[/
 / Copyright (c) 2003-2010 Christopher M. Kohlhoff (chris at kohlhoff dot com)
 /
 / Distributed under the Boost Software License, Version 1.0. (See accompanying
 / file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 /]

[section:ssl SSL]

Boost.Asio contains classes and class templates for basic SSL support. These classes
allow encrypted communication to be layered on top of an existing stream, such
as a TCP socket.

Before creating an encrypted stream, an application must construct an SSL
context object. This object is used to set SSL options such as verification
mode, certificate files, and so on. As an illustration, client-side
initialisation may look something like:

  ssl::context ctx(my_io_service, ssl::context::sslv23);
  ctx.set_verify_mode(ssl::context::verify_peer);
  ctx.load_verify_file("ca.pem");

To use SSL with a TCP socket, one may write:

  ssl::stream<ip::tcp::socket> ssl_sock(my_io_service, ctx);

To perform socket-specific operations, such as establishing an outbound
connection or accepting an incoming one, the underlying socket must first be
obtained using the `ssl::stream` template's [link
boost_asio.reference.ssl__stream.lowest_layer `lowest_layer()`] member function:

  ip::tcp::socket::lowest_layer_type& sock = ssl_sock.lowest_layer();
  sock.connect(my_endpoint);

In some use cases the underlying stream object will need to have a longer
lifetime than the SSL stream, in which case the template parameter should be a
reference to the stream type:

  ip::tcp::socket sock(my_io_service);
  ssl::stream<ip::tcp::socket&> ssl_sock(sock, ctx);

SSL handshaking must be performed prior to transmitting or receiving data over
an encrypted connection. This is accomplished using the `ssl::stream`
template's [link boost_asio.reference.ssl__stream.handshake handshake()] or
[link boost_asio.reference.ssl__stream.async_handshake async_handshake()] member
functions.

Once connected, SSL stream objects are used as synchronous or asynchronous read
and write streams. This means the objects can be used with any of the [link
boost_asio.reference.read read()], [link boost_asio.reference.async_read async_read()],
[link boost_asio.reference.write write()], [link boost_asio.reference.async_write
async_write()], [link boost_asio.reference.read_until read_until()] or [link
boost_asio.reference.async_read_until async_read_until()] free functions.

[heading See Also]

[link boost_asio.reference.ssl__basic_context ssl::basic_context],
[link boost_asio.reference.ssl__context ssl::context],
[link boost_asio.reference.ssl__context_base ssl::context_base],
[link boost_asio.reference.ssl__context_service ssl::context_service],
[link boost_asio.reference.ssl__stream ssl::stream],
[link boost_asio.reference.ssl__stream_base ssl::stream_base],
[link boost_asio.reference.ssl__stream_service ssl::stream_service],
[link boost_asio.examples.ssl SSL example].

[heading Notes]

[@http://www.openssl.org OpenSSL] is required to make use of Boost.Asio's SSL
support. When an application needs to use OpenSSL functionality that is not
wrapped by Boost.Asio, the underlying OpenSSL types may be obtained by calling [link
boost_asio.reference.ssl__basic_context.impl `ssl::context::impl()`] or [link
boost_asio.reference.ssl__stream.impl `ssl::stream::impl()`].

[endsect]