文章目录
1 引言
1.1 编写目的
记录本次开发SSL/TLS加解密功能中对OpenSSL的二次开发和设计细节
1.2 背景
目前开发产品是以旁路方式接入网络，监控访问客户服务器的网络流量，为了支持对HTTPS数据的解析，需要开发解密TLS密文的功能。
通过实现对SSL/TLS协议的解析，加密数据的解密，可以提供明文的应用层数据为后续的特征检测、样本还原等功能提供支持。
1.3 参考资料
2 总体设计
2.1 需求概述
本次通过调研和选型，最终确定总体方案是基于OpenSSL 1.0.2u源码进行二次开发和设计，最终支持旁路接入流量，对流量进行解密的功能。
2.2 总体设计图
2.3 流程设计
为了实现以上的方案，需要对当前的OpenSSL源码进行如下一些定制化修改或重新设计：
- OpenSSL中已有的SSL/TLS协议解析功能，需要融入到现在项目代码的协议解析框架中。
- OpenSSL原有设计是支持客户端和服务器端的方式，如果旁路接入，客户端和服务器的流量都会接入，需要使用统一的接口，对双向的流量进行解析和解密。
- 因为是旁路接入，在SSL/TLS协商过程中，对部分协商细节需要进行改写或者裁剪。
- 目前进行的是单包解析，就是在SSL/TLS层之前已经完成对数据包的重组，在SSL/TLS层已经是按照最大传输单元大小的有序的数据包进行解析。因为TLS层的最大加密数据块大小是2^14字节，解密时必须按照加密块的大小进行解密，所以在传输层一定会进行分包，因此，在解密时，需要把分包的数据进行重组，然后再解密。
下边对以上几个功能详细介绍下具体的设计细节。
- 首先介绍下对旁路OpenSSL的总体设计：
在原有OpenSSL的设计是可以把OpenSSL分别部署到客户端或者服务端，使用OpenSSL中提供的客户端和服务端适配的接口，可以实现SSL/TLS建立连接、加解密等功能。
对于旁路OpenSSL来说，只存在解密的操作，当接入客户端请求的数据时，旁路OpenSSL扮演服务端的角色，对客户端的数据进行解析，获取计算密钥需要的参数，当接入服务端响应数据时，旁路OpenSSL扮演客户端的角色，对服务端的数据进行解析，获取计算密钥需要的参数。
为实现以上功能，目前基于对OpenSSL的服务端进行改写，OpenSSL的服务端读的操作流程不需要改动，可以把写的操作流程改为读取服务端响应数据，从而实现双向数据的解密功能。
2.4 功能描述
2.5 功能设计
2.5.1 SSL/TLS协议解析
在OpenSSL1.0.2u中已经有了对SSL/TLS协议的解析，本模块主要是把这部分功能融入到当前项目的协议解析框架中。
在当前协议解析的框架中，TCP层会通过端口号进行判断应用层协议类型，然后调用相应的应用层协议解析接口，并把应用层数据传输过去。
为了解析SSL/TLS协议，先参考RFC规范，提取需要的字段信息，定义如下结构体，记录相应的信息：
struct ssltls_private_area
{
u_int8_t *cache; //缓存, 为了缓存分包的数据
int cache_used_len; //目前缓存的数据长度
u_int32_t ssl_ack_seq; //记录数据包的ack号
u_int32_t ssl_seq; //记录数据包的seq号
u_int8_t ssltls_flg;
struct TLSPlaintext tls_plaintext; //TLS记录层协议头部信息
struct ProtocolVersion temp_version; //TLS版本号
//client hello
struct ProtocolVersion client_version; //记录客户端请求数据包的TLS版本号
struct HSRandom client_random; //客户端请求数据包的Random
u_int8_t client_SessionID_len; //客户端请求数据包中的SessionID长度
u_int8_t client_SessionID[TLS_MAX_SESSION_ID_LEN]; //客户端请求数据包中的SessionID
//server hello
struct ProtocolVersion server_version; //记录服务端响应数据包的TLS版本号
struct HSRandom server_random; //服务端响应数据包的Random
u_int8_t server_SessionID_len; //服务端响应数据包中的SessionID长度
u_int8_t server_SessionID[TLS_MAX_SESSION_ID_LEN]; //客服务端响应数据包中的SessionID
u_int16_t server_CipherSuite; //加密套件
u_int8_t server_Compression; //压缩方法
//server certificates
int server_CertificatesLen;
//ssl info
struct SSLSocketInfo ssl_info; //ssl连接信息
};
在SSL/TLS协议解析中，在解析SSL/TLS协商数据包时提取信息，填充以上结构体，关于TLS版本号、客户端和服务端的Random、SessionID等信息。
以上信息都在SSL/TLS协商的前两个数据包中，一个是客户端的请求数据包ClientHello，一个是服务端的响应数据包ServerHello。
关于SSL/TLS的协商数据包的分析，参考文章TLS/SSL协议笔记
//解析ClientHello子消息
static u_int8_t handshake_client_hello(Packet_t *packet, u_int8_t *data, int datalen)
//解析ServerHello子消息
static u_int8_t handshake_server_hello(Packet_t *packet, u_int8_t *data, int datalen)
在提取以上信息之后，需要调用ssl3_accept接口，这个接口是OpenSSL提供的TLS建立连接的接口，其中会完成整个TLS协商过程，关于对密码套件的解析，提取计算非对称加密、对称加密密钥需要的一些参数等，但是在调用接口前，需要把TLS层的数据保存到TLS的缓冲区。对于客户端请求数据包和服务端响应数据包，需要分别保存到读缓冲区和写缓冲区
//拷贝服务端响应数据到wbuff
int copy_skb_to_wbuff(int8_t *tdp_payload, int32_t tdp_payloadlen, SSL* s)；
//拷贝客户端请求数据到rbuff
int copy_skb_to_rbuff(int8_t *tdp_payload, int32_t tdp_payloadlen, SSL* s)；
2.5.2 SSL/TLS建立连接
SSL/TLS建立连接的过程主要调用ssl3_accept接口函数，函数中会解析不同的协商数据包，通过切换到不同的状态，直到最后状态变为SSL_ST_OK，表示SSL/TLS连接建立成功。
下边是整个协商过程中，在ssl3_accept接口函数中切换的状态：
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。
下边是改写后的ssl3_accept接口源码，因为函数源码实在太长，这里裁剪了一些主要流程中的代码，只介绍SSL/TLS的主要握手流程中的状态切换过程：
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;
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;
#ifndef MODIFY_BY_VENUS_FLAG
char pbuf[SSL3_RT_MAX_PLAIN_LENGTH + 1460] = {0};
int num = 0;
int i = 0;
int total_num = get_ssl3_ciphers_num();
#endif
#ifdef MODIFY_BY_VENUS_FLAG
//在调用ssl3_accept接口前已对ssl状态进行初始化，初始化状态为SSL_ST_ACCEPT|SSL_ST_BEFORE
// s->in_handshake的值标识整个SSL/TLS握手状态是否完成，初始值为0，在调用ssl3_accept接口前会执行s->in_handshake++，在整个SSL/TLS握手过程中其值为1，如果SSL/TLS握手成功，会设置为0
/* init things to blank */
s->in_handshake++;
if (!SSL_in_init(s) || SSL_in_before(s))
SSL_clear(s);
#endif
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:
case SSL_ST_OK | SSL_ST_ACCEPT:
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;
}
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;
}
//初始化摘要验证
if (!ssl3_init_finished_mac(s)) {
ret = -1;
s->state = SSL_ST_ERR;
goto end;
}
//设置为第一个状态SSL3_ST_SR_CLNT_HELLO_A
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:
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SR_CLNT_HELLO_A\n");
#endif
s->shutdown = 0;
//解析ClientHello数据包，第一个客户端请求数据包
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;
//设置为第二个状态SSL3_ST_SW_SRVR_HELLO_A
s->state = SSL3_ST_SW_SRVR_HELLO_A;
s->init_num = 0;
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SR_CLNT_HELLO_A end\n");
return 1; //因为是单包解析，这里返回，继续接受下个数据包进行解析
#else
break;
#endif
case SSL3_ST_SW_SRVR_HELLO_A:
case SSL3_ST_SW_SRVR_HELLO_B:
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SW_SRVR_HELLO_A\n");
printf("ssl3_get_server_hello start\n");
//解析ServerHello数据包
ret = ssl3_get_server_hello(s);
{
char estring[500] = {0};
unsigned long err;
err = ERR_get_error();
if(err != 0){
ERR_error_string(err, estring);
printf("%s():%d [%s]\n", __FUNCTION__, __LINE__, estring);
const char *file = NULL;
int line;
ERR_get_error_line(&file, &line);
if(NULL != file)
printf("%s():%d [err file :%s , err line : %d]\n",__FUNCTION__, __LINE__, file, line);
}
}
if (ret <= 0)
goto end;
printf("ssl3_get_server_hello end\n");
if(s->tdp_payloadlen < 77){
//s->flag = 2;
printf(" SSL3_ST_SW_SRVR_HELLO_A invalid ");
return 0;
}
if((*(char*)(s->tdp_payload)) != 22 ||(*(char*)(s->tdp_payload + 5)) != 2){
//s->flag = 2;
printf(" SSL3_ST_SW_SRVR_HELLO_A invalid .");
return 0;
}
//从缓存中查询SessionID，看是否存在，如果存在，会进入会话恢复流程
get_old_session(s);
for(i = 0; i < total_num; i++) {
//printf("i =%d s->cipher_suite_num = %d, cipherid = %ld\n", i, s->cipher_suite_num, (ssl3_ciphers[i].id & 0xFF));
if(s->cipher_suite_num == (ssl3_ciphers[i].id & 0xFFFF)){
s->s3->tmp.new_cipher = s->session->cipher = &ssl3_ciphers[i];
s->session->cipher_id = s->session->cipher->id;
break;
}
}
if(i >= total_num) {
printf("s->cipher_suite_num = %d, find cipher suite fail!\r\n", s->cipher_suite_num);
ret = -1;
goto end;
}
printf("s->hit = %d\n", s->hit);
#else
ret = ssl3_send_server_hello(s);
if (ret <= 0)
goto end;
#endif
#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
if (s->hit)
//进入SessionID或SessionTicket会话恢复流程
s->state = SSL3_ST_SW_CHANGE_A;
#endif
else//进入下一个状态
s->state = SSL3_ST_SW_CERT_A;
s->init_num = 0;
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SW_SRVR_HELLO_A end\n");
#endif
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
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SW_CERT_A\n");
#endif
/* 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;
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SW_CERT_A end\n");
#endif
break;
case SSL3_ST_SW_KEY_EXCH_A:
case SSL3_ST_SW_KEY_EXCH_B:
//此状态解析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
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SW_KEY_EXCH_A\n");
#endif
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;
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SW_KEY_EXCH_A end\n");
#endif
break;
case SSL3_ST_SW_CERT_REQ_A:
case SSL3_ST_SW_CERT_REQ_B:
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SW_CERT_REQ_A\n");
#endif
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;
}
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SW_CERT_REQ_A end\n");
#endif
break;
case SSL3_ST_SW_SRVR_DONE_A:
case SSL3_ST_SW_SRVR_DONE_B:
//此消息标识服务端数据已经发送完毕
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SW_SRVR_DONE_A\n");
#endif
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;
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SW_SRVR_DONE_A end\n");
#endif
break;
case SSL3_ST_SW_FLUSH:
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SW_FLUSH\n");
#else
/*
* 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;
#endif
s->state = s->s3->tmp.next_state;
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SW_FLUSH end\n");
//标识客户端或服务端的数据已发送完毕，进入下一个数据包
if(s->state != SSL_ST_OK){
return 1;
}
#endif
break;
case SSL3_ST_SR_CERT_A:
case SSL3_ST_SR_CERT_B:
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SR_CERT_A\n");
#endif
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;
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SR_CERT_A end\n");
#endif
break;
case SSL3_ST_SR_KEY_EXCH_A:
case SSL3_ST_SR_KEY_EXCH_B:
//接收客户端发送的数据，此数据中包含客户端给的preMasterKey（为服务端计算主密钥使用），客户端发送此消息时，客户端已经计算出传输过程中需要的密钥信息
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SR_KEY_EXCH_A\n");
#endif
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;
}
}
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SR_KEY_EXCH_A end\n");
#endif
break;
case SSL3_ST_SR_CERT_VRFY_A:
case SSL3_ST_SR_CERT_VRFY_B:
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SR_CERT_VRFY_A\n");
#endif
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;
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SR_CERT_VRFY_A end\n");
#endif
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:
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SR_FINISHED_A\n");
#endif
/*
* 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;
#ifndef MODIFY_BY_VENUS_FLAG
//服务端根据客户端发送的参数信息，计算用于解密的主密钥等
//解析客户端发送的Finished子消息，验证客户端消息完整性，防止消息被篡改
ret = do_ssl3_get_finished(s, SSL3_ST_SR_FINISHED_A, SSL3_ST_SR_FINISHED_B);
{
char estring[500] = {0};
unsigned long err;
err = ERR_get_error();
if(err != 0){
ERR_error_string(err, estring);
printf("%s():%d [%s]\n", __FUNCTION__, __LINE__, estring);
const char *file = NULL;
int line;
ERR_get_error_line(&file, &line);
if(NULL != file)
printf("%s():%d [err file :%s , err line : %d]\n",__FUNCTION__, __LINE__, file, line);
}
}
#else
ret = ssl3_get_finished(s, SSL3_ST_SR_FINISHED_A,
SSL3_ST_SR_FINISHED_B);
#endif
if (ret <= 0){
#ifndef MODIFY_BY_VENUS_FLAG
if(-2 != ret) {
goto end;
}
#else
goto end;
#endif
}
#ifndef MODIFY_BY_VENUS_FLAG
s->init_num = 0;
#endif
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;
#ifndef MODIFY_BY_VENUS_FLAG
return 1;
#endif
}
#endif
else{
s->state = SSL3_ST_SW_CHANGE_A;
#ifndef MODIFY_BY_VENUS_FLAG
return 1;
#endif
}
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SR_FINISHED_A end\n");
#else
s->init_num = 0;
#endif
break;
#ifndef OPENSSL_NO_TLSEXT
case SSL3_ST_SW_SESSION_TICKET_A:
case SSL3_ST_SW_SESSION_TICKET_B:
//解析SessionTicket子消息
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SW_SESSION_TICKET_A start\n");
#endif
#ifndef MODIFY_BY_VENUS_FLAG
ret = ssl3_get_new_session_ticket(s);
{
char estring[500] = {0};
unsigned long err;
err = ERR_get_error();
if(err != 0){
ERR_error_string(err, estring);
printf("%s():%d [%s]\n", __FUNCTION__, __LINE__, estring);
const char *file = NULL;
int line;
ERR_get_error_line(&file, &line);
if(NULL != file)
printf("%s():%d [err file :%s , err line : %d]\n",__FUNCTION__, __LINE__, file, line);
}
}
#else
ret = ssl3_send_newsession_ticket(s);
#endif
if (ret <= 0)
goto end;
s->state = SSL3_ST_SW_CHANGE_A;
s->init_num = 0;
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SW_SESSION_TICKET_A start\n");
#endif
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:
//服务端计算加密所用的秘钥信息
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SW_CHANGE_A\n");
#endif
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;
}
#ifndef MODIFY_BY_VENUS_FLAG
ret = do_ssl3_send_change_cipher_spec(s, SSL3_ST_SW_CHANGE_A, SSL3_ST_SW_CHANGE_B);
#else
ret = ssl3_send_change_cipher_spec(s, SSL3_ST_SW_CHANGE_A, SSL3_ST_SW_CHANGE_B);
#endif
if (ret <= 0)
goto end;
s->state = SSL3_ST_SW_FINISHED_A;
s->init_num = 0;
#ifndef MODIFY_BY_VENUS_FLAG
if (!s->method->ssl3_enc->change_cipher_state(s, SSL3_CHANGE_CIPHER_CLIENT_READ))
#else
if (!s->method->ssl3_enc->change_cipher_state(s, SSL3_CHANGE_CIPHER_SERVER_WRITE))
#endif
{
ret = -1;
s->state = SSL_ST_ERR;
goto end;
}
#ifndef MODIFY_BY_VENUS_FLAG
{
char estring[500] = {0};
unsigned long err;
err = ERR_get_error();
if(err != 0){
ERR_error_string(err, estring);
printf("%s():%d [%s]\n", __FUNCTION__, __LINE__, estring);
const char *file = NULL;
int line;
ERR_get_error_line(&file, &line);
if(NULL != file)
printf("%s():%d [err file :%s , err line : %d]\n",__FUNCTION__, __LINE__, file, line);
}
}
printf("SSL3_ST_SW_CHANGE_A end\n");
#endif
break;
case SSL3_ST_SW_FINISHED_A:
case SSL3_ST_SW_FINISHED_B:
//此状态，告诉客户端密钥已经计算完成，可以进行密文通信，并且 发送finished消息，让客户端验证之前消息的完整性
//对于旁路的OpenSSL，不需要验证消息完整性，可以在此状态直接解密服务端响应的数据
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SW_FINISHED_A tdp_payloadlen = %d\n", s->tdp_payloadlen);
printf("s->s3->wbuf.offset = %d, s->s3->wbuf.left = %d s->s3->wbuf.len = %zu\n",
s->s3->wbuf.offset, s->s3->wbuf.left, s->s3->wbuf.len);
num = *(char*)(s->tdp_payload);
if(num != 22 && num != 20){
printf("SSL3_ST_SW_FINISHED_A return -1, num = %d\n", *(char*)(s->tdp_payload));
return -1;
}
//if (!s->hit)
num = 6;
// num = ((*(char *)(s->s3->wbuf.buf + 3))<<8) + (*(char *)(s->s3->wbuf.buf + 4)) + 11;
if(s->s3->wbuf.left <= num){
return 0;
}
s->s3->wbuf.offset += num;
num = s->s3->wbuf.len - s->res_packet_length;
printf("before SL3_ST_SW_FLUSH begin num = %d\n", num);
ssl3_read(s, pbuf, num);
s->s3->wbuf.left = 0;
s->s3->wbuf.offset = 0;
(&(s->s3->wrec))->length = 0;
#else
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;
#endif
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;
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL3_ST_SW_FINISHED_A end\n");
#endif
break;
case SSL_ST_OK:
//标识SSL/TLS握手成功
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL_ST_OK\n");
#endif
/* 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;
//把本次SSL/TLS建立连接的SessionID等信息保存起来，为了下次会话恢复使用
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;
#ifndef MODIFY_BY_VENUS_FLAG
printf("SSL_ST_OK end\n");
#endif
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;
}
#ifndef MODIFY_BY_VENUS_FLAG
return 1;
#endif
end:
/* BIO_flush(s->wbio); */
#ifndef MODIFY_BY_VENUS_FLAG
printf("goto end\n");
#endif
s->in_handshake--;
if (cb != NULL)
cb(s, SSL_CB_ACCEPT_EXIT, ret);
return (ret);
}
对于以上ssl3_accept接口中的不同状态，下边介绍几个需要重点关注的状态：
解析ServerHello扩展信息
在服务端响应数据包Serverhello中，包括了很多服务端选定的信息，比如：使用的密码套件、支持的TLS扩展字段等。其中的扩展字段信息，会对后边的状态切换或者计算主密钥有影响，解析扩展字段的接口
int ssl_parse_serverhello_tlsext(SSL *s, unsigned char **p, unsigned char *d, int n)
给出关于两个扩展字段的介绍，其中扩展主密钥字段会对计算主密钥信息有影响：
上图是扩展主密钥字段在报文中的位置。
计算主密钥的消息验证
在SSL3_ST_SR_FINISHED_A状态中，服务端首先按照前几个状态中客户端与服务端协商的几个参数，调用接口计算主密钥，然后使用计算的密钥，解密Finished消息，取出消息摘要，进行消息摘要验证，防止协商消息篡改
int do_ssl3_get_finished(SSL *s, int a, int b)
2.5.3 TLS数据解密
通过判断TLS记录层中的类型，Content Type如果是23，则是加密后的应用层数据，如下是数据包格式：
其中包括密文数据的长度和TLS版本号等信息。这里的的Length长度不包括头部长度，并且最大长度按照协议规范是不超过2^14
协议解析的接口函数如下：
static u_int8_t application_data_protocol(Packet_t *packet, u_int8_t *data, int datalen)
函数调用之前的rbuff和wbuff，把响应包或请求包应用层数据放入OpenSSL缓冲区，最后调用ssl3_read接口对密文数据进行解密
int ssl3_read(SSL *s, void *buf, int len)
buf是解密后的明文，len是要解密的密文长度
2.5.4 TLS密文重组和解密
在应用层，最大的解密块大小是2^14，远远大于传输层的最大最大传输单元，在下层会进行分包传输。
在解密之前需要把所有分包的密文数据重组之后才能调用ssl3_read接口进行解密。
在接收到分包后的第一个密文包是，里边有记录层头部标识密文数据的长度，这边可以通过判断头部的数据长度和实际的数据长度，确定密文是否分包传输了。
如果分包后，需要把当前数据包的密文先保存到缓冲区：
int ssltls_cache_store(struct ssltls_private_area *ssltls_data, unsigned char *data, int datalen)
int ssltls_cache_prepare(struct ssltls_private_area *ssltls_data, unsigned char *data, int datalen, unsigned char **dest, int *destlen)
上边的接口会把分包后的数据包都保存到struct ssltls_private_area *ssltls_data 结构体的cache中，并记录缓存的长度cache_used_len。
实际上真正缓存的数据会大于2^14（16384），如果最大传输单元为1460，则一个16384字节的应用层数据加密后，加上记录层头部的5个字节，共16389，需要分为12个包传输，并且第12个包按说不会放满，但是在实际传输时，第12个包会依然是1460字节大小，因为里边可以包括下一个密文的数据。所以在缓存中实际上会放12个包才会调用ssl3_read接口进行解密。解密后输出解密数据的长度，然后从缓冲区中删除解密的密文，把剩余的下个数据继续缓存起来
if(ssltls_data->cache_used_len != 0){
packet->tcp_ack_seq = ssltls_data->ssl_ack_seq;
packet->tcp_seq = ssltls_data->ssl_seq;
if((ssltls_data->tls_plaintext.length + 5) >= ssltls_data->cache_used_len)
ssltls_cache_reset(ssltls_data);
else{
int cache_len = ssltls_data->cache_used_len;
u_int8_t *pCache = ssltls_data->cache;
//删除已解密的密文长度
ssltls_data->cache_used_len = ssltls_data->cache_used_len - (ssltls_data->tls_plaintext.length + 5);
//把后边未解密的密文拷贝到cache前边
memcpy(pCache, ssltls_data->cache + ssltls_data->tls_plaintext.length + 5, ssltls_data->cache_used_len);
memset(pCache + ssltls_data->cache_used_len, 0, cache_len - ssltls_data->cache_used_len);
}
}