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  

// 载入SSL错误信息

    SSL_load_error_strings();

// 加入�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);

//载入本地证书文件

    status=SSL_CTX_use_certificate_file(ctx, cert, SSL_FILETYPE_ASN1);

    if (status <= 0) {

        frintf(stderr, “Use cert fail, status=%d/n”, status);

        goto bad;

    }

// 载入私钥文件

    if (SSL_CTX_use_PrivateKey_file(ctx, key, SSL_FILETYPE_PEM) <= 0) {

        fprintf(stderr, “Use private key fail/n”);

        goto bad;

    }

// 检查证书和私钥是否匹配

    if (!SSL_CTX_check_private_key(ctx)) {

        fprintf(“Private key does not match the certificate public key/n”);

        goto bad;

    }

    fprintf(“Cert and key OK/n”);

    return ctx;

bad:

    SSL_CTX_free (ctx);

    return NULL;

}

1.2 建立SSL新连接

server：

// 建立SSL

ssl = SSL_new (ctx);

// 将SSL与TCP socket连接

SSL_set_fd (ssl, sd);

//接受新SSL连接

err = SSL_accept (ssl);

client：

// 建立SSL

ssl = SSL_new (ctx);

// 将SSL与TCP socket连接

SSL_set_fd (ssl, sd);

// SSL连接

err = SSL_connect (ssl);

server的SSL_accept()和client的SSL_connect()函数共同完毕SSL的握手协商过程。

 

1.3 SSL通信

和普通的read()/write()调用一样，用以下的函数完毕数据的SSL发送和接收，函数输入数据是明文，SSL自己主动将数据封装进SSL中：

读/接收：SSL_read()

写/发送：SSL_write()

1.4 SSL释放

SSL释放非常easy：

 SSL_free (ssl);

 

2. SSL实现分析

下面SSL源码取自openssl-0.9.7b。

2.1 SSL_load_error_strings

该函数载入错误字符串信息：

void SSL_load_error_strings(void)

 {

#ifndef OPENSSL_NO_ERR

 ERR_load_crypto_strings();

 ERR_load_SSL_strings();

#endif

 }

最后将会进入函数：

static void err_load_strings(int lib, ERR_STRING_DATA *str)

 {

 while (str->error)

  {

  str->error|=ERR_PACK(lib,0,0);

  ERRFN(err_set_item)(str);

  str++;

  }

 }

当中：

#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()，函数比較简单，就是载入各种加密和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。假设想固定协议，能够仅仅用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); // server接受SSL连接

 int (*ssl_connect)(SSL *s); // client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版本号

 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，每一个进程仅仅初始化一次

 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;

// 依据SSL的版本号设置SSL的详细方法函数

   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，预计不久将出现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server方法函数为例，其它方法相似：

/* ssl/s3_srvr.c */

SSL_METHOD *SSLv3_server_method(void)

 {

 static int init=1;

 static SSL_METHOD SSLv3_server_data;

// 仅仅初始化一次

 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server端的事实上是同样的，仅仅是不定义结构中的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 ()

该函数依据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參数

 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) <= 0)

  {

  SSLerr(SSL_F_SSL_CTX_NEW,SSL_R_LIBRARY_HAS_NO_CIPHERS);

  goto err2;

  }

 

// 定义上下文结构中HASH算法

 if ((ret->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…