Securing the socket
--#--
OpenSSL uses two central structures for opening and managing 
secure connections -- SSL_ctx and SSL. SSL_ctx is a context 
object. It holds a list of ciphers, CA certificates for authenticating 
the server, client-side certificates, protocol specifiers, validation 
routines and other things that determine how secure the connection will 
be. In this example, we won't do a lot with it, but will rely on most 
of the OpenSSL defaults.<br>
<br>
SSL is a central structure to the program. Once the connection is 
established, SSL holds pointers to practically everything -- including 
the SSL_ctx. That said, you don't really need to worry much about it, 
except to remember to keep tossing the SSL struct around to any of the 
business functions.<br>
<br>
Let's start by initializing the two structures:<br>
<br>
<code>
#include <openssl/ssl.h>

SSL *ssl = NULL;
SSL_CTX *ssl_ctx = NULL;

ssl_ctx = SSL_CTX_new(SSLv23_client_method());
ssl = SSL_new(ssl_ctx);
</code>
<br>
Not hard, was it? The only parameter we pass to the SSL_CTX initializer 
is a function pointer. In this case, we tell the context that we 
want to use a client method that will attempt an SSL v3 connection, 
but can fall back to SSL v2.<br>
<br>
Now we need to define a function that will open a regular Internet socket 
for HTTP transfers, and rig it up for SSL. Rename sockets.c ssl_sockets.c 
and put this function there.<br>
<br>
<code>
int SSLsocket(SSL *ssl, char *host, int port) {
	int sock, result;

	sock = openSocket(host, port);
	SSL_set_fd(ssl, sock);
	result = SSL_connect(ssl);
	return result;
}
</code>
<br>
This function opens the socket just like Paul did, then associates the the 
SSL struct with the socket. The next line, <i>result = SSL_connect(ssl)</i> 
looks real simple, but a mountain of code runs as a result! This kicks off 
the famous <i>SSL handshake</i> where both ends of the connection 
exchange random bytes and agree on a key-exchange method and encryption 
cipher. If this function returns -1, the connection failed. Otherwise, 
we can use it.<br>
<br>