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res_rtp_asterisk: Enable Forward Secrecy (PFS) for DTLS.

Browse Source 
Since July 2014, TLS based protocols (SIP over TLS, Secure WebSockets, HTTPS)
support PFS thanks to ASTERISK-23905. In July 2015, the same feature was added
for DTLS. The source code from main/tcptls.c should have been re-used to ease
security audits. Therefore, this change rolls back the change from July 2015 and
re-uses the code from July 2014. This has the additional benefits to work under
CentOS 7 and enabling not just ECDHE but DHE based cipher suites as well.

ASTERISK-25659 #close
Reported by: StefanEng86, urbaniak, pay123
Tested by: sarumjanuch, traud
patches:
res_rtp_asterisk.patch submitted by sarumjanuch
dtls_centos_step_1.patch submitted by traud
dtls_centos_step_2.patch submitted by traud

Change-Id: I537cadf4421f092a613146b230f2c0ee1be28d5c
changes/68/3068/4
Alexander Traud 10 years ago
parent 1623a5faf7
commit 8653da4fa2
5 changed files with 55 additions and 79 deletions
Show Stats Download Patch File Download Diff File

22
CHANGES
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@ -8,6 +8,28 @@
===
==============================================================================
------------------------------------------------------------------------------
--- Functionality changes since Asterisk 11.24 -------------------------------
------------------------------------------------------------------------------
res_rtp_asterisk
------------------
* The DTLS part in Asterisk now supports Perfect Forward Secrecy (PFS).
Enabling PFS is attempted by default, and is dependent on the configuration
of the module using TLS.
- Ephemeral ECDH (ECDHE) is enabled by default. To disable it, do not
specify a ECDHE cipher suite in sip.conf, for example:
dtlscipher=AES128-SHA
- Ephemeral DH (DHE) is disabled by default. To enable it, add DH parameters
into the private key file, e.g., sip.conf dtlsprivatekey. For example:
openssl dhparam -out ./dh.pem 2048
- Because clients expect the server to prefer PFS, and because OpenSSL sorts
its cipher suites by bit strength, see "openssl ciphers -v DEFAULT".
Consider re-ordering your cipher suites in the respective configuration
file. For example:
dtlscipher=ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256
which forces PFS and requires at least DTLS 1.2.
------------------------------------------------------------------------------
--- Functionality changes since Asterisk 11.21 -------------------------------
------------------------------------------------------------------------------

63
configure vendored
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@ -1056,10 +1056,6 @@ PBX_DAHDI
DAHDI_DIR
DAHDI_INCLUDE
DAHDI_LIB
PBX_OPENSSL_ECDH_AUTO
OPENSSL_ECDH_AUTO_DIR
OPENSSL_ECDH_AUTO_INCLUDE
OPENSSL_ECDH_AUTO_LIB
PBX_OPENSSL_SRTP
OPENSSL_SRTP_DIR
OPENSSL_SRTP_INCLUDE
@ -8527,18 +8523,6 @@ PBX_OPENSSL_SRTP=0
OPENSSL_ECDH_AUTO_DESCRIP="OpenSSL Auto ECDH Support"
OPENSSL_ECDH_AUTO_OPTION=crypto
OPENSSL_ECDH_AUTO_DIR=${CRYPTO_DIR}
PBX_OPENSSL_ECDH_AUTO=0
DAHDI_DESCRIP="DAHDI"
DAHDI_OPTION="dahdi"
PBX_DAHDI=0
@ -28475,53 +28459,6 @@ _ACEOF
fi
fi
if test "$PBX_OPENSSL" = "1";
then
if test "x${PBX_OPENSSL_ECDH_AUTO}" != "x1" -a "${USE_OPENSSL_ECDH_AUTO}" != "no"; then
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for SSL_CTX_set_ecdh_auto declared in openssl/ssl.h" >&5
$as_echo_n "checking for SSL_CTX_set_ecdh_auto declared in openssl/ssl.h... " >&6; }
saved_cppflags="${CPPFLAGS}"
if test "x${OPENSSL_ECDH_AUTO_DIR}" != "x"; then
OPENSSL_ECDH_AUTO_INCLUDE="-I${OPENSSL_ECDH_AUTO_DIR}/include"
fi
CPPFLAGS="${CPPFLAGS} ${OPENSSL_ECDH_AUTO_INCLUDE}"
cat confdefs.h - <<_ACEOF >conftest.$ac_ext
/* end confdefs.h. */
#include <openssl/ssl.h>
int
main ()
{
#if !defined(SSL_CTX_set_ecdh_auto)
(void) SSL_CTX_set_ecdh_auto;
#endif
;
return 0;
}
_ACEOF
if ac_fn_c_try_compile "$LINENO"; then :
{ $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
$as_echo "yes" >&6; }
PBX_OPENSSL_ECDH_AUTO=1
$as_echo "#define HAVE_OPENSSL_ECDH_AUTO 1" >>confdefs.h
else
{ $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
$as_echo "no" >&6; }
fi
rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
CPPFLAGS="${saved_cppflags}"
fi
fi
if test "$PBX_OPENSSL" = "1";

6
configure.ac
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@ -392,7 +392,6 @@ AST_EXT_LIB_SETUP_OPTIONAL([COROSYNC_CFG_STATE_TRACK], [A callback only in coros
AST_EXT_LIB_SETUP([CURSES], [curses], [curses])
AST_EXT_LIB_SETUP([CRYPTO], [OpenSSL Cryptography], [crypto])
AST_EXT_LIB_SETUP_OPTIONAL([OPENSSL_SRTP], [OpenSSL SRTP Extension Support], [CRYPTO], [crypto])
AST_EXT_LIB_SETUP_OPTIONAL([OPENSSL_ECDH_AUTO], [OpenSSL Auto ECDH Support], [CRYPTO], [crypto])
AST_EXT_LIB_SETUP([DAHDI], [DAHDI], [dahdi])
AST_EXT_LIB_SETUP([FFMPEG], [Ffmpeg and avcodec], [avcodec])
AST_EXT_LIB_SETUP([GSM], [External GSM], [gsm], [, use 'internal' GSM otherwise])
@ -2229,11 +2228,6 @@ then
AST_EXT_LIB_CHECK([OPENSSL_SRTP], [ssl], [SSL_CTX_set_tlsext_use_srtp], [openssl/ssl.h], [-lcrypto])
fi
if test "$PBX_OPENSSL" = "1";
then
AST_C_DECLARE_CHECK([OPENSSL_ECDH_AUTO], [SSL_CTX_set_ecdh_auto], [openssl/ssl.h])
fi
if test "$PBX_OPENSSL" = "1";
then
AST_C_DEFINE_CHECK([SSL_OP_NO_TLSV1_1], [SSL_OP_NO_TLSv1_1], [openssl/ssl.h])

3
include/asterisk/autoconfig.h.in
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@ -530,9 +530,6 @@
/* Define to 1 if you have the OpenSSL Secure Sockets Layer library. */
#undef HAVE_OPENSSL
/* Define if your system has SSL_CTX_set_ecdh_auto declared. */
#undef HAVE_OPENSSL_ECDH_AUTO
/* Define to 1 if CRYPTO has the OpenSSL SRTP Extension Support feature. */
#undef HAVE_OPENSSL_SRTP

40
res/res_rtp_asterisk.c
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@ -1285,7 +1285,7 @@ static int ast_rtp_dtls_set_configuration(struct ast_rtp_instance *instance, con
{
struct ast_rtp *rtp = ast_rtp_instance_get_data(instance);
int res;
#ifndef HAVE_OPENSSL_ECDH_AUTO
#ifdef HAVE_OPENSSL_EC
EC_KEY *ecdh;
#endif
@ -1309,15 +1309,41 @@ static int ast_rtp_dtls_set_configuration(struct ast_rtp_instance *instance, con
SSL_CTX_set_read_ahead(rtp->ssl_ctx, 1);
#ifdef HAVE_OPENSSL_ECDH_AUTO
SSL_CTX_set_ecdh_auto(rtp->ssl_ctx, 1);
#else
#ifdef HAVE_OPENSSL_EC
if (!ast_strlen_zero(dtls_cfg->pvtfile)) {
BIO *bio = BIO_new_file(dtls_cfg->pvtfile, "r");
if (bio != NULL) {
DH *dh = PEM_read_bio_DHparams(bio, NULL, NULL, NULL);
if (dh != NULL) {
if (SSL_CTX_set_tmp_dh(rtp->ssl_ctx, dh)) {
long options = SSL_OP_CIPHER_SERVER_PREFERENCE |
SSL_OP_SINGLE_DH_USE | SSL_OP_SINGLE_ECDH_USE;
options = SSL_CTX_set_options(rtp->ssl_ctx, options);
ast_verb(2, "DTLS DH initialized, PFS enabled\n");
}
DH_free(dh);
}
BIO_free(bio);
}
}
/* enables AES-128 ciphers, to get AES-256 use NID_secp384r1 */
ecdh = EC_KEY_new_by_curve_name(NID_X9_62_prime256v1);
if (ecdh) {
SSL_CTX_set_tmp_ecdh(rtp->ssl_ctx, ecdh);
if (ecdh != NULL) {
if (SSL_CTX_set_tmp_ecdh(rtp->ssl_ctx, ecdh)) {
#ifndef SSL_CTRL_SET_ECDH_AUTO
#define SSL_CTRL_SET_ECDH_AUTO 94
#endif
/* SSL_CTX_set_ecdh_auto(rtp->ssl_ctx, on); requires OpenSSL 1.0.2 which wraps: */
if (SSL_CTX_ctrl(rtp->ssl_ctx, SSL_CTRL_SET_ECDH_AUTO, 1, NULL)) {
ast_verb(2, "DTLS ECDH initialized (automatic), faster PFS enabled\n");
} else {
ast_verb(2, "DTLS ECDH initialized (secp256r1), faster PFS enabled\n");
}
EC_KEY_free(ecdh);
}
#endif
#endif /* #ifdef HAVE_OPENSSL_EC */
rtp->dtls_verify = dtls_cfg->verify;

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