sign_server()

This is the “guts” of the program. Calls server_establish_context() to accept the context, receives the data, unwraps it, verifies it, then generates a MIC to send back to the client. Finally, it deletes the context.

Example A–12 sign_server()

/*
 * Function: sign_server
 *
 * Purpose: Performs the "sign" service.
 *
 * Arguments:
 *
 *      s               (r) a TCP socket on which a connection has been
 *                      accept()ed
 *      service_name    (r) the ASCII name of the GSS-API service to
 *                      establish a context as
 *
 * Returns: -1 on error
 *
 * Effects:
 *
 * sign_server establishes a context, and performs a single sign request.
 *
 * A sign request is a single GSS-API wrapped token.  The token is
 * unwrapped and a signature block, produced with gss_get_mic, is returned
 * to the sender.  The context is the destroyed and the connection
 * closed.
 *
 * If any error occurs, -1 is returned.
 */
int sign_server(s, server_creds)
     int s;
     gss_cred_id_t server_creds;
{
     gss_buffer_desc client_name, xmit_buf, msg_buf;
     gss_ctx_id_t context;
     OM_uint32 maj_stat, min_stat;
     int i, conf_state, ret_flags;
     char       *cp;

     /* Establish a context with the client */
     if (server_establish_context(s, server_creds, &context,
                                  &client_name, &ret_flags) < 0)
        return(-1);

     printf("Accepted connection: \"%.*s\"\n",
            (int) client_name.length, (char *) client_name.value);
     (void) gss_release_buffer(&min_stat, &client_name);

     for (i=0; i < 3; i++)
             if (test_import_export_context(&context))
                     return -1;

     /* Receive the wrapped message token */
     if (recv_token(s, &xmit_buf) < 0)
        return(-1);

     if (verbose && log) {
        fprintf(log, "Wrapped message token:\n");
        print_token(&xmit_buf);
     }

     maj_stat = gss_unwrap(&min_stat, context, &xmit_buf, &msg_buf,
                           &conf_state, (gss_qop_t *) NULL);
     if (maj_stat != GSS_S_COMPLETE) {
        display_status("unwrapping message", maj_stat, min_stat);
        return(-1);
     } else if (! conf_state) {
        fprintf(stderr, "Warning!  Message not encrypted.\n");
     }

     (void) gss_release_buffer(&min_stat, &xmit_buf);

     fprintf(log, "Received message: ");
     cp = msg_buf.value;
     if (isprint(cp[0]) && isprint(cp[1]))
        fprintf(log, "\"%s\"\n", cp);
     else {
        printf("\n");
        print_token(&msg_buf);
     }

     /* Produce a signature block for the message */
     maj_stat = gss_get_mic(&min_stat, context, GSS_C_QOP_DEFAULT,
                            &msg_buf, &xmit_buf);
     if (maj_stat != GSS_S_COMPLETE) {
        display_status("signing message", maj_stat, min_stat);
        return(-1);
     }

     (void) gss_release_buffer(&min_stat, &msg_buf);

     /* Send the signature block to the client */
     if (send_token(s, &xmit_buf) < 0)
        return(-1);

     (void) gss_release_buffer(&min_stat, &xmit_buf);

     /* Delete context */
     maj_stat = gss_delete_sec_context(&min_stat, &context, NULL);
     if (maj_stat != GSS_S_COMPLETE) {
        display_status("deleting context", maj_stat, min_stat);
        return(-1);
     }

     fflush(log);

     return(0);
}