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nsock_ssl.c

/***************************************************************************
 * nsock_ssl.c -- This contains functions that relate somewhat exclusively *
 * to SSL (over TCP) support in nsock.  Where SSL support is incidental,   *
 * it is often in other files where code can be more easily shared between *
 * the SSL and NonSSL paths.                                               *
 *                                                                         *
 ***********************IMPORTANT NSOCK LICENSE TERMS***********************
 *                                                                         *
 * The nsock parallel socket event library is (C) 1999-2009 Insecure.Com   *
 * LLC This library is free software; you may redistribute and/or          *
 * modify it under the terms of the GNU General Public License as          *
 * published by the Free Software Foundation; Version 2.  This guarantees  *
 * your right to use, modify, and redistribute this software under certain *
 * conditions.  If this license is unacceptable to you, Insecure.Com LLC   *
 * may be willing to sell alternative licenses (contact                    *
 * sales@insecure.com ).                                                   *
 *                                                                         *
 * As a special exception to the GPL terms, Insecure.Com LLC grants        *
 * permission to link the code of this program with any version of the     *
 * OpenSSL library which is distributed under a license identical to that  *
 * listed in the included COPYING.OpenSSL file, and distribute linked      *
 * combinations including the two. You must obey the GNU GPL in all        *
 * respects for all of the code used other than OpenSSL.  If you modify    *
 * this file, you may extend this exception to your version of the file,   *
 * but you are not obligated to do so.                                     *
 *                                                                         * 
 * If you received these files with a written license agreement stating    *
 * terms other than the (GPL) terms above, then that alternative license   *
 * agreement takes precedence over this comment.                          *
 *                                                                         *
 * Source is provided to this software because we believe users have a     *
 * right to know exactly what a program is going to do before they run it. *
 * This also allows you to audit the software for security holes (none     *
 * have been found so far).                                                *
 *                                                                         *
 * Source code also allows you to port Nmap to new platforms, fix bugs,    *
 * and add new features.  You are highly encouraged to send your changes   *
 * to nmap-dev@insecure.org for possible incorporation into the main       *
 * distribution.  By sending these changes to Fyodor or one of the         *
 * Insecure.Org development mailing lists, it is assumed that you are      *
 * offering the Nmap Project (Insecure.Com LLC) the unlimited,             *
 * non-exclusive right to reuse, modify, and relicense the code.  Nmap     *
 * will always be available Open Source, but this is important because the *
 * inability to relicense code has caused devastating problems for other   *
 * Free Software projects (such as KDE and NASM).  We also occasionally    *
 * relicense the code to third parties as discussed above.  If you wish to *
 * specify special license conditions of your contributions, just say so   *
 * when you send them.                                                     *
 *                                                                         *
 * This program is distributed in the hope that it will be useful, but     *
 * WITHOUT ANY WARRANTY; without even the implied warranty of              *
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU       *
 * General Public License v2.0 for more details                            *
 * (http://www.gnu.org/licenses/gpl-2.0.html).                             *
 *                                                                         *
 ***************************************************************************/

/* $Id: nsock_ssl.c 13078 2009-04-25 21:22:57Z fyodor $ */


#include "nsock.h"
#include "nsock_internal.h"
#include "nsock_ssl.h"
#include "netutils.h"

#if HAVE_OPENSSL

/* Disallow anonymous ciphers (Diffie-Hellman key agreement), low bit-strength
   ciphers, export-crippled ciphers, and MD5. Prefer ciphers in decreasing order
   of key size. The cipher list is taken from the book Network Security with
   OpenSSL. To see exactly what ciphers are enabled, use the command
     openssl ciphers -v '...'
   where ... is the string below. */
#define CIPHERS_SECURE "ALL:!ADH:!LOW:!EXP:!MD5:@STRENGTH"

/* This list of ciphers is for speed and compatibility, not security. Any cipher
   is accepted, and the list is sorted by speed based on Brian Hatch's
   (bri@ifokr.org) tests on an Pentium 686 against the ciphers listed. */
#define CIPHERS_FAST "RC4-SHA:RC4-MD5:NULL-SHA:EXP-DES-CBC-SHA:EXP-EDH-RSA-DES-CBC-SHA:EXP-RC4-MD5:NULL-MD5:EDH-RSA-DES-CBC-SHA:EXP-RC2-CBC-MD5:EDH-RSA-DES-CBC3-SHA:EXP-ADH-RC4-MD5:DHE-RSA-AES128-SHA:DHE-RSA-AES256-SHA:EXP-ADH-DES-CBC-SHA:ADH-AES256-SHA:ADH-DES-CBC-SHA:ADH-RC4-MD5:AES256-SHA:DES-CBC-SHA:DES-CBC3-SHA:ADH-DES-CBC3-SHA:AES128-SHA:ADH-AES128-SHA:eNULL:ALL"

extern struct timeval nsock_tod;

/* Create an SSL_CTX and do initialization that is common to nsp_ssl_init and
   nsp_ssl_init_max_speed. */
static SSL_CTX *ssl_init_common() {
  SSL_CTX *ctx;

  SSL_load_error_strings();
  SSL_library_init();

  ctx = SSL_CTX_new( SSLv23_client_method() );
  if ( ! ctx ) {
    fatal("OpenSSL failed to create a new SSL_CTX: %s", 
        ERR_error_string(ERR_get_error(), NULL));
  }

  /* Our SSL* will always have the SSL_SESSION* inside it, so we neither
     need to use nor waste memory for the session cache.
     (Use '1' because '0' means 'infinite'.)   */
  SSL_CTX_set_session_cache_mode(
     ctx,  SSL_SESS_CACHE_OFF | SSL_SESS_CACHE_NO_AUTO_CLEAR );
  SSL_CTX_sess_set_cache_size( ctx, 1 ); 
  SSL_CTX_set_timeout( ctx, 3600); /* pretty unnecessary */

  return ctx;
}
#endif /* HAVE_OPENSSL */

/* Initializes an Nsock pool to create SSL connections. This sets an internal
   SSL_CTX, which is like a template that sets options for all connections that
   are made from it. The connections made from this context will use only secure
   ciphers but no server certificate verification is done. Returns the SSL_CTX
   so you can set your own options. */
nsock_ssl_ctx nsp_ssl_init(nsock_pool ms_pool) {
#if HAVE_OPENSSL
  mspool *ms = (mspool *) ms_pool;
  char rndbuf[128];

  if (ms->sslctx == NULL)
    ms->sslctx = ssl_init_common();
  
  /* get_random_bytes may or may not provide high-quality randomness. Add it to
     the entropy pool without increasing the entropy estimate (third argument of
     RAND_add is 0). We rely on OpenSSL's entropy gathering, called implicitly
     by RAND_status, to give us what we need, or else bail out if it fails. */
  get_random_bytes(rndbuf, sizeof(rndbuf));
  RAND_add(rndbuf, sizeof(rndbuf), 0);
  if (!RAND_status())
    fatal("nsp_ssl_init: Failed to seed OpenSSL PRNG (RAND_status returned false).");

  /* By default, do no server certificate verification. To enable it, do
     something like
       SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER, NULL);
     on the SSL_CTX returned. If you do, it is then up to the application to
     load trusted certificates with SSL_CTX_load_verify_locations or
     SSL_CTX_set_default_verify_paths, or else every connection will fail. It is
     also up to the application to do any further checks such as domain name
     validation. */
  SSL_CTX_set_verify(ms->sslctx, SSL_VERIFY_NONE, NULL);

  /* SSL_OP_ALL sets bug-compatibility for pretty much everything.
     SSL_OP_NO_SSLv2 disables the less-secure SSLv2 while allowing us to use the
     SSLv2-compatible SSLv23_client_method. */
  SSL_CTX_set_options(ms->sslctx, SSL_OP_ALL | SSL_OP_NO_SSLv2);

  if (!SSL_CTX_set_cipher_list(ms->sslctx, CIPHERS_SECURE)) {
    fatal("Unable to set OpenSSL cipher list: %s", 
        ERR_error_string(ERR_get_error(), NULL));
  }

  return ms->sslctx;
#else
  fatal("%s called with no OpenSSL support", __func__);
#endif
}

/* Initializes an Nsock pool to create SSL connections that emphasize speed over
   security. Insecure ciphers are used when they are faster and no certificate
   verification is done. Returns the SSL_CTX so you can set your own options. */
nsock_ssl_ctx nsp_ssl_init_max_speed(nsock_pool ms_pool) {
#if HAVE_OPENSSL
  mspool *ms = (mspool *) ms_pool;
  char rndbuf[128];

  if (ms->sslctx == NULL)
    ms->sslctx = ssl_init_common();

  /* get_random_bytes may or may not provide high-quality randomness. */
  get_random_bytes(rndbuf, sizeof(rndbuf));
  RAND_seed(rndbuf, sizeof(rndbuf));

  SSL_CTX_set_verify(ms->sslctx, SSL_VERIFY_NONE, NULL);
  SSL_CTX_set_options(ms->sslctx, SSL_OP_ALL);
  if (!SSL_CTX_set_cipher_list(ms->sslctx, CIPHERS_FAST)) {
    fatal("Unable to set OpenSSL cipher list: %s", 
        ERR_error_string(ERR_get_error(), NULL));
  }

  return ms->sslctx;
#else
  fatal("%s called with no OpenSSL support", __func__);
#endif
}

/* Check server certificate verification, after a connection is established. We
   check first that a certificate was even offered, then call
   SSL_get_verify_result to get the overall status of verification. (Just
   calling SSL_get_verify_result is not enough because that function returns
   X509_V_OK when 0 certificates are presented.) If the verification mode of the
   SSL object is SSL_VERIFY_NONE, or if OpenSSL is disabled, this function
   always returns true. */
int nsi_ssl_post_connect_verify(const nsock_iod nsockiod) {
  msiod *iod = (msiod *) nsockiod;

#if HAVE_OPENSSL
  assert(iod->ssl != NULL);
  if (SSL_get_verify_mode(iod->ssl) != SSL_VERIFY_NONE) {
    X509 *cert;

    cert = SSL_get_peer_certificate(iod->ssl);
    if (cert == NULL)
      /* No certificate presented. */
      return 0;
    X509_free(cert);

    if (SSL_get_verify_result(iod->ssl) != X509_V_OK)
      /* Something wrong with verification. */
      return 0;
  }
#endif

  return 1;
}

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