SSL: Support ECDH key exchange

This sets up ECDH key exchange, when compiling against OpenSSL that
supports EC.  Then the ECDHE-RSA and ECDHE-ECDSA cipher suites can be
used for SSL connections.  The latter one means that EC keys are now
usable.

The reason for EC key exchange is that it's faster than DHE and it
allows to go to higher security levels where RSA will be horribly slow.

There is also new GUC option ssl_ecdh_curve that specifies the curve
name used for ECDH.  It defaults to "prime256v1", which is the most
common curve in use in HTTPS.

From: Marko Kreen <markokr@gmail.com>
Reviewed-by: Adrian Klaver <adrian.klaver@gmail.com>

doc/src/sgml/config.sgml

@@ -907,6 +907,24 @@ include 'filename'
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-ssl-ecdh-curve" xreflabel="ssl_ecdh_curve">
+      <term><varname>ssl_ecdh_curve</varname> (<type>string</type>)</term>
+      <indexterm>
+       <primary><varname>ssl_ecdh_curve</> configuration parameter</primary>
+      </indexterm>
+      <listitem>
+       <para>
+        Specifies the name of the curve to use in ECDH key exchanges.  The
+        default is <literal>prime256p1</>.
+       </para>
+
+       <para>
+        The list of available curves can be shown with the command
+        <literal>openssl ecparam -list_curves</literal>.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-password-encryption" xreflabel="password_encryption">
       <term><varname>password_encryption</varname> (<type>boolean</type>)</term>
       <indexterm>

src/backend/libpq/be-secure.c

@@ -69,6 +69,9 @@
 #if SSLEAY_VERSION_NUMBER >= 0x0907000L
 #include <openssl/conf.h>
 #endif
+#if (OPENSSL_VERSION_NUMBER >= 0x0090800fL) && !defined(OPENSSL_NO_ECDH)
+#include <openssl/ec.h>
+#endif
 #endif   /* USE_SSL */
 
 #include "libpq/libpq.h"
@@ -112,6 +115,9 @@ static bool ssl_loaded_verify_locations = false;
 /* GUC variable controlling SSL cipher list */
 char	   *SSLCipherSuites = NULL;
 
+/* GUC variable for default ECHD curve. */
+char	   *SSLECDHCurve;
+
 /* GUC variable: if false, prefer client ciphers */
 bool	   SSLPreferServerCiphers;
 
@@ -774,6 +780,31 @@ info_cb(const SSL *ssl, int type, int args)
 	}
 }
 
+#if (OPENSSL_VERSION_NUMBER >= 0x0090800fL) && !defined(OPENSSL_NO_ECDH)
+static void
+initialize_ecdh(void)
+{
+	EC_KEY	   *ecdh;
+	int			nid;
+
+	nid = OBJ_sn2nid(SSLECDHCurve);
+	if (!nid)
+		ereport(FATAL,
+				(errmsg("ECDH: unrecognized curve name: %s", SSLECDHCurve)));
+
+	ecdh = EC_KEY_new_by_curve_name(nid);
+	if (!ecdh)
+		ereport(FATAL,
+				(errmsg("ECDH: could not create key")));
+
+	SSL_CTX_set_options(SSL_context, SSL_OP_SINGLE_ECDH_USE);
+	SSL_CTX_set_tmp_ecdh(SSL_context, ecdh);
+	EC_KEY_free(ecdh);
+}
+#else
+#define initialize_ecdh()
+#endif
+
 /*
  *	Initialize global SSL context.
  */
@@ -853,6 +884,9 @@ initialize_SSL(void)
 	SSL_CTX_set_tmp_dh_callback(SSL_context, tmp_dh_cb);
 	SSL_CTX_set_options(SSL_context, SSL_OP_SINGLE_DH_USE | SSL_OP_NO_SSLv2);
 
+	/* set up ephemeral ECDH keys */
+	initialize_ecdh();
+
 	/* set up the allowed cipher list */
 	if (SSL_CTX_set_cipher_list(SSL_context, SSLCipherSuites) != 1)
 		elog(FATAL, "could not set the cipher list (no valid ciphers available)");

src/backend/utils/misc/guc.c

@@ -127,6 +127,7 @@ extern char *temp_tablespaces;
 extern bool ignore_checksum_failure;
 extern bool synchronize_seqscans;
 extern char *SSLCipherSuites;
+extern char *SSLECDHCurve;
 extern bool SSLPreferServerCiphers;
 
 #ifdef TRACE_SORT
@@ -3150,6 +3151,21 @@ static struct config_string ConfigureNamesString[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"ssl_ecdh_curve", PGC_POSTMASTER, CONN_AUTH_SECURITY,
+			gettext_noop("Sets the curve to use for ECDH."),
+			NULL,
+			GUC_SUPERUSER_ONLY
+		},
+		&SSLECDHCurve,
+#ifdef USE_SSL
+		"prime256v1",
+#else
+		"none",
+#endif
+		NULL, NULL, NULL
+	},
+
 	{
 		{"application_name", PGC_USERSET, LOGGING_WHAT,
 			gettext_noop("Sets the application name to be reported in statistics and logs."),

src/backend/utils/misc/postgresql.conf.sample

@@ -82,6 +82,7 @@
 #ssl_ciphers = 'DEFAULT:!LOW:!EXP:!MD5:@STRENGTH'	# allowed SSL ciphers
 					# (change requires restart)
 #ssl_prefer_server_ciphers = on		# (change requires restart)
+#ssl_ecdh_curve = 'prime256v1'		# (change requires restart)
 #ssl_renegotiation_limit = 512MB	# amount of data between renegotiations
 #ssl_cert_file = 'server.crt'		# (change requires restart)
 #ssl_key_file = 'server.key'		# (change requires restart)