client.c

/**
 * gcc -g -o client client.c -lssl -lcrypt -lcrypto
 */
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <malloc.h>
#include <string.h>
#include <sys/socket.h>
#include <resolv.h>
#include <netdb.h>
#include <openssl/ssl.h>
#include <openssl/err.h>

#define FAIL    -1

int OpenConnection(const char *hostname, int port)
{
    int sd;
    struct hostent *host;
    struct sockaddr_in addr;
    if ((host = gethostbyname(hostname)) == NULL)
    {
        printf("Eroor: %s\n", hostname);
        perror(hostname);
        abort();
    }

    sd = socket(PF_INET, SOCK_STREAM, 0);
    sw_memset_zero(&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 = SSLv3_client_method(); /* Create new client-method instance */
    method = TLSv1_2_client_method();

    ctx = SSL_CTX_new(method); /* Create new context */
    if (ctx == NULL)
    {
        ERR_print_errors_fp(stderr);
        printf("Eroor: %s\n", stderr);
        abort();
    }
    return ctx;
}

void ShowCerts(SSL* ssl)
{
    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("Subject: %s\n", line);
        free(line);
        line = X509_NAME_oneline(X509_get_issuer_name(cert), 0, 0);
        printf("Issuer: %s\n", line);
        free(line);
        X509_free(cert);
    }
    else
        printf("No certificates.\n");
}

int main(int count, char *strings[])
{
    SSL_CTX *ctx;
    int server;
    SSL *ssl;
    char buf[1024];
    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 */
    TLSv1_2_client_method();
    if (SSL_connect(ssl) == FAIL) /* perform the connection */
    {
        printf("Eroor: %s\n", stderr);
        ERR_print_errors_fp(stderr);
    }
    else
    {
        char *msg = "HelloWorld";
        printf("Connected with %s encryption\n", SSL_get_cipher(ssl));
        ShowCerts(ssl); /* get any certs */
        SSL_write(ssl, msg, strlen(msg)); /* 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;
}