BIO_f_ssl(3)                 OpenSSL                 BIO_f_ssl(3)


     BIO_f_ssl, BIO_set_ssl, BIO_get_ssl, BIO_set_ssl_mode,
     BIO_set_ssl_renegotiate_bytes, BIO_get_num_renegotiates,
     BIO_set_ssl_renegotiate_timeout, BIO_new_ssl,
     BIO_new_ssl_connect, BIO_new_buffer_ssl_connect,
     BIO_ssl_copy_session_id, BIO_ssl_shutdown - SSL BIO


      #include <openssl/bio.h>
      #include <openssl/ssl.h>

      BIO_METHOD *BIO_f_ssl(void);

      #define BIO_set_ssl(b,ssl,c)   BIO_ctrl(b,BIO_C_SET_SSL,c,(char *)ssl)
      #define BIO_get_ssl(b,sslp)    BIO_ctrl(b,BIO_C_GET_SSL,0,(char *)sslp)
      #define BIO_set_ssl_mode(b,client)     BIO_ctrl(b,BIO_C_SSL_MODE,client,NULL)
      #define BIO_set_ssl_renegotiate_bytes(b,num) \
      #define BIO_set_ssl_renegotiate_timeout(b,seconds) \
      #define BIO_get_num_renegotiates(b) \

      BIO *BIO_new_ssl(SSL_CTX *ctx,int client);
      BIO *BIO_new_ssl_connect(SSL_CTX *ctx);
      BIO *BIO_new_buffer_ssl_connect(SSL_CTX *ctx);
      int BIO_ssl_copy_session_id(BIO *to,BIO *from);
      void BIO_ssl_shutdown(BIO *bio);

      #define BIO_do_handshake(b)    BIO_ctrl(b,BIO_C_DO_STATE_MACHINE,0,NULL)


     BIO_f_ssl() returns the SSL BIO method. This is a filter BIO
     which is a wrapper round the OpenSSL SSL routines adding a
     BIO "flavour" to SSL I/O.

     I/O performed on an SSL BIO communicates using the SSL
     protocol with the SSLs read and write BIOs. If an SSL
     connection is not established then an attempt is made to
     establish one on the first I/O call.

     If a BIO is appended to an SSL BIO using BIO_push() it is
     automatically used as the SSL BIOs read and write BIOs.

     Calling BIO_reset() on an SSL BIO closes down any current
     SSL connection by calling SSL_shutdown(). BIO_reset() is
     then sent to the next BIO in the chain: this will typically
     disconnect the underlying transport.  The SSL BIO is then
     reset to the initial accept or connect state.

     If the close flag is set when an SSL BIO is freed then the
     internal SSL structure is also freed using SSL_free().

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BIO_f_ssl(3)                 OpenSSL                 BIO_f_ssl(3)

     BIO_set_ssl() sets the internal SSL pointer of BIO b to ssl
     using the close flag c.

     BIO_get_ssl() retrieves the SSL pointer of BIO b, it can
     then be manipulated using the standard SSL library

     BIO_set_ssl_mode() sets the SSL BIO mode to client. If
     client is 1 client mode is set. If client is 0 server mode
     is set.

     BIO_set_ssl_renegotiate_bytes() sets the renegotiate byte
     count to num. When set after every num bytes of I/O (read
     and write) the SSL session is automatically renegotiated.
     num must be at least 512 bytes.

     BIO_set_ssl_renegotiate_timeout() sets the renegotiate
     timeout to seconds. When the renegotiate timeout elapses the
     session is automatically renegotiated.

     BIO_get_num_renegotiates() returns the total number of
     session renegotiations due to I/O or timeout.

     BIO_new_ssl() allocates an SSL BIO using SSL_CTX ctx and
     using client mode if client is non zero.

     BIO_new_ssl_connect() creates a new BIO chain consisting of
     an SSL BIO (using ctx) followed by a connect BIO.

     BIO_new_buffer_ssl_connect() creates a new BIO chain
     consisting of a buffering BIO, an SSL BIO (using ctx) and a
     connect BIO.

     BIO_ssl_copy_session_id() copies an SSL session id between
     BIO chains from and to. It does this by locating the SSL
     BIOs in each chain and calling SSL_copy_session_id() on the
     internal SSL pointer.

     BIO_ssl_shutdown() closes down an SSL connection on BIO
     chain bio. It does this by locating the SSL BIO in the chain
     and calling SSL_shutdown() on its internal SSL pointer.

     BIO_do_handshake() attempts to complete an SSL handshake on
     the supplied BIO and establish the SSL connection. It
     returns 1 if the connection was established successfully. A
     zero or negative value is returned if the connection could
     not be established, the call BIO_should_retry() should be
     used for non blocking connect BIOs to determine if the call
     should be retried. If an SSL connection has already been
     established this call has no effect.

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BIO_f_ssl(3)                 OpenSSL                 BIO_f_ssl(3)


     SSL BIOs are exceptional in that if the underlying transport
     is non blocking they can still request a retry in
     exceptional circumstances. Specifically this will happen if
     a session renegotiation takes place during a BIO_read()
     operation, one case where this happens is when step up

     In OpenSSL 0.9.6 and later the SSL flag SSL_AUTO_RETRY can
     be set to disable this behaviour. That is when this flag is
     set an SSL BIO using a blocking transport will never request
     a retry.

     Since unknown BIO_ctrl() operations are sent through filter
     BIOs the servers name and port can be set using
     BIO_set_host() on the BIO returned by BIO_new_ssl_connect()
     without having to locate the connect BIO first.

     Applications do not have to call BIO_do_handshake() but may
     wish to do so to separate the handshake process from other
     I/O processing.




     This SSL/TLS client example, attempts to retrieve a page
     from an SSL/TLS web server. The I/O routines are identical
     to those of the unencrypted example in BIO_s_connect(3).

      BIO *sbio, *out;
      int len;
      char tmpbuf[1024];
      SSL_CTX *ctx;
      SSL *ssl;


      /* We would seed the PRNG here if the platform didn't
       * do it automatically

      ctx = SSL_CTX_new(SSLv23_client_method());

      /* We'd normally set some stuff like the verify paths and
       * mode here because as things stand this will connect to
       * any server whose certificate is signed by any CA.

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BIO_f_ssl(3)                 OpenSSL                 BIO_f_ssl(3)

      sbio = BIO_new_ssl_connect(ctx);

      BIO_get_ssl(sbio, &ssl);

      if(!ssl) {
        fprintf(stderr, "Can't locate SSL pointer\n");
        /* whatever ... */

      /* Don't want any retries */
      SSL_set_mode(ssl, SSL_MODE_AUTO_RETRY);

      /* We might want to do other things with ssl here */

      BIO_set_conn_hostname(sbio, "localhost:https");

      out = BIO_new_fp(stdout, BIO_NOCLOSE);
      if(BIO_do_connect(sbio) <= 0) {
             fprintf(stderr, "Error connecting to server\n");
             /* whatever ... */

      if(BIO_do_handshake(sbio) <= 0) {
             fprintf(stderr, "Error establishing SSL connection\n");
             /* whatever ... */

      /* Could examine ssl here to get connection info */

      BIO_puts(sbio, "GET / HTTP/1.0\n\n");
      for(;;) {
             len = BIO_read(sbio, tmpbuf, 1024);
             if(len <= 0) break;
             BIO_write(out, tmpbuf, len);

     Here is a simple server example. It makes use of a buffering
     BIO to allow lines to be read from the SSL BIO using
     BIO_gets.  It creates a pseudo web page containing the
     actual request from a client and also echoes the request to
     standard output.

      BIO *sbio, *bbio, *acpt, *out;
      int len;
      char tmpbuf[1024];
      SSL_CTX *ctx;
      SSL *ssl;

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BIO_f_ssl(3)                 OpenSSL                 BIO_f_ssl(3)


      /* Might seed PRNG here */

      ctx = SSL_CTX_new(SSLv23_server_method());

      if (!SSL_CTX_use_certificate_file(ctx,"server.pem",SSL_FILETYPE_PEM)
             || !SSL_CTX_use_PrivateKey_file(ctx,"server.pem",SSL_FILETYPE_PEM)
             || !SSL_CTX_check_private_key(ctx)) {

             fprintf(stderr, "Error setting up SSL_CTX\n");
             return 0;

      /* Might do other things here like setting verify locations and
       * DH and/or RSA temporary key callbacks

      /* New SSL BIO setup as server */

      BIO_get_ssl(sbio, &ssl);

      if(!ssl) {
        fprintf(stderr, "Can't locate SSL pointer\n");
        /* whatever ... */

      /* Don't want any retries */
      SSL_set_mode(ssl, SSL_MODE_AUTO_RETRY);

      /* Create the buffering BIO */

      bbio = BIO_new(BIO_f_buffer());

      /* Add to chain */
      sbio = BIO_push(bbio, sbio);


      /* By doing this when a new connection is established
       * we automatically have sbio inserted into it. The
       * BIO chain is now 'swallowed' by the accept BIO and
       * will be freed when the accept BIO is freed.


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BIO_f_ssl(3)                 OpenSSL                 BIO_f_ssl(3)

      out = BIO_new_fp(stdout, BIO_NOCLOSE);

      /* Setup accept BIO */
      if(BIO_do_accept(acpt) <= 0) {
             fprintf(stderr, "Error setting up accept BIO\n");
             return 0;

      /* Now wait for incoming connection */
      if(BIO_do_accept(acpt) <= 0) {
             fprintf(stderr, "Error in connection\n");
             return 0;

      /* We only want one connection so remove and free
       * accept BIO

      sbio = BIO_pop(acpt);


      if(BIO_do_handshake(sbio) <= 0) {
             fprintf(stderr, "Error in SSL handshake\n");
             return 0;

      BIO_puts(sbio, "HTTP/1.0 200 OK\r\nContent-type: text/plain\r\n\r\n");
      BIO_puts(sbio, "\r\nConnection Established\r\nRequest headers:\r\n");
      BIO_puts(sbio, "--------------------------------------------------\r\n");

      for(;;) {
             len = BIO_gets(sbio, tmpbuf, 1024);
             if(len <= 0) break;
             BIO_write(sbio, tmpbuf, len);
             BIO_write(out, tmpbuf, len);
             /* Look for blank line signifying end of headers*/
             if((tmpbuf[0] == '\r') || (tmpbuf[0] == '\n')) break;

      BIO_puts(sbio, "--------------------------------------------------\r\n");
      BIO_puts(sbio, "\r\n");

      /* Since there is a buffering BIO present we had better flush it */


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BIO_f_ssl(3)                 OpenSSL                 BIO_f_ssl(3)


     In OpenSSL versions before 1.0.0 the BIO_pop() call was
     handled incorrectly, the I/O BIO reference count was
     incorrectly incremented (instead of decremented) and
     dissociated with the SSL BIO even if the SSL BIO was not
     explicitly being popped (e.g. a pop higher up the chain).
     Applications which included workarounds for this bug (e.g.
     freeing BIOs more than once) should be modified to handle
     this fix or they may free up an already freed BIO.



1.0.2t               Last change: 2019-09-10                    7

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