文章目錄
1 引言
1.1 編寫目的
記錄本次開發SSL/TLS加解密功能中對OpenSSL的二次開發和設計細節
1.2 背景
目前開發產品是以旁路方式接入網絡，監控訪問客戶服務器的網絡流量，爲了支持對HTTPS數據的解析，需要開發解密TLS密文的功能。
通過實現對SSL/TLS協議的解析，加密數據的解密，可以提供明文的應用層數據爲後續的特徵檢測、樣本還原等功能提供支持。
1.3 參考資料
2 總體設計
2.1 需求概述
本次通過調研和選型，最終確定總體方案是基於OpenSSL 1.0.2u源碼進行二次開發和設計，最終支持旁路接入流量，對流量進行解密的功能。
2.2 總體設計圖
2.3 流程設計
爲了實現以上的方案，需要對當前的OpenSSL源碼進行如下一些定製化修改或重新設計：
- OpenSSL中已有的SSL/TLS協議解析功能，需要融入到現在項目代碼的協議解析框架中。
- OpenSSL原有設計是支持客戶端和服務器端的方式，如果旁路接入，客戶端和服務器的流量都會接入，需要使用統一的接口，對雙向的流量進行解析和解密。
- 因爲是旁路接入，在SSL/TLS協商過程中，對部分協商細節需要進行改寫或者裁剪。
- 目前進行的是單包解析，就是在SSL/TLS層之前已經完成對數據包的重組，在SSL/TLS層已經是按照最大傳輸單元大小的有序的數據包進行解析。因爲TLS層的最大加密數據塊大小是2^14字節，解密時必須按照加密塊的大小進行解密，所以在傳輸層一定會進行分包，因此，在解密時，需要把分包的數據進行重組，然後再解密。
下邊對以上幾個功能詳細介紹下具體的設計細節。
- 首先介紹下對旁路OpenSSL的總體設計：
在原有OpenSSL的設計是可以把OpenSSL分別部署到客戶端或者服務端，使用OpenSSL中提供的客戶端和服務端適配的接口，可以實現SSL/TLS建立連接、加解密等功能。
對於旁路OpenSSL來說，只存在解密的操作，當接入客戶端請求的數據時，旁路OpenSSL扮演服務端的角色，對客戶端的數據進行解析，獲取計算密鑰需要的參數，當接入服務端響應數據時，旁路OpenSSL扮演客戶端的角色，對服務端的數據進行解析，獲取計算密鑰需要的參數。
爲實現以上功能，目前基於對OpenSSL的服務端進行改寫，OpenSSL的服務端讀的操作流程不需要改動，可以把寫的操作流程改爲讀取服務端響應數據，從而實現雙向數據的解密功能。
2.4 功能描述
2.5 功能設計
2.5.1 SSL/TLS協議解析
在OpenSSL1.0.2u中已經有了對SSL/TLS協議的解析，本模塊主要是把這部分功能融入到當前項目的協議解析框架中。
在當前協議解析的框架中，TCP層會通過端口號進行判斷應用層協議類型，然後調用相應的應用層協議解析接口，並把應用層數據傳輸過去。
爲了解析SSL/TLS協議，先參考RFC規範，提取需要的字段信息，定義如下結構體，記錄相應的信息：
struct ssltls_private_area
{
u_int8_t *cache; //緩存, 爲了緩存分包的數據
int cache_used_len; //目前緩存的數據長度
u_int32_t ssl_ack_seq; //記錄數據包的ack號
u_int32_t ssl_seq; //記錄數據包的seq號
u_int8_t ssltls_flg;
struct TLSPlaintext tls_plaintext; //TLS記錄層協議頭部信息
struct ProtocolVersion temp_version; //TLS版本號
//client hello
struct ProtocolVersion client_version; //記錄客戶端請求數據包的TLS版本號
struct HSRandom client_random; //客戶端請求數據包的Random
u_int8_t client_SessionID_len; //客戶端請求數據包中的SessionID長度
u_int8_t client_SessionID[TLS_MAX_SESSION_ID_LEN]; //客戶端請求數據包中的SessionID
//server hello
struct ProtocolVersion server_version; //記錄服務端響應數據包的TLS版本號
struct HSRandom server_random; //服務端響應數據包的Random
u_int8_t server_SessionID_len; //服務端響應數據包中的SessionID長度
u_int8_t server_SessionID[TLS_MAX_SESSION_ID_LEN]; //客服務端響應數據包中的SessionID
u_int16_t server_CipherSuite; //加密套件
u_int8_t server_Compression; //壓縮方法
//server certificates
int server_CertificatesLen;
//ssl info
struct SSLSocketInfo ssl_info; //ssl連接信息
};
在SSL/TLS協議解析中，在解析SSL/TLS協商數據包時提取信息，填充以上結構體，關於TLS版本號、客戶端和服務端的Random、SessionID等信息。
以上信息都在SSL/TLS協商的前兩個數據包中，一個是客戶端的請求數據包ClientHello，一個是服務端的響應數據包ServerHello。
關於SSL/TLS的協商數據包的分析，參考文章TLS/SSL協議筆記
//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)
在提取以上信息之後，需要調用ssl3_accept接口，這個接口是OpenSSL提供的TLS建立連接的接口，其中會完成整個TLS協商過程，關於對密碼套件的解析，提取計算非對稱加密、對稱加密密鑰需要的一些參數等，但是在調用接口前，需要把TLS層的數據保存到TLS的緩衝區。對於客戶端請求數據包和服務端響應數據包，需要分別保存到讀緩衝區和寫緩衝區
//拷貝服務端響應數據到wbuff
int copy_skb_to_wbuff(int8_t *tdp_payload, int32_t tdp_payloadlen, SSL* s)；
//拷貝客戶端請求數據到rbuff
int copy_skb_to_rbuff(int8_t *tdp_payload, int32_t tdp_payloadlen, SSL* s)；
2.5.2 SSL/TLS建立連接
SSL/TLS建立連接的過程主要調用ssl3_accept接口函數，函數中會解析不同的協商數據包，通過切換到不同的狀態，直到最後狀態變爲SSL_ST_OK，表示SSL/TLS連接建立成功。
下邊是整個協商過程中，在ssl3_accept接口函數中切換的狀態：
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。
下邊是改寫後的ssl3_accept接口源碼，因爲函數源碼實在太長，這裏裁剪了一些主要流程中的代碼，只介紹SSL/TLS的主要握手流程中的狀態切換過程：
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
//在調用ssl3_accept接口前已對ssl狀態進行初始化，初始化狀態爲SSL_ST_ACCEPT|SSL_ST_BEFORE
// s->in_handshake的值標識整個SSL/TLS握手狀態是否完成，初始值爲0，在調用ssl3_accept接口前會執行s->in_handshake++，在整個SSL/TLS握手過程中其值爲1，如果SSL/TLS握手成功，會設置爲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;
}
//初始化摘要驗證
if (!ssl3_init_finished_mac(s)) {
ret = -1;
s->state = SSL_ST_ERR;
goto end;
}
//設置爲第一個狀態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數據包，第一個客戶端請求數據包
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;
//設置爲第二個狀態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; //因爲是單包解析，這裏返回，繼續接受下個數據包進行解析
#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數據包
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;
}
//從緩存中查詢SessionID，看是否存在，如果存在，會進入會話恢復流程
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)
//進入SessionID或SessionTicket會話恢復流程
s->state = SSL3_ST_SW_CHANGE_A;
#endif
else//進入下一個狀態
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:
//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
#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:
//此狀態解析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
#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:
//此消息標識服務端數據已經發送完畢
#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");
//標識客戶端或服務端的數據已發送完畢，進入下一個數據包
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:
//接收客戶端發送的數據，此數據中包含客戶端給的preMasterKey（爲服務端計算主密鑰使用），客戶端發送此消息時，客戶端已經計算出傳輸過程中需要的密鑰信息
#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
//服務端根據客戶端發送的參數信息，計算用於解密的主密鑰等
//解析客戶端發送的Finished子消息，驗證客戶端消息完整性，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:
//服務端計算加密所用的祕鑰信息
#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:
//此狀態，告訴客戶端密鑰已經計算完成，可以進行密文通信，並且 發送finished消息，讓客戶端驗證之前消息的完整性
//對於旁路的OpenSSL，不需要驗證消息完整性，可以在此狀態直接解密服務端響應的數據
#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:
//標識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建立連接的SessionID等信息保存起來，爲了下次會話恢復使用
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);
}
對於以上ssl3_accept接口中的不同狀態，下邊介紹幾個需要重點關注的狀態：
解析ServerHello擴展信息
在服務端響應數據包Serverhello中，包括了很多服務端選定的信息，比如：使用的密碼套件、支持的TLS擴展字段等。其中的擴展字段信息，會對後邊的狀態切換或者計算主密鑰有影響，解析擴展字段的接口
int ssl_parse_serverhello_tlsext(SSL *s, unsigned char **p, unsigned char *d, int n)
給出關於兩個擴展字段的介紹，其中擴展主密鑰字段會對計算主密鑰信息有影響：
上圖是擴展主密鑰字段在報文中的位置。
計算主密鑰的消息驗證
在SSL3_ST_SR_FINISHED_A狀態中，服務端首先按照前幾個狀態中客戶端與服務端協商的幾個參數，調用接口計算主密鑰，然後使用計算的密鑰，解密Finished消息，取出消息摘要，進行消息摘要驗證，防止協商消息篡改
int do_ssl3_get_finished(SSL *s, int a, int b)
2.5.3 TLS數據解密
通過判斷TLS記錄層中的類型，Content Type如果是23，則是加密後的應用層數據，如下是數據包格式：
其中包括密文數據的長度和TLS版本號等信息。這裏的的Length長度不包括頭部長度，並且最大長度按照協議規範是不超過2^14
協議解析的接口函數如下：
static u_int8_t application_data_protocol(Packet_t *packet, u_int8_t *data, int datalen)
函數調用之前的rbuff和wbuff，把響應包或請求包應用層數據放入OpenSSL緩衝區，最後調用ssl3_read接口對密文數據進行解密
int ssl3_read(SSL *s, void *buf, int len)
buf是解密後的明文，len是要解密的密文長度
2.5.4 TLS密文重組和解密
在應用層，最大的解密塊大小是2^14，遠遠大於傳輸層的最大最大傳輸單元，在下層會進行分包傳輸。
在解密之前需要把所有分包的密文數據重組之後才能調用ssl3_read接口進行解密。
在接收到分包後的第一個密文包是，裏邊有記錄層頭部標識密文數據的長度，這邊可以通過判斷頭部的數據長度和實際的數據長度，確定密文是否分包傳輸了。
如果分包後，需要把當前數據包的密文先保存到緩衝區：
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)
上邊的接口會把分包後的數據包都保存到struct ssltls_private_area *ssltls_data 結構體的cache中，並記錄緩存的長度cache_used_len。
實際上真正緩存的數據會大於2^14（16384），如果最大傳輸單元爲1460，則一個16384字節的應用層數據加密後，加上記錄層頭部的5個字節，共16389，需要分爲12個包傳輸，並且第12個包按說不會放滿，但是在實際傳輸時，第12個包會依然是1460字節大小，因爲裏邊可以包括下一個密文的數據。所以在緩存中實際上會放12個包纔會調用ssl3_read接口進行解密。解密後輸出解密數據的長度，然後從緩衝區中刪除解密的密文，把剩餘的下個數據繼續緩存起來
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;
//刪除已解密的密文長度
ssltls_data->cache_used_len = ssltls_data->cache_used_len - (ssltls_data->tls_plaintext.length + 5);
//把後邊未解密的密文拷貝到cache前邊
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);
}
}