO_TLSEXT
        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;

#endif

        case SSL3_ST_SW_CHANGE_A:
        case SSL3_ST_SW_CHANGE_B:
        //此狀態是服務端計算加密密鑰
            s->session->cipher = s->s3->tmp.new_cipher;
            if (!s->method->ssl3_enc->setup_key_block(s)) {
                ret = -1;
                s->state = SSL_ST_ERR;
                goto end;
            }

            ret = ssl3_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;
                s->state = SSL_ST_ERR;
                goto end;
            }

            break;

        case SSL3_ST_SW_FINISHED_A:
        case SSL3_ST_SW_FINISHED_B:
        //服務端發送Finished消息，供客戶端進行摘要驗證
            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) {
#if defined(OPENSSL_NO_TLSEXT) || defined(OPENSSL_NO_NEXTPROTONEG)
                s->s3->tmp.next_state = SSL3_ST_SR_FINISHED_A;
#else
                if (s->s3->next_proto_neg_seen) {
                    s->s3->tmp.next_state = SSL3_ST_SR_NEXT_PROTO_A;
                } else
                    s->s3->tmp.next_state = SSL3_ST_SR_FINISHED_A;
#endif
            } else
                s->s3->tmp.next_state = SSL_ST_OK;
            s->init_num = 0;
            break;

        case SSL_ST_OK:
        //SSL/TLS協商成功
            /* clean a few things up */
            ssl3_cleanup_key_block(s);

            BUF_MEM_free(s->init_buf);
            s->init_buf = NULL;

            /* 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 = ssl3_accept;

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

            ret = 1;
            goto end;
            /* break; */

        case SSL_ST_ERR:
        default:
            SSLerr(SSL_F_SSL3_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);
}