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,
BIO_do_handshake —
SSL BIO
#include
<openssl/bio.h>
#include
<openssl/ssl.h>
const BIO_METHOD *
BIO_f_ssl(
void);
long
BIO_set_ssl(
BIO
*b,
SSL *ssl,
long c);
long
BIO_get_ssl(
BIO
*b,
SSL *sslp);
long
BIO_set_ssl_mode(
BIO
*b,
long client);
long
BIO_set_ssl_renegotiate_bytes(
BIO
*b,
long num);
long
BIO_set_ssl_renegotiate_timeout(
BIO
*b,
long seconds);
long
BIO_get_num_renegotiates(
BIO
*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);
long
BIO_do_handshake(
BIO
*b);
BIO_f_ssl() returns the
SSL BIO
method. This is a filter
BIO which is a
wrapper around the OpenSSL
SSL routines
adding a
BIO “flavor” to SSL
I/O.
I/O performed on an
SSL
BIO communicates using the SSL protocol with
the
SSL's 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(3) it is
automatically used as the
SSL
BIO's read and write
BIOs.
Calling
BIO_reset(3) on an
SSL BIO
closes down any current SSL connection by calling
SSL_shutdown(3).
BIO_reset(3) 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(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 functions.
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 nonzero.
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(3)
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(3) 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(3)
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.
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(3) operation. One
case where this happens is when step up occurs.
In OpenSSL 0.9.6 and later the SSL flag
SSL_AUTO_RETRY can be set to disable this
behaviour. In other words, when this flag is set an
SSL BIO
using a blocking transport will never request a retry.
Since unknown
BIO_ctrl(3)
operations are sent through filter
BIOs the
server name and port can be set using
BIO_set_conn_hostname(3)
and
BIO_set_conn_port(3)
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.
BIO_set_ssl(),
BIO_get_ssl(),
BIO_set_ssl_mode(),
BIO_set_ssl_renegotiate_bytes(),
BIO_set_ssl_renegotiate_timeout(),
BIO_get_num_renegotiates(), and
BIO_do_handshake() are implemented as
macros.
BIO_f_ssl() returns a pointer to a static
BIO_METHOD structure.
BIO_set_ssl(),
BIO_get_ssl(),
BIO_set_ssl_mode(),
BIO_set_ssl_renegotiate_bytes(),
BIO_set_ssl_renegotiate_timeout(), and
BIO_get_num_renegotiates() return 1 on
success or a value less than or equal to 0 if an error occurred.
BIO_new_ssl(),
BIO_new_ssl_connect(), and
BIO_new_buffer_ssl_connect() returns a
pointer to a newly allocated
BIO chain or
NULL if an error occurred.
BIO_ssl_copy_session_id() returns 1 on
success or 0 on error.
BIO_do_handshake() returns 1 if the
connection was established successfully or a value less than or equal to 0
otherwise.
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;
ERR_load_crypto_strings();
ERR_load_SSL_strings();
OpenSSL_add_all_algorithms();
/*
* 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.
*/
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");
ERR_print_errors_fp(stderr);
/* whatever ... */
}
if (BIO_do_handshake(sbio) <= 0) {
fprintf(stderr, "Error establishing SSL connection\n");
ERR_print_errors_fp(stderr);
/* 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);
}
BIO_free_all(sbio);
BIO_free(out);
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(3). 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;
ERR_load_crypto_strings();
ERR_load_SSL_strings();
OpenSSL_add_all_algorithms();
/* 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");
ERR_print_errors_fp(stderr);
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 */
sbio = BIO_new_ssl(ctx,0);
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);
acpt = BIO_new_accept("4433");
/*
* 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.
*/
BIO_set_accept_bios(acpt,sbio);
out = BIO_new_fp(stdout, BIO_NOCLOSE);
/* Wait for incoming connection */
if (BIO_do_accept(acpt) <= 0) {
fprintf(stderr, "Error setting up accept BIO\n");
ERR_print_errors_fp(stderr);
return 0;
}
/* We only want one connection so remove and free accept BIO */
sbio = BIO_pop(acpt);
BIO_free_all(acpt);
if (BIO_do_handshake(sbio) <= 0) {
fprintf(stderr, "Error in SSL handshake\n");
ERR_print_errors_fp(stderr);
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 */
BIO_flush(sbio);
BIO_free_all(sbio);
BIO_f_ssl(),
BIO_set_ssl(), and
BIO_get_ssl() first appeared in SSLeay
0.6.0.
BIO_set_ssl_mode(),
BIO_new_ssl(), and
BIO_ssl_copy_session_id() first appeared in
SSLeay 0.8.0.
BIO_ssl_shutdown() and
BIO_do_handshake() first appeared in SSLeay
0.8.1.
BIO_set_ssl_renegotiate_bytes(),
BIO_get_num_renegotiates(),
BIO_set_ssl_renegotiate_timeout(),
BIO_new_ssl_connect(), and
BIO_new_buffer_ssl_connect() first appeared
in SSLeay 0.9.0. All these functions have been available since
OpenBSD 2.4.
In OpenSSL versions before 1.0.0 the
BIO_pop(3) 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.
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