SSLかんたんな例

ssl_server.c

// OpenSSL the most SIMPLE example
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <openssl/ssl.h>
#include <sys/socket.h>
#include <netdb.h>
#define PORT 12335

int main( void )
{
  // Set up for socket
  int sb = socket( AF_INET, SOCK_STREAM, 0 );
  struct sockaddr_in addr;
  bzero((char*) &addr, sizeof(addr));
  addr.sin_family = PF_INET;
  addr.sin_port = htons(PORT);
  addr.sin_family = htonl(INADDR_ANY);
  if( bind( sb, (struct sockaddr*)&addr, sizeof(addr) ) < 0 ){
    perror("bind");
    exit(1);
  }
  listen( sb, 1 );
  int s = accept( sb, NULL, NULL );
  // SSL initialize
  SSL_library_init(); 
  SSL_CTX* ctx = SSL_CTX_new( SSLv2_server_method() ); 
  SSL* ssl = SSL_new( ctx );
  SSL_set_fd( ssl, s );

  // SSL set up for a certificate
  SSL_use_certificate_file( ssl, "public.key", SSL_FILETYPE_PEM );
  SSL_use_PrivateKey_file( ssl, "private.key", SSL_FILETYPE_PEM );
  // SSL accept
  SSL_accept(ssl);

  char msg[64];
  int len;
  len = SSL_read( ssl, msg, sizeof(msg) );
  msg[len] = '\0';
  printf("Server received : %s\n", msg );
  // SSL shutdown
  SSL_shutdown(ssl); 
  SSL_free(ssl); 
  SSL_CTX_free(ctx);
  // socket close
  close(s);
  close(sb);
  return 0;
}

ssl_client.c

// OpenSSL the most SIMPLE client example
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <openssl/ssl.h>
#include <sys/socket.h>
#include <netdb.h>

#define PORT 12335
#define HOST "127.0.0.1"

int main( void )
{
  // Initialize a socket
  int s = socket( AF_INET, SOCK_STREAM, 0 );

  struct sockaddr_in addr;
  bzero((char*) &addr, sizeof(addr));
  addr.sin_family = AF_INET;
  addr.sin_port = htons(PORT);
  addr.sin_addr.s_addr = inet_addr(HOST);

  if( connect( s, (struct sockaddr*)&addr, sizeof(addr) ) < 0 ){
    perror("connect");
    exit(1);
  }

  // SSL initialize
  SSL_library_init(); 
  SSL_CTX* ctx = SSL_CTX_new( SSLv2_client_method() );
  SSL* ssl = SSL_new( ctx );

  // SSL connect
  SSL_set_fd( ssl, s );
  SSL_connect( ssl );

  char msg[64] = "This is client.";
  SSL_write( ssl, msg, strlen(msg) );
  // SSL shutdown
  SSL_shutdown(ssl); 
  SSL_free(ssl); 
  SSL_CTX_free(ctx);
  // close socket
  close(s);
  return 0;
}

でもって
# openssl req -new -x509 -nodes -out public.key -keyout private.key
# gcc -o server -lssl -lcrypt ssl_server.c
# gcc -o client -lssl -lcrypt ssl_client.c
# ./server &
# ./client

http://www-cms.phys.s.u-tokyo.ac.jp/~naoki/CIPINTRO/NETWORK/openssl.html
を参考にしてfedoraでコンパイル通るように修正しました。