Move EDH support to common files

The EDH support is not really specific to the OpenSSL implementation, so
move the support and documentation comments to common files.

src/backend/libpq/README.SSL

@@ -58,3 +58,25 @@ SSL
    Fail with unknown
 
 ---------------------------------------------------------------------------
+
+Ephemeral DH
+============
+
+Since the server static private key ($DataDir/server.key) will
+normally be stored unencrypted so that the database backend can
+restart automatically, it is important that we select an algorithm
+that continues to provide confidentiality even if the attacker has the
+server's private key.  Ephemeral DH (EDH) keys provide this and more
+(Perfect Forward Secrecy aka PFS).
+
+N.B., the static private key should still be protected to the largest
+extent possible, to minimize the risk of impersonations.
+
+Another benefit of EDH is that it allows the backend and clients to
+use DSA keys.  DSA keys can only provide digital signatures, not
+encryption, and are often acceptable in jurisdictions where RSA keys
+are unacceptable.
+
+The downside to EDH is that it makes it impossible to use ssldump(1)
+if there's a problem establishing an SSL session.  In this case you'll
+need to temporarily disable EDH (see initialize_dh()).

src/backend/libpq/be-secure-openssl.c

@@ -11,28 +11,6 @@
  * IDENTIFICATION
  *	  src/backend/libpq/be-secure-openssl.c
  *
- *	  Since the server static private key ($DataDir/server.key)
- *	  will normally be stored unencrypted so that the database
- *	  backend can restart automatically, it is important that
- *	  we select an algorithm that continues to provide confidentiality
- *	  even if the attacker has the server's private key.  Ephemeral
- *	  DH (EDH) keys provide this and more (Perfect Forward Secrecy
- *	  aka PFS).
- *
- *	  N.B., the static private key should still be protected to
- *	  the largest extent possible, to minimize the risk of
- *	  impersonations.
- *
- *	  Another benefit of EDH is that it allows the backend and
- *	  clients to use DSA keys.  DSA keys can only provide digital
- *	  signatures, not encryption, and are often acceptable in
- *	  jurisdictions where RSA keys are unacceptable.
- *
- *	  The downside to EDH is that it makes it impossible to
- *	  use ssldump(1) if there's a problem establishing an SSL
- *	  session.  In this case you'll need to temporarily disable
- *	  EDH (see initialize_dh()).
- *
  *-------------------------------------------------------------------------
  */
 
@@ -87,40 +65,6 @@ static SSL_CTX *SSL_context = NULL;
 static bool SSL_initialized = false;
 static bool ssl_passwd_cb_called = false;
 
-/* ------------------------------------------------------------ */
-/*						 Hardcoded values						*/
-/* ------------------------------------------------------------ */
-
-/*
- *	Hardcoded DH parameters, used in ephemeral DH keying.
- *	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 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 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
- *	Protocols" (http://www.skip-vpn.org/spec/numbers.html)
- *	for suggestions.
- */
-
-static const char file_dh2048[] =
-"-----BEGIN DH PARAMETERS-----\n\
-MIIBCAKCAQEA9kJXtwh/CBdyorrWqULzBej5UxE5T7bxbrlLOCDaAadWoxTpj0BV\n\
-89AHxstDqZSt90xkhkn4DIO9ZekX1KHTUPj1WV/cdlJPPT2N286Z4VeSWc39uK50\n\
-T8X8dryDxUcwYc58yWb/Ffm7/ZFexwGq01uejaClcjrUGvC/RgBYK+X0iP1YTknb\n\
-zSC0neSRBzZrM2w4DUUdD3yIsxx8Wy2O9vPJI8BD8KVbGI2Ou1WMuF040zT9fBdX\n\
-Q6MdGGzeMyEstSr/POGxKUAYEY18hKcKctaGxAMZyAcpesqVDNmWn6vQClCbAkbT\n\
-CD1mpF1Bn5x8vYlLIhkmuquiXsNV6TILOwIBAg==\n\
------END DH PARAMETERS-----\n";
-
 
 /* ------------------------------------------------------------ */
 /*						 Public interface						*/
@@ -1080,7 +1024,7 @@ initialize_dh(SSL_CTX *context, bool isServerStart)
 	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);
+		dh = load_dh_buffer(FILE_DH2048, sizeof(FILE_DH2048));
 	if (!dh)
 	{
 		ereport(isServerStart ? FATAL : LOG,

src/include/libpq/libpq-be.h

@@ -193,6 +193,25 @@ typedef struct Port
 } Port;
 
 #ifdef USE_SSL
+/*
+ *	Hardcoded DH parameters, used in ephemeral DH keying.  (See also
+ *	README.SSL for more details on EDH.)
+ *
+ *	If you want to create your own hardcoded DH parameters
+ *	for fun and profit, review "Assigned Number for SKIP
+ *	Protocols" (http://www.skip-vpn.org/spec/numbers.html)
+ *	for suggestions.
+ */
+#define FILE_DH2048 \
+"-----BEGIN DH PARAMETERS-----\n\
+MIIBCAKCAQEA9kJXtwh/CBdyorrWqULzBej5UxE5T7bxbrlLOCDaAadWoxTpj0BV\n\
+89AHxstDqZSt90xkhkn4DIO9ZekX1KHTUPj1WV/cdlJPPT2N286Z4VeSWc39uK50\n\
+T8X8dryDxUcwYc58yWb/Ffm7/ZFexwGq01uejaClcjrUGvC/RgBYK+X0iP1YTknb\n\
+zSC0neSRBzZrM2w4DUUdD3yIsxx8Wy2O9vPJI8BD8KVbGI2Ou1WMuF040zT9fBdX\n\
+Q6MdGGzeMyEstSr/POGxKUAYEY18hKcKctaGxAMZyAcpesqVDNmWn6vQClCbAkbT\n\
+CD1mpF1Bn5x8vYlLIhkmuquiXsNV6TILOwIBAg==\n\
+-----END DH PARAMETERS-----\n"
+
 /*
  * These functions are implemented by the glue code specific to each
  * SSL implementation (e.g. be-secure-openssl.c)