On 07/13/2017 11:07 PM, Heikki Linnakangas wrote:
On 07/13/2017 10:13 PM, Robert Haas wrote:
On Thu, Jul 13, 2017 at 1:30 PM, Tom Lane <t...@sss.pgh.pa.us> wrote:
Heikki Linnakangas <hlinn...@iki.fi> writes:
I don't think this can be backpatched. It changes the default DH
parameters from 1024 bits to 2048 bits. That's a good thing for
security, but older clients might not support it, and would refuse to
connect or would fall back to something less secure.
Do we have any hard information about which versions of which clients
might not support that? (In particular I'm wondering if any still exist
in the wild.)
Yeah. If we break clients for v10 two months from release, some
drivers won't be updated by release time, and that sounds pretty
unfriendly to me. On the other hand, if there is only a theoretical
risk of breakage and no clients that we actually know about will have
a problem with it, then the argument for waiting is weaker. I'm not
generally very excited about changing things after beta2, which is
where are, but if this is a security issue then we might need to hold
our nose and go ahead. I'm against it if it's likely to cause
real-world connectivity problems, though.
Googling around, I believe Java 6 is the only straggler [1]. So we would
be breaking that. Java 7 also doesn't support DH parameters > 1024 bits,
but it supports ECDHE, which is prioritized over DH ciphers, so it
doesn't matter.
Java 6 was released back in 2006. The last public release was in 2013.
It wouldn't surprise me to still see it bundled with random proprietary
software packages, though. The official PostgreSQL JDBC driver still
supports it, but there has been discussion recently on dropping support
for it, and even for Java 7. [2]
I would be OK with breaking DH with Java 6 in PostgreSQL 10, especially
since there's a simple workaround (generate a 1024-bit DH parameters
file). I would be less enthusiastic about doing that in a minor release,
although maybe that wouldn't be too bad either, if we put a prominent
notice with the workaround in the release notes.
Some more information on the situation with JDK version 6: I installed
Debian wheezy on a VM, with a OpenJDK 6, and tested connecting to a
patched server with the JDBC driver. It worked! Googling around, it
seems that this was fixed in later versions of OpenJDK 6
(https://bugs.openjdk.java.net/browse/JDK-8062834). I then downloaded
the latest Oracle JRE binary version, 6u45, available from
http://www.oracle.com/technetwork/java/javase/downloads/java-archive-downloads-javase6-419409.html.
With that, it does not work, you get errors like:
org.postgresql.util.PSQLException: SSL error:
java.lang.RuntimeException: Could not generate DH keypair
...
Caused by: java.security.InvalidAlgorithmParameterException: Prime size
must be multiple of 64, and can only range from 512 to 1024 (inclusive)
So, the last binary version downloadable from Oracle is affected, but
recent versions of OpenJDK 6 work.
Rebased patch attached, with proposed release notes included. Barring
new objections or arguments, I'll commit this (only) to v10 later today.
- Heikki
>From 93ef6ce1c203028384cf9febf3b4add715fff26f Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakan...@iki.fi>
Date: Mon, 31 Jul 2017 13:39:01 +0300
Subject: [PATCH 1/2] Always use 2048 bit DH parameters for OpenSSL ephemeral
DH ciphers.
1024 bits is considered weak these days, but OpenSSL always passes 1024 as
the key length to the tmp_dh callback. All the code to handle other key
lengths is, in fact, dead.
To remedy those issues:
* Only include hard-coded 2048-bit parameters.
* Set the parameters directly with SSL_CTX_set_tmp_dh(), without the
callback
* The name of the file containing the DH parameters is now a GUC. This
replaces the old hardcoded "dh1024.pem" filename. (The files for other
key lengths, dh512.pem, dh2048.pem, etc. were never actually used.)
Per report by Nicolas Guini and Damian Quiroga. Reviewed by Michael Paquier.
Discussion: https://www.postgresql.org/message-id/camxbouyjooautvozn6ofzym828anrdjuccotccquxjws-l2...@mail.gmail.com
---
doc/src/sgml/config.sgml | 24 +++
src/backend/libpq/be-secure-openssl.c | 264 +++++++++-----------------
src/backend/libpq/be-secure.c | 1 +
src/backend/utils/misc/guc.c | 11 ++
src/backend/utils/misc/postgresql.conf.sample | 1 +
src/include/libpq/libpq.h | 1 +
6 files changed, 133 insertions(+), 169 deletions(-)
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index b45b7f7f69..c33d6a0349 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1203,6 +1203,30 @@ include_dir 'conf.d'
</listitem>
</varlistentry>
+ <varlistentry id="guc-ssl-dh-params-file" xreflabel="ssl_dh_params_file">
+ <term><varname>ssl_dh_params_file</varname> (<type>string</type>)
+ <indexterm>
+ <primary><varname>ssl_dh_params_file</> configuration parameter</primary>
+ </indexterm>
+ </term>
+ <listitem>
+ <para>
+ Specifies the name of the file containing Diffie-Hellman parameters
+ used for so-called ephemeral DH family of SSL ciphers. The default is
+ empty, in which case compiled-in default DH parameters used. Using
+ custom DH parameters reduces the exposure if an attacker manages to
+ crack the well-known compiled-in DH parameters. You can create your own
+ DH parameters file with the command
+ <command>openssl dhparam -out dhparams.pem 2048</command>.
+ </para>
+
+ <para>
+ This parameter can only be set in the <filename>postgresql.conf</>
+ file or on the server command line.
+ </para>
+ </listitem>
+ </varlistentry>
+
<varlistentry id="guc-krb-server-keyfile" xreflabel="krb_server_keyfile">
<term><varname>krb_server_keyfile</varname> (<type>string</type>)
<indexterm>
diff --git a/src/backend/libpq/be-secure-openssl.c b/src/backend/libpq/be-secure-openssl.c
index 67145e9412..dc307c101f 100644
--- a/src/backend/libpq/be-secure-openssl.c
+++ b/src/backend/libpq/be-secure-openssl.c
@@ -61,6 +61,7 @@
#include "libpq/libpq.h"
#include "miscadmin.h"
#include "pgstat.h"
+#include "storage/fd.h"
#include "storage/latch.h"
#include "tcop/tcopprot.h"
#include "utils/memutils.h"
@@ -71,13 +72,12 @@ static int my_sock_write(BIO *h, const char *buf, int size);
static BIO_METHOD *my_BIO_s_socket(void);
static int my_SSL_set_fd(Port *port, int fd);
-static DH *load_dh_file(int keylength);
+static DH *load_dh_file(char *filename, bool isServerStart);
static DH *load_dh_buffer(const char *, size_t);
-static DH *generate_dh_parameters(int prime_len, int generator);
-static DH *tmp_dh_cb(SSL *s, int is_export, int keylength);
static int ssl_passwd_cb(char *buf, int size, int rwflag, void *userdata);
static int verify_cb(int, X509_STORE_CTX *);
static void info_cb(const SSL *ssl, int type, int args);
+static bool initialize_dh(SSL_CTX *context, bool isServerStart);
static bool initialize_ecdh(SSL_CTX *context, bool isServerStart);
static const char *SSLerrmessage(unsigned long ecode);
@@ -96,17 +96,14 @@ static bool ssl_passwd_cb_called = false;
* As discussed above, EDH protects the confidentiality of
* sessions even if the static private key is compromised,
* so we are *highly* motivated to ensure that we can use
- * EDH even if the DBA... or an attacker... deletes the
- * $DataDir/dh*.pem files.
+ * EDH even if the DBA has not provided custom DH parameters.
*
* We could refuse SSL connections unless a good DH parameter
* file exists, but some clients may quietly renegotiate an
* unsecured connection without fully informing the user.
- * Very uncool.
- *
- * Alternatively, the backend could attempt to load these files
- * on startup if SSL is enabled - and refuse to start if any
- * do not exist - but this would tend to piss off DBAs.
+ * Very uncool. Alternatively, the system could refuse to start
+ * if a DH parameters is not specified, but this would tend to
+ * piss off DBAs.
*
* If you want to create your own hardcoded DH parameters
* for fun and profit, review "Assigned Number for SKIP
@@ -114,19 +111,6 @@ static bool ssl_passwd_cb_called = false;
* for suggestions.
*/
-static const char file_dh512[] =
-"-----BEGIN DH PARAMETERS-----\n\
-MEYCQQD1Kv884bEpQBgRjXyEpwpy1obEAxnIByl6ypUM2Zafq9AKUJsCRtMIPWak\n\
-XUGfnHy9iUsiGSa6q6Jew1XpKgVfAgEC\n\
------END DH PARAMETERS-----\n";
-
-static const char file_dh1024[] =
-"-----BEGIN DH PARAMETERS-----\n\
-MIGHAoGBAPSI/VhOSdvNILSd5JEHNmszbDgNRR0PfIizHHxbLY7288kjwEPwpVsY\n\
-jY67VYy4XTjTNP18F1dDox0YbN4zISy1Kv884bEpQBgRjXyEpwpy1obEAxnIByl6\n\
-ypUM2Zafq9AKUJsCRtMIPWakXUGfnHy9iUsiGSa6q6Jew1XpL3jHAgEC\n\
------END DH PARAMETERS-----\n";
-
static const char file_dh2048[] =
"-----BEGIN DH PARAMETERS-----\n\
MIIBCAKCAQEA9kJXtwh/CBdyorrWqULzBej5UxE5T7bxbrlLOCDaAadWoxTpj0BV\n\
@@ -137,21 +121,6 @@ Q6MdGGzeMyEstSr/POGxKUAYEY18hKcKctaGxAMZyAcpesqVDNmWn6vQClCbAkbT\n\
CD1mpF1Bn5x8vYlLIhkmuquiXsNV6TILOwIBAg==\n\
-----END DH PARAMETERS-----\n";
-static const char file_dh4096[] =
-"-----BEGIN DH PARAMETERS-----\n\
-MIICCAKCAgEA+hRyUsFN4VpJ1O8JLcCo/VWr19k3BCgJ4uk+d+KhehjdRqNDNyOQ\n\
-l/MOyQNQfWXPeGKmOmIig6Ev/nm6Nf9Z2B1h3R4hExf+zTiHnvVPeRBhjdQi81rt\n\
-Xeoh6TNrSBIKIHfUJWBh3va0TxxjQIs6IZOLeVNRLMqzeylWqMf49HsIXqbcokUS\n\
-Vt1BkvLdW48j8PPv5DsKRN3tloTxqDJGo9tKvj1Fuk74A+Xda1kNhB7KFlqMyN98\n\
-VETEJ6c7KpfOo30mnK30wqw3S8OtaIR/maYX72tGOno2ehFDkq3pnPtEbD2CScxc\n\
-alJC+EL7RPk5c/tgeTvCngvc1KZn92Y//EI7G9tPZtylj2b56sHtMftIoYJ9+ODM\n\
-sccD5Piz/rejE3Ome8EOOceUSCYAhXn8b3qvxVI1ddd1pED6FHRhFvLrZxFvBEM9\n\
-ERRMp5QqOaHJkM+Dxv8Cj6MqrCbfC4u+ZErxodzuusgDgvZiLF22uxMZbobFWyte\n\
-OvOzKGtwcTqO/1wV5gKkzu1ZVswVUQd5Gg8lJicwqRWyyNRczDDoG9jVDxmogKTH\n\
-AaqLulO7R8Ifa1SwF2DteSGVtgWEN8gDpN3RBmmPTDngyF2DHb5qmpnznwtFKdTL\n\
-KWbuHn491xNO25CQWMtem80uKw+pTnisBRF/454n1Jnhub144YRBoN8CAQI=\n\
------END DH PARAMETERS-----\n";
-
/* ------------------------------------------------------------ */
/* Public interface */
@@ -316,13 +285,14 @@ be_tls_init(bool isServerStart)
goto error;
}
- /* set up ephemeral DH keys, and disallow SSL v2/v3 while at it */
- SSL_CTX_set_tmp_dh_callback(context, tmp_dh_cb);
+ /* disallow SSL v2/v3 */
SSL_CTX_set_options(context,
SSL_OP_SINGLE_DH_USE |
SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3);
- /* set up ephemeral ECDH keys */
+ /* set up ephemeral DH and ECDH keys */
+ if (!initialize_dh(context, isServerStart))
+ goto error;
if (!initialize_ecdh(context, isServerStart))
goto error;
@@ -918,53 +888,57 @@ err:
* what we expect it to contain.
*/
static DH *
-load_dh_file(int keylength)
+load_dh_file(char *filename, bool isServerStart)
{
FILE *fp;
- char fnbuf[MAXPGPATH];
DH *dh = NULL;
int codes;
/* attempt to open file. It's not an error if it doesn't exist. */
- snprintf(fnbuf, sizeof(fnbuf), "dh%d.pem", keylength);
- if ((fp = fopen(fnbuf, "r")) == NULL)
+ if ((fp = AllocateFile(filename, "r")) == NULL)
+ {
+ ereport(isServerStart ? FATAL : LOG,
+ (errcode_for_file_access(),
+ errmsg("could not open DH parameters file \"%s\": %m",
+ filename)));
return NULL;
+ }
-/* flock(fileno(fp), LOCK_SH); */
dh = PEM_read_DHparams(fp, NULL, NULL, NULL);
-/* flock(fileno(fp), LOCK_UN); */
- fclose(fp);
+ FreeFile(fp);
- /* is the prime the correct size? */
- if (dh != NULL && 8 * DH_size(dh) < keylength)
+ if (dh == NULL)
{
- elog(LOG, "DH errors (%s): %d bits expected, %d bits found",
- fnbuf, keylength, 8 * DH_size(dh));
- dh = NULL;
+ ereport(isServerStart ? FATAL : LOG,
+ (errcode(ERRCODE_CONFIG_FILE_ERROR),
+ errmsg("could not load DH parameters file: %s",
+ SSLerrmessage(ERR_get_error()))));
+ return NULL;
}
/* make sure the DH parameters are usable */
- if (dh != NULL)
+ if (DH_check(dh, &codes) == 0)
{
- if (DH_check(dh, &codes) == 0)
- {
- elog(LOG, "DH_check error (%s): %s", fnbuf,
- SSLerrmessage(ERR_get_error()));
- return NULL;
- }
- if (codes & DH_CHECK_P_NOT_PRIME)
- {
- elog(LOG, "DH error (%s): p is not prime", fnbuf);
- return NULL;
- }
- if ((codes & DH_NOT_SUITABLE_GENERATOR) &&
- (codes & DH_CHECK_P_NOT_SAFE_PRIME))
- {
- elog(LOG,
- "DH error (%s): neither suitable generator or safe prime",
- fnbuf);
- return NULL;
- }
+ ereport(isServerStart ? FATAL : LOG,
+ (errcode(ERRCODE_CONFIG_FILE_ERROR),
+ errmsg("invalid DH parameters: %s",
+ SSLerrmessage(ERR_get_error()))));
+ return NULL;
+ }
+ if (codes & DH_CHECK_P_NOT_PRIME)
+ {
+ ereport(isServerStart ? FATAL : LOG,
+ (errcode(ERRCODE_CONFIG_FILE_ERROR),
+ errmsg("invalid DH parameters: p is not prime")));
+ return NULL;
+ }
+ if ((codes & DH_NOT_SUITABLE_GENERATOR) &&
+ (codes & DH_CHECK_P_NOT_SAFE_PRIME))
+ {
+ ereport(isServerStart ? FATAL : LOG,
+ (errcode(ERRCODE_CONFIG_FILE_ERROR),
+ errmsg("invalid DH parameters: neither suitable generator or safe prime")));
+ return NULL;
}
return dh;
@@ -996,102 +970,6 @@ load_dh_buffer(const char *buffer, size_t len)
}
/*
- * Generate DH parameters.
- *
- * Last resort if we can't load precomputed nor hardcoded
- * parameters.
- */
-static DH *
-generate_dh_parameters(int prime_len, int generator)
-{
- DH *dh;
-
- if ((dh = DH_new()) == NULL)
- return NULL;
-
- if (DH_generate_parameters_ex(dh, prime_len, generator, NULL))
- return dh;
-
- DH_free(dh);
- return NULL;
-}
-
-/*
- * Generate an ephemeral DH key. Because this can take a long
- * time to compute, we can use precomputed parameters of the
- * common key sizes.
- *
- * Since few sites will bother to precompute these parameter
- * files, we also provide a fallback to the parameters provided
- * by the OpenSSL project.
- *
- * These values can be static (once loaded or computed) since
- * the OpenSSL library can efficiently generate random keys from
- * the information provided.
- */
-static DH *
-tmp_dh_cb(SSL *s, int is_export, int keylength)
-{
- DH *r = NULL;
- static DH *dh = NULL;
- static DH *dh512 = NULL;
- static DH *dh1024 = NULL;
- static DH *dh2048 = NULL;
- static DH *dh4096 = NULL;
-
- switch (keylength)
- {
- case 512:
- if (dh512 == NULL)
- dh512 = load_dh_file(keylength);
- if (dh512 == NULL)
- dh512 = load_dh_buffer(file_dh512, sizeof file_dh512);
- r = dh512;
- break;
-
- case 1024:
- if (dh1024 == NULL)
- dh1024 = load_dh_file(keylength);
- if (dh1024 == NULL)
- dh1024 = load_dh_buffer(file_dh1024, sizeof file_dh1024);
- r = dh1024;
- break;
-
- case 2048:
- if (dh2048 == NULL)
- dh2048 = load_dh_file(keylength);
- if (dh2048 == NULL)
- dh2048 = load_dh_buffer(file_dh2048, sizeof file_dh2048);
- r = dh2048;
- break;
-
- case 4096:
- if (dh4096 == NULL)
- dh4096 = load_dh_file(keylength);
- if (dh4096 == NULL)
- dh4096 = load_dh_buffer(file_dh4096, sizeof file_dh4096);
- r = dh4096;
- break;
-
- default:
- if (dh == NULL)
- dh = load_dh_file(keylength);
- r = dh;
- }
-
- /* this may take a long time, but it may be necessary... */
- if (r == NULL || 8 * DH_size(r) < keylength)
- {
- ereport(DEBUG2,
- (errmsg_internal("DH: generating parameters (%d bits)",
- keylength)));
- r = generate_dh_parameters(keylength, DH_GENERATOR_2);
- }
-
- return r;
-}
-
-/*
* Passphrase collection callback
*
* If OpenSSL is told to use a passphrase-protected server key, by default
@@ -1172,6 +1050,54 @@ info_cb(const SSL *ssl, int type, int args)
}
}
+/*
+ * Set DH parameters for generating ephemeral DH keys. The
+ * DH parameters can take a long time to compute, so they must be
+ * precomputed.
+ *
+ * Since few sites will bother to create a parameter file, we also
+ * also provide a fallback to the parameters provided by the
+ * OpenSSL project.
+ *
+ * These values can be static (once loaded or computed) since the
+ * OpenSSL library can efficiently generate random keys from the
+ * information provided.
+ */
+static bool
+initialize_dh(SSL_CTX *context, bool isServerStart)
+{
+ DH *dh = NULL;
+
+ SSL_CTX_set_options(context, SSL_OP_SINGLE_DH_USE);
+
+ if (ssl_dh_params_file[0])
+ dh = load_dh_file(ssl_dh_params_file, isServerStart);
+ if (!dh)
+ dh = load_dh_buffer(file_dh2048, sizeof file_dh2048);
+ if (!dh)
+ {
+ ereport(isServerStart ? FATAL : LOG,
+ (errcode(ERRCODE_CONFIG_FILE_ERROR),
+ (errmsg("DH: could not load DH parameters"))));
+ return false;
+ }
+
+ if (SSL_CTX_set_tmp_dh(context, dh) != 1)
+ {
+ ereport(isServerStart ? FATAL : LOG,
+ (errcode(ERRCODE_CONFIG_FILE_ERROR),
+ (errmsg("DH: could not set DH parameters: %s",
+ SSLerrmessage(ERR_get_error())))));
+ return false;
+ }
+ return true;
+}
+
+/*
+ * Set ECDH parameters for generating ephemeral Elliptic Curve DH
+ * keys. This is much simpler than the DH parameters, as we just
+ * need to provide the name of the curve to OpenSSL.
+ */
static bool
initialize_ecdh(SSL_CTX *context, bool isServerStart)
{
diff --git a/src/backend/libpq/be-secure.c b/src/backend/libpq/be-secure.c
index 785dadb6c2..53fefd1b29 100644
--- a/src/backend/libpq/be-secure.c
+++ b/src/backend/libpq/be-secure.c
@@ -44,6 +44,7 @@ char *ssl_cert_file;
char *ssl_key_file;
char *ssl_ca_file;
char *ssl_crl_file;
+char *ssl_dh_params_file;
#ifdef USE_SSL
bool ssl_loaded_verify_locations = false;
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 82e54c084b..246fea8693 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -3607,6 +3607,17 @@ static struct config_string ConfigureNamesString[] =
},
{
+ {"ssl_dh_params_file", PGC_SIGHUP, CONN_AUTH_SECURITY,
+ gettext_noop("Location of the SSL DH params file."),
+ NULL,
+ GUC_SUPERUSER_ONLY
+ },
+ &ssl_dh_params_file,
+ "",
+ NULL, NULL, NULL
+ },
+
+ {
{"application_name", PGC_USERSET, LOGGING_WHAT,
gettext_noop("Sets the application name to be reported in statistics and logs."),
NULL,
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 1906b5a33c..df5d2f3f22 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -80,6 +80,7 @@
#ssl_ciphers = 'HIGH:MEDIUM:+3DES:!aNULL' # allowed SSL ciphers
#ssl_prefer_server_ciphers = on
#ssl_ecdh_curve = 'prime256v1'
+#ssl_dh_params_file = ''
#ssl_cert_file = 'server.crt'
#ssl_key_file = 'server.key'
#ssl_ca_file = ''
diff --git a/src/include/libpq/libpq.h b/src/include/libpq/libpq.h
index 78851b1060..fd2dd5853c 100644
--- a/src/include/libpq/libpq.h
+++ b/src/include/libpq/libpq.h
@@ -79,6 +79,7 @@ extern char *ssl_cert_file;
extern char *ssl_key_file;
extern char *ssl_ca_file;
extern char *ssl_crl_file;
+extern char *ssl_dh_params_file;
extern int secure_initialize(bool isServerStart);
extern bool secure_loaded_verify_locations(void);
--
2.11.0
>From af22f1ed09fcce06c20d39df9bb9f1478e5ddabc Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakan...@iki.fi>
Date: Mon, 31 Jul 2017 14:23:17 +0300
Subject: [PATCH 2/2] Update release notes for the DH parameter changes.
---
doc/src/sgml/release-10.sgml | 37 +++++++++++++++++++++++++++++++++++++
1 file changed, 37 insertions(+)
diff --git a/doc/src/sgml/release-10.sgml b/doc/src/sgml/release-10.sgml
index cf743aa2f7..b5ee88984e 100644
--- a/doc/src/sgml/release-10.sgml
+++ b/doc/src/sgml/release-10.sgml
@@ -408,6 +408,43 @@
<listitem>
<!--
+2017-07-31 [XXXXXXXXX] Always use 2048 bit DH parameters for OpenSSL ephemeral
+-->
+ <para>
+ Add configuration option <xref linkend="guc-ssl-dh-params-file"> to
+ specify filename for custom OpenSSL DH parameters (Heikki Linnakangas)
+ </para>
+
+ <para>
+ This replaces the hardcoded, undocumented <filename>dh1024.pem</>
+ filename. Note that <filename>dh1024.pem</> is no longer used by default;
+ you must set the option to use custom DH parameters.
+ </para>
+ </listitem>
+
+ <listitem>
+<!--
+2017-07-31 [XXXXXXXXX] Always use 2048 bit DH parameters for OpenSSL ephemeral
+-->
+ <para>
+ Increase the size of DH parameters used for OpenSSL ephemeral DH ciphers
+ to 2048 bits (Heikki Linnakangas)
+ </para>
+
+ <para>
+ The size of the compiled-in DH parameters has been increased from 1024
+ to 2048 bits, making DH key exchange more resistent to a brute-force
+ attack. However, some old SSL implementations, notably some revisions of
+ Java Runtime Environment version 6, will not accept DH parameters longer
+ than 1024 bits, and will not be able to connect over SSL. As a
+ work-around, you can use custom 1024-bit DH parameters, instead of the
+ compiled-in defaults. See <xref linkend="guc-ssl-dh-params-file"> for
+ information on using custom DH parameters.
+ </para>
+ </listitem>
+
+ <listitem>
+<!--
2017-02-13 [7ada2d31f] Remove contrib/tsearch2.
-->
<para>
--
2.11.0
--
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