相关配置等请參看上一篇关于server端文章：http://blog.csdn.net/pingd/article/details/47805349

1.Client端源代码：

openssl_client.c

#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <sys/socket.h>
#include <resolv.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <openssl/ssl.h>
#include <openssl/err.h>

#define MAXBUF 1024

void ShowCerts(SSL * ssl)
{
    X509 *cert;
    char *line;

    cert = SSL_get_peer_certificate(ssl);
    if (cert != NULL) {
        printf("Digital cert info:\n");
        line = X509_NAME_oneline(X509_get_subject_name(cert), 0, 0);
        printf("Cert: %s\n", line);
        free(line);
        line = X509_NAME_oneline(X509_get_issuer_name(cert), 0, 0);
        printf("Owner: %s\n", line);
        free(line);
        X509_free(cert);
    } else
        printf("No cert info\n");
}

int main(int argc, char **argv)
{
    int sockfd, len;
    struct sockaddr_in dest;
    char buffer[MAXBUF + 1];
    SSL_CTX *ctx;
    SSL *ssl;

    if (argc != 3)
	{
        printf("Usage:%s [server_ip] [server_port]\n",argv[0]);
        exit(-1);
    }

    /* SSL 库初始化，參看 ssl-server.c 代码 */
    SSL_library_init();
    OpenSSL_add_all_algorithms();
    SSL_load_error_strings();
    ctx = SSL_CTX_new(SSLv23_client_method());
    if (ctx == NULL) 
	{
        ERR_print_errors_fp(stdout);
        exit(-1);
    }

    /* 创建一个 socket 用于 tcp 通信 */
    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) 
	{
        perror("Socket");
        exit(errno);
    }
    printf("socket created\n");

    /* 初始化服务器端（对方）的地址和端口信息 */
    bzero(&dest, sizeof(dest));
    dest.sin_family = AF_INET;
    dest.sin_port = htons(atoi(argv[2]));
    if (inet_aton(argv[1], (struct in_addr *) &dest.sin_addr.s_addr) == 0) {
        perror(argv[1]);
        exit(errno);
    }
    printf("address created\n");

    /* 连接服务器 */
    if (connect(sockfd, (struct sockaddr *) &dest, sizeof(dest)) != 0) {
        perror("Connect ");
        exit(errno);
    }
    printf("server connected\n");

    /* 基于 ctx 产生一个新的 SSL */
    ssl = SSL_new(ctx);
    SSL_set_fd(ssl, sockfd);
    /* 建立 SSL 连接 */
    if (SSL_connect(ssl) == -1)
        ERR_print_errors_fp(stderr);
    else {
        printf("Connected with %s encryption\n", SSL_get_cipher(ssl));
        ShowCerts(ssl);
    }

    /* 接收对方发过来的消息，最多接收 MAXBUF 个字节 */
    bzero(buffer, MAXBUF + 1);
    /* 接收服务器来的消息 */
    len = SSL_read(ssl, buffer, MAXBUF);
    if (len > 0)
        printf("recv message ‘%s‘ ok.total size:‘%d‘\n",
               buffer, len);
    else {
        printf("recv message error!error code:‘%d‘,error info:‘%s‘\n",
             errno, strerror(errno));
        goto finish;
    }
    bzero(buffer, MAXBUF + 1);
    strcpy(buffer, "from client->server");
    /* 发消息给服务器 */
    len = SSL_write(ssl, buffer, strlen(buffer));
    if (len < 0)
        printf("send message ‘%s‘ error!error code:‘%d‘,error info:‘%s‘\n",
             buffer, errno, strerror(errno));
    else
        printf("send message ‘%s‘ ok,total size:‘%d‘\n",buffer, len);

  finish:
    /* 关闭连接 */
    SSL_shutdown(ssl);
    SSL_free(ssl);
    close(sockfd);
    SSL_CTX_free(ctx);
    return 0;
}

2.编译

gcc -o openssl_client openssl_client.c -Wall -lssl -lcrypto -L./openssl-1.0.2d/ -Wl,-rpath=./openssl-1.0.2d 

Usage:openssl_client [server_ip] [server_port]