一直在思考如果Server端用C，client用Java来实现，如何实现两者之间的安全通信。其实这个比较成熟了，c语言推荐使用gnutls(考虑license问题)，Java使用 JSSE就可以解决这个问题。以下是示例代码:

C Server 代码：echoserver.c

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include
#endif

#include
#include
#include
#include
#include
#include
#include
#include
#include
#include

#define KEYFILE "collectd.csmtg.ericsson.com.key"
#define CERTFILE "collectd.csmtg.ericsson.com.cert"
#define CAFILE "ca.ericsson.com.cert"
#define CRLFILE "ca.ericsson.com.crl"

/* This is a sample TLS 1.0 echo server, using X.509 authentication.
*/

#define MAX_BUF 1024
#define PORT 5556 /* listen to 5556 port */

/* These are global */
gnutls_certificate_credentials_t x509_cred;
gnutls_priority_t priority_cache;

static gnutls_session_t
initialize_tls_session (void)
{
gnutls_session_t session;

gnutls_init (&session, GNUTLS_SERVER);

gnutls_priority_set (session, priority_cache);

gnutls_credentials_set (session, GNUTLS_CRD_CERTIFICATE, x509_cred);

/* We don't request any certificate from the client.
* If we did we would need to verify it.
*/
gnutls_certificate_server_set_request (session, GNUTLS_CERT_IGNORE);

return session;
}

static gnutls_dh_params_t dh_params;

static int
generate_dh_params (void)
{
int bits = gnutls_sec_param_to_pk_bits (GNUTLS_PK_DH, GNUTLS_SEC_PARAM_LOW);

/* Generate Diffie-Hellman parameters - for use with DHE
* kx algorithms. When short bit length is used, it might
* be wise to regenerate parameters often.
*/
gnutls_dh_params_init (&dh_params);
gnutls_dh_params_generate2 (dh_params, bits);

return 0;
}

int
main (void)
{
int listen_sd;
int sd, ret;
struct sockaddr_in sa_serv;
struct sockaddr_in sa_cli;
socklen_t client_len;
char topbuf[512];
gnutls_session_t session;
char buffer[MAX_BUF + 1];
int optval = 1;

/* this must be called once in the program
*/
gnutls_global_init ();

gnutls_certificate_allocate_credentials (&x509_cred);
/* gnutls_certificate_set_x509_system_trust(xcred); */
gnutls_certificate_set_x509_trust_file (x509_cred, CAFILE,
GNUTLS_X509_FMT_PEM);

gnutls_certificate_set_x509_crl_file (x509_cred, CRLFILE,
GNUTLS_X509_FMT_PEM);

ret = gnutls_certificate_set_x509_key_file (x509_cred, CERTFILE, KEYFILE,
GNUTLS_X509_FMT_PEM);
if (ret < 0)
{
printf("No certificate or key were found\n");
exit(1);
}

generate_dh_params ();

gnutls_priority_init (&priority_cache, "PERFORMANCE:%SERVER_PRECEDENCE", NULL);

gnutls_certificate_set_dh_params (x509_cred, dh_params);

/* Socket operations
*/
listen_sd = socket (AF_INET, SOCK_STREAM, 0);

memset (&sa_serv, '\0', sizeof (sa_serv));
sa_serv.sin_family = AF_INET;
sa_serv.sin_addr.s_addr = INADDR_ANY;
sa_serv.sin_port = htons (PORT); /* Server Port number */

setsockopt (listen_sd, SOL_SOCKET, SO_REUSEADDR, (void *) &optval,
sizeof (int));

bind (listen_sd, (struct sockaddr *) & sa_serv, sizeof (sa_serv));

listen (listen_sd, 1024);

printf ("Server ready. Listening to port '%d'.\n\n", PORT);

client_len = sizeof (sa_cli);
for (;;)
{
session = initialize_tls_session ();

sd = accept (listen_sd, (struct sockaddr *) & sa_cli, &client_len);