networkprogramming/sslconnect.c at master · patrikarlos/networkprogramming · GitHub

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#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>

#ifndef MacBuild
#include <malloc.h>
#endif

#include <string.h>
#include <sys/socket.h>
#include <resolv.h>
#include <netdb.h>
#include <openssl/ssl.h>
#include <openssl/err.h>

/*
https://indienote.tistory.com/361
Install the OpenSSL library, for the ubuntu use the below command.

sudo apt-get install libssl–dev

Before compiling the client and server program you will need a Certificate. You can generate your own certificate using the below command.

openssl req -x509 -nodes -days 365 -newkey rsa:4096 -keyout mycert.pem -out mycert.pem

Note: Here certificate name is mycert.pem.

Example Client code for TLS1.2 communication
Compile the Client : gcc -Wall -o sslclient  sslconnect.c <-L/usr/lib> -lssl -lcrypto
Run :   ./sslclient <host_name> <port_number>

*/

#define FAIL    -1

int OpenConnection(const char *hostname, int port)
{   int sd;
    struct hostent *host;
    struct sockaddr_in addr;

    if ( (host = gethostbyname(hostname)) == NULL )
    {
        perror(hostname);
        abort();
    }
    sd = socket(PF_INET, SOCK_STREAM, 0);
    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 )
    {
        close(sd);
        perror(hostname);
        abort();
    }
    return sd;
}

SSL_CTX* InitCTX(void)
{   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)
{   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[])
{   SSL_CTX *ctx;
    int server;
    SSL *ssl;
    char buf[1024];
    char acClientRequest[1024] ={0};
    int bytes;
    char *hostname, *portnum;

    if ( count != 3 )
    {
        printf("usage: %s <hostname> <portnum>\n", strings[0]);
        exit(0);
    }
    SSL_library_init();
    hostname=strings[1];
    portnum=strings[2];

    ctx = InitCTX();

    server = OpenConnection(hostname, atoi(portnum));
    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
    {
      char acUsername[16] ={0};
      char acPassword[16] ={0};
      const char *cpRequestMessage = "<Body><UserName>%s<UserName><Password>%s<Password><\\Body>";

      printf("Enter the User Name : ");
      scanf("%s",acUsername);

      printf("Enter the Password : ");
      scanf("%s",acPassword);

      sprintf(acClientRequest, cpRequestMessage, acUsername,acPassword);   /* construct reply */

      printf("\n\nConnected with %s encryption\n", SSL_get_cipher(ssl));
      ShowCerts(ssl);        /* get any certs */
      SSL_write(ssl,acClientRequest, strlen(acClientRequest));   /* encrypt & send message */
      bytes = SSL_read(ssl, buf, sizeof(buf)); /* get reply & decrypt */
      buf[bytes] = 0;
      printf("Received: \"%s\"\n", buf);
      SSL_free(ssl);        /* release connection state */
    }
    close(server);         /* close socket */
    SSL_CTX_free(ctx);        /* release context */
    return 0;
}