openssl demo

cli.cpp

/* cli.cpp  -  Minimal ssleay client for Unix
   30.9.1996, Sampo Kellomaki <[email protected]> */

/* mangled to work with SSLeay-0.9.0b and OpenSSL 0.9.2b
   Simplified to be even more minimal
   12/98 - 4/99 Wade Scholine <[email protected]> */

#include <unistd.h>
#include <stdio.h>
#include <memory.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

#include <openssl/crypto.h>
#include <openssl/x509.h>
#include <openssl/pem.h>
#include <openssl/ssl.h>
#include <openssl/err.h>

#define CERTF "client.crt"
#define KEYF "client.key"
#define CACERT "ca.crt"


#define CHK_NULL(x) if ((x)==NULL) exit (1)
#define CHK_ERR(err,s) if ((err)==-1) { perror(s); exit(1); }
#define CHK_SSL(err) if ((err)==-1) { ERR_print_errors_fp(stderr); exit(2); }

int main ()
{
  int err;
  int sd;
  struct sockaddr_in sa;
  SSL_CTX* ctx;
  SSL*     ssl;
  X509*    server_cert;
  char*    str;
  char     buf [4096];
  SSL_METHOD *meth;

  SSLeay_add_ssl_algorithms();
  meth = SSLv23_client_method();
  SSL_load_error_strings();
  ctx = SSL_CTX_new (meth);                        CHK_NULL(ctx);

  CHK_SSL(err);


  SSL_CTX_set_verify(ctx,SSL_VERIFY_PEER,NULL);
  SSL_CTX_load_verify_locations(ctx,CACERT,NULL);

  if (SSL_CTX_use_certificate_file(ctx, CERTF, SSL_FILETYPE_PEM) <= 0) {
          ERR_print_errors_fp(stderr);
          exit(-2);
  }

  if (SSL_CTX_use_PrivateKey_file(ctx, KEYF, SSL_FILETYPE_PEM) <= 0) {
          ERR_print_errors_fp(stderr);
          exit(-3);
  }

  if (!SSL_CTX_check_private_key(ctx)) {
          printf("Private key does not match the certificate public keyn");
          exit(-4);
  }

  /* ----------------------------------------------- */
  /* Create a socket and connect to server using normal socket calls. */

  sd = socket (AF_INET, SOCK_STREAM, 0);       CHK_ERR(sd, "socket");

  memset (&sa, '\0', sizeof(sa));
  sa.sin_family      = AF_INET;
  sa.sin_addr.s_addr = inet_addr ("127.0.0.1");   /* Server IP */
  sa.sin_port        = htons     (1111);          /* Server Port number */

  err = connect(sd, (struct sockaddr*) &sa,
                sizeof(sa));                   CHK_ERR(err, "connect");

  /* ----------------------------------------------- */
  /* Now we have TCP conncetion. Start SSL negotiation. */

  ssl = SSL_new (ctx);                         CHK_NULL(ssl);
  SSL_set_fd (ssl, sd);
  err = SSL_connect (ssl);                     CHK_SSL(err);

  /* Following two steps are optional and not required for
     data exchange to be successful. */

  /* Get the cipher - opt */

  printf ("SSL connection using %s\n", SSL_get_cipher (ssl));

  /* Get server's certificate (note: beware of dynamic allocation) - opt */

  server_cert = SSL_get_peer_certificate (ssl);       CHK_NULL(server_cert);
  printf ("Server certificate:\n");

  str = X509_NAME_oneline (X509_get_subject_name (server_cert),0,0);
  CHK_NULL(str);
  printf ("\t subject: %s\n", str);
  OPENSSL_free (str);

  str = X509_NAME_oneline (X509_get_issuer_name  (server_cert),0,0);
  CHK_NULL(str);
  printf ("\t issuer: %s\n", str);
  OPENSSL_free (str);

  /* We could do all sorts of certificate verification stuff here before
     deallocating the certificate. */

  X509_free (server_cert);

  /* --------------------------------------------------- */
  /* DATA EXCHANGE - Send a message and receive a reply. */

  err = SSL_write (ssl, "Hello World!", strlen("Hello World!"));  CHK_SSL(err);

  err = SSL_read (ssl, buf, sizeof(buf) - 1);                     CHK_SSL(err);
  buf[err] = '\0';
  printf ("Got %d chars:'%s'\n", err, buf);
  SSL_shutdown (ssl);  /* send SSL/TLS close_notify */

  /* Clean up. */

  close (sd);
  SSL_free (ssl);
  SSL_CTX_free (ctx);

  return 0;
}
/* EOF - cli.cpp */

Makefile

INC=/usr/local/ssl/include/
LIB=/usr/local/ssl/lib/

all:
        g++ -I$(INC) -L$(LIB) cli.cpp -o cli -lssl -lcrypto -ldl -fpermissive
        g++ -I$(INC) -L$(LIB) serv.cpp -o serv -lssl -lcrypto -ldl -fpermissive

clean:
        rm -rf *~ cli serv

serv.cpp

/* serv.cpp  -  Minimal ssleay server for Unix
   30.9.1996, Sampo Kellomaki <[email protected]> */


/* mangled to work with SSLeay-0.9.0b and OpenSSL 0.9.2b
   Simplified to be even more minimal
   12/98 - 4/99 Wade Scholine <[email protected]> */

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <memory.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

#include <openssl/rsa.h>       /* SSLeay stuff */
#include <openssl/crypto.h>
#include <openssl/x509.h>
#include <openssl/pem.h>
#include <openssl/ssl.h>
#include <openssl/err.h>


/* define HOME to be dir for key and cert files... */
#define HOME "./"
/* Make these what you want for cert & key files */
#define CERTF  HOME "server.crt"
#define KEYF  HOME  "server.key"
#define CACERT HOME "ca.crt"


#define CHK_NULL(x) if ((x)==NULL) exit (1)
#define CHK_ERR(err,s) if ((err)==-1) { perror(s); exit(1); }
#define CHK_SSL(err) if ((err)==-1) { ERR_print_errors_fp(stderr); exit(2); }

int main ()
{
  int err;
  int listen_sd;
  int sd;
  struct sockaddr_in sa_serv;
  struct sockaddr_in sa_cli;
  size_t client_len;
  SSL_CTX* ctx;
  SSL*     ssl;
  X509*    client_cert;
  char*    str;
  char     buf [4096];
  SSL_METHOD *meth;

  /* SSL preliminaries. We keep the certificate and key with the context. */

  SSL_load_error_strings();
  SSLeay_add_ssl_algorithms();
  meth = SSLv23_server_method();
  ctx = SSL_CTX_new (meth);
  if (!ctx) {
    ERR_print_errors_fp(stderr);
    exit(2);
  }

  SSL_CTX_set_verify(ctx,SSL_VERIFY_PEER,NULL); /* whether verify the certificate */
  SSL_CTX_load_verify_locations(ctx,CACERT,NULL);

  if (SSL_CTX_use_certificate_file(ctx, CERTF, SSL_FILETYPE_PEM) <= 0) {
    ERR_print_errors_fp(stderr);
    exit(3);
  }
  if (SSL_CTX_use_PrivateKey_file(ctx, KEYF, SSL_FILETYPE_PEM) <= 0) {
    ERR_print_errors_fp(stderr);
    exit(4);
  }

  if (!SSL_CTX_check_private_key(ctx)) {
    fprintf(stderr,"Private key does not match the certificate public key\n");
    exit(5);
  }

  /* ----------------------------------------------- */
  /* Prepare TCP socket for receiving connections */

  listen_sd = socket (AF_INET, SOCK_STREAM, 0);   CHK_ERR(listen_sd, "socket");

  memset (&sa_serv, '\0', sizeof(sa_serv));
  sa_serv.sin_family      = AF_INET;
  sa_serv.sin_addr.s_addr = INADDR_ANY;
  sa_serv.sin_port        = htons (1111);          /* Server Port number */

  err = bind(listen_sd, (struct sockaddr*) &sa_serv,
             sizeof (sa_serv));                   CHK_ERR(err, "bind");

  /* Receive a TCP connection. */

  err = listen (listen_sd, 5);                    CHK_ERR(err, "listen");

  client_len = sizeof(sa_cli);
  sd = accept (listen_sd, (struct sockaddr*) &sa_cli, &client_len);
  CHK_ERR(sd, "accept");
  close (listen_sd);

  printf ("Connection from %lx, port %x\n",
          sa_cli.sin_addr.s_addr, sa_cli.sin_port);

  /* ----------------------------------------------- */
  /* TCP connection is ready. Do server side SSL. */

  ssl = SSL_new (ctx);                           CHK_NULL(ssl);
  SSL_set_fd (ssl, sd);
  err = SSL_accept (ssl);                        CHK_SSL(err);

  /* Get the cipher - opt */

  printf ("SSL connection using %s\n", SSL_get_cipher (ssl));

  /* Get client's certificate (note: beware of dynamic allocation) - opt */

  client_cert = SSL_get_peer_certificate (ssl);
  if (client_cert != NULL) {
    printf ("Client certificate:\n");

    str = X509_NAME_oneline (X509_get_subject_name (client_cert), 0, 0);
    CHK_NULL(str);
    printf ("\t subject: %s\n", str);
    OPENSSL_free (str);

    str = X509_NAME_oneline (X509_get_issuer_name  (client_cert), 0, 0);
    CHK_NULL(str);
    printf ("\t issuer: %s\n", str);
    OPENSSL_free (str);

    /* We could do all sorts of certificate verification stuff here before
       deallocating the certificate. */

    X509_free (client_cert);
  } else
    printf ("Client does not have certificate.\n");

  /* DATA EXCHANGE - Receive message and send reply. */

  err = SSL_read (ssl, buf, sizeof(buf) - 1);                   CHK_SSL(err);
  buf[err] = '\0';
  printf ("Got %d chars:'%s'\n", err, buf);

  err = SSL_write (ssl, "I hear you.", strlen("I hear you."));  CHK_SSL(err);

  /* Clean up. */

  close (sd);
  SSL_free (ssl);
  SSL_CTX_free (ctx);

  return 0;
}
/* EOF - serv.cpp */

1.证书的生成
生成server.csr和client.csr
openssl genrsa -des3 -out server.key 1024
openssl req -new -key server.key -out server.csr
openssl genrsa -des3 -out client.key 1024
openssl req -new -key client.key -out client.csr
生成ca.crt
openssl genrsa -des3 -out ca.key 1024
openssl req -new -x509 -key ca.key -out ca.crt
通过ca.crt颁发server.crt和client.crt
openssl ca -in server.csr -out server.crt -cert ca.crt -keyfile ca.key
openssl ca -in client.csr -out client.crt -cert ca.crt -keyfile ca.key
注：
这两条执行的时候可能因为没有指定openssl.cnf 会报错
不过没关系，我们用默认的 /etc/pki/tls/openssl.cnf 就可以
不过用默认的时候需要先执行下面两行：
touch /etc/pki/CA/index.txt
echo 00 > /etc/pki/CA/serial
2.证书的作用
证书主要用于在安全通信开始之前的认证
这个程序中client和server均需要通过证书认证彼此，这些过程主要通过OpenSSL库的API完成
client和server如果需要对对方进行认证，需要有ca.crt这个文件，因为client.crt和server.crt都是通过ca.crt签发的，ca.crt用来确认crt文件的合法性
认证完成后，client和server之间会协商一个对阵加密算法，对阵加密相关信息通过非对称加密传输，之后的数据通信是对称加密的，SSL connection using AES256-GCM-SHA384
3.SSL安全通信流程
OpenSSL初始化过程，设置证书文件和私钥文件，设置认证方式，生成SSL上下文ctx
通过Socket API获得用于网络通信的fd，通过ctx生成ssl，绑定ssl与fd
通过SSL_read()和SSL_Write()读写ssl进行安全通信