ssl-client.c

#include <stdio.h>	/*standard i/o*/
#include <errno.h>	/*USING THE ERROR LIBRARY FOR FINDING ERRORS*/
#include <unistd.h>	/*FOR USING FORK for at a time send and receive messages*/ 
#include <malloc.h>	/*FOR MEMORY ALLOCATION */
#include <string.h>	/*using fgets funtions for geting input from user*/
#include <sys/socket.h>	/*for creating sockets*/
#include <resolv.h>	/*server to find out the runner's IP address*/	
#include <netdb.h>	/*definitions for network database operations */
#include <openssl/ssl.h>	/*using openssl function's and certificates and configuring them*/
#include <openssl/err.h>	/* helps in finding out openssl errors*/
#include <unistd.h>		/*FOR USING FORK for at a time send and receive messages*/ 
 
#define FAIL    -1	/*for error output == -1 */
#define BUFFER  1024 	/*buffer for reading messages*/
int OpenConnection(const char *hostname, int port)
{   int sd;
    struct hostent *host;
    struct sockaddr_in addr;			/*creating the sockets*/
 
    if ( (host = gethostbyname(hostname)) == NULL )
    {
        perror(hostname);
        abort();
    }
    sd = socket(PF_INET, SOCK_STREAM, 0);			/* setting the connection as tcp it creates endpoint for connection */
    bzero(&addr, sizeof(addr));
    addr.sin_family = AF_INET;
    addr.sin_port = htons(port);
    addr.sin_addr.s_addr = *(long*)(host->h_addr);
    if ( connect(sd, (struct sockaddr*)&addr, sizeof(addr)) != 0 ) 	/*initiate a connection on a socket*/
    {
        close(sd);
        perror(hostname);
        abort();
    }
    return sd;
}
 
SSL_CTX* InitCTX(void)					/*creating and setting up ssl context structure*/
{   SSL_METHOD *method;
    SSL_CTX *ctx;
 
    OpenSSL_add_all_algorithms();  /* Load cryptos, et.al. */
    SSL_load_error_strings();   /* Bring in and register error messages */
    method = TLSv1_2_client_method();  /* Create new client-method instance */
    ctx = SSL_CTX_new(method);   /* Create new context */
    if ( ctx == NULL )
    {
        ERR_print_errors_fp(stderr);
        abort();
    }
    return ctx;
}
 
void ShowCerts(SSL* ssl)		/*show the ceritficates to server and match them but here we are not using any client certificate*/
{   X509 *cert;
    char *line;
 
    cert = SSL_get_peer_certificate(ssl); /* get the server's certificate */
    if ( cert != NULL )
    {
        printf("Server certificates:\n");
        line = X509_NAME_oneline(X509_get_subject_name(cert), 0, 0);
        printf("Subject: %s\n", line);
        free(line);       /* free the malloc'ed string */
        line = X509_NAME_oneline(X509_get_issuer_name(cert), 0, 0);
        printf("Issuer: %s\n", line);
        free(line);       /* free the malloc'ed string */
        X509_free(cert);     /* free the malloc'ed certificate copy */
    }
    else
        printf("Info: No client certificates configured.\n");
}
 
int main(int count, char *strings[])			/* getting port and ip as an argument*/
{   SSL_CTX *ctx;
    int server;
    SSL *ssl;
    char buf[1024];
    char input[BUFFER];
    int bytes;
    char *hostname, *portnum;
    pid_t cpid;					/* fork variable*/
    
    if ( count != 3 )
    {
        printf("usage: %s <hostname> <portnum>\n", strings[0]);
        exit(0);
    }
    SSL_library_init();			/*load encryption and hash algo's in ssl*/
    hostname=strings[1];
    portnum=strings[2];
 
    ctx = InitCTX();
    server = OpenConnection(hostname, atoi(portnum));			/*converting ascii port to interger */
    ssl = SSL_new(ctx);      /* create new SSL connection state */
    SSL_set_fd(ssl, server);    /* attach the socket descriptor */
    if ( SSL_connect(ssl) == FAIL )   /* perform the connection */
        ERR_print_errors_fp(stderr);
    else
		
    {    
	
 
        printf("Connected with %s encryption\n", SSL_get_cipher(ssl));
        ShowCerts(ssl);
        /* get any certs */
	cpid=fork();
/*Fork system call is used to create a new process*/
if(cpid==0)
{
	while(1){
	printf("\nMESSAGE TO SERVER:");
	 fgets(input, BUFFER, stdin);
	
        SSL_write(ssl, input, strlen(input));   /* encrypt & send message */}}
else {
     while(1)
{

   bytes = SSL_read(ssl, buf, sizeof(buf)); /* get request */
      
	 if ( bytes > 0 )
        {	
            buf[bytes] = 0;
            printf("\nMESSAGE FROM SERVER: %s\n", buf);
        }

} }
       SSL_free(ssl);        /* release connection state */
    

 }   close(server);         /* close socket */
    SSL_CTX_free(ctx);        /* release context */
 
   return 0;
}