Index: wp-includes/default-constants.php
===================================================================
--- wp-includes/default-constants.php	(revision 19715)
+++ wp-includes/default-constants.php	(working copy)
@@ -140,8 +140,6 @@
  * @since 3.0.0
  */
 function wp_cookie_constants( ) {
-	global $wp_default_secret_key;
-
 	/**
 	 * Used to guarantee unique hash cookies
 	 * @since 1.5
@@ -155,12 +153,6 @@
 	}
 
 	/**
-	 * Should be exactly the same as the default value of SECRET_KEY in wp-config-sample.php
-	 * @since 2.5.0
-	 */
-	$wp_default_secret_key = 'put your unique phrase here';
-
-	/**
 	 * @since 2.0.0
 	 */
 	if ( !defined('USER_COOKIE') )
Index: wp-includes/pluggable.php
===================================================================
--- wp-includes/pluggable.php	(revision 19715)
+++ wp-includes/pluggable.php	(working copy)
@@ -1313,7 +1313,30 @@
  * @return string Salt value
  */
 function wp_salt($scheme = 'auth') {
-	global $wp_default_secret_key;
+	$secret_keys = array();
+
+	if ( defined( 'AUTH_KEY' ) )
+		$secret_keys[] = AUTH_KEY;
+	if ( defined( 'SECURE_AUTH_KEY' ) )
+		$secret_keys[] = SECURE_AUTH_KEY;
+	if ( defined( 'LOGGED_IN_KEY' ) )
+		$secret_keys[] = LOGGED_IN_KEY;
+	if ( defined( 'NONCE_KEY' ) )
+		$secret_keys[] = NONCE_KEY;
+	if ( defined( 'AUTH_SALT' ) )
+		$secret_keys[] = AUTH_SALT;
+	if ( defined( 'SECURE_AUTH_SALT' ) )
+		$secret_keys[] = SECURE_AUTH_SALT;
+	if ( defined( 'LOGGED_IN_SALT' ) )
+		$secret_keys[] = LOGGED_IN_SALT;
+	if ( defined( 'NONCE_SALT' ) )
+		$secret_keys[] = NONCE_SALT;
+
+	$wp_default_secret_key = '';
+	$secret_keys_diff = array_diff_assoc( $secret_keys, array_unique( $secret_keys ) );
+	if ( !empty( $secret_keys_diff ) )
+		$wp_default_secret_key = array_shift( $secret_keys_diff );
+
 	$secret_key = '';
 	if ( defined('SECRET_KEY') && ('' != SECRET_KEY) && ( $wp_default_secret_key != SECRET_KEY) )
 		$secret_key = SECRET_KEY;