Add ./configure option '--disable-gex-new' to fallback on

older diffie-hellman-group-exchange-sha1 syntax.

i.e. Use SSH_MSG_KEX_DH_GEX_REQUEST_OLD
rather then SSH_MSG_KEX_DH_GEX_REQUEST

See draft-ietf-secsh-dh-group-exchange section 7 for details.

README

@@ -13,6 +13,8 @@ Version 0.5
 
   Added libssh2_channel_forward_listen_ex(), libssh2_channel_forward_cancel(), and libssh2_channel_forward_accept().
 
+  Added ./configure option '--disable-gex-new' to allow using the older group-exchange format
+
 Version 0.4
 -----------
 

configure.in

@@ -138,6 +138,13 @@ AC_ARG_ENABLE(mac-none,
   AC_HELP_STRING([--enable-mac-none],[Permit "none" MAC -- NOT RECOMMENDED]),
   [AC_DEFINE(LIBSSH2_MAC_NONE, 1, [Enable "none" MAC -- NOT RECOMMENDED])])
 
+AC_ARG_ENABLE(gex-new,
+  AC_HELP_STRING([--disable-gex-new],[Disable "new" diffie-hellman-group-exchange-sha1 method]),
+  [GEX_NEW=$enableval])
+if test "$GEX_NEW" != "no"; then
+  AC_DEFINE(LIBSSH2_DH_GEX_NEW, 1, [Enable newer diffie-hellman-group-exchange-sha1 syntax])
+fi
+
 # Checks for header files.
 # AC_HEADER_STDC
 AC_CHECK_HEADERS([errno.h fcntl.h stdio.h stdlib.h unistd.h])

include/libssh2.h

@@ -97,9 +97,6 @@
 #endif
 /* LIBSSH2_MAC_NONE already defined (or not) by ./configure */
 
-/* Enable the "new" version of diffie-hellman-group-exchange-sha1 */
-#define LIBSSH2_DH_GEX_NEW
-
 /* Default generate and safe prime sizes for diffie-hellman-group-exchange-sha1 */
 #define LIBSSH2_DH_GEX_MINGROUP     1024
 #define LIBSSH2_DH_GEX_OPTGROUP     1536

include/libssh2_config.h.in

@@ -39,6 +39,9 @@
 /* Enable "none" cipher -- NOT RECOMMENDED */
 #undef LIBSSH2_CRYPT_NONE
 
+/* Enable newer diffie-hellman-group-exchange-sha1 syntax */
+#undef LIBSSH2_DH_GEX_NEW
+
 /* Compile in zlib support */
 #undef LIBSSH2_HAVE_ZLIB