SSL连接建立过程分析(2)

SSL连接建立过程分析(2)

 

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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。