SSL连接建立过程分析(2)
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) */
/* 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 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。
...... 待续 ......
