Real time embedded FreeRTOS RSS feed 
Real time embedded FreeRTOS mailing list 
Homepage FreeRTOS+ Products FreeRTOS Labs Integration Services Contact / Enquiries

Simple CyaSSL Server Side Example

The three steps to using CyaSSL in a client side FreeRTOS application
The three steps to using CyaSSL in a server side application


This page describes how, in just a few easy steps, the CyaSSL library can be used to to ensure the security and integrity of a server side networking application.

The information on this page is nearly identical to that found on the Simple CyaSSL Client Side Example page. It is repeated here for consistency - with the differences highlighted where they exist.

Header files

cyassl/ssl.h contains the CyaSSL structures, data definitions, and function prototypes. It must be included in all the source files that use the CyaSSL library.

#include "cyassl/ssl.h"
The header file that must be included in all source files that use the CyaSSL library

Initialising the library and creating a CyaSSL context

CyaSSL_Init() prepares the CyaSSL library for use, and must be called before any other CyaSSL API functions.

Next, a variable of type CYASSL_CTX is required to store context information, and can be created using CyaSSL_CTX_new(). The SSL or TLS protocol to use is specified as the context is created using the function's parameter. Options include SSLv3, TLSv1, TLSv1.1, TLSv1.2, or DTLS. This example demonstrates the TLSv1 server protocol being selected (the client side example selects TLSv1 client). The values to use to select the other protocol options are listed in the user manual.

The client side example demonstrated a Certificate Authority (CA) file being loaded into the CyaSSL context. In addition to the CA, the server context must also be loaded with the server certificate, and a key file. This allows the server to send its certificate to the client for verification. CyaSSL_CTX_load_verify_locations() is called to load the CA, CyaSSL_CTX_use_certificate_file() to load the certificate, and CyaSSL_CTX_use_PrivateKey_file to load the private key file.

/* Define a structure to hold the CyaSSL context. */
CYASSL_CTX* xCyaSSL_Context;

    /* Initialise CyaSSL.  This must be done before any other CyaSSL functions
    are called. */

    /* Attempt to create a context that uses the TLS V1 server protocol. */
    xCyaSSL_Context = CyaSSL_CTX_new( CyaTLSv1_server_method() );

    if( xCyaSSL_Context != NULL )
        /* Load the CA certificate.  Real applications should ensure that
        CyaSSL_CTX_load_verify_locations() returns SSL_SUCCESS before proceeding. */
        CyaSSL_CTX_load_verify_locations( xCyaSSL_Context, "ca-cert.pem", 0 );
        /* Again, checking of the return values is omitted from this example,
        just for clarity.  Real applications must ensure the following two 
        functions return SSL_SUCCESS. */
        CyaSSL_CTX_use_certificate_file( xCyaSSL_Context, "server-cert.pem", SSL_FILETYPE_PEM );
        CyaSSL_CTX_use_PrivateKey_file( xCyaSSL_Context, "server-key.pem", SSL_FILETYPE_PEM );
Library initialisation, protocol selection, and loading the CA certificate,
server certificate and private key into the CyaSSL context.

Associating a CyaSSL object with a connected socket

Each accepted connection must be associated with a CyaSSL object. CyaSSL objects are created using CyaSSL_new(), and associated with a TCP socket using CyaSSL_set_fd().

CYASSL* xCyaSSL_Object;

    /* A connection has been accepted by the server.  Create a CyaSSL
    object for use with the newly connected socket. */
    xCyaSSL_Object = CyaSSL_new( xCyaSSL_Context );
    if( xCyaSSL_Object != NULL )
        /* Associate the created CyaSSL object with the connected socket
        (sockfd). */
        CyaSSL_set_fd( xCyaSSL_Object, sockfd );
Creating a CyaSSL object, and associating it with an accepted connection

Using the socket

Secure communication can now be made through the socket by using CyaSSL_write() in place of the standard sockets write() or send() functions, and CyaSSL_read() in place of the standard sockets read() or recv().

Note that the first parameter to both CyaSSL_write() and CyaSSL_read() is not the socket descriptor, but the CyaSSL object that is associated with the socket descriptor.

char ucTxBuf[ MAXLINE ], ucRxBuf[ MAXLINE ];

    if( CyaSSL_write( xCyaSSL_Object, ucTxBuf, strlen( ucTxBuf ) ) != strlen( ucTxBuf ) )
        /* Send failed. */

    if( CyaSSL_read( xCyaSSL_Object, ucRxBuf, MAXLINE ) <= 0 )
        /* Read failed. */
Writing to and reading from a socket using the CyaSSL API

Deleting allocated resources

CyaSSL API functions that result in dynamic resource allocation have a counterpart function that should be called to free the resource when it is no longer required. The code snippet below shows how the objects created in this small example should be freed.

    /* CyaSSL objects should be deleted when they are no longer required. */
    CyaSSL_free( xCyaSSL_Object );
    /* The CyaSSL context should be deleted if it is no longer required.  However, 
    because most deeply embedded applications will keep the context for the lifetime 
    of the application, and only ever be restarted when the system is rebooted, it 
    might be that the context is never explicitly freed. */
    CyaSSL_CTX_free( xCyaSSL_Context );
    /* The library itself should be shut down cleanly if it too is no longer
    required.  Again, because most deeply embedded applications will require the
    library for the lifetime of the application, and only ever be restarted when 
    the system is rebooted, it might be that the library is never explicitly closed. */

Deleting objects that were dynamically allocated in this example

[ Back to the top ]    [ About FreeRTOS ]    [ FreeRTOS+ Sitemap ]    [ Main FreeRTOS Sitemap ]    [ ]

Copyright (C) 2004-2010 Richard Barry. Copyright (C) 2010-2015 Real Time Engineers Ltd.
Any and all data, files, source code, html content and documentation included in the FreeRTOSTM distribution or available on this site are the exclusive property of Real Time Engineers Ltd.. See the files license.txt (included in the distribution) and this copyright notice for more information. FreeRTOSTM and FreeRTOS.orgTM are trade marks of Real Time Engineers Ltd.