ssl-server.c

#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 <arpa/inet.h>		/*for using ascii to network bit*/	
#include <sys/socket.h>		/*for creating sockets*/
#include <sys/types.h>		/*for using sockets*/
#include <netinet/in.h>        /* network to asii bit */
#include <resolv.h>		/*server to find out the runner's IP address*/	
#include "openssl/ssl.h"	/*using openssl function's and certificates and configuring them*/
#include "openssl/err.h"	/* helps in finding out openssl errors*/
#include <stdio.h> 		/*standard i/o*/
#define FAIL    -1		/*for error output == -1 */
#define BUFFER 1024		/*buffer for reading messages*/
 
int OpenListener(int port)			
{   int sd;
    struct sockaddr_in addr;			/*creating the sockets*/
 
    sd = socket(PF_INET, SOCK_STREAM, 0);
    bzero(&addr, sizeof(addr));				/*free output the garbage space in memory*/
    addr.sin_family = AF_INET;				/*getting ip address form machine */
    addr.sin_port = htons(port);			/* converting host bit to n/w bit */
    addr.sin_addr.s_addr = INADDR_ANY;
    if ( bind(sd, (struct sockaddr*)&addr, sizeof(addr)) != 0 ) /* assiging the ip address and port*/
    {
        perror("can't bind port");				/* reporting error using errno.h library */
        abort();						/*if error will be there then abort the process */
    }
    if ( listen(sd, 10) != 0 )					/*for listening to max of 10 clients in the queue*/
    {
        perror("Can't configure listening port");		/* reporting error using errno.h library */
        abort();						/*if erroor will be there then abort the process */
    }
    return sd;
}
 
int isRoot()								/*for checking if the root user is executing the server*/
{
    if (getuid() != 0)				
    {
        return 0;
    }
    else
    {
        return 1;							/* if root user is not executing report must be user */		
    }
 
}
SSL_CTX* InitServerCTX(void)						/*creating and setting up ssl context structure*/
{   SSL_METHOD *method;
    SSL_CTX *ctx;							
 
    OpenSSL_add_all_algorithms();  					/* load & register all cryptos, etc. */
    SSL_load_error_strings();   					/* load all error messages */
    method = TLSv1_2_server_method();				  	/* create new server-method instance */
    ctx = SSL_CTX_new(method);  					 /* create new context from method */
    if ( ctx == NULL )
    {
        ERR_print_errors_fp(stderr);
        abort();
    }
    return ctx;
}
 
void LoadCertificates(SSL_CTX* ctx, char* CertFile, char* KeyFile)			/* to load a certificate into an SSL_CTX structure*/
{
    /* set the local certificate from CertFile */
    if ( SSL_CTX_use_certificate_file(ctx, CertFile, SSL_FILETYPE_PEM) <= 0 )
    {
        ERR_print_errors_fp(stderr);
        abort();
    }
    /* set the private key from KeyFile (may be the same as CertFile) */
    if ( SSL_CTX_use_PrivateKey_file(ctx, KeyFile, SSL_FILETYPE_PEM) <= 0 )
    {
        ERR_print_errors_fp(stderr);
        abort();
    }
    /* verify private key */
    if ( !SSL_CTX_check_private_key(ctx) )
    {
        fprintf(stderr, "Private key does not match the public certificate\n");
        abort();
    }
}
 
void ShowCerts(SSL* ssl)					/*show the ceritficates to client and match them*/
{   X509 *cert;
    char *line;
 
    cert = SSL_get_peer_certificate(ssl); /* Get certificates (if available) */
    if ( cert != NULL )
    {
        printf("Server certificates:\n");
        line = X509_NAME_oneline(X509_get_subject_name(cert), 0, 0);		
        printf("Server: %s\n", line);					/*server certifcates*/
        free(line);
        line = X509_NAME_oneline(X509_get_issuer_name(cert), 0, 0);
        printf("client: %s\n", line);					/*client certificates*/
        free(line);
        X509_free(cert);
    }
    else
        printf("No certificates.\n");
}
 
void Servlet(SSL* ssl) /* Serve the connection -- threadable */
{   char buf[1024];
    int sd, bytes;
    char input[BUFFER]; 	
    pid_t cpid;	
    if ( SSL_accept(ssl) == FAIL )     /* do SSL-protocol accept */
    ERR_print_errors_fp(stderr);
    else
    {	
        ShowCerts(ssl);        /* get any certificates */
	/*Fork system call is used to create a new process*/
       cpid=fork();
	if(cpid==0)
	{	
	while(1){
	bytes = SSL_read(ssl, buf, sizeof(buf)); /* get request and read message from server*/
      
	 if ( bytes > 0 )
        {	
            buf[bytes] = 0;
            printf("\nMESSAGE FROM CLIENT:%s\n", buf);
      
        }  
        else
            ERR_print_errors_fp(stderr);
   } }
else {

while(1){

printf("\nMESSAGE TO CLIENT:");
	 fgets(input, BUFFER, stdin);  /* get request and reply to client*/
	
        SSL_write(ssl, input, strlen(input)); 
}
	
}		
}
    sd = SSL_get_fd(ssl);       /* get socket connection */
    SSL_free(ssl);         /* release SSL state */
    close(sd);          /* close connection */
}
 
int main(int count, char *strings[])			/* getting port as a argument*/
{   SSL_CTX *ctx;
    int server;
    char *portnum;
   
 
    if(!isRoot())								/* if root user is not executing server report must be root user */
    {
        printf("This program must be run as root/sudo user!!");
        exit(0);
    }
    if ( count != 2 )
    {
        printf("Usage: %s <portnum>\n", strings[0]);			/*send the usage guide if syntax of setting port is different*/
        exit(0);
    }
    SSL_library_init();                                                 /*load encryption and hash algo's in ssl*/
 
    portnum = strings[1];
    ctx = InitServerCTX();        /* initialize SSL */
    LoadCertificates(ctx, "certi.pem", "privkey.pem"); /* load certs */
    server = OpenListener(atoi(portnum));    /* create server socket */
    
     struct sockaddr_in addr;						/*socket for server*/
        socklen_t len = sizeof(addr);
        SSL *ssl;
 	listen(server,5);						/*setting 5 clients at a time to queue*/
        int client = accept(server, (struct sockaddr*)&addr, &len);  /* accept connection as usual */
        printf("Connection: %s:%d\n",inet_ntoa(addr.sin_addr), ntohs(addr.sin_port));		/*printing connected client information*/
        ssl = SSL_new(ctx);              /* get new SSL state with context */
        SSL_set_fd(ssl, client);      /* set connection socket to SSL state */
	        
Servlet(ssl);         /* service connection */
    
    close(server);          /* close server socket */
    SSL_CTX_free(ctx);         /* release context */
}