On Thu, Dec 12, 2013 at 01:33:57PM +0100, Magnus Hagander wrote:
> On Thu, Dec 12, 2013 at 11:30 AM, Marko Kreen <mark...@gmail.com> wrote:
> > On Wed, Dec 11, 2013 at 10:08:44PM -0500, Tom Lane wrote:
> > I know that SChannel SSL library in Windows XP (and earlier) is such
> > RC4+3DES only implementation, but I have not heard about anything
> > using it to connect to Postgres.
> >
> > Also I have not heard about any Postgres clients actually allowing
> > to configure ciphers, so my impression all client libraries
> > use defaults, which usually prefer AES anyway.
> >
> I don't know, but I would assume that npgsql which sit on top of dotnet,
> would sit on top of schannel in the end.

Probably yes.

> That said, this is XP and earlier, right? Newer versions of Windows have
> better defaults?

Yes, since Vista it supports AES:


> > So my new proposal would be to pick one from following defaults:
> >
> > 1) HIGH:+3DES:!aNULL - disables RC4, orders 3DES last.
> >
> > 2) HIGH:MEDIUM:+3DES:!aNULL - no suite changes from current one,
> >    except 3DES is ordered last.
> >
> > +3DES reorders already picked 3DES suites to the end.  As my
> > impression is that no clients ever have actually used 3DES,
> > it's fine to use !3DES there.  It's clearer too.  But if max
> > compatibility is goal, then +3DES is better.
> >
> > It's not as nice and simple as I hoped though. :(
> >
> We definitely want to explain in a comment next to the default value the
> exact reasoning behind the default value, I think. That doesn't mean people
> will understand it, but it means they at least have a chance.
> That said, #2 seems reasonable I think, but I wouldn't object to #1 either
> :)

Although I don't think that making .NET users on XP use 3DES is a big
problem, there is also no urgent need to drop RC4, as long as all
reasonable alternatives are used first.

Attached patch changes default ciphersuite to HIGH:MEDIUM:+3DES:!aNULL
and also adds documentation about reasoning for it.  (I tried to be
consistent there about "cipher" vs. "cipher suite", not sure whether
I succeeded.)

Summary: this default with previous server-order-first patch make sure
that MEDIUM ciphers are never picked accidentally (eg. the bad default
in Java 6), but only when explicitly requested or when only alternative
is 3DES.


diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 8896988..2755f55 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -876,12 +876,62 @@ include 'filename'
-        Specifies a list of <acronym>SSL</> ciphers that are allowed to be
+        Specifies a list of <acronym>SSL</> cipher suites that are allowed to be
         used on secure connections.  See
         the <citerefentry><refentrytitle>ciphers</></citerefentry> manual page
         in the <application>OpenSSL</> package for the syntax of this setting
-        and a list of supported values.  The default value is usually
-        reasonable, unless you have specific security requirements.
+        and a list of supported values.  The default value is
+        <literal>HIGH:MEDIUM:+3DES:!aNULL</>.  It is usually reasonable,
+        unless you have specific security requirements.
+       </para>
+       <para>
+        Explanation for default value:
+        <variablelist>
+         <varlistentry>
+          <term><literal>HIGH</literal></term>
+          <listitem>
+           <para>
+            Cipher suites that use ciphers from <literal>HIGH</> section.
+            (AES, Camellia, 3DES)
+           </para>
+          </listitem>
+         </varlistentry>
+         <varlistentry>
+          <term><literal>MEDIUM</literal></term>
+          <listitem>
+           <para>
+            Cipher suites that use ciphers from <literal>MEDIUM</> section.
+            (RC4, SEED)
+           </para>
+          </listitem>
+         </varlistentry>
+         <varlistentry>
+          <term><literal>+3DES</literal></term>
+          <listitem>
+           <para>
+            OpenSSL default order for <literal>HIGH</> is problematic as it orders 3DES
+            higher than AES128.  This is wrong as 3DES offers less security than AES128
+            and it is also much slower.  <literal>+3DES</> reorders it after all other
+            <literal>HIGH</> and <literal>MEDIUM</> ciphers.
+           </para>
+          </listitem>
+         </varlistentry>
+         <varlistentry>
+          <term><literal>!aNULL</literal></term>
+          <listitem>
+           <para>
+            Disables anonymous cipher suites that do no authentication.
+            Such cipher suites are vulnerable to a "man in the middle"
+            attack and so should not be used.
+           </para>
+          </listitem>
+         </varlistentry>
+        </variablelist>
+        Available cipher suite details will vary across OpenSSL versions, these values
+        are taken from <application>OpenSSL</> 1.0.1.  Use command
+        <literal>openssl ciphers -v 'HIGH:MEDIUM:+3DES:!aNULL'</literal>
+        to see actual details for currently installed <application>OpenSSL</> version.
+        Note that this list is filtered on runtime based on server key type.
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index e69e132..0ad02e8 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -3156,7 +3156,7 @@ static struct config_string ConfigureNamesString[] =
 #ifdef USE_SSL
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index f8bdce3..aff9f84 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -79,7 +79,7 @@
 #authentication_timeout = 1min		# 1s-600s
 #ssl = off				# (change requires restart)
-#ssl_ciphers = 'DEFAULT:!LOW:!EXP:!MD5:@STRENGTH'	# allowed SSL ciphers
+#ssl_ciphers = 'HIGH:MEDIUM:+3DES:!aNULL' # allowed SSL ciphers
 					# (change requires restart)
 #ssl_prefer_server_ciphers = on		# (change requires restart)
 #ssl_ecdh_curve = 'prime256v1'		# (change requires restart)
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