SSL连接建立过程分析(1)

2024-07-05 09:36| 来源: 网络整理| 查看: 265

Https协议:SSL建立过程分析

web访问的两种方式:

http协议,我们一般情况下是通过它访问web,因为它不要求太多的安全机制,使用起来也简单,很多web站点也只支持这种方式下的访问.

https协议(Hypertext Transfer Protocol over Secure Socket Layer),对于安全性要求比较高的情况,可以通过它访问web,比如工商银行https://www.icbc.com.cn/icbc/(当然也可以通过http协议访问,只是没那么安全了).其安全基础是SSL协议.

SSL协议,当前版本为3.1(SSL3.1就是TLS1.0)。它已被广泛地用于Web浏览器与服务器之间的身份认证和加密数据传输.它位于TCP/IP协议与各种应用层协议之间，为数据通讯提供安全支持。SSL协议可分为两层： SSL记录协议（SSL Record Protocol）：它建立在可靠的传输协议（如TCP）之上，为高层协议提供数据封装、压缩、加密等基本功能的支持。 SSL握手协议（SSL Handshake Protocol）：它建立在SSL记录协议之上，用于在实际的数据传输开始前，通讯双方进行身份认证、协商加密算法、交换加密密钥等。

为了了解详细过程,可以通过网络抓包工具(Commview,Iris)分析https协议,SSL连接建立过程中,数据包交换情况.

数据包分析过程用到的几个图.

图,SSL Protocol Stack

图.SSL Record Format

图.SSL Record Protocol Payload

图.Handshake Protocol Action

它们来之.Cryptography and Network Security Principles and Practices, Fourth Edition-Chapter 17. Web Security-17.2. Secure Socket Layer and Transport Layer Security(密码学与网络安全原理与实践第四版,17章web安全,17.2节,SSL与TLS)具体细节参考本书.

下面跟踪握手过程(图Handshake Protocol Action)中,数据包的交换.

以为https方式访问www.sun.com为例子,一般大型公司,银行的web都支持https访问,如工商银行,sun,微软,IBM.

在IE中输入:https://wwww.sun.com,因为这是https协议,所以在实际访问web前,会建立SSL连接.

通过Commview抓包工具,过滤443端口(一般情况下,HTTPS使用端口443，HTTP使用端口80)可以得到数据包.

数据包大致情况和(图Handshake Protocol Action)对应.

SSL连接建立过程分析(1)

1. 应用程序接口 1.1 SSL初始化 SSL_CTX* InitSSL(int server, char *cert, char *key, char *pw) { SSL_CTX* ctx; SSL_METHOD *meth; int status; // 算法初始化 // 加载SSL错误信息 SSL_load_error_strings(); // 添加SSL的加密/HASH算法 SSLeay_add_ssl_algorithms(); // 服务器还是客户端 If(server) meth = SSLv23_server_method(); else meth = SSLv23_client_method(); // 建立新的SSL上下文 ctx = SSL_CTX_new (meth); if(!ctx) return NULL; // 设置证书文件的口令 SSL_CTX_set_default_passwd_cb_userdata(ctx, pw); //加载本地证书文件 status=SSL_CTX_use_certificate_file(ctx, cert, SSL_FILETYPE_ASN1); if (status error|=ERR_PACK(lib,0,0); ERRFN(err_set_item)(str); str++; } } 其中： #define ERR_PACK(l,f,r) (((((unsigned long)l)&0xffL)*0x1000000)| / ((((unsigned long)f)&0xfffL)*0x1000)| / ((((unsigned long)r)&0xfffL))) #define ERRFN(a) err_fns->cb_##a ERRFN(err_set_item)(str)的实际函数实现为： static ERR_STRING_DATA *int_err_set_item(ERR_STRING_DATA *d) { ERR_STRING_DATA *p; LHASH *hash; err_fns_check(); hash = ERRFN(err_get)(1); if (!hash) return NULL; CRYPTO_w_lock(CRYPTO_LOCK_ERR); p = (ERR_STRING_DATA *)lh_insert(hash, d); CRYPTO_w_unlock(CRYPTO_LOCK_ERR); return p; } Lh_insert()将错误信息插入到一个链表中如关于加密算法的错误信息： /* crypto/err/err.c */ static ERR_STRING_DATA ERR_str_functs[]= …… static ERR_STRING_DATA ERR_str_libraries[]= …… static ERR_STRING_DATA ERR_str_reasons[]= …… 2.2 SSLeay_add_ssl_algorithms() 这实际是个宏： #define OpenSSL_add_ssl_algorithms() SSL_library_init() #define SSLeay_add_ssl_algorithms() SSL_library_init() 实际函数为SSL_library_init()，函数比较简单，就是加载各种加密和HASH算法： /* ssl/ssl_algs.c */ int SSL_library_init(void) { #ifndef OPENSSL_NO_DES EVP_add_cipher(EVP_des_cbc()); EVP_add_cipher(EVP_des_ede3_cbc()); #endif #ifndef OPENSSL_NO_IDEA EVP_add_cipher(EVP_idea_cbc()); #endif #ifndef OPENSSL_NO_RC4 EVP_add_cipher(EVP_rc4()); #endif #ifndef OPENSSL_NO_RC2 EVP_add_cipher(EVP_rc2_cbc()); #endif #ifndef OPENSSL_NO_AES EVP_add_cipher(EVP_aes_128_cbc()); EVP_add_cipher(EVP_aes_192_cbc()); EVP_add_cipher(EVP_aes_256_cbc()); #endif #ifndef OPENSSL_NO_MD2 EVP_add_digest(EVP_md2()); #endif #ifndef OPENSSL_NO_MD5 EVP_add_digest(EVP_md5()); EVP_add_digest_alias(SN_md5,"ssl2-md5"); EVP_add_digest_alias(SN_md5,"ssl3-md5"); #endif #ifndef OPENSSL_NO_SHA EVP_add_digest(EVP_sha1()); /* RSA with sha1 */ EVP_add_digest_alias(SN_sha1,"ssl3-sha1"); EVP_add_digest_alias(SN_sha1WithRSAEncryption,SN_sha1WithRSA); #endif #if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_DSA) EVP_add_digest(EVP_dss1()); /* DSA with sha1 */ EVP_add_digest_alias(SN_dsaWithSHA1,SN_dsaWithSHA1_2); EVP_add_digest_alias(SN_dsaWithSHA1,"DSS1"); EVP_add_digest_alias(SN_dsaWithSHA1,"dss1"); #endif /* If you want support for phased out ciphers, add the following */ #if 0 EVP_add_digest(EVP_sha()); EVP_add_digest(EVP_dss()); #endif return(1); } 2.3 SSL23_server_method() 建立服务器端的方法库，这是个通用函数，可动态选择SSL协议。如果想固定协议，可以只用SSLv2_server_method(), SSLv3_server_method() 等函数来初始化，该函数返回一个SSL_METHOD结构： /* ssl/ssl.h */ /* Used to hold functions for SSLv2 or SSLv3/TLSv1 functions */ typedef struct ssl_method_st { int version; // 版本号 int (*ssl_new)(SSL *s); // 建立新SSL void (*ssl_clear)(SSL *s); // 清除SSL void (*ssl_free)(SSL *s); // 释放SSL int (*ssl_accept)(SSL *s); // 服务器接受SSL连接 int (*ssl_connect)(SSL *s); // 客户端的SSL连接 int (*ssl_read)(SSL *s,void *buf,int len); // SSL读 int (*ssl_peek)(SSL *s,void *buf,int len); // SSL查看数据 int (*ssl_write)(SSL *s,const void *buf,int len); // SSL写 int (*ssl_shutdown)(SSL *s); // SSL半关闭 int (*ssl_renegotiate)(SSL *s); // SSL重协商 int (*ssl_renegotiate_check)(SSL *s); // SSL重协商检查 long (*ssl_ctrl)(SSL *s,int cmd,long larg,void *parg); // SSL控制 long (*ssl_ctx_ctrl)(SSL_CTX *ctx,int cmd,long larg,void *parg); //SSL上下文控制 SSL_CIPHER *(*get_cipher_by_char)(const unsigned char *ptr); // 通过名称获取SSL的算法 int (*put_cipher_by_char)(const SSL_CIPHER *cipher,unsigned char *ptr); int (*ssl_pending)(SSL *s); int (*num_ciphers)(void); // 算法数 SSL_CIPHER *(*get_cipher)(unsigned ncipher); // 获取算法 struct ssl_method_st *(*get_ssl_method)(int version); long (*get_timeout)(void); // 超时 struct ssl3_enc_method *ssl3_enc; /* Extra SSLv3/TLS stuff */ // SSL3加密 int (*ssl_version)(); // SSL版本 long (*ssl_callback_ctrl)(SSL *s, int cb_id, void (*fp)()); // SSL控制回调函数 long (*ssl_ctx_callback_ctrl)(SSL_CTX *s, int cb_id, void (*fp)()); //SSL上下文控制回调函数 } SSL_METHOD; /* ssl/s23_srvr.c */ SSL_METHOD *SSLv23_server_method(void) { static int init=1; // 静态量，每个进程只初始化一次 static SSL_METHOD SSLv23_server_data; if (init) { CRYPTO_w_lock(CRYPTO_LOCK_SSL_METHOD); if (init) { // ssl23的基本方法结构 memcpy((char *)&SSLv23_server_data, (char *)sslv23_base_method(),sizeof(SSL_METHOD)); // 服务器,所以要定义accept方法 SSLv23_server_data.ssl_accept=ssl23_accept; // 根据SSL的版本设置SSL的具体方法函数 SSLv23_server_data.get_ssl_method=ssl23_get_server_method; init=0; } CRYPTO_w_unlock(CRYPTO_LOCK_SSL_METHOD); } return(&SSLv23_server_data); } static SSL_METHOD *ssl23_get_server_method(int ver) { #ifndef OPENSSL_NO_SSL2 if (ver == SSL2_VERSION) return(SSLv2_server_method()); #endif if (ver == SSL3_VERSION) return(SSLv3_server_method()); else if (ver == TLS1_VERSION) return(TLSv1_server_method()); // 随着TLS1.1(RFC4346)的推出，估计不久将出现TLSv1_1_server_method() else return(NULL); } // SSL23的方法基本数据定义 /* ssl/s23_lib.c */ SSL_METHOD *sslv23_base_method(void) { return(&SSLv23_data); } static SSL_METHOD SSLv23_data= { TLS1_VERSION, tls1_new, tls1_clear, tls1_free, ssl_undefined_function, ssl_undefined_function, ssl23_read, ssl23_peek, ssl23_write, ssl_undefined_function, ssl_undefined_function, ssl_ok, ssl3_ctrl, ssl3_ctx_ctrl, ssl23_get_cipher_by_char, ssl23_put_cipher_by_char, ssl_undefined_function, ssl23_num_ciphers, ssl23_get_cipher, ssl_bad_method, ssl23_default_timeout, &ssl3_undef_enc_method, ssl_undefined_function, ssl3_callback_ctrl, ssl3_ctx_callback_ctrl, }; 以SSL3的服务器方法函数为例，其他方法类似： /* ssl/s3_srvr.c */ SSL_METHOD *SSLv3_server_method(void) { static int init=1; static SSL_METHOD SSLv3_server_data; // 只初始化一次 if (init) { CRYPTO_w_lock(CRYPTO_LOCK_SSL_METHOD); if (init) { // ssl3的基本方法结构 memcpy((char *)&SSLv3_server_data,(char *)sslv3_base_method(), sizeof(SSL_METHOD)); // ssl3的接受方法 SSLv3_server_data.ssl_accept=ssl3_accept; // ssl3获取服务器的方法函数 SSLv3_server_data.get_ssl_method=ssl3_get_server_method; init=0; } CRYPTO_w_unlock(CRYPTO_LOCK_SSL_METHOD); } return(&SSLv3_server_data); } // SSL3的方法基本数据定义 /* ssl/s3_lib.c */ static SSL_METHOD SSLv3_data= { SSL3_VERSION, ssl3_new, ssl3_clear, ssl3_free, ssl_undefined_function, ssl_undefined_function, ssl3_read, ssl3_peek, ssl3_write, ssl3_shutdown, ssl3_renegotiate, ssl3_renegotiate_check, ssl3_ctrl, ssl3_ctx_ctrl, ssl3_get_cipher_by_char, ssl3_put_cipher_by_char, ssl3_pending, ssl3_num_ciphers, ssl3_get_cipher, ssl_bad_method, ssl3_default_timeout, &SSLv3_enc_data, ssl_undefined_function, ssl3_callback_ctrl, ssl3_ctx_callback_ctrl, }; 2.4 SSL23_client_method() 和服务器端的其实是相同的，只是不定义结构中的ssl_accept而是定义ssl_connnect： SSL_METHOD *SSLv23_client_method(void) { static int init=1; static SSL_METHOD SSLv23_client_data; if (init) { CRYPTO_w_lock(CRYPTO_LOCK_SSL_METHOD); if (init) { memcpy((char *)&SSLv23_client_data, (char *)sslv23_base_method(),sizeof(SSL_METHOD)); SSLv23_client_data.ssl_connect=ssl23_connect; SSLv23_client_data.get_ssl_method=ssl23_get_client_method; init=0; } CRYPTO_w_unlock(CRYPTO_LOCK_SSL_METHOD); } return(&SSLv23_client_data); } 2.5 SSL_CTX_new () 该函数根据SSL方法获取一个SSL上下文结构，该结构定义为： /* ssl/ssl.h */ struct ssl_ctx_st { SSL_METHOD *method; STACK_OF(SSL_CIPHER) *cipher_list; /* same as above but sorted for lookup */ STACK_OF(SSL_CIPHER) *cipher_list_by_id; struct x509_store_st /* X509_STORE */ *cert_store; struct lhash_st /* LHASH */ *sessions; /* a set of SSL_SESSIONs */ /* Most session-ids that will be cached, default is * SSL_SESSION_CACHE_MAX_SIZE_DEFAULT. 0 is unlimited. */ unsigned long session_cache_size; struct ssl_session_st *session_cache_head; struct ssl_session_st *session_cache_tail; /* This can have one of 2 values, ored together, * SSL_SESS_CACHE_CLIENT, * SSL_SESS_CACHE_SERVER, * Default is SSL_SESSION_CACHE_SERVER, which means only * SSL_accept which cache SSL_SESSIONS. */ int session_cache_mode; /* If timeout is not 0, it is the default timeout value set * when SSL_new() is called. This has been put in to make * life easier to set things up */ long session_timeout; /* If this callback is not null, it will be called each * time a session id is added to the cache. If this function * returns 1, it means that the callback will do a * SSL_SESSION_free() when it has finished using it. Otherwise, * on 0, it means the callback has finished with it. * If remove_session_cb is not null, it will be called when * a session-id is removed from the cache. After the call, * OpenSSL will SSL_SESSION_free() it. */ int (*new_session_cb)(struct ssl_st *ssl,SSL_SESSION *sess); void (*remove_session_cb)(struct ssl_ctx_st *ctx,SSL_SESSION *sess); SSL_SESSION *(*get_session_cb)(struct ssl_st *ssl, unsigned char *data,int len,int *copy); struct { int sess_connect; /* SSL new conn - started */ int sess_connect_renegotiate;/* SSL reneg - requested */ int sess_connect_good; /* SSL new conne/reneg - finished */ int sess_accept; /* SSL new accept - started */ int sess_accept_renegotiate;/* SSL reneg - requested */ int sess_accept_good; /* SSL accept/reneg - finished */ int sess_miss; /* session lookup misses */ int sess_timeout; /* reuse attempt on timeouted session */ int sess_cache_full; /* session removed due to full cache */ int sess_hit; /* session reuse actually done */ int sess_cb_hit; /* session-id that was not * in the cache was * passed back via the callback. This * indicates that the application is * supplying session-id's from other * processes - spooky :-) */ } stats; int references; /* if defined, these override the X509_verify_cert() calls */ int (*app_verify_callback)(X509_STORE_CTX *, void *); void *app_verify_arg; /* before OpenSSL 0.9.7, 'app_verify_arg' was ignored * ('app_verify_callback' was called with just one argument) */ /* Default password callback. */ pem_password_cb *default_passwd_callback; /* Default password callback user data. */ void *default_passwd_callback_userdata; /* get client cert callback */ int (*client_cert_cb)(SSL *ssl, X509 **x509, EVP_PKEY **pkey); CRYPTO_EX_DATA ex_data; const EVP_MD *rsa_md5;/* For SSLv2 - name is 'ssl2-md5' */ const EVP_MD *md5; /* For SSLv3/TLSv1 'ssl3-md5' */ const EVP_MD *sha1; /* For SSLv3/TLSv1 'ssl3->sha1' */ STACK_OF(X509) *extra_certs; STACK_OF(SSL_COMP) *comp_methods; /* stack of SSL_COMP, SSLv3/TLSv1 */ /* Default values used when no per-SSL value is defined follow */ void (*info_callback)(const SSL *ssl,int type,int val); /* used if SSL's info_callback is NULL */ /* what we put in client cert requests */ STACK_OF(X509_NAME) *client_CA; /* Default values to use in SSL structures follow (these are copied by SSL_new) */ unsigned long options; unsigned long mode; long max_cert_list; struct cert_st /* CERT */ *cert; int read_ahead; /* callback that allows applications to peek at protocol messages */ void (*msg_callback)(int write_p, int version, int content_type, const void *buf, size_t len, SSL *ssl, void *arg); void *msg_callback_arg; int verify_mode; int verify_depth; unsigned int sid_ctx_length; unsigned char sid_ctx[SSL_MAX_SID_CTX_LENGTH]; int (*default_verify_callback)(int ok,X509_STORE_CTX *ctx); /* called 'verify_callback' in the SSL */ /* Default generate session ID callback. */ GEN_SESSION_CB generate_session_id; int purpose; /* Purpose setting */ int trust; /* Trust setting */ int quiet_shutdown; }; typedef struct ssl_ctx_st SSL_CTX; /* ssl/ssl_lib.h */ SSL_CTX *SSL_CTX_new(SSL_METHOD *meth) { SSL_CTX *ret=NULL; if (meth == NULL) { SSLerr(SSL_F_SSL_CTX_NEW,SSL_R_NULL_SSL_METHOD_PASSED); return(NULL); } if (SSL_get_ex_data_X509_STORE_CTX_idx() < 0) { SSLerr(SSL_F_SSL_CTX_NEW,SSL_R_X509_VERIFICATION_SETUP_PROBLEMS); goto err; } // 分配上下文的内存空间 ret=(SSL_CTX *)OPENSSL_malloc(sizeof(SSL_CTX)); if (ret == NULL) goto err; memset(ret,0,sizeof(SSL_CTX)); // 初始化上下文的结构参数 ret->method=meth; ret->cert_store=NULL; ret->session_cache_mode=SSL_SESS_CACHE_SERVER; ret->session_cache_size=SSL_SESSION_CACHE_MAX_SIZE_DEFAULT; ret->session_cache_head=NULL; ret->session_cache_tail=NULL; /* We take the system default */ ret->session_timeout=meth->get_timeout(); ret->new_session_cb=0; ret->remove_session_cb=0; ret->get_session_cb=0; ret->generate_session_id=0; memset((char *)&ret->stats,0,sizeof(ret->stats)); ret->references=1; ret->quiet_shutdown=0; /* ret->cipher=NULL;*/ /* ret->s2->challenge=NULL; ret->master_key=NULL; ret->key_arg=NULL; ret->s2->conn_id=NULL; */ ret->info_callback=NULL; ret->app_verify_callback=0; ret->app_verify_arg=NULL; ret->max_cert_list=SSL_MAX_CERT_LIST_DEFAULT; ret->read_ahead=0; ret->msg_callback=0; ret->msg_callback_arg=NULL; ret->verify_mode=SSL_VERIFY_NONE; ret->verify_depth=-1; /* Don't impose a limit (but x509_lu.c does) */ ret->sid_ctx_length=0; ret->default_verify_callback=NULL; if ((ret->cert=ssl_cert_new()) == NULL) goto err; ret->default_passwd_callback=0; ret->default_passwd_callback_userdata=NULL; ret->client_cert_cb=0; ret->sessions=lh_new(LHASH_HASH_FN(SSL_SESSION_hash), LHASH_COMP_FN(SSL_SESSION_cmp)); if (ret->sessions == NULL) goto err; ret->cert_store=X509_STORE_new(); if (ret->cert_store == NULL) goto err; // 建立加密算法链表 ssl_create_cipher_list(ret->method, &ret->cipher_list,&ret->cipher_list_by_id, SSL_DEFAULT_CIPHER_LIST); if (ret->cipher_list == NULL || sk_SSL_CIPHER_num(ret->cipher_list) rsa_md5=EVP_get_digestbyname("ssl2-md5")) == NULL) { SSLerr(SSL_F_SSL_CTX_NEW,SSL_R_UNABLE_TO_LOAD_SSL2_MD5_ROUTINES); goto err2; } if ((ret->md5=EVP_get_digestbyname("ssl3-md5")) == NULL) { SSLerr(SSL_F_SSL_CTX_NEW,SSL_R_UNABLE_TO_LOAD_SSL3_MD5_ROUTINES); goto err2; } if ((ret->sha1=EVP_get_digestbyname("ssl3-sha1")) == NULL) { SSLerr(SSL_F_SSL_CTX_NEW,SSL_R_UNABLE_TO_LOAD_SSL3_SHA1_ROUTINES); goto err2; } if ((ret->client_CA=sk_X509_NAME_new_null()) == NULL) goto err; CRYPTO_new_ex_data(CRYPTO_EX_INDEX_SSL_CTX, ret, &ret->ex_data); ret->extra_certs=NULL; // 压缩算法 ret->comp_methods=SSL_COMP_get_compression_methods(); return(ret); err: SSLerr(SSL_F_SSL_CTX_NEW,ERR_R_MALLOC_FAILURE); err2: if (ret != NULL) SSL_CTX_free(ret); return(NULL); } ...待续...

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