SSL/TLS建立连接之状态切换
本文基于OpenSSL 1.0.2u学习OpenSSL中对SSL/TLS协商过程的实现
协商过程的状态切换
OpenSSL中服务端ssl3_accept接口实现对协商过程数据包的解析，解析完不同的数据包之后，切换到下一个状态：
上图是ssl3_accept中状态切换的大概流程，其中根据s->hit判断是否进入会话恢复流程，在SessionID和SessionTicket会话恢复流程中，会有一些状态差异，因为恢复过程中，比如重新计算密钥等过程就不需要了，会复用之前会话的密钥等信息。
ssl3_accept接口注释
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;
//设置随机种子
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标识协商过程是否完成，刚开始是1，协商完成后设置为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: //初始化状态
case SSL_ST_OK | SSL_ST_ACCEPT:
//这是服务端程序，设为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;
}
//申请TLS缓冲区，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;
}
//初始化消息摘要验证
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状态解析客户端第一个请求数据包ClientHello
//获取客户端支持的密码套件和扩展字段等信息
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此状态是服务端响应ClientHello的消息
//根据客户端支持的密码套件和扩展字段信息，把最终确定后续要使用的密码套件和服务端选定的扩展字段发送给客户端
//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
//通过在服务端判断ClientHello中的SessionId是否存在，确定是否走会话恢复流程
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:
//这个状态是服务端把自己的证书发送给客户端，让客户端进行验证，确认服务端的身份
/* 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:
//此状态是服务端发送Server Key Exchange子消息，这个子消息是否发送，是根据不同密码套件有关，比如是DH、ECDHE密钥协商算法，则会发送此消息
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:
//此消息是服务端响应，说明服务端消息已发送完毕
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缓冲区
/*
* 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:
//此状态是读取客户端的证书信息，在需要验证客户端身份信息（双向认证）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:
//解析客户端的Client Key Exchange子消息，客户端在发送此消息时，客户端实际已经计算出后续加密通信需要的密钥等信息，此消息中包含preMaster key信息，服务端通过preMaster key计算主密钥等信息
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:
//此状态解析客户端发送的Change Cipher Spec和Finished子消息
//在Change Cipher Spec子消息过程中，服务端调用计算主密钥等接口，计算后续解密通信中使用的密钥信息
//Finished子消息中是客户端把从开始协商到发送此数据包为止的所有数据计算摘要值，并使用计算出的密钥进行加密后的数据，服务端使用解密的密钥解密数据，然后做摘要验证，防止协商数据中间被篡改
/*
* 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:
//此状态是服务端计算加密密钥
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:
//服务端发送Finished消息，供客户端进行摘要验证
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协商成功
/* 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);
}