zhaozg's blog: OpenSSL协议实现分析

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 <= 0) {
frintf(stderr, "Use cert fail, status=%dn", status);
goto bad;
}
// 加载私钥文件
if (SSL_CTX_use_PrivateKey_file(ctx, key, SSL_FILETYPE_PEM) <= 0) {
fprintf(stderr, "Use private key failn");
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 keyn");
goto bad;
}
fprintf("Cert and key OKn");
return ctx;
bad:
SSL_CTX_free (ctx);
return NULL;
}

1.2 建立SSL新连接

服务器：

// 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);

客户端：
// 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);

服务器的SSL_accept()和客户端的SSL_connect()函数共同完成SSL的握手协商过程。

1.3 SSL通信

和普通的read()/write()调用一样，用下面的函数完成数据的SSL发送和接收，函数输入数据是明文，SSL自动将数据封装进SSL中：

读/接收：SSL_read()
写/发送：SSL_write()

1.4 SSL释放

SSL释放很简单：

SSL_free (ssl);

2. SSL实现分析

以下SSL源代码取自openssl-0.9.7b。

2.1 SSL_load_error_strings

该函数加载错误字符串信息：

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++;
}
}
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) <= 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);
}
2.6 SSL_CTX_set_default_passwd_cb[_userdata]()

这个函数比较简单，就是设置SSL要加载的证书的口令，如果不设置的话加载证书时会出提示符要求输入口令的，这样在程序中使用就比较麻烦，该函数就是预先将口令保存，在读证书时自动使用。

实现该功能的有两个函数SSL_CTX_set_default_passwd_cb()和SSL_CTX_set_default_passwd_cb_userdata()，前者是定义一个口令回调函数，要获取口令时口令由该函数获取；后者是直接将口令设置好。

/* ssl/ssl_lib.c */
void SSL_CTX_set_default_passwd_cb(SSL_CTX *ctx, pem_password_cb *cb)
{
ctx->default_passwd_callback=cb;
}

void SSL_CTX_set_default_passwd_cb_userdata(SSL_CTX *ctx,void *u)
{
ctx->default_passwd_callback_userdata=u;
}

举例：

static int
pass_cb(char *buf, int len, int verify, void *password)
{
snprintf(buf,len, "123456");
return strlen(buf);
}
SSL_CTX_set_default_passwd_cb(ctx, pass_cb);

等价于：

SSL_CTX_set_default_passwd_cb_userdata(ctx, "123456");

2.7 SSL_CTX_use_certificate_file()

该函数读取证书文件，证书文件通常都进行了加密保护。普及一下，证书文件里肯定是有公钥的，一般没私钥，某些情况会把私钥也包含进去，但那样作太不安全了，原则上私钥是永远不会给别人看到的，就算是进行了加密保护。

/* ssl/ssl_rsa.c */
int SSL_use_certificate_file(SSL *ssl, const char *file, int type)
{
int j;
BIO *in;
int ret=0;
X509 *x=NULL;

in=BIO_new(BIO_s_file_internal());
if (in == NULL)
{
SSLerr(SSL_F_SSL_USE_CERTIFICATE_FILE,ERR_R_BUF_LIB);
goto end;
}

if (BIO_read_filename(in,file) <= 0)
{
SSLerr(SSL_F_SSL_USE_CERTIFICATE_FILE,ERR_R_SYS_LIB);
goto end;
}

// 根据证书是PEM还是DER分别读取进行解码
// DER是二进制格式，PEM则是对DER用BASE64编码的后的文本格式
if (type == SSL_FILETYPE_ASN1)
{
j=ERR_R_ASN1_LIB;
x=d2i_X509_bio(in,NULL);
}
else if (type == SSL_FILETYPE_PEM)
{
j=ERR_R_PEM_LIB;
x=PEM_read_bio_X509(in,NULL,ssl->ctx->default_passwd_callback,ssl->ctx->default_passwd_callback_userdata);
}
else
{
SSLerr(SSL_F_SSL_USE_CERTIFICATE_FILE,SSL_R_BAD_SSL_FILETYPE);
goto end;
}

if (x == NULL)
{
SSLerr(SSL_F_SSL_USE_CERTIFICATE_FILE,j);
goto end;
}
// 加载解码后后的证书
ret=SSL_use_certificate(ssl,x);
end:
if (x != NULL) X509_free(x);
if (in != NULL) BIO_free(in);
return(ret);
}

2.8 SSL_CTX_use_PrivateKey_file()

该函数加载私钥文件，和SSL_CTX_use_certificate_file()是类似的，因为RSA算法的公钥私钥是对称的，刚生成密钥时谁作私钥都行。

SSL_CTX_use_PrivateKey_file()只加载PEM格式私钥，DER格式的用函数SSL_use_PrivateKey_ASN1()加载。

/* ssl/ssl_rsa.c */
int SSL_use_PrivateKey_file(SSL *ssl, const char *file, int type)
{
int j,ret=0;
BIO *in;
EVP_PKEY *pkey=NULL;

in=BIO_new(BIO_s_file_internal());
if (in == NULL)
{
SSLerr(SSL_F_SSL_USE_PRIVATEKEY_FILE,ERR_R_BUF_LIB);
goto end;
}

if (BIO_read_filename(in,file) <= 0)
{
SSLerr(SSL_F_SSL_USE_PRIVATEKEY_FILE,ERR_R_SYS_LIB);
goto end;
}
// 私钥只支持PEM格式
if (type == SSL_FILETYPE_PEM)
{
j=ERR_R_PEM_LIB;
pkey=PEM_read_bio_PrivateKey(in,NULL,
ssl->ctx->default_passwd_callback,ssl->ctx->default_passwd_callback_userdata);
}
else
{
SSLerr(SSL_F_SSL_USE_PRIVATEKEY_FILE,SSL_R_BAD_SSL_FILETYPE);
goto end;
}
if (pkey == NULL)
{
SSLerr(SSL_F_SSL_USE_PRIVATEKEY_FILE,j);
goto end;
}
// 加载私钥
ret=SSL_use_PrivateKey(ssl,pkey);
EVP_PKEY_free(pkey);
end:
if (in != NULL) BIO_free(in);
return(ret);
}

2.9 SSL_CTX_check_private_key()

该函数检查所用的公钥私钥是否是匹配的

int SSL_CTX_check_private_key(SSL_CTX *ctx)
{
if ( (ctx == NULL) ||
(ctx->cert == NULL) ||
(ctx->cert->key->x509 == NULL))
{
SSLerr(SSL_F_SSL_CTX_CHECK_PRIVATE_KEY,SSL_R_NO_CERTIFICATE_ASSIGNED);
return(0);
}
if (ctx->cert->key->privatekey == NULL)
{
SSLerr(SSL_F_SSL_CTX_CHECK_PRIVATE_KEY,SSL_R_NO_PRIVATE_KEY_ASSIGNED);
return(0);
}
// 这才是真正比较函数，在crypto/x509/x509_cmp.c中定义
return(X509_check_private_key(ctx->cert->key->x509, ctx->cert->key->privatekey));
}

2.10 SSL_new

该函数根据SSL_CTX实现一个SSL结构实例，SSL结构是个很复杂的结构，定义如下：

/* ssl/ssl.h */

typedef struct ssl_st SSL;

struct ssl_st
{
/* protocol version
* (one of SSL2_VERSION, SSL3_VERSION, TLS1_VERSION)
*/
int version;
int type; /* SSL_ST_CONNECT or SSL_ST_ACCEPT */

SSL_METHOD *method; /* SSLv3 */

/* There are 2 BIO's even though they are normally both the
* same. This is so data can be read and written to different
* handlers */

#ifndef OPENSSL_NO_BIO
BIO *rbio; /* used by SSL_read */
BIO *wbio; /* used by SSL_write */
BIO *bbio; /* used during session-id reuse to concatenate
* messages */
#else
char *rbio; /* used by SSL_read */
char *wbio; /* used by SSL_write */
char *bbio;
#endif
/* This holds a variable that indicates what we were doing
* when a 0 or -1 is returned. This is needed for
* non-blocking IO so we know what request needs re-doing when
* in SSL_accept or SSL_connect */
int rwstate;

/* true when we are actually in SSL_accept() or SSL_connect() */
int in_handshake;
int (*handshake_func)();

/* Imagine that here's a boolean member "init" that is
* switched as soon as SSL_set_{accept/connect}_state
* is called for the first time, so that "state" and
* "handshake_func" are properly initialized. But as
* handshake_func is == 0 until then, we use this
* test instead of an "init" member.
*/

int server; /* are we the server side? - mostly used by SSL_clear*/

int new_session;/* 1 if we are to use a new session.
* 2 if we are a server and are inside a handshake
* (i.e. not just sending a HelloRequest)
* NB: For servers, the 'new' session may actually be a previously
* cached session or even the previous session unless
* SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION is set */
int quiet_shutdown;/* don't send shutdown packets */
int shutdown; /* we have shut things down, 0x01 sent, 0x02
* for received */
int state; /* where we are */
int rstate; /* where we are when reading */

BUF_MEM *init_buf; /* buffer used during init */
void *init_msg; /* pointer to handshake message body, set by ssl3_get_message() */
int init_num; /* amount read/written */
int init_off; /* amount read/written */

/* used internally to point at a raw packet */
unsigned char *packet;
unsigned int packet_length;

struct ssl2_state_st *s2; /* SSLv2 variables */
struct ssl3_state_st *s3; /* SSLv3 variables */

int read_ahead; /* Read as many input bytes as possible
* (for non-blocking reads) */

int hit; /* reusing a previous session */

int purpose; /* Purpose setting */
int trust; /* Trust setting */

/* crypto */
STACK_OF(SSL_CIPHER) *cipher_list;
STACK_OF(SSL_CIPHER) *cipher_list_by_id;

/* These are the ones being used, the ones in SSL_SESSION are
* the ones to be 'copied' into these ones */

EVP_CIPHER_CTX *enc_read_ctx; /* cryptographic state */
const EVP_MD *read_hash; /* used for mac generation */
#ifndef OPENSSL_NO_COMP
COMP_CTX *expand; /* uncompress */
#else
char *expand;
#endif

EVP_CIPHER_CTX *enc_write_ctx; /* cryptographic state */
const EVP_MD *write_hash; /* used for mac generation */
#ifndef OPENSSL_NO_COMP
COMP_CTX *compress; /* compression */
#else
char *compress;
#endif

/* session info */

/* client cert? */
/* This is used to hold the server certificate used */
struct cert_st /* CERT */ *cert;

/* the session_id_context is used to ensure sessions are only reused
* in the appropriate context */
unsigned int sid_ctx_length;
unsigned char sid_ctx[SSL_MAX_SID_CTX_LENGTH];

/* This can also be in the session once a session is established */
SSL_SESSION *session;

/* Default generate session ID callback. */
GEN_SESSION_CB generate_session_id;

/* Used in SSL2 and SSL3 */
int verify_mode; /* 0 don't care about verify failure.
* 1 fail if verify fails */
int verify_depth;
int (*verify_callback)(int ok,X509_STORE_CTX *ctx); /* fail if callback returns 0 */

void (*info_callback)(const SSL *ssl,int type,int val); /* optional informational callback */

int error; /* error bytes to be written */
int error_code; /* actual code */

#ifndef OPENSSL_NO_KRB5
KSSL_CTX *kssl_ctx; /* Kerberos 5 context */
#endif /* OPENSSL_NO_KRB5 */

SSL_CTX *ctx;
/* set this flag to 1 and a sleep(1) is put into all SSL_read()
* and SSL_write() calls, good for nbio debuging :-) */
int debug;

/* extra application data */
long verify_result;
CRYPTO_EX_DATA ex_data;

/* for server side, keep the list of CA_dn we can use */
STACK_OF(X509_NAME) *client_CA;

int references;
unsigned long options; /* protocol behaviour */
unsigned long mode; /* API behaviour */
long max_cert_list;
int first_packet;
int client_version; /* what was passed, used for
* SSLv3/TLS rollback check */
};

/* ssl/ssl_lib.c */

SSL *SSL_new(SSL_CTX *ctx)
{
SSL *s;

// 一些必要检查
if (ctx == NULL)
{
SSLerr(SSL_F_SSL_NEW,SSL_R_NULL_SSL_CTX);
return(NULL);
}
if (ctx->method == NULL)
{
SSLerr(SSL_F_SSL_NEW,SSL_R_SSL_CTX_HAS_NO_DEFAULT_SSL_VERSION);
return(NULL);
}
// 分配SSL实例的空间
s=(SSL *)OPENSSL_malloc(sizeof(SSL));
if (s == NULL) goto err;
memset(s,0,sizeof(SSL));

// 初始化SSL结构参数
#ifndef OPENSSL_NO_KRB5
s->kssl_ctx = kssl_ctx_new();
#endif /* OPENSSL_NO_KRB5 */

s->options=ctx->options;
s->mode=ctx->mode;
s->max_cert_list=ctx->max_cert_list;

if (ctx->cert != NULL)
{
/* Earlier library versions used to copy the pointer to
* the CERT, not its contents; only when setting new
* parameters for the per-SSL copy, ssl_cert_new would be
* called (and the direct reference to the per-SSL_CTX
* settings would be lost, but those still were indirectly
* accessed for various purposes, and for that reason they
* used to be known as s->ctx->default_cert).
* Now we don't look at the SSL_CTX's CERT after having
* duplicated it once. */

s->cert = ssl_cert_dup(ctx->cert);
if (s->cert == NULL)
goto err;
}
else
s->cert=NULL; /* Cannot really happen (see SSL_CTX_new) */

s->read_ahead=ctx->read_ahead;
s->msg_callback=ctx->msg_callback;
s->msg_callback_arg=ctx->msg_callback_arg;
s->verify_mode=ctx->verify_mode;
s->verify_depth=ctx->verify_depth;
s->sid_ctx_length=ctx->sid_ctx_length;
OPENSSL_assert(s->sid_ctx_length <= sizeof s->sid_ctx);
memcpy(&s->sid_ctx,&ctx->sid_ctx,sizeof(s->sid_ctx));
s->verify_callback=ctx->default_verify_callback;
s->generate_session_id=ctx->generate_session_id;
s->purpose = ctx->purpose;
s->trust = ctx->trust;
s->quiet_shutdown=ctx->quiet_shutdown;

CRYPTO_add(&ctx->references,1,CRYPTO_LOCK_SSL_CTX);
s->ctx=ctx;

s->verify_result=X509_V_OK;

s->method=ctx->method;

if (!s->method->ssl_new(s))
goto err;

s->references=1;
s->server=(ctx->method->ssl_accept == ssl_undefined_function)?0:1;

SSL_clear(s);

CRYPTO_new_ex_data(CRYPTO_EX_INDEX_SSL, s, &s->ex_data);

return(s);
err:
if (s != NULL)
{
if (s->cert != NULL)
ssl_cert_free(s->cert);
if (s->ctx != NULL)
SSL_CTX_free(s->ctx); /* decrement reference count */
OPENSSL_free(s);
}
SSLerr(SSL_F_SSL_NEW,ERR_R_MALLOC_FAILURE);
return(NULL);
}

2.11 SSL_set_fd

SSL_set_fd()函数将建立的SSL结构与TCP套接字联系，使SSL结构对套接字中的TCP数据进行SSL封装。

/* ssl/ssl_lib.c */

int SSL_set_fd(SSL *s,int fd)
{
int ret=0;
BIO *bio=NULL;

// 建立一个BIO，BIO是OpenSSL提供的用来进行算法封装的处理结构，还可以将多个算法
// 串联起来，这样可以很方便地实现数据的封装
bio=BIO_new(BIO_s_socket());

if (bio == NULL)
{
SSLerr(SSL_F_SSL_SET_FD,ERR_R_BUF_LIB);
goto err;
}
// 把套接字和BIO联系
BIO_set_fd(bio,fd,BIO_NOCLOSE);
// 把SSL和BIO联系起来，包括读写操作
SSL_set_bio(s,bio,bio);
ret=1;
err:
return(ret);
}

void SSL_set_bio(SSL *s,BIO *rbio,BIO *wbio)
{
/* If the output buffering BIO is still in place, remove it
*/
if (s->bbio != NULL)
{
if (s->wbio == s->bbio)
{
s->wbio=s->wbio->next_bio;
s->bbio->next_bio=NULL;
}
}
if ((s->rbio != NULL) && (s->rbio != rbio))
BIO_free_all(s->rbio);
if ((s->wbio != NULL) && (s->wbio != wbio) && (s->rbio != s->wbio))
BIO_free_all(s->wbio);
// 设置SSL读写BIO
s->rbio=rbio;
s->wbio=wbio;
}

SSL_set_fd()还有两个类似函数：
SSL_set_wfd()：对写的数据进行SSL封装
SSL_set_rfd()：对都的数据进行SSL封装
不过一般情况下用得比较少。
2.12 SSL_accept

SSL_accept()函数完成SSL协商的服务器端操作:

/* ssl/ssl_lib.c */
int SSL_accept(SSL *s)
{
if (s->handshake_func == 0)
/* Not properly initialized yet */
SSL_set_accept_state(s);

return(s->method->ssl_accept(s));
}

其中SSL_set_accept_state(s)函数初始化SSL协商处理:

void SSL_set_accept_state(SSL *s)
{
// 服务器端
s->server=1;
s->shutdown=0;
// 初始化服务器端状态值
s->state=SSL_ST_ACCEPT|SSL_ST_BEFORE;
// 握手函数即是ssl_accept函数
s->handshake_func=s->method->ssl_accept;
/* clear the current cipher */
// 清除SSL读写加密算法上下文
ssl_clear_cipher_ctx(s);
}

因此最重要的就是ssl_accept()这个成员函数，是前面SSLv[2][3]_server_method()中定义的，如对于 SSLv23方法，处理函数分别为ssl23_accept()函数，其它SSLv2和SSLv3方法分别对应ssl2_accept()和 ssl3_accept()，后两者就没有协商过程了，ssl23_accept()实际在协商确定协议版本后也是调用ssl2[3]_accept ()。

SSL很多状态都分A,B两种，A状态表示刚进入该状态还没有收发数据，B状态表示进行的收发数据处理但还没完成善后操作。

/* ssl/s23_srvr.c */
int ssl23_accept(SSL *s)
{
BUF_MEM *buf;
unsigned long Time=time(NULL);
void (*cb)(const SSL *ssl,int type,int val)=NULL;
int ret= -1;
int new_state,state;

// 用当前时间作为随机种子
RAND_add(&Time,sizeof(Time),0);
ERR_clear_error();
clear_sys_error();

// 在SSL_new()函数中，s->info_callback并没有定义
// 是通过SSL_set_info_callback()函数单独定义的
if (s->info_callback != NULL)
cb=s->info_callback;
// SSL_CTX_new()函数中，ctx->info_callback也没定义
// 是通过SSL_CTX_set_info_callback()宏单独定义的
else if (s->ctx->info_callback != NULL)
cb=s->ctx->info_callback;

// 握手计数
s->in_handshake++;

// 如果SSL已用，清除SSL原来的值
if (!SSL_in_init(s) || SSL_in_before(s)) SSL_clear(s);

for (;;)
{
// 保存SSL当前状态
state=s->state;
// 在SSL_set_accept_state中s->state被初始化为SSL_ST_ACCEPT|SSL_ST_BEFORE
switch(s->state)
{
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);

/* s->version=SSL3_VERSION; */
s->type=SSL_ST_ACCEPT;

if (s->init_buf == NULL)
{
// 生成一个SSL缓冲区
if ((buf=BUF_MEM_new()) == NULL)
{
ret= -1;
goto end;
}
if (!BUF_MEM_grow(buf,SSL3_RT_MAX_PLAIN_LENGTH))
{
ret= -1;
goto end;
}
s->init_buf=buf;
}
// 初始化认证码MAC
ssl3_init_finished_mac(s);
// SSL状态设置为SSL23_ST_SR_CLNT_HELLO_A,进入客户端的HELLO A状态
s->state=SSL23_ST_SR_CLNT_HELLO_A;
// 接受的SSL会话统计
s->ctx->stats.sess_accept++;
s->init_num=0;
// 重新进行循环接收客户端数据
break;

case SSL23_ST_SR_CLNT_HELLO_A:
case SSL23_ST_SR_CLNT_HELLO_B:
s->shutdown=0;
// 获取对方的HELLO信息,也就是进行SSL握手协议
ret=ssl23_get_client_hello(s);
if (ret >= 0) cb=NULL;
goto end;
/* break; */

default:
SSLerr(SSL_F_SSL23_ACCEPT,SSL_R_UNKNOWN_STATE);
ret= -1;
goto end;
/* break; */
}
// 如果SSL状态改变,而又定义了信息回调函数,执行之
if ((cb != NULL) && (s->state != state))
{
new_state=s->state;
s->state=state;
cb(s,SSL_CB_ACCEPT_LOOP,1);
s->state=new_state;
}
}
end:
s->in_handshake--;
if (cb != NULL)
cb(s,SSL_CB_ACCEPT_EXIT,ret);
return(ret);
}

可见，SSL握手协议是在ssl23_get_client_hello(s)函数中完成，也算个很复杂的函数：

int ssl23_get_client_hello(SSL *s)
{
//
// SSL握手协议头首部空间,11字节
// 客户端发出的HELLO，如果第一字节最高位为1
// 头两字节是包长度，不包括第一字节的第一位；
// 第3字节是握手类型类型，取值如下：
// enum {
// hello_request(0), client_hello(1), server_hello(2),
// certificate(11), server_key_exchange (12), certificate_request(13),
// server_done(14), certificate_verify(15), client_key_exchange(16),
// finished(20), (255)
// } HandshakeType;
// 第4，5字节是版本类型，TLS1为0301,SSL3为0300，SSL2为0002
// 第6，7字节是加密算法部分(cipher_specs)信息长度
// 第8，9字节是会话ID(session id)
// 第10，11字节是挑战信息长度(challenge)
//
//
// 如果第一字节最高位不为1或者非客户端发出的HELLO
// 第一字节为类型，取值为：
// enum {
// change_cipher_spec(20), alert(21), handshake(22),
// application_data(23), (255)
// } ContentType
// 第2，3字节是服务器端SSL版本类型，TLS1为0301,SSL3为0300，SSL2为0002
// 第4，5字节为握手部分长度
// 第6字节为消息类型
// 第7，8，9字节为握手信息长度
// 第10，11字节为客户端SSL版本
//
// 本函数的主要功能是识别客户端SSL版本,根据服务器自身支持的SSL版本,选定合适的SSL
// 版本进行下一步的accept,即ssl2_accept或ssl3_accept
//
char buf_space[11]; /* Request this many bytes in initial read.
* We can detect SSL 3.0/TLS 1.0 Client Hellos
* ('type == 3') correctly only when the following
* is in a single record, which is not guaranteed by
* the protocol specification:
* Byte Content
* 0 type
* 1/2 version > record header
* 3/4 length /
* 5 msg_type
* 6-8 length > Client Hello message
* 9/10 client_version /
*/
char *buf= &(buf_space[0]);
unsigned char *p,*d,*d_len,*dd;
unsigned int i;
unsigned int csl,sil,cl;
int n=0,j;
int type=0;
int v[2];
#ifndef OPENSSL_NO_RSA
int use_sslv2_strong=0;
#endif

if (s->state == SSL23_ST_SR_CLNT_HELLO_A)
{
/* read the initial header */
v[0]=v[1]=0;

if (!ssl3_setup_buffers(s)) goto err;
// 读取首部空间长度的数据
n=ssl23_read_bytes(s, sizeof buf_space);
if (n != sizeof buf_space) return(n); /* n == -1 || n == 0 */
// 数据保存在s->packet缓冲区中
p=s->packet;
// 拷贝到buf_space
memcpy(buf,p,n);

if ((p[0] & 0x80) && (p[2] == SSL2_MT_CLIENT_HELLO))
{
/*
* SSLv2 header
*/
if ((p[3] == 0x00) && (p[4] == 0x02))
{
// 客户端为SSLv2
v[0]=p[3]; v[1]=p[4];
/* SSLv2 */
if (!(s->options & SSL_OP_NO_SSLv2))
type=1;
}
else if (p[3] == SSL3_VERSION_MAJOR)
{
// 客户端主版本SSLv3
v[0]=p[3]; v[1]=p[4];
/* SSLv3/TLSv1 */
if (p[4] >= TLS1_VERSION_MINOR)
{
// 次版本表明是客户端TLS1.0, 服务器为SSL3或TLS1时type设为2,为SSL2时设为1
if (!(s->options & SSL_OP_NO_TLSv1))
{
// 服务器支持TLS1.0，SSL类型设置为TLS1
s->version=TLS1_VERSION;
/* type=2; */ /* done later to survive restarts */
s->state=SSL23_ST_SR_CLNT_HELLO_B;
}
else if (!(s->options & SSL_OP_NO_SSLv3))
{
// 服务器不支持TLS，支持SSL3，SSL类型设置为SSL3
s->version=SSL3_VERSION;
/* type=2; */
s->state=SSL23_ST_SR_CLNT_HELLO_B;
}
else if (!(s->options & SSL_OP_NO_SSLv2))
{
// 服务器这边不支持SSL3，TLS1，协商为SSL2, type为1
type=1;
}
}
else if (!(s->options & SSL_OP_NO_SSLv3))
{
// 次版本号表明客户端是SSLv3
s->version=SSL3_VERSION;
/* type=2; */
s->state=SSL23_ST_SR_CLNT_HELLO_B;
}
else if (!(s->options & SSL_OP_NO_SSLv2))
type=1;

}
}
else if ((p[0] == SSL3_RT_HANDSHAKE) &&
// p[1]为SSL3主版本号
(p[1] == SSL3_VERSION_MAJOR) &&
// p[5]为消息类型
(p[5] == SSL3_MT_CLIENT_HELLO) &&
// p[3],p[4]为握手部分长度，如果只是记录头部分，长度小于5，
((p[3] == 0 && p[4] < 5 /* silly record length? */)
// p[9]是客户端主版本号
|| (p[9] == p[1])))
{
/*
* SSLv3 or tls1 header
*/
// 主版本为SSL3
v[0]=p[1]; /* major version (= SSL3_VERSION_MAJOR) */
/* We must look at client_version inside the Client Hello message
* to get the correct minor version.
* However if we have only a pathologically small fragment of the
* Client Hello message, this would be difficult, and we'd have
* to read more records to find out.
* No known SSL 3.0 client fragments ClientHello like this,
* so we simply assume TLS 1.0 to avoid protocol version downgrade
* attacks. */
if (p[3] == 0 && p[4] < 6)
{
// 如果握手长度小于6认为就是TLS1
#if 0
SSLerr(SSL_F_SSL23_GET_CLIENT_HELLO,SSL_R_RECORD_TOO_SMALL);
goto err;
#else
v[1] = TLS1_VERSION_MINOR;
#endif
}
else
v[1]=p[10]; /* minor version according to client_version */
if (v[1] >= TLS1_VERSION_MINOR)
{
// 客户端为TLS1.0，按上面相同的方法设置服务器端的版本
// 注意这时的type设置为3
if (!(s->options & SSL_OP_NO_TLSv1))
{
s->version=TLS1_VERSION;
type=3;
}
else if (!(s->options & SSL_OP_NO_SSLv3))
{
s->version=SSL3_VERSION;
type=3;
}
}
else
{
/* client requests SSL 3.0 */
// 客户端为SSL3，设置服务器段SSL版本
// type为3
if (!(s->options & SSL_OP_NO_SSLv3))
{
s->version=SSL3_VERSION;
type=3;
}
else if (!(s->options & SSL_OP_NO_TLSv1))
{
/* we won't be able to use TLS of course,
* but this will send an appropriate alert */
s->version=TLS1_VERSION;
type=3;
}
}
}
else if ((strncmp("GET ", (char *)p,4) == 0) ||
(strncmp("POST ",(char *)p,5) == 0) ||
(strncmp("HEAD ",(char *)p,5) == 0) ||
(strncmp("PUT ", (char *)p,4) == 0))
{
// 在SSL通道中走HTTP的明文数据，出错
SSLerr(SSL_F_SSL23_GET_CLIENT_HELLO,SSL_R_HTTP_REQUEST);
goto err;
}
else if (strncmp("CONNECT",(char *)p,7) == 0)
{
SSLerr(SSL_F_SSL23_GET_CLIENT_HELLO,SSL_R_HTTPS_PROXY_REQUEST);
goto err;
}
}

// 进入HELLO B状态，也就是客户端数据是SSL3或TLS，而且(p[0] & 0x80) &&
// (p[2] == SSL2_MT_CLIENT_HELLO)，已经找出服务器端的对应版本
if (s->state == SSL23_ST_SR_CLNT_HELLO_B)
{
/* we have SSLv3/TLSv1 in an SSLv2 header
* (other cases skip this state) */
// 服务器是SSL3或TLS1,类型为2
type=2;
p=s->packet;
v[0] = p[3]; /* == SSL3_VERSION_MAJOR */
v[1] = p[4];

// p[0],p[1]是HELLO包长
n=((p[0]&0x7f)<<8)|p[1];
if (n > (1024*4))
{
// 一个SSL段不能超过4096字节
SSLerr(SSL_F_SSL23_GET_CLIENT_HELLO,SSL_R_RECORD_TOO_LARGE);
goto err;
}
// 读取整个包长数据，"2"是因为p[0],p[1]表示包长不包括自身长度(2字节)
// 这个读操作数据初始指针是不移动的,注意前面已经用这函数读了11字节了
j=ssl23_read_bytes(s,n+2);

if (j <= 0) return(j);

// MAC认证
ssl3_finish_mac(s, s->packet+2, s->packet_length-2);
if (s->msg_callback)
s->msg_callback(0, SSL2_VERSION, 0, s->packet+2, s->packet_length-2, s, s->msg_callback_arg); /* CLIENT-HELLO */

// 回到数据头
p=s->packet;
// 跳过前面的5字节，长度、类型、版本信息
p+=5;
// cipher_specs的长度
n2s(p,csl);
// session id
n2s(p,sil);
// challenge长度
n2s(p,cl);

// SSL缓冲区头
d=(unsigned char *)s->init_buf->data;
if ((csl+sil+cl+11) != s->packet_length)
{
// 检查包长是否正确
SSLerr(SSL_F_SSL23_GET_CLIENT_HELLO,SSL_R_RECORD_LENGTH_MISMATCH);
goto err;
}

// 以下开始填充作为ssl3_accept定义的客户端SSL握手包
/* record header: msg_type ... */
// 数据类型
*(d++) = SSL3_MT_CLIENT_HELLO;
/* ... and length (actual value will be written later) */
d_len = d;

// 数据类型1字节,长度2字节
d += 3;

/* client_version */
// 版本号
*(d++) = SSL3_VERSION_MAJOR; /* == v[0] */
*(d++) = v[1];

/* lets populate the random area */
/* get the challenge_length */
// 拷贝挑战信息,最多SSL3_RANDOM_SIZE(32)
i=(cl > SSL3_RANDOM_SIZE)?SSL3_RANDOM_SIZE:cl;
memset(d,0,SSL3_RANDOM_SIZE);
// 如果挑战信息长度不到SSL3_RANDOM_SIZE,相当于前面多余字节补0,不是在后面
memcpy(&(d[SSL3_RANDOM_SIZE-i]),&(p[csl+sil]),i);
d+=SSL3_RANDOM_SIZE;

/* no session-id reuse */
// 会话ID没用
*(d++)=0;

/* ciphers */
// cipher_specs域
j=0;
// 头指针备份
dd=d;
// 留出长度空间
d+=2;
for (i=0; i<csl; i+=3)
{
// p[0]位置现在是收到包中cipher_specs数据头
if (p[i] != 0) continue;
// 每3字节为一个单位,拷贝后两字节,第1字节忽略
*(d++)=p[i+1];
*(d++)=p[i+2];
j+=2;
}
// 写cipher_specs长度,网络序
s2n(j,dd);

/* COMPRESSION */
*(d++)=1;
*(d++)=0;

// 实际数据长度
i = (d-(unsigned char *)s->init_buf->data) - 4;
l2n3((long)i, d_len);

/* get the data reused from the init_buf */
s->s3->tmp.reuse_message=1;
s->s3->tmp.message_type=SSL3_MT_CLIENT_HELLO;
s->s3->tmp.message_size=i;
}

/* imaginary new state (for program structure): */
/* s->state = SSL23_SR_CLNT_HELLO_C */

if (type == 1)
{
// 服务器只支持SSL2的情况,实际已经很少见了
#ifdef OPENSSL_NO_SSL2
SSLerr(SSL_F_SSL23_GET_CLIENT_HELLO,SSL_R_UNSUPPORTED_PROTOCOL);
goto err;
#else
/* we are talking sslv2 */
/* we need to clean up the SSLv3/TLSv1 setup and put in the
* sslv2 stuff. */

if (s->s2 == NULL)
{
// 新分配一个SSL2结构
if (!ssl2_new(s))
goto err;
}
else
ssl2_clear(s);

// 释放SSL3结构
if (s->s3 != NULL) ssl3_free(s);

// 将缓冲区扩到SSL2的最大记录情况
if (!BUF_MEM_grow_clean(s->init_buf,
SSL2_MAX_RECORD_LENGTH_3_BYTE_HEADER))
{
goto err;
}

// 这个状态是"SSL2_ST"系列(SSL2服务器端)的
s->state=SSL2_ST_GET_CLIENT_HELLO_A;
if ((s->options & SSL_OP_MSIE_SSLV2_RSA_PADDING) ||
use_sslv2_strong ||
(s->options & SSL_OP_NO_TLSv1 && s->options & SSL_OP_NO_SSLv3))
s->s2->ssl2_rollback=0;
else
/* reject SSL 2.0 session if client supports SSL 3.0 or TLS 1.0
* (SSL 3.0 draft/RFC 2246, App. E.2) */
s->s2->ssl2_rollback=1;

/* setup the n bytes we have read so we get them from
* the sslv2 buffer */
s->rstate=SSL_ST_READ_HEADER;
s->packet_length=n;
s->packet= &(s->s2->rbuf[0]);
// buf是接收数据缓冲区头,n正常的话是11
memcpy(s->packet,buf,n);
s->s2->rbuf_left=n;
s->s2->rbuf_offs=0;

// SSL封装方法是SSL2
s->method=SSLv2_server_method();
// 实际函数为ssl2_accept
s->handshake_func=s->method->ssl_accept;
#endif
}

if ((type == 2) || (type == 3))
{
// 服务器自身可以支持SSL3或TLS1
/* we have SSLv3/TLSv1 (type 2: SSL2 style, type 3: SSL3/TLS style) */
// 初始化写缓冲区
if (!ssl_init_wbio_buffer(s,1)) goto err;

/* we are in this state */
// SSL3_ST类,SSL3服务器收到客户端的HELLO的A状态
s->state=SSL3_ST_SR_CLNT_HELLO_A;

// 进行一些初始化操作
if (type == 3)
{
/* put the 'n' bytes we have read into the input buffer
* for SSLv3 */
s->rstate=SSL_ST_READ_HEADER;
s->packet_length=n;
s->packet= &(s->s3->rbuf.buf[0]);
memcpy(s->packet,buf,n);
s->s3->rbuf.left=n;
s->s3->rbuf.offset=0;
}
else
{
s->packet_length=0;
s->s3->rbuf.left=0;
s->s3->rbuf.offset=0;
}

if (s->version == TLS1_VERSION)
// 实际上TLS1中的accept方法也就是ssl3_accept
s->method = TLSv1_server_method();
else
// 就是ssl3_accept
s->method = SSLv3_server_method();
s->handshake_func=s->method->ssl_accept;
}

if ((type < 1) || (type > 3))
{
/* bad, very bad */
SSLerr(SSL_F_SSL23_GET_CLIENT_HELLO,SSL_R_UNKNOWN_PROTOCOL);
goto err;
}
s->init_num=0;

if (buf != buf_space) OPENSSL_free(buf);
s->first_packet=1;
// 递归调用SSL_accept()，这时方法是固定的，就是调用ssl2_accept()或ssl3_accept()
return(SSL_accept(s));
err:
if (buf != buf_space) OPENSSL_free(buf);
return(-1);
}

ssl23_get_client_hello()函数最后就是确定了服务器端的方法类型,然后再进行SSL_accept(),实际就是调用ssl2_accept()或ssl3_accept()。

举例ssl3_accept()函数定义如下，ssl2_accept()就不分析了:

/* ssl/s3_srvr.c */

int ssl3_accept(SSL *s)
{
BUF_MEM *buf;
unsigned long l,Time=time(NULL);
void (*cb)(const SSL *ssl,int type,int val)=NULL;
long num1;
int ret= -1;
int new_state,state,skip=0;

// 和前面ssl23_accpet一样进行初始化
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 */
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);
}

for (;;)
{
state=s->state;

switch (s->state)
{
case SSL_ST_RENEGOTIATE:
s->new_session=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:
// 这些是客户端服务器固定就用SSL3进行连接时进入的初始状态,如果是从ssl23_accpet
// 过来的是进不到这状态的
// 下面是ssl23_accept时类似的初始化
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);
return -1;
}
s->type=SSL_ST_ACCEPT;

if (s->init_buf == NULL)
{
if ((buf=BUF_MEM_new()) == NULL)
{
ret= -1;
goto end;
}
if (!BUF_MEM_grow(buf,SSL3_RT_MAX_PLAIN_LENGTH))
{
ret= -1;
goto end;
}
s->init_buf=buf;
}

if (!ssl3_setup_buffers(s))
{
ret= -1;
goto end;
}

s->init_num=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; goto end; }

ssl3_init_finished_mac(s);
s->state=SSL3_ST_SR_CLNT_HELLO_A;
s->ctx->stats.sess_accept++;
}
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:
// 此状态是是写服务器端的回应的HELLO请求信息
s->shutdown=0;
// 发送服务器端的HELLO
ret=ssl3_send_hello_request(s);
if (ret <= 0) goto end;
// 转入REQ_C状态
s->s3->tmp.next_state=SSL3_ST_SW_HELLO_REQ_C;
s->state=SSL3_ST_SW_FLUSH;
s->init_num=0;

ssl3_init_finished_mac(s);
break;

case SSL3_ST_SW_HELLO_REQ_C:
s->state=SSL_ST_OK;
break;

// 从ssl23_accept过来时的状态是SSL3_ST_SR_CLNT_HELLO_A,属于读数据状态
case SSL3_ST_SR_CLNT_HELLO_A:
case SSL3_ST_SR_CLNT_HELLO_B:
case SSL3_ST_SR_CLNT_HELLO_C:
s->shutdown=0;
// 读取客户端数据,如果是ssl23_accept过来的话数据是由ssl23_get_client_hello()
// 函数自己构造的,而不是实际收到的
ret=ssl3_get_client_hello(s);
if (ret <= 0) goto end;
s->new_session = 2;
// 状态转为服务器准备写HELLO的A状态
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:
// 此状态是是写服务器端的HELLO信息
ret=ssl3_send_server_hello(s);
if (ret <= 0) goto end;
// s->hit用来标志该ssl会话是否是重用(reuse)的,在ssl3_get_client_hello()函数
// 中检查客户端的hello信息后设置
if (s->hit)
// 如果会话是reuse的,状态为CHANGE
s->state=SSL3_ST_SW_CHANGE_A;
else
// 否则为新SSL会话,进入证书处理A状态
s->state=SSL3_ST_SW_CERT_A;
s->init_num=0;
break;

case SSL3_ST_SW_CERT_A:
case SSL3_ST_SW_CERT_B:
// 该状态下进行证书交换,用来计算连接共享密钥
/* Check if it is anon DH */
if (!(s->s3->tmp.new_cipher->algorithms & SSL_aNULL))
{
// 非NULL加密的话发送服务器端的证书
ret=ssl3_send_server_certificate(s);
if (ret <= 0) goto end;
}
else
skip=1;
// 进入密钥交换状态
s->state=SSL3_ST_SW_KEY_EXCH_A;
s->init_num=0;
break;

case SSL3_ST_SW_KEY_EXCH_A:
case SSL3_ST_SW_KEY_EXCH_B:
// 该状态下进行数据加密密钥的交换操作
// 算法类型,由一个常数表示
l=s->s3->tmp.new_cipher->algorithms;

/* clear this, it may get reset by
* send_server_key_exchange */
if ((s->options & SSL_OP_EPHEMERAL_RSA)
#ifndef OPENSSL_NO_KRB5
&& !(l & SSL_KRB5)
#endif /* OPENSSL_NO_KRB5 */
)
// 临时性RSA密钥交换
/* option SSL_OP_EPHEMERAL_RSA sends temporary RSA key
* even when forbidden by protocol specs
* (handshake may fail as clients are not required to
* be able to handle this) */
s->s3->tmp.use_rsa_tmp=1;
else
s->s3->tmp.use_rsa_tmp=0;

/* only send if a DH key exchange, fortezza or
* RSA but we have a sign only certificate */
if (s->s3->tmp.use_rsa_tmp
|| (l & (SSL_DH|SSL_kFZA))
|| ((l & 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)
)
)
)
)
{
// 进行RSA密钥交换
ret=ssl3_send_server_key_exchange(s);
if (ret <= 0) goto end;
}
else
skip=1;
// 转入证书请求阶段
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:
// 此阶段进入对方证书请求
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->session->peer != NULL) &&
(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->algorithms & 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->algorithms & SSL_aKRB5))
{
// 在大多数情况下不需要客户端的证书
// 如果想认证对方,只要以上条件之一不满足就可以认证对方
// CTX的verify_mode则通过SSL_CTX_set_verify()来修改
// s->verify_mode可通过函数SSL_set_verify()来修改,
// s->verify_mode的初始值是ctx->verify_mode赋予的
/* no cert request */
skip=1;
s->s3->tmp.cert_request=0;
// 服务器端协商发送结束
s->state=SSL3_ST_SW_SRVR_DONE_A;
}
else
{
// 发送要获取对方证书的请求
s->s3->tmp.cert_request=1;
ret=ssl3_send_certificate_request(s);
if (ret <= 0) goto end;
#ifndef NETSCAPE_HANG_BUG
// 没预定义HANG_BUG的话服务器端协商写数据应该完成了
s->state=SSL3_ST_SW_SRVR_DONE_A;
#else
// 否则进入清除写缓冲状态
// 下一个状态是准备接收证书A
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:
// 发送服务器协商数据完成信息
ret=ssl3_send_server_done(s);
if (ret <= 0) goto end;
// 下一个状态将是接收证书A状态
s->s3->tmp.next_state=SSL3_ST_SR_CERT_A;
// 转入写缓冲清除状态
s->state=SSL3_ST_SW_FLUSH;
s->init_num=0;
break;

case SSL3_ST_SW_FLUSH:
// 清除写缓冲区
/* number of bytes to be flushed */
num1=BIO_ctrl(s->wbio,BIO_CTRL_INFO,0,NULL);
if (num1 > 0)
{
s->rwstate=SSL_WRITING;
num1=BIO_flush(s->wbio);
if (num1 <= 0) { ret= -1; goto end; }
s->rwstate=SSL_NOTHING;
}
// 进入预先保存的下一状态
s->state=s->s3->tmp.next_state;
break;

case SSL3_ST_SR_CERT_A:
case SSL3_ST_SR_CERT_B:
// 此状态下接收对方证书
/* Check for second client hello (MS SGC) */
// 检查对方的HELLO信息
ret = ssl3_check_client_hello(s);
if (ret <= 0)
goto end;
if (ret == 2)
s->state = SSL3_ST_SR_CLNT_HELLO_C;
else {
/* could be sent for a DH cert, even if we
* have not asked for it :-) */
// 获取对方证书
ret=ssl3_get_client_certificate(s);
if (ret <= 0) goto end;
s->init_num=0;
// 准备进入密钥交换状态
s->state=SSL3_ST_SR_KEY_EXCH_A;
}
break;

case SSL3_ST_SR_KEY_EXCH_A:
case SSL3_ST_SR_KEY_EXCH_B:
// 该状态处理密钥交换
ret=ssl3_get_client_key_exchange(s);
if (ret <= 0) goto end;
// 准备进入证书验证状态
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 */
// 验证证书的MAC码
s->method->ssl3_enc->cert_verify_mac(s,
&(s->s3->finish_dgst1),
&(s->s3->tmp.cert_verify_md[0]));
s->method->ssl3_enc->cert_verify_mac(s,
&(s->s3->finish_dgst2),
&(s->s3->tmp.cert_verify_md[MD5_DIGEST_LENGTH]));

break;

case SSL3_ST_SR_CERT_VRFY_A:
case SSL3_ST_SR_CERT_VRFY_B:
// 验证证书
/* we should decide if we expected this one */
ret=ssl3_get_cert_verify(s);
if (ret <= 0) goto end;
// 状态转为接收结束A状态
s->state=SSL3_ST_SR_FINISHED_A;
s->init_num=0;
break;

case SSL3_ST_SR_FINISHED_A:
case SSL3_ST_SR_FINISHED_B:
// 本状态为服务器端接收结束
// 获取结束信息
ret=ssl3_get_finished(s,SSL3_ST_SR_FINISHED_A,
SSL3_ST_SR_FINISHED_B);
if (ret <= 0) goto end;
if (s->hit)
// 如果会话是reuse的, 连接已经建立
s->state=SSL_ST_OK;
else
// 转CHANGE_A
s->state=SSL3_ST_SW_CHANGE_A;
s->init_num=0;
break;

case SSL3_ST_SW_CHANGE_A:
case SSL3_ST_SW_CHANGE_B:
// 本状态为服务器发送修改信息
// SSL加密算法
s->session->cipher=s->s3->tmp.new_cipher;
if (!s->method->ssl3_enc->setup_key_block(s))
{ ret= -1; goto end; }

// 发送修改加密算法信息
ret=ssl3_send_change_cipher_spec(s,
SSL3_ST_SW_CHANGE_A,SSL3_ST_SW_CHANGE_B);

if (ret <= 0) goto end;
// 转发送结束
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;
goto end;
}

break;

case SSL3_ST_SW_FINISHED_A:
case SSL3_ST_SW_FINISHED_B:
// 服务器发送结束,SSL握手完成
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;
// 清除SSL写缓冲
s->state=SSL3_ST_SW_FLUSH;

if (s->hit)
// 如果会话是reuse的,状态转为接收结束
s->s3->tmp.next_state=SSL3_ST_SR_FINISHED_A;
else
// SSL连接成功完成
s->s3->tmp.next_state=SSL_ST_OK;
s->init_num=0;
break;

case SSL_ST_OK:
// 清除连接过程中分配的资源
/* 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->new_session == 2) /* skipped if we just sent a HelloRequest */
{
/* actually not necessarily a 'new' session unless
* SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION is set */

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; */

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); */

// accept结束, ret=1
s->in_handshake--;
if (cb != NULL)
cb(s,SSL_CB_ACCEPT_EXIT,ret);
return(ret);
}
2.13 SSL_connect

SSL_connect()这个函数完成SSL协商的客户端操作:

/* ssl/ssl_lib.c */

int SSL_connect(SSL *s)
{
if (s->handshake_func == 0)
/* Not properly initialized yet */
SSL_set_connect_state(s);

return(s->method->ssl_connect(s));
}

其中SSL_set_connect_state(s)函数初始化SSL协商处理:

void SSL_set_connect_state(SSL *s)
{
// 客户端
s->server=0;
s->shutdown=0;
// 初始化客户端状态值
s->state=SSL_ST_CONNECT|SSL_ST_BEFORE;
// 握手函数即是ssl_connect函数
s->handshake_func=s->method->ssl_connect;
/* clear the current cipher */
// 清除SSL读写加密算法上下文
ssl_clear_cipher_ctx(s);
}

因此最重要的就是ssl_connect()这两个成员函数，是前面SSLv[2][3]_client_method()函数中定义的，如对于SSLv23方法，处理函数分别为ssl23_connect()函数，其它SSLv2和SSLv3方法分别对应ssl2_connect() 和ssl3_connect()，后两者就没有协商过程了，ssl23_connect()实际在协商确定协议版本后也是调用ssl2[3] _connect()。掌握了服务器端的accept过程，理解客户端的connect过程就简单了。

/* ssl/s23_clnt.c */

int ssl23_connect(SSL *s)
{
BUF_MEM *buf=NULL;
unsigned long Time=time(NULL);
void (*cb)(const SSL *ssl,int type,int val)=NULL;
int ret= -1;
int new_state,state;

// 和服务器端一样进行基本的初始化
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;

s->in_handshake++;
if (!SSL_in_init(s) || SSL_in_before(s)) SSL_clear(s);

for (;;)
{
state=s->state;
// 在SSL_set_connect_state中s->state被初始化为SSL_ST_CONNECT|SSL_ST_BEFORE
switch(s->state)
{
case SSL_ST_BEFORE:
case SSL_ST_CONNECT:
case SSL_ST_BEFORE|SSL_ST_CONNECT:
case SSL_ST_OK|SSL_ST_CONNECT:
// 进行基本初始化,分配缓冲区
if (s->session != NULL)
{
SSLerr(SSL_F_SSL23_CONNECT,SSL_R_SSL23_DOING_SESSION_ID_REUSE);
ret= -1;
goto end;
}
s->server=0;
if (cb != NULL) cb(s,SSL_CB_HANDSHAKE_START,1);

/* s->version=TLS1_VERSION; */
s->type=SSL_ST_CONNECT;

if (s->init_buf == NULL)
{
if ((buf=BUF_MEM_new()) == NULL)
{
ret= -1;
goto end;
}
if (!BUF_MEM_grow(buf,SSL3_RT_MAX_PLAIN_LENGTH))
{
ret= -1;
goto end;
}
s->init_buf=buf;
buf=NULL;
}

if (!ssl3_setup_buffers(s)) { ret= -1; goto end; }

ssl3_init_finished_mac(s);

// SSL客户端状态转为准备发送HELLO信息
s->state=SSL23_ST_CW_CLNT_HELLO_A;
s->ctx->stats.sess_connect++;
s->init_num=0;
break;

case SSL23_ST_CW_CLNT_HELLO_A:
case SSL23_ST_CW_CLNT_HELLO_B:
// 发送客户端的HELLO信息
s->shutdown=0;
ret=ssl23_client_hello(s);
if (ret <= 0) goto end;
// 转为准备接收服务器端的HELLO状态
s->state=SSL23_ST_CR_SRVR_HELLO_A;
s->init_num=0;

break;

case SSL23_ST_CR_SRVR_HELLO_A:
case SSL23_ST_CR_SRVR_HELLO_B:
// 读取服务器端的HELLO信息,完成SSL握手协商
ret=ssl23_get_server_hello(s);
if (ret >= 0) cb=NULL;
goto end;
/* break; */

default:
SSLerr(SSL_F_SSL23_CONNECT,SSL_R_UNKNOWN_STATE);
ret= -1;
goto end;
/* break; */
}

if (s->debug) { (void)BIO_flush(s->wbio); }

if ((cb != NULL) && (s->state != state))
{
new_state=s->state;
s->state=state;
cb(s,SSL_CB_CONNECT_LOOP,1);
s->state=new_state;
}
}
end:
s->in_handshake--;
if (buf != NULL)
BUF_MEM_free(buf);
if (cb != NULL)
cb(s,SSL_CB_CONNECT_EXIT,ret);
return(ret);
}

ssl23_client_hello()函数发送客户端的HELLO信息:

/* ssl/s23_clnt.c */
static int ssl23_client_hello(SSL *s)
{
unsigned char *buf;
unsigned char *p,*d;
int i,ch_len;
int ret;

buf=(unsigned char *)s->init_buf->data;
if (s->state == SSL23_ST_CW_CLNT_HELLO_A)
{
// 准备发送HELLO, 构造发送缓冲区的数据,数据格式见SSL_accept一节中的说明
p=s->s3->client_random;
RAND_pseudo_bytes(p,SSL3_RANDOM_SIZE);

/* Do the message type and length last */
d= &(buf[2]);
// p指向SSL握手记录头(11字节长)后的第一字节处
p=d+9;
// 消息类型
*(d++)=SSL2_MT_CLIENT_HELLO;
// 填写客户端版本号
if (!(s->options & SSL_OP_NO_TLSv1))
{
*(d++)=TLS1_VERSION_MAJOR;
*(d++)=TLS1_VERSION_MINOR;
s->client_version=TLS1_VERSION;
}
else if (!(s->options & SSL_OP_NO_SSLv3))
{
*(d++)=SSL3_VERSION_MAJOR;
*(d++)=SSL3_VERSION_MINOR;
s->client_version=SSL3_VERSION;
}
else if (!(s->options & SSL_OP_NO_SSLv2))
{
*(d++)=SSL2_VERSION_MAJOR;
*(d++)=SSL2_VERSION_MINOR;
s->client_version=SSL2_VERSION;
}
else
{
SSLerr(SSL_F_SSL23_CLIENT_HELLO,SSL_R_NO_PROTOCOLS_AVAILABLE);
return(-1);
}
// 填写cipher_specs信息
/* Ciphers supported */
i=ssl_cipher_list_to_bytes(s,SSL_get_ciphers(s),p);
if (i == 0)
{
/* no ciphers */
SSLerr(SSL_F_SSL23_CLIENT_HELLO,SSL_R_NO_CIPHERS_AVAILABLE);
return(-1);
}
s2n(i,d);
p+=i;

// 填写会话ID
/* put in the session-id, zero since there is no
* reuse. */
s2n(0,d);

if (s->options & SSL_OP_NETSCAPE_CHALLENGE_BUG)
ch_len=SSL2_CHALLENGE_LENGTH;
else
ch_len=SSL2_MAX_CHALLENGE_LENGTH;

// 填写挑战信息
/* write out sslv2 challenge */
if (SSL3_RANDOM_SIZE < ch_len)
i=SSL3_RANDOM_SIZE;
else
i=ch_len;
s2n(i,d);
memset(&(s->s3->client_random[0]),0,SSL3_RANDOM_SIZE);
RAND_pseudo_bytes(&(s->s3->client_random[SSL3_RANDOM_SIZE-i]),i);
memcpy(p,&(s->s3->client_random[SSL3_RANDOM_SIZE-i]),i);
p+=i;

// 数据长度
i= p- &(buf[2]);
buf[0]=((i>>8)&0xff)|0x80;
buf[1]=(i&0xff);

// 数据完成,状态转为HELLO B准备发送
s->state=SSL23_ST_CW_CLNT_HELLO_B;
/* number of bytes to write */
s->init_num=i+2;
s->init_off=0;

ssl3_finish_mac(s,&(buf[2]),i);
}

/* SSL3_ST_CW_CLNT_HELLO_B */
// 发送HELLO数据
ret = ssl23_write_bytes(s);
if (ret >= 2)
if (s->msg_callback)
s->msg_callback(1, SSL2_VERSION, 0, s->init_buf->data+2, ret-2, s, s->msg_callback_arg); /* CLIENT-HELLO */
return ret;
}

ssl23_get_server_hello()接收服务器端的回应，识别服务器的SSL版本，最后再相应调用ssl2_connect()或ssl3_connect()函数。

/* ssl/s23_clnt.c */
static int ssl23_get_server_hello(SSL *s)
{
char buf[8];
unsigned char *p;
int i;
int n;

// 读7字节的服务器端数据
n=ssl23_read_bytes(s,7);

if (n != 7) return(n);
p=s->packet;

memcpy(buf,p,n);

if ((p[0] & 0x80) && (p[2] == SSL2_MT_SERVER_HELLO) &&
(p[5] == 0x00) && (p[6] == 0x02))
{
// 服务器是SSL2版本
#ifdef OPENSSL_NO_SSL2
SSLerr(SSL_F_SSL23_GET_SERVER_HELLO,SSL_R_UNSUPPORTED_PROTOCOL);
goto err;
#else
/* we are talking sslv2 */
/* we need to clean up the SSLv3 setup and put in the
* sslv2 stuff. */
int ch_len;

if (s->options & SSL_OP_NO_SSLv2)
{
SSLerr(SSL_F_SSL23_GET_SERVER_HELLO,SSL_R_UNSUPPORTED_PROTOCOL);
goto err;
}
// 初始化SSL结构中的SSL2支持，ssl_connect将为ssl2_connect
if (s->s2 == NULL)
{
if (!ssl2_new(s))
goto err;
}
else
ssl2_clear(s);

if (s->options & SSL_OP_NETSCAPE_CHALLENGE_BUG)
ch_len=SSL2_CHALLENGE_LENGTH;
else
ch_len=SSL2_MAX_CHALLENGE_LENGTH;

/* write out sslv2 challenge */
i=(SSL3_RANDOM_SIZE < ch_len)
?SSL3_RANDOM_SIZE:ch_len;
s->s2->challenge_length=i;
memcpy(s->s2->challenge,
&(s->s3->client_random[SSL3_RANDOM_SIZE-i]),i);

if (s->s3 != NULL) ssl3_free(s);

if (!BUF_MEM_grow_clean(s->init_buf,
SSL2_MAX_RECORD_LENGTH_3_BYTE_HEADER))
{
SSLerr(SSL_F_SSL23_GET_SERVER_HELLO,ERR_R_BUF_LIB);
goto err;
}

s->state=SSL2_ST_GET_SERVER_HELLO_A;
if (!(s->client_version == SSL2_VERSION))
/* use special padding (SSL 3.0 draft/RFC 2246, App. E.2) */
s->s2->ssl2_rollback=1;

/* setup the 5 bytes we have read so we get them from
* the sslv2 buffer */
s->rstate=SSL_ST_READ_HEADER;
s->packet_length=n;
s->packet= &(s->s2->rbuf[0]);
memcpy(s->packet,buf,n);
s->s2->rbuf_left=n;
s->s2->rbuf_offs=0;

/* we have already written one */
s->s2->write_sequence=1;

s->method=SSLv2_client_method();
s->handshake_func=s->method->ssl_connect;
#endif
}
else if ((p[0] == SSL3_RT_HANDSHAKE) &&
(p[1] == SSL3_VERSION_MAJOR) &&
((p[2] == SSL3_VERSION_MINOR) ||
(p[2] == TLS1_VERSION_MINOR)) &&
(p[5] == SSL3_MT_SERVER_HELLO))
{
// 服务器版本为SSL3或TLS1，ssl_connect将为ssl3_connect
/* we have sslv3 or tls1 */

if (!ssl_init_wbio_buffer(s,1)) goto err;

/* we are in this state */
s->state=SSL3_ST_CR_SRVR_HELLO_A;

/* put the 5 bytes we have read into the input buffer
* for SSLv3 */
s->rstate=SSL_ST_READ_HEADER;
s->packet_length=n;
s->packet= &(s->s3->rbuf.buf[0]);
memcpy(s->packet,buf,n);
s->s3->rbuf.left=n;
s->s3->rbuf.offset=0;

if ((p[2] == SSL3_VERSION_MINOR) &&
!(s->options & SSL_OP_NO_SSLv3))
{
s->version=SSL3_VERSION;
s->method=SSLv3_client_method();
}
else if ((p[2] == TLS1_VERSION_MINOR) &&
!(s->options & SSL_OP_NO_TLSv1))
{
s->version=TLS1_VERSION;
s->method=TLSv1_client_method();
}
else
{
SSLerr(SSL_F_SSL23_GET_SERVER_HELLO,SSL_R_UNSUPPORTED_PROTOCOL);
goto err;
}

s->handshake_func=s->method->ssl_connect;
}
else if ((p[0] == SSL3_RT_ALERT) &&
(p[1] == SSL3_VERSION_MAJOR) &&
((p[2] == SSL3_VERSION_MINOR) ||
(p[2] == TLS1_VERSION_MINOR)) &&
(p[3] == 0) &&
(p[4] == 2))
{
// SSL告警信息
void (*cb)(const SSL *ssl,int type,int val)=NULL;
int j;

/* An alert */
if (s->info_callback != NULL)
cb=s->info_callback;
else if (s->ctx->info_callback != NULL)
cb=s->ctx->info_callback;

i=p[5];
if (cb != NULL)
{
j=(i<<8)|p[6];
cb(s,SSL_CB_READ_ALERT,j);
}

s->rwstate=SSL_NOTHING;
SSLerr(SSL_F_SSL23_GET_SERVER_HELLO,SSL_AD_REASON_OFFSET+p[6]);
goto err;
}
else
{
SSLerr(SSL_F_SSL23_GET_SERVER_HELLO,SSL_R_UNKNOWN_PROTOCOL);
goto err;
}
s->init_num=0;

/* Since, if we are sending a ssl23 client hello, we are not
* reusing a session-id */
if (!ssl_get_new_session(s,0))
goto err;

s->first_packet=1;
// 递归调用SSL_connect，实际将执行ssl2_connect()或ssl3_connect()
return(SSL_connect(s));
err:
return(-1);
}

举例ssl3_conect()函数定义如下，ssl2_connect()就不分析了:

/* ssl/s3_clnt.c */

int ssl3_connect(SSL *s)
{
BUF_MEM *buf=NULL;
unsigned long Time=time(NULL),l;
long num1;
void (*cb)(const SSL *ssl,int type,int val)=NULL;
int ret= -1;
int new_state,state,skip=0;;

// 对SSL3连接的初始化
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;

s->in_handshake++;
if (!SSL_in_init(s) || SSL_in_before(s)) SSL_clear(s);

for (;;)
{
state=s->state;

switch(s->state)
{
case SSL_ST_RENEGOTIATE:
// 重协商的话从头开始, 注意break是注释掉的
s->new_session=1;
s->state=SSL_ST_CONNECT;
s->ctx->stats.sess_connect_renegotiate++;
/* break */
// 初始状态应该是SSL_ST_BEFORE|SSL_ST_CONNECT
case SSL_ST_BEFORE:
case SSL_ST_CONNECT:
case SSL_ST_BEFORE|SSL_ST_CONNECT:
case SSL_ST_OK|SSL_ST_CONNECT:
// server=0表示是客户端
s->server=0;
if (cb != NULL) cb(s,SSL_CB_HANDSHAKE_START,1);
// 如果本地版本不是SSL3则出错
if ((s->version & 0xff00 ) != 0x0300)
{
SSLerr(SSL_F_SSL3_CONNECT, ERR_R_INTERNAL_ERROR);
ret = -1;
goto end;
}
/* s->version=SSL3_VERSION; */
s->type=SSL_ST_CONNECT;

// 初始化连接缓冲区
if (s->init_buf == NULL)
{
if ((buf=BUF_MEM_new()) == NULL)
{
ret= -1;
goto end;
}
if (!BUF_MEM_grow(buf,SSL3_RT_MAX_PLAIN_LENGTH))
{
ret= -1;
goto end;
}
s->init_buf=buf;
buf=NULL;
}

if (!ssl3_setup_buffers(s)) { ret= -1; goto end; }

/* setup buffing BIO */
if (!ssl_init_wbio_buffer(s,0)) { ret= -1; goto end; }

/* don't push the buffering BIO quite yet */

ssl3_init_finished_mac(s);
// 准备发送HELLO信息
s->state=SSL3_ST_CW_CLNT_HELLO_A;
s->ctx->stats.sess_connect++;
s->init_num=0;
break;

case SSL3_ST_CW_CLNT_HELLO_A:
case SSL3_ST_CW_CLNT_HELLO_B:
// 该状态发送客户端SSL3信息
s->shutdown=0;
ret=ssl3_client_hello(s);
if (ret <= 0) goto end;
// 发送成功,状态转为准备接收服务器的HELLO回应
s->state=SSL3_ST_CR_SRVR_HELLO_A;
s->init_num=0;

/* turn on buffering for the next lot of output */
if (s->bbio != s->wbio)
s->wbio=BIO_push(s->bbio,s->wbio);

break;

case SSL3_ST_CR_SRVR_HELLO_A:
case SSL3_ST_CR_SRVR_HELLO_B:
// 该状态下接收服务器发送的HELLO信息
ret=ssl3_get_server_hello(s);
if (ret <= 0) goto end;
if (s->hit)
// 如果是reuse的连接,状态转为接收结束
s->state=SSL3_ST_CR_FINISHED_A;
else
// 否则状态转为准备接收服务器的证书
s->state=SSL3_ST_CR_CERT_A;
s->init_num=0;
break;

case SSL3_ST_CR_CERT_A:
case SSL3_ST_CR_CERT_B:
// 该状态下接收服务器发送的证书
/* Check if it is anon DH */
if (!(s->s3->tmp.new_cipher->algorithms & SSL_aNULL))
{
ret=ssl3_get_server_certificate(s);
if (ret <= 0) goto end;
}
else
skip=1;
// 状态转为接收密钥交换信息
s->state=SSL3_ST_CR_KEY_EXCH_A;
s->init_num=0;
break;

case SSL3_ST_CR_KEY_EXCH_A:
case SSL3_ST_CR_KEY_EXCH_B:
// 该状态下接收密钥交换信息
ret=ssl3_get_key_exchange(s);
if (ret <= 0) goto end;
// 状态转为接收证书请求
s->state=SSL3_ST_CR_CERT_REQ_A;
s->init_num=0;

/* at this point we check that we have the
* required stuff from the server */
if (!ssl3_check_cert_and_algorithm(s))
{
ret= -1;
goto end;
}
break;

case SSL3_ST_CR_CERT_REQ_A:
case SSL3_ST_CR_CERT_REQ_B:
// 该状态下接收服务器的证书请求
ret=ssl3_get_certificate_request(s);
if (ret <= 0) goto end;
s->state=SSL3_ST_CR_SRVR_DONE_A;
s->init_num=0;
break;

case SSL3_ST_CR_SRVR_DONE_A:
case SSL3_ST_CR_SRVR_DONE_B:
// 该状态下接收服务器信息结束
ret=ssl3_get_server_done(s);
if (ret <= 0) goto end;
if (s->s3->tmp.cert_req)
// 发送客户端证书
s->state=SSL3_ST_CW_CERT_A;
else
// 发送密钥交换信息
s->state=SSL3_ST_CW_KEY_EXCH_A;
s->init_num=0;

break;

case SSL3_ST_CW_CERT_A:
case SSL3_ST_CW_CERT_B:
case SSL3_ST_CW_CERT_C:
case SSL3_ST_CW_CERT_D:
// 该状态下发送客户端证书
ret=ssl3_send_client_certificate(s);
if (ret <= 0) goto end;
// 状态转为发送密钥交换信息
s->state=SSL3_ST_CW_KEY_EXCH_A;
s->init_num=0;
break;

case SSL3_ST_CW_KEY_EXCH_A:
case SSL3_ST_CW_KEY_EXCH_B:
// 该状态下发送密钥交换信息
ret=ssl3_send_client_key_exchange(s);
if (ret <= 0) goto end;
// 加密算法
l=s->s3->tmp.new_cipher->algorithms;
/* EAY EAY EAY need to check for DH fix cert
* sent back */
/* For TLS, cert_req is set to 2, so a cert chain
* of nothing is sent, but no verify packet is sent */
if (s->s3->tmp.cert_req == 1)
{
// 发送证书验证
s->state=SSL3_ST_CW_CERT_VRFY_A;
}
else
{
// TLS, 不用发送证书认证信息,直接转为修改算法状态
s->state=SSL3_ST_CW_CHANGE_A;
s->s3->change_cipher_spec=0;
}

s->init_num=0;
break;

case SSL3_ST_CW_CERT_VRFY_A:
case SSL3_ST_CW_CERT_VRFY_B:
// 该状态发送证书验证信息
ret=ssl3_send_client_verify(s);
if (ret <= 0) goto end;
// 状态转为发送修改算法信息
s->state=SSL3_ST_CW_CHANGE_A;
s->init_num=0;
s->s3->change_cipher_spec=0;
break;

case SSL3_ST_CW_CHANGE_A:
case SSL3_ST_CW_CHANGE_B:
// 该状态下发送修改算法信息
ret=ssl3_send_change_cipher_spec(s,
SSL3_ST_CW_CHANGE_A,SSL3_ST_CW_CHANGE_B);
if (ret <= 0) goto end;
// 状态转为发送结束
s->state=SSL3_ST_CW_FINISHED_A;
s->init_num=0;

// 设置会话加密算法
s->session->cipher=s->s3->tmp.new_cipher;
if (s->s3->tmp.new_compression == NULL)
s->session->compress_meth=0;
else
s->session->compress_meth=
s->s3->tmp.new_compression->id;
if (!s->method->ssl3_enc->setup_key_block(s))
{
ret= -1;
goto end;
}

if (!s->method->ssl3_enc->change_cipher_state(s,
SSL3_CHANGE_CIPHER_CLIENT_WRITE))
{
ret= -1;
goto end;
}

break;

case SSL3_ST_CW_FINISHED_A:
case SSL3_ST_CW_FINISHED_B:
// 该状态下发送协商结束信息
ret=ssl3_send_finished(s,
SSL3_ST_CW_FINISHED_A,SSL3_ST_CW_FINISHED_B,
s->method->ssl3_enc->client_finished_label,
s->method->ssl3_enc->client_finished_label_len);
if (ret <= 0) goto end;
// 转为刷新写缓冲状态
s->state=SSL3_ST_CW_FLUSH;

/* clear flags */
s->s3->flags&= ~SSL3_FLAGS_POP_BUFFER;
if (s->hit)
{
// 如果是reuse的会话, FLUSH后的下一个状态转为协商成功
s->s3->tmp.next_state=SSL_ST_OK;
if (s->s3->flags & SSL3_FLAGS_DELAY_CLIENT_FINISHED)
{
s->state=SSL_ST_OK;
s->s3->flags|=SSL3_FLAGS_POP_BUFFER;
s->s3->delay_buf_pop_ret=0;
}
}
else
{
// 否则状态转为准备接收服务器的协商结束信息
s->s3->tmp.next_state=SSL3_ST_CR_FINISHED_A;
}
s->init_num=0;
break;

case SSL3_ST_CR_FINISHED_A:
case SSL3_ST_CR_FINISHED_B:
// 该状态接收服务器发送的协商结束信息
ret=ssl3_get_finished(s,SSL3_ST_CR_FINISHED_A,
SSL3_ST_CR_FINISHED_B);
if (ret <= 0) goto end;

if (s->hit)
// 如果会话是reuse的,状态转为发送算法
s->state=SSL3_ST_CW_CHANGE_A;
else
// 否则协商成功
s->state=SSL_ST_OK;
s->init_num=0;
break;

case SSL3_ST_CW_FLUSH:
// 该状态下刷新写缓冲区
/* number of bytes to be flushed */
num1=BIO_ctrl(s->wbio,BIO_CTRL_INFO,0,NULL);
if (num1 > 0)
{
s->rwstate=SSL_WRITING;
num1=BIO_flush(s->wbio);
if (num1 <= 0) { ret= -1; goto end; }
s->rwstate=SSL_NOTHING;
}

s->state=s->s3->tmp.next_state;
break;

case SSL_ST_OK:
// 该状态下协商成功结束
// 释放协商时分配的资源
/* clean a few things up */
ssl3_cleanup_key_block(s);

if (s->init_buf != NULL)
{
BUF_MEM_free(s->init_buf);
s->init_buf=NULL;
}

/* If we are not 'joining' the last two packets,
* remove the buffering now */
if (!(s->s3->flags & SSL3_FLAGS_POP_BUFFER))
ssl_free_wbio_buffer(s);
/* else do it later in ssl3_write */

s->init_num=0;
s->new_session=0;

ssl_update_cache(s,SSL_SESS_CACHE_CLIENT);
if (s->hit) s->ctx->stats.sess_hit++;

ret=1;
/* s->server=0; */
s->handshake_func=ssl3_connect;
s->ctx->stats.sess_connect_good++;

if (cb != NULL) cb(s,SSL_CB_HANDSHAKE_DONE,1);

goto end;
/* break; */

default:
SSLerr(SSL_F_SSL3_CONNECT,SSL_R_UNKNOWN_STATE);
ret= -1;
goto end;
/* break; */
}

/* did we do anything */
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_CONNECT_LOOP,1);
s->state=new_state;
}
}
skip=0;
}
end:
s->in_handshake--;
if (buf != NULL)
BUF_MEM_free(buf);
if (cb != NULL)
cb(s,SSL_CB_CONNECT_EXIT,ret);
return(ret);
}
2.14 SSL_read

SSL结构(struct ssl_st)中的s2,s3指针分别指向SSL2和SSL3的状态结构，这些状态结构中都有用于读的rbuf，其中保存SSL会话接收到的原始数据，另外还有保存记录的rrec，用来保存解码后的数据。在SSL结构中有个指针packet是指向原始数据的。

SSL_read()实现从SSL通道中读取数据，送到应用程序的数据是已经经过SSL解封装的了。

/* ssl/ssl_lib.c */

int SSL_read(SSL *s,void *buf,int num)
{
if (s->handshake_func == 0)
{
SSLerr(SSL_F_SSL_READ, SSL_R_UNINITIALIZED);
return -1;
}
// 发现接收shutdown标志，接收结束
if (s->shutdown & SSL_RECEIVED_SHUTDOWN)
{
s->rwstate=SSL_NOTHING;
return(0);
}
// 调用具体方法的接收函数, 如ssl3_read(), ssl2_read()等
return(s->method->ssl_read(s,buf,num));
}

下面以ssl3_read()函数进行详细说明，ssl3_read()函数本质是调用ssl3_read_internal()

/* ssl/s3_lib.c */
int ssl3_read(SSL *s, void *buf, int len)
{
// 最后一个参数为0，表示是实实在在的读数据，不是偷看(peek)
// peek的意思是读数据,但不会把已读数据从缓冲区中去掉,因此下一次读还会读到
return ssl3_read_internal(s, buf, len, 0);
}

static int ssl3_read_internal(SSL *s, void *buf, int len, int peek)
{
int ret;
// 清除错误信息
clear_sys_error();
// 检查协商是否成功
if (s->s3->renegotiate) ssl3_renegotiate_check(s);
// 标志现在在读应用层数据
s->s3->in_read_app_data=1;
// ssl3读取数据, 类型是SSL3_RT_APPLICATION_DATA，应用数据
ret=ssl3_read_bytes(s,SSL3_RT_APPLICATION_DATA,buf,len,peek);
if ((ret == -1) && (s->s3->in_read_app_data == 2))
{
// s->s3->in_read_app_data == 2表示要读协商数据
/* ssl3_read_bytes decided to call s->handshake_func, which
* called ssl3_read_bytes to read handshake data.
* However, ssl3_read_bytes actually found application data
* and thinks that application data makes sense here; so disable
* handshake processing and try to read application data again. */
s->in_handshake++;
// 重新读数据
ret=ssl3_read_bytes(s,SSL3_RT_APPLICATION_DATA,buf,len,peek);
s->in_handshake--;
}
else
s->s3->in_read_app_data=0;

return(ret);
}

读取数据的主要函数实际为ssl3_read_bytes():

/* ssl/ssl3_pkt.c */
int ssl3_read_bytes(SSL *s, int type, unsigned char *buf, int len, int peek)
{
int al,i,j,ret;
unsigned int n;
SSL3_RECORD *rr;
void (*cb)(const SSL *ssl,int type2,int val)=NULL;

// 检查是否分配了接收缓冲区
if (s->s3->rbuf.buf == NULL) /* Not initialized yet */
if (!ssl3_setup_buffers(s))
return(-1);

// 只处理两种数据,或是应用层数据或者是SSL握手协商数据,
// peek只处理应用层数据，其他则出错
if ((type && (type != SSL3_RT_APPLICATION_DATA) &&
(type != SSL3_RT_HANDSHAKE) && type) ||
(peek && (type != SSL3_RT_APPLICATION_DATA)))
{
SSLerr(SSL_F_SSL3_READ_BYTES, ERR_R_INTERNAL_ERROR);
return -1;
}

if ((type == SSL3_RT_HANDSHAKE) && (s->s3->handshake_fragment_len > 0))
/* (partially) satisfy request from storage */
{
// 握手数据碎片, 处理完直到不再是碎片
unsigned char *src = s->s3->handshake_fragment;
unsigned char *dst = buf;
unsigned int k;

/* peek == 0 */
n = 0;
while ((len > 0) && (s->s3->handshake_fragment_len > 0))
{
*dst++ = *src++;
len--; s->s3->handshake_fragment_len--;
n++;
}
/* move any remaining fragment bytes: */
for (k = 0; k < s->s3->handshake_fragment_len; k++)
s->s3->handshake_fragment[k] = *src++;
return n;
}

/* Now s->s3->handshake_fragment_len == 0 if type == SSL3_RT_HANDSHAKE. */

if (!s->in_handshake && SSL_in_init(s))
{
// 没进握手阶段但属于SSL初始化阶段, 调用SSL握手处理
/* type == SSL3_RT_APPLICATION_DATA */
i=s->handshake_func(s);
if (i < 0) return(i);
if (i == 0)
{
SSLerr(SSL_F_SSL3_READ_BYTES,SSL_R_SSL_HANDSHAKE_FAILURE);
return(-1);
}
}
start:
// 正常的接收数据开始, 开始读写状态为NOTHING
s->rwstate=SSL_NOTHING;

/* s->s3->rrec.type - is the type of record
* s->s3->rrec.data, - data
* s->s3->rrec.off, - offset into 'data' for next read
* s->s3->rrec.length, - number of bytes. */
// 记录类型指针
rr = &(s->s3->rrec);

/* get new packet if necessary */
if ((rr->length == 0) || (s->rstate == SSL_ST_READ_BODY))
{
// 当前没记录,获取新的记录信息, 该函数获取SSL记录数据
ret=ssl3_get_record(s);
if (ret <= 0) return(ret);
}

/* we now have a packet which can be read and processed */

if (s->s3->change_cipher_spec /* set when we receive ChangeCipherSpec,
* reset by ssl3_get_finished */
&& (rr->type != SSL3_RT_HANDSHAKE))
{
// 只允许在握手状态下修改当前的算法信息，否则出错
al=SSL_AD_UNEXPECTED_MESSAGE;
SSLerr(SSL_F_SSL3_READ_BYTES,SSL_R_DATA_BETWEEN_CCS_AND_FINISHED);
goto err;
}

/* If the other end has shut down, throw anything we read away
* (even in 'peek' mode) */
if (s->shutdown & SSL_RECEIVED_SHUTDOWN)
{
// 接收到对方的FIN信息, 接收结束
rr->length=0;
s->rwstate=SSL_NOTHING;
return(0);
}

if (type == rr->type) /* SSL3_RT_APPLICATION_DATA or SSL3_RT_HANDSHAKE */
{
// 读到是数据类型和期待读到的数据类型一致
// 这是正常大多数的情况
/* make sure that we are not getting application data when we
* are doing a handshake for the first time */
if (SSL_in_init(s) && (type == SSL3_RT_APPLICATION_DATA) &&
(s->enc_read_ctx == NULL))
{
// 在初始阶段只应该读握手信息而不该读应用信息
al=SSL_AD_UNEXPECTED_MESSAGE;
SSLerr(SSL_F_SSL3_READ_BYTES,SSL_R_APP_DATA_IN_HANDSHAKE);
goto f_err;
}

if (len <= 0) return(len);

// 在期待读取的数据长度len和已经读到的数据记录长度rr->length取小值作为返回的数据长度
if ((unsigned int)len > rr->length)
n = rr->length;
else
n = (unsigned int)len;

memcpy(buf,&(rr->data[rr->off]),n);
if (!peek)
{
// 如果不是peek,移动记录缓冲的数据偏移指针，长度减
rr->length-=n;
rr->off+=n;
if (rr->length == 0)
{
s->rstate=SSL_ST_READ_HEADER;
rr->off=0;
}
}
// 正常返回
return(n);
}

/* If we get here, then type != rr->type; if we have a handshake
* message, then it was unexpected (Hello Request or Client Hello). */

/* In case of record types for which we have 'fragment' storage,
* fill that so that we can process the data at a fixed place.
*/
// 现在情况是读取的数据类型和期待读取的数据类型不一致
// 已经读到的数据不丢弃,而是作为碎片存储起来以后备用
{
unsigned int dest_maxlen = 0;
unsigned char *dest = NULL;
unsigned int *dest_len = NULL;

if (rr->type == SSL3_RT_HANDSHAKE)
{
// 握手类型数据存到握手碎片区
dest_maxlen = sizeof s->s3->handshake_fragment;
dest = s->s3->handshake_fragment;
dest_len = &s->s3->handshake_fragment_len;
}
else if (rr->type == SSL3_RT_ALERT)
{
// 告警信息存到告警碎片区
dest_maxlen = sizeof s->s3->alert_fragment;
dest = s->s3->alert_fragment;
dest_len = &s->s3->alert_fragment_len;
}

if (dest_maxlen > 0)
{
// 有缓冲区, 计算可用的最大缓冲区
n = dest_maxlen - *dest_len; /* available space in 'dest' */
// 如果要写入的长度小于可用空间大小,可全部写入
if (rr->length < n)
n = rr->length; /* available bytes */
// 写入缓冲区
/* now move 'n' bytes: */
while (n-- > 0)
{
dest[(*dest_len)++] = rr->data[rr->off++];
rr->length--;
}

if (*dest_len < dest_maxlen)
goto start; /* fragment was too small */
}
}

/* s->s3->handshake_fragment_len == 4 iff rr->type == SSL3_RT_HANDSHAKE;
* s->s3->alert_fragment_len == 2 iff rr->type == SSL3_RT_ALERT.
* (Possibly rr is 'empty' now, i.e. rr->length may be 0.) */

/* If we are a client, check for an incoming 'Hello Request': */
if ((!s->server) &&
(s->s3->handshake_fragment_len >= 4) &&
(s->s3->handshake_fragment[0] == SSL3_MT_HELLO_REQUEST) &&
(s->session != NULL) && (s->session->cipher != NULL))
{
// 本地是客户端
// 握手碎片长度至少是4字节, 类型是HELLO的握手信息时进行处理

s->s3->handshake_fragment_len = 0;

if ((s->s3->handshake_fragment[1] != 0) ||
(s->s3->handshake_fragment[2] != 0) ||
(s->s3->handshake_fragment[3] != 0))
{
// SSL3_MT_HELLO_REQUEST类型后三个字节都要是0
al=SSL_AD_DECODE_ERROR;
SSLerr(SSL_F_SSL3_READ_BYTES,SSL_R_BAD_HELLO_REQUEST);
goto err;
}

if (s->msg_callback)
s->msg_callback(0, s->version, SSL3_RT_HANDSHAKE, s->s3->handshake_fragment, 4, s, s->msg_callback_arg);

if (SSL_is_init_finished(s) &&
// 协商结束但没设置不需重协商算法标志
!(s->s3->flags & SSL3_FLAGS_NO_RENEGOTIATE_CIPHERS) &&
// 没设置该ssl3会话的重协商标志
!s->s3->renegotiate)
{
// 进行ssl3重协商,实际是将s->s3->renegotiate置1
ssl3_renegotiate(s);
if (ssl3_renegotiate_check(s))
{
// 进行重协商
i=s->handshake_func(s);
if (i < 0) return(i);
if (i == 0)
{
SSLerr(SSL_F_SSL3_READ_BYTES,SSL_R_SSL_HANDSHAKE_FAILURE);
return(-1);
}

if (!(s->mode & SSL_MODE_AUTO_RETRY))
// 该SSL会话不是自动重试模式
{
if (s->s3->rbuf.left == 0) /* no read-ahead left? */
{
BIO *bio;
/* In the case where we try to read application data,
* but we trigger an SSL handshake, we return -1 with
* the retry option set. Otherwise renegotiation may
* cause nasty problems in the blocking world */
s->rwstate=SSL_READING;
bio=SSL_get_rbio(s);
// 清除读BIO重试标志
BIO_clear_retry_flags(bio);
// 设置读BIO重试标志
BIO_set_retry_read(bio);
return(-1);
}
}
}
}
/* we either finished a handshake or ignored the request,
* now try again to obtain the (application) data we were asked for */
// 重新读数据
goto start;
}

if (s->s3->alert_fragment_len >= 2)
{
// 处理告警碎片信息, 长度大于等于2字节时就处理
int alert_level = s->s3->alert_fragment[0];
int alert_descr = s->s3->alert_fragment[1];

s->s3->alert_fragment_len = 0;

// 分别处理msg和info的回调
if (s->msg_callback)
s->msg_callback(0, s->version, SSL3_RT_ALERT, s->s3->alert_fragment, 2, s, s->msg_callback_arg);

if (s->info_callback != NULL)
cb=s->info_callback;
else if (s->ctx->info_callback != NULL)
cb=s->ctx->info_callback;

if (cb != NULL)
{
j = (alert_level << 8) | alert_descr;
cb(s, SSL_CB_READ_ALERT, j);
}

if (alert_level == 1) /* warning */
{
// 普通报警信息
s->s3->warn_alert = alert_descr;
if (alert_descr == SSL_AD_CLOSE_NOTIFY)
{
s->shutdown |= SSL_RECEIVED_SHUTDOWN;
return(0);
}
}
else if (alert_level == 2) /* fatal */
{
// 严重错误信息, 断开SSL会话
char tmp[16];

s->rwstate=SSL_NOTHING;
s->s3->fatal_alert = alert_descr;
SSLerr(SSL_F_SSL3_READ_BYTES, SSL_AD_REASON_OFFSET + alert_descr);
BIO_snprintf(tmp,sizeof tmp,"%d",alert_descr);
ERR_add_error_data(2,"SSL alert number ",tmp);
s->shutdown|=SSL_RECEIVED_SHUTDOWN;
SSL_CTX_remove_session(s->ctx,s->session);
return(0);
}
else
{
al=SSL_AD_ILLEGAL_PARAMETER;
SSLerr(SSL_F_SSL3_READ_BYTES,SSL_R_UNKNOWN_ALERT_TYPE);
goto f_err;
}

goto start;
}

if (s->shutdown & SSL_SENT_SHUTDOWN) /* but we have not received a shutdown */
{
// SSL会话设置发送SHUTDOWN, 表示不再发送数据
s->rwstate=SSL_NOTHING;
rr->length=0;
return(0);
}

if (rr->type == SSL3_RT_CHANGE_CIPHER_SPEC)
{
// 数据记录类型是更改算法参数
/* 'Change Cipher Spec' is just a single byte, so we know
* exactly what the record payload has to look like */
if ( (rr->length != 1) || (rr->off != 0) ||
(rr->data[0] != SSL3_MT_CCS))
{
// 错误检查
i=SSL_AD_ILLEGAL_PARAMETER;
SSLerr(SSL_F_SSL3_READ_BYTES,SSL_R_BAD_CHANGE_CIPHER_SPEC);
goto err;
}

rr->length=0;

if (s->msg_callback)
s->msg_callback(0, s->version, SSL3_RT_CHANGE_CIPHER_SPEC, rr->data, 1, s, s->msg_callback_arg);

// 加密算法更改处理,成功时转到重新接收数据
s->s3->change_cipher_spec=1;
if (!do_change_cipher_spec(s))
goto err;
else
goto start;
}

/* Unexpected handshake message (Client Hello, or protocol violation) */
if ((s->s3->handshake_fragment_len >= 4) && !s->in_handshake)
{
// 异常的握手信息
// SSL3_FLAGS_NO_RENEGOTIATE_CIPHERS标志表示不需要重新协商加密算法
if (((s->state&SSL_ST_MASK) == SSL_ST_OK) &&
!(s->s3->flags & SSL3_FLAGS_NO_RENEGOTIATE_CIPHERS))
{
#if 0 /* worked only because C operator preferences are not as expected (and
* because this is not really needed for clients except for detecting
* protocol violations): */
s->state=SSL_ST_BEFORE|(s->server)
?SSL_ST_ACCEPT
:SSL_ST_CONNECT;
#else
// 如果是服务器端,SSL状态转为接受;如果是客户端, 转为连接
s->state = s->server ? SSL_ST_ACCEPT : SSL_ST_CONNECT;
#endif
// 重新进行新会话
s->new_session=1;
}
// 重新握手协商
i=s->handshake_func(s);
if (i < 0) return(i);
if (i == 0)
{
SSLerr(SSL_F_SSL3_READ_BYTES,SSL_R_SSL_HANDSHAKE_FAILURE);
return(-1);
}

if (!(s->mode & SSL_MODE_AUTO_RETRY))
{
if (s->s3->rbuf.left == 0) /* no read-ahead left? */
{
BIO *bio;
/* In the case where we try to read application data,
* but we trigger an SSL handshake, we return -1 with
* the retry option set. Otherwise renegotiation may
* cause nasty problems in the blocking world */
s->rwstate=SSL_READING;
bio=SSL_get_rbio(s);
BIO_clear_retry_flags(bio);
BIO_set_retry_read(bio);
return(-1);
}
}
goto start;
}

// 最后再根据记录类型进行处理
switch (rr->type)
{
default:
#ifndef OPENSSL_NO_TLS
/* TLS just ignores unknown message types */
// 如果会话是TLS1版本转为重新接收数据
// 其他版本则认为出错
if (s->version == TLS1_VERSION)
{
rr->length = 0;
goto start;
}
#endif
al=SSL_AD_UNEXPECTED_MESSAGE;
SSLerr(SSL_F_SSL3_READ_BYTES,SSL_R_UNEXPECTED_RECORD);
goto f_err;
case SSL3_RT_CHANGE_CIPHER_SPEC:
case SSL3_RT_ALERT:
case SSL3_RT_HANDSHAKE:
// 这几种类型前面已经处理过了, 到这还有的话是哪出错了
/* we already handled all of these, with the possible exception
* of SSL3_RT_HANDSHAKE when s->in_handshake is set, but that
* should not happen when type != rr->type */
al=SSL_AD_UNEXPECTED_MESSAGE;
SSLerr(SSL_F_SSL3_READ_BYTES,ERR_R_INTERNAL_ERROR);
goto f_err;
case SSL3_RT_APPLICATION_DATA:
// 这时情况是收到的是应用数据,而期望接收的是握手数据
/* At this point, we were expecting handshake data,
* but have application data. If the library was
* running inside ssl3_read() (i.e. in_read_app_data
* is set) and it makes sense to read application data
* at this point (session renegotiation not yet started),
* we will indulge it.
*/
// 要接收应用数据
if (s->s3->in_read_app_data &&
// 需要重协商
(s->s3->total_renegotiations != 0) &&
((
(s->state & SSL_ST_CONNECT) &&
(s->state >= SSL3_ST_CW_CLNT_HELLO_A) &&
(s->state <= SSL3_ST_CR_SRVR_HELLO_A)
) || (
(s->state & SSL_ST_ACCEPT) &&
(s->state <= SSL3_ST_SW_HELLO_REQ_A) &&
(s->state >= SSL3_ST_SR_CLNT_HELLO_A)
)
))
{
// in_read_app_data设置为2，会重新执行ssl3_read_bytes()
s->s3->in_read_app_data=2;
return(-1);
}
else
{
al=SSL_AD_UNEXPECTED_MESSAGE;
SSLerr(SSL_F_SSL3_READ_BYTES,SSL_R_UNEXPECTED_RECORD);
goto f_err;
}
}
/* not reached */

f_err:
// 错误时发送告警信息
ssl3_send_alert(s,SSL3_AL_FATAL,al);
err:
return(-1);
}

可以看出接收数据的重点函数是ssl3_get_record():

/* ssl/s3_pkt.c */
static int ssl3_get_record(SSL *s)
{
int ssl_major,ssl_minor,al;
int enc_err,n,i,ret= -1;
SSL3_RECORD *rr;
SSL_SESSION *sess;
unsigned char *p;
unsigned char md[EVP_MAX_MD_SIZE];
short version;
unsigned int mac_size;
int clear=0;
size_t extra;
int decryption_failed_or_bad_record_mac = 0;
unsigned char *mac = NULL;

// 所读数据的记录指针
rr= &(s->s3->rrec);
sess=s->session;

if (s->options & SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER)
// MS的SSL实现可附带较大数据
extra=SSL3_RT_MAX_EXTRA;
else
extra=0;
if (extra != s->s3->rbuf.len - SSL3_RT_MAX_PACKET_SIZE)
// 普通情况下读缓冲大小就是SSL3_RT_MAX_PACKET_SIZE
{
/* actually likely an application error: SLS_OP_MICROSOFT_BIG_SSLV3_BUFFER
* set after ssl3_setup_buffers() was done */
SSLerr(SSL_F_SSL3_GET_RECORD, ERR_R_INTERNAL_ERROR);
return -1;
}

again:
/* check if we have the header */
if ( (s->rstate != SSL_ST_READ_BODY) ||
// 接收的数据长度还不够记录长度
(s->packet_length < SSL3_RT_HEADER_LENGTH))
{
// 读至少SSL3_RT_HEADER_LENGTH长度,最大s->s3->rbuf.len
n=ssl3_read_n(s, SSL3_RT_HEADER_LENGTH, s->s3->rbuf.len, 0);
if (n <= 0) return(n); /* error or non-blocking */
s->rstate=SSL_ST_READ_BODY;

// p现在是SSL收到的原始数据头
p=s->packet;

/* Pull apart the header into the SSL3_RECORD */
// SSL记录类型
rr->type= *(p++);
// 版本信息
ssl_major= *(p++);
ssl_minor= *(p++);
version=(ssl_major<<8)|ssl_minor;
// 数据长度
n2s(p,rr->length);

/* Lets check version */
if (s->first_packet)
{
s->first_packet=0;
}
else
{
// 已经不是第一个包了
// 检查版本是否等于SSL会话版本,这时应该协商好应该是相同的了
// 如果不同就是错的
if (version != s->version)
{
SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_WRONG_VERSION_NUMBER);
/* Send back error using their
* version number :-) */
s->version=version;
al=SSL_AD_PROTOCOL_VERSION;
goto f_err;
}
}
// 检查版本是否是SSL3
if ((version>>8) != SSL3_VERSION_MAJOR)
{
SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_WRONG_VERSION_NUMBER);
goto err;
}
// 接收数据过长出错
if (rr->length > SSL3_RT_MAX_ENCRYPTED_LENGTH+extra)
{
al=SSL_AD_RECORD_OVERFLOW;
SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_PACKET_LENGTH_TOO_LONG);
goto f_err;
}

/* now s->rstate == SSL_ST_READ_BODY */
}

/* s->rstate == SSL_ST_READ_BODY, get and decode the data */
// SSL3_RT_HEADER_LENGTH = 5
if (rr->length > s->packet_length-SSL3_RT_HEADER_LENGTH)
{
// 已收到的数据还不够记录长度, 继续读够记录长度
/* now s->packet_length == SSL3_RT_HEADER_LENGTH */
i=rr->length;
n=ssl3_read_n(s,i,i,1);
if (n <= 0) return(n); /* error or non-blocking io */
/* now n == rr->length,
* and s->packet_length == SSL3_RT_HEADER_LENGTH + rr->length */
}
//
// 状态转为已经接收到SSL头信息
s->rstate=SSL_ST_READ_HEADER; /* set state for later operations */

/* At this point, s->packet_length == SSL3_RT_HEADER_LNGTH + rr->length,
* and we have that many bytes in s->packet
*/
// input指向SSL原始数据头后的数据
rr->input= &(s->packet[SSL3_RT_HEADER_LENGTH]);

/* ok, we can now read from 's->packet' data into 'rr'
* rr->input points at rr->length bytes, which
* need to be copied into rr->data by either
* the decryption or by the decompression
* When the data is 'copied' into the rr->data buffer,
* rr->input will be pointed at the new buffer */

/* We now have - encrypted [ MAC [ compressed [ plain ] ] ]
* rr->length bytes of encrypted compressed stuff. */

/* check is not needed I believe */
if (rr->length > SSL3_RT_MAX_ENCRYPTED_LENGTH+extra)
{
// 数据又读多了
al=SSL_AD_RECORD_OVERFLOW;
SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_ENCRYPTED_LENGTH_TOO_LONG);
goto f_err;
}

/* decrypt in place in 'rr->input' */
// 记录数据
rr->data=rr->input;

// 对数据进行解密
enc_err = s->method->ssl3_enc->enc(s,0);
if (enc_err <= 0)
{
if (enc_err == 0)
/* SSLerr() and ssl3_send_alert() have been called */
goto err;

/* Otherwise enc_err == -1, which indicates bad padding
* (rec->length has not been changed in this case).
* To minimize information leaked via timing, we will perform
* the MAC computation anyway. */
// 注意 enc_err<0 时并不立即转到错误处理,只是作个标志
decryption_failed_or_bad_record_mac = 1;
}

/* r->length is now the compressed data plus mac */
if ( (sess == NULL) ||
(s->enc_read_ctx == NULL) ||
(s->read_hash == NULL))
// 会话,加密上下文,读认证码操作都为空的情况，设置标志clear
clear=1;

if (!clear)
{
// HASH算法的认证码长度
mac_size=EVP_MD_size(s->read_hash);

if (rr->length > SSL3_RT_MAX_COMPRESSED_LENGTH+extra+mac_size)
{
#if 0 /* OK only for stream ciphers (then rr->length is visible from ciphertext anyway) */
al=SSL_AD_RECORD_OVERFLOW;
SSLerr(SSL_F_SSL3_GET_RECORD,
SSL_R_PRE_MAC_LENGTH_TOO_LONG);
goto f_err;
#else
// 长度过长, 设置出错标志
decryption_failed_or_bad_record_mac = 1;
#endif
}
/* check the MAC for rr->input (it's in mac_size bytes at the tail) */
if (rr->length >= mac_size)
{
// 记录长度中减去认证码长度
rr->length -= mac_size;
// 认证码数据指针
mac = &rr->data[rr->length];
}
else
{
/* record (minus padding) is too short to contain a MAC */
#if 0 /* OK only for stream ciphers */
al=SSL_AD_DECODE_ERROR;
SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_LENGTH_TOO_SHORT);
goto f_err;
#else
// 记录长度还没认证码长度长, 设置出错标志
decryption_failed_or_bad_record_mac = 1;
rr->length = 0;
#endif
}
// 用认证码对数据进行认证
i=s->method->ssl3_enc->mac(s,md,0);
if (mac == NULL || memcmp(md, mac, mac_size) != 0)
{
decryption_failed_or_bad_record_mac = 1;
}
}

if (decryption_failed_or_bad_record_mac)
{
// 解密错误, 跳出
/* A separate 'decryption_failed' alert was introduced with TLS 1.0,
* SSL 3.0 only has 'bad_record_mac'. But unless a decryption
* failure is directly visible from the ciphertext anyway,
* we should not reveal which kind of error occured -- this
* might become visible to an attacker (e.g. via a logfile) */
al=SSL_AD_BAD_RECORD_MAC;
SSLerr(SSL_F_SSL3_GET_RECORD,
SSL_R_DECRYPTION_FAILED_OR_BAD_RECORD_MAC);
goto f_err;
}

/* r->length is now just compressed */
if (s->expand != NULL)
// 现在数据是经过压缩处理的
{
if (rr->length > SSL3_RT_MAX_COMPRESSED_LENGTH+extra)
{
// 压缩数据长度又太长了
al=SSL_AD_RECORD_OVERFLOW;
SSLerr(SSL_F_SSL3_GET_RECORD,
SSL_R_COMPRESSED_LENGTH_TOO_LONG);
goto f_err;
}
// 对数据解压
if (!do_uncompress(s))
{
// 解压失败, 跳出
al=SSL_AD_DECOMPRESSION_FAILURE;
SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_BAD_DECOMPRESSION);
goto f_err;
}
}

if (rr->length > SSL3_RT_MAX_PLAIN_LENGTH+extra)
{
// 解压缩后的明文数据长度过长, 跳出
al=SSL_AD_RECORD_OVERFLOW;
SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_DATA_LENGTH_TOO_LONG);
goto f_err;
}

rr->off=0;
/* So at this point the following is true
* ssl->s3->rrec.type is the type of record
* ssl->s3->rrec.length == number of bytes in record
* ssl->s3->rrec.off == offset to first valid byte
* ssl->s3->rrec.data == where to take bytes from, increment
* after use :-).
*/

/* we have pulled in a full packet so zero things */
s->packet_length=0;

/* just read a 0 length packet */
// 如果记录长度为0, 转到继续接收数据
if (rr->length == 0) goto again;

return(1);

f_err:
// 错误发送告警信息
ssl3_send_alert(s,SSL3_AL_FATAL,al);
err:
return(ret);
}

最后看一下ssl3_read_n()函数，接收SSL原始数据, 该函数只被ssl3_get_record()函数调用，是static的：

/* ssl/s3_pkt.c */
static int ssl3_read_n(SSL *s, int n, int max, int extend)
{
// extend为0时表示要读全新数据，非0表示可以用现在缓冲中的数据
/* If extend == 0, obtain new n-byte packet; if extend == 1, increase
* packet by another n bytes.
* The packet will be in the sub-array of s->s3->rbuf.buf specified
* by s->packet and s->packet_length.
* (If s->read_ahead is set, 'max' bytes may be stored in rbuf
* [plus s->packet_length bytes if extend == 1].)
*/
int i,off,newb;

if (!extend)
{
/* start with empty packet ... */
// 确定包缓冲地址, 置当前的包长为0
if (s->s3->rbuf.left == 0)
s->s3->rbuf.offset = 0;
s->packet = s->s3->rbuf.buf + s->s3->rbuf.offset;
s->packet_length = 0;
/* ... now we can act as if 'extend' was set */
}

/* if there is enough in the buffer from a previous read, take some */
if (s->s3->rbuf.left >= (int)n)
{
// 如果已读缓冲区中剩余数据超过要读的数据,直接移动指针即可
s->packet_length+=n;
s->s3->rbuf.left-=n;
s->s3->rbuf.offset+=n;
return(n);
}

/* else we need to read more data */
// 预读数据长度为0
if (!s->read_ahead)
max=n;

{
/* avoid buffer overflow */
// 当前缓冲区最大空闲值
int max_max = s->s3->rbuf.len - s->packet_length;
if (max > max_max)
max = max_max;
}
if (n > max) /* does not happen */
{
// 要读的数据量超过了缓冲区量,出错
SSLerr(SSL_F_SSL3_READ_N,ERR_R_INTERNAL_ERROR);
return -1;
}

off = s->packet_length;
// newb为读缓冲区中剩下的有效数据长度
newb = s->s3->rbuf.left;
/* Move any available bytes to front of buffer:
* 'off' bytes already pointed to by 'packet',
* 'newb' extra ones at the end */
if (s->packet != s->s3->rbuf.buf)
{
/* off > 0 */
memmove(s->s3->rbuf.buf, s->packet, off+newb);
s->packet = s->s3->rbuf.buf;
}

while (newb < n)
{
/* Now we have off+newb bytes at the front of s->s3->rbuf.buf and need
* to read in more until we have off+n (up to off+max if possible) */

clear_sys_error();
if (s->rbio != NULL)
{
s->rwstate=SSL_READING;
// 通过SSL的读BIO读取数据
i=BIO_read(s->rbio, &(s->s3->rbuf.buf[off+newb]), max-newb);
}
else
{
SSLerr(SSL_F_SSL3_READ_N,SSL_R_READ_BIO_NOT_SET);
i = -1;
}

if (i <= 0)
{
// 读完或出错, newb为缓冲区剩余有效数据长度
s->s3->rbuf.left = newb;
return(i);
}
newb+=i;
}

/* done reading, now the book-keeping */
// 读数据完成, 修改偏移量和剩余数据长度
s->s3->rbuf.offset = off + n;
s->s3->rbuf.left = newb - n;
s->packet_length += n;
s->rwstate=SSL_NOTHING;
return(n);
}
2.15 SSL_write

SSL结构(struct ssl_st)中的s2,s3指针分别指向SSL2和SSL3的状态结构，这些状态结构中都有用于写的wbuf，写操作相对读操作要简单一些。

SSL_write()实现向SSL通道中写数据，应用程序只需要向里写入明文数据，SSL通道自动对这些数据进行加密封装。

/* ssl/ssl_lib.c */

int SSL_write(SSL *s,const void *buf,int num)
{
if (s->handshake_func == 0)
{
SSLerr(SSL_F_SSL_WRITE, SSL_R_UNINITIALIZED);
return -1;
}
// 发现发送shutdown标志，发送失败
if (s->shutdown & SSL_SENT_SHUTDOWN)
{
s->rwstate=SSL_NOTHING;
SSLerr(SSL_F_SSL_WRITE,SSL_R_PROTOCOL_IS_SHUTDOWN);
return(-1);
}
// 调用具体方法的发送函数, 如ssl3_write(), ssl2_write()等
return(s->method->ssl_write(s,buf,num));
}

下面以ssl3_write()函数进行详细说明，

/* ssl/s3_lib.c */

int ssl3_write(SSL *s, const void *buf, int len)
{
int ret,n;

#if 0
if (s->shutdown & SSL_SEND_SHUTDOWN)
{
s->rwstate=SSL_NOTHING;
return(0);
}
#endif
// 和read操作类似的一些检查工作
clear_sys_error();
if (s->s3->renegotiate) ssl3_renegotiate_check(s);

/* This is an experimental flag that sends the
* last handshake message in the same packet as the first
* use data - used to see if it helps the TCP protocol during
* session-id reuse */
/* The second test is because the buffer may have been removed */
if ((s->s3->flags & SSL3_FLAGS_POP_BUFFER) && (s->wbio == s->bbio))
{
// 这个标志导致的操作更多的是实验性功能
/* First time through, we write into the buffer */
if (s->s3->delay_buf_pop_ret == 0)
{
ret=ssl3_write_bytes(s,SSL3_RT_APPLICATION_DATA,
buf,len);
if (ret <= 0) return(ret);

s->s3->delay_buf_pop_ret=ret;
}

s->rwstate=SSL_WRITING;
n=BIO_flush(s->wbio);
if (n <= 0) return(n);
s->rwstate=SSL_NOTHING;

/* We have flushed the buffer, so remove it */
ssl_free_wbio_buffer(s);
s->s3->flags&= ~SSL3_FLAGS_POP_BUFFER;

ret=s->s3->delay_buf_pop_ret;
s->s3->delay_buf_pop_ret=0;
}
else
{
// 正常的SSL3写数据,类型为SSL3_RT_APPLICATION_DATA,应用层数据
ret=ssl3_write_bytes(s,SSL3_RT_APPLICATION_DATA,
buf,len);
if (ret <= 0) return(ret);
}

return(ret);
}

写数据操作主要由ssl3_write_bytes()完成:

/* ssl/s3_pkt.c */

/* Call this to write data in records of type 'type'
* It will return <= 0 if not all data has been sent or non-blocking IO.
*/
int ssl3_write_bytes(SSL *s, int type, const void *buf_, int len)
{
const unsigned char *buf=buf_;
unsigned int tot,n,nw;
int i;

// 状态参数初始化
s->rwstate=SSL_NOTHING;
// s3->wnum是写缓冲区中还没写完的数据长度
tot=s->s3->wnum;
s->s3->wnum=0;

if (SSL_in_init(s) && !s->in_handshake)
{
// 检查是否需要协商
i=s->handshake_func(s);
if (i < 0) return(i);
if (i == 0)
{
SSLerr(SSL_F_SSL3_WRITE_BYTES,SSL_R_SSL_HANDSHAKE_FAILURE);
return -1;
}
}

// 实际要写的数据量
n=(len-tot);
for (;;)
{
// 限制一次写入的最大数据量
if (n > SSL3_RT_MAX_PLAIN_LENGTH)
nw=SSL3_RT_MAX_PLAIN_LENGTH;
else
nw=n;

// 进行具体的写操作
i=do_ssl3_write(s, type, &(buf[tot]), nw, 0);
if (i <= 0)
{
// 写入失败, 恢复未写入数据长度值
s->s3->wnum=tot;
return i;
}

if ((i == (int)n) ||
(type == SSL3_RT_APPLICATION_DATA &&
(s->mode & SSL_MODE_ENABLE_PARTIAL_WRITE)))
{
// 写完或允许只进行部分写时可以成功返回
/* next chunk of data should get another prepended empty fragment
* in ciphersuites with known-IV weakness: */
s->s3->empty_fragment_done = 0;

return tot+i;
}

n-=i;
tot+=i;
}
}

do_ssl3_write()完成对应用层数据的SSL封装,再调用底层发送函数发送数据, 这是一个static的内部函数:

/* ssl/s3_pkt.c */
static int do_ssl3_write(SSL *s, int type, const unsigned char *buf,
unsigned int len, int create_empty_fragment)
{
unsigned char *p,*plen;
int i,mac_size,clear=0;
int prefix_len = 0;
SSL3_RECORD *wr;
SSL3_BUFFER *wb;
SSL_SESSION *sess;

/* first check if there is a SSL3_BUFFER still being written
* out. This will happen with non blocking IO */
// 还有没写完的数据时先写这些数据
if (s->s3->wbuf.left != 0)
return(ssl3_write_pending(s,type,buf,len));

/* If we have an alert to send, lets send it */
if (s->s3->alert_dispatch)
{
// 要发送告警信息
i=ssl3_dispatch_alert(s);
if (i <= 0)
return(i);
/* if it went, fall through and send more stuff */
}

if (len == 0 && !create_empty_fragment)
return 0;
// wr为写的数据记录
wr= &(s->s3->wrec);
// wb指向要写的数据缓冲
wb= &(s->s3->wbuf);
sess=s->session;

if ( (sess == NULL) ||
(s->enc_write_ctx == NULL) ||
(s->write_hash == NULL))
clear=1;

// 实际发送的数据总长要追加的认证码长度
if (clear)
mac_size=0;
else
mac_size=EVP_MD_size(s->write_hash);

/* 'create_empty_fragment' is true only when this function calls itself */
if (!clear && !create_empty_fragment && !s->s3->empty_fragment_done)
{
/* countermeasure against known-IV weakness in CBC ciphersuites
* (see http://www.openssl.org/~bodo/tls-cbc.txt) */

if (s->s3->need_empty_fragments && type == SSL3_RT_APPLICATION_DATA)
{
// 需要空的碎片段的情况
/* recursive function call with 'create_empty_fragment' set;
* this prepares and buffers the data for an empty fragment
* (these 'prefix_len' bytes are sent out later
* together with the actual payload) */
// 以len为0,create_empty_fragment为1递归调用本函数建立空碎片数据,
// 基本就只是IV,供后续的实际数据使用
prefix_len = do_ssl3_write(s, type, buf, 0, 1);
if (prefix_len <= 0)
goto err;

if (s->s3->wbuf.len < (size_t)prefix_len + SSL3_RT_MAX_PACKET_SIZE)
{
// 发送缓冲区大小检查
/* insufficient space */
SSLerr(SSL_F_DO_SSL3_WRITE, ERR_R_INTERNAL_ERROR);
goto err;
}
}
// 设置进行了空碎片操作标志
s->s3->empty_fragment_done = 1;
}
// 具体的要发送的网络数据指针, wb=&(s->s3->wbuf)
p = wb->buf + prefix_len;

/* write the header */
// 类型
*(p++)=type&0xff;
// 写记录的类型
wr->type=type;

// 版本号
*(p++)=(s->version>>8);
*(p++)=s->version&0xff;

/* field where we are to write out packet length */
// 长度,先在保留指针位置,最后数据处理完才写具体长度
plen=p;
p+=2;

/* lets setup the record stuff. */
// 写记录的基本数据
wr->data=p;
wr->length=(int)len;
// 写记录的输入就是原始输入数据
wr->input=(unsigned char *)buf;

/* we now 'read' from wr->input, wr->length bytes into
* wr->data */

/* first we compress */
if (s->compress != NULL)
{
// 需要压缩的话先对数据进行压缩,明文压缩率才比较大,密文的压缩率几乎为0
if (!do_compress(s))
{
SSLerr(SSL_F_DO_SSL3_WRITE,SSL_R_COMPRESSION_FAILURE);
goto err;
}
}
else
{
// 不压缩就直接把输入数据拷贝到输出记录缓冲区
memcpy(wr->data,wr->input,wr->length);
wr->input=wr->data;
}

/* we should still have the output to wr->data and the input
* from wr->input. Length should be wr->length.
* wr->data still points in the wb->buf */

if (mac_size != 0)
{
// 计算认证码
s->method->ssl3_enc->mac(s,&(p[wr->length]),1);
// 将认证码长度添加到数据总长上,注意是对明文或压缩后的明文进行认证
// 而不是对密文进行认证
wr->length+=mac_size;
wr->input=p;
wr->data=p;
}

/* ssl3_enc can only have an error on read */
// 对数据进行加密, 对写数据加密是不会出错的
s->method->ssl3_enc->enc(s,1);

/* record length after mac and block padding */
// 写入实际加密后数据的长度
s2n(wr->length,plen);

/* we should now have
* wr->data pointing to the encrypted data, which is
* wr->length long */
// 写入记录的类型和总长
wr->type=type; /* not needed but helps for debugging */
wr->length+=SSL3_RT_HEADER_LENGTH;

if (create_empty_fragment)
{
/* we are in a recursive call;
* just return the length, don't write out anything here
*/
// 如果是空碎片,直接就返回了,不实际发送
return wr->length;
}

// 实际的要发送的原始数据
/* now let's set up wb */
wb->left = prefix_len + wr->length;
wb->offset = 0;

/* memorize arguments so that ssl3_write_pending can detect bad write retries later */
// 要发送的数据长度
s->s3->wpend_tot=len;
// 要发送明文的缓冲区, 实际是不发送的, 实际发送的是wb指向的缓冲区
s->s3->wpend_buf=buf;
// 数据类型
s->s3->wpend_type=type;
// 如果发送成功返回的数据长度, 这是指明文数据的长度, 供应用层程序判断用的
// 不是实际发送的压缩加密后的数据长度
s->s3->wpend_ret=len;

/* we now just need to write the buffer */
// 调用ssl3_write_pending()发送数据
return ssl3_write_pending(s,type,buf,len);
err:
return -1;
}

ssl3_write_pending()完成实际的数据发送, 这也是个static的函数, 和和普通write()一样, 这个函数可能会阻塞, 而如果套接字是NON_BLOCK的发送不出去会直接返回:

/* if s->s3->wbuf.left != 0, we need to call this */
static int ssl3_write_pending(SSL *s, int type, const unsigned char *buf,
unsigned int len)
{
int i;

/* XXXX */
// 判断数据长度是否出错用的是wpend_buf
if ((s->s3->wpend_tot > (int)len)
|| ((s->s3->wpend_buf != buf) &&
!(s->mode & SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER))
|| (s->s3->wpend_type != type))
{
SSLerr(SSL_F_SSL3_WRITE_PENDING,SSL_R_BAD_WRITE_RETRY);
return(-1);
}

for (;;)
// 循环直到全部数据发送完
{
clear_sys_error();
if (s->wbio != NULL)
{
s->rwstate=SSL_WRITING;
// 实际进行BIO写操作的是s3->wbuf中的数据,这是已经进行了压缩加密了的数据
i=BIO_write(s->wbio,
(char *)&(s->s3->wbuf.buf[s->s3->wbuf.offset]),
(unsigned int)s->s3->wbuf.left);
}
else
{
SSLerr(SSL_F_SSL3_WRITE_PENDING,SSL_R_BIO_NOT_SET);
i= -1;
}
if (i == s->s3->wbuf.left)
{
s->s3->wbuf.left=0;
s->rwstate=SSL_NOTHING;
// 发送完实际数据,返回的是原始明文数据的长度
return(s->s3->wpend_ret);
}
else if (i <= 0)
return(i);
s->s3->wbuf.offset+=i;
s->s3->wbuf.left-=i;
}
}

2.16 SSL_free

SSL_free()函数释放SSL结构:

/* ssl/ssl_lib.c */

void SSL_free(SSL *s)
{
int i;

if(s == NULL)
return;
// 加密锁引用减1
i=CRYPTO_add(&s->references,-1,CRYPTO_LOCK_SSL);
#ifdef REF_PRINT
REF_PRINT("SSL",s);
#endif
if (i > 0) return;
#ifdef REF_CHECK
if (i < 0)
{
fprintf(stderr,"SSL_free, bad reference countn");
abort(); /* ok */
}
#endif
// 释放加密库所需附加数据
CRYPTO_free_ex_data(CRYPTO_EX_INDEX_SSL, s, &s->ex_data);

if (s->bbio != NULL)
{
// 释放BIO缓冲
/* If the buffering BIO is in place, pop it off */
if (s->bbio == s->wbio)
{
s->wbio=BIO_pop(s->wbio);
}
BIO_free(s->bbio);
s->bbio=NULL;
}
// 释放读BIO
if (s->rbio != NULL)
BIO_free_all(s->rbio);
// 释放写BIO
if ((s->wbio != NULL) && (s->wbio != s->rbio))
BIO_free_all(s->wbio);
// 释放初始化缓冲区
if (s->init_buf != NULL) BUF_MEM_free(s->init_buf);

/* add extra stuff */
// 释放加密库链表
if (s->cipher_list != NULL) sk_SSL_CIPHER_free(s->cipher_list);
if (s->cipher_list_by_id != NULL) sk_SSL_CIPHER_free(s->cipher_list_by_id);

/* Make the next call work :-) */
// 清除SSL的会话
if (s->session != NULL)
{
ssl_clear_bad_session(s);
SSL_SESSION_free(s->session);
}
// 释放SSL的读写上下文
ssl_clear_cipher_ctx(s);
// 释放证书
if (s->cert != NULL) ssl_cert_free(s->cert);
/* Free up if allocated */
// 释放加密算法上下文
if (s->ctx) SSL_CTX_free(s->ctx);
if (s->client_CA != NULL)
sk_X509_NAME_pop_free(s->client_CA,X509_NAME_free);
// 释放SSL方法
if (s->method != NULL) s->method->ssl_free(s);
// 释放SSL结构本身
OPENSSL_free(s);
}

zhaozg's blog

星期三, 五月 09, 2007

OpenSSL协议实现分析

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