Remove OpenSSL tmp_rsa_callback. Removes support for ephemeral RSA in TLS.

This code would not really generate ephemeral keys every time it is called,
but a single key that would be reused during process lifetime and returned
each time the function was called; probably not what users would expect.

TLS allowes ephemeral keys to be used only when no other key exchange, such
as (ephemeral) Diffie-Hellman, is performed. The end result is that it was
only used by a number of (weak) export ciphers, which could give users a
false sense of security.

So, instead of fixing a weak cipher mode, we'll just remove support for it
completely. Plenty of better alternatives are available in TLS.

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1388607026-12297-5-git-send-email-steffan@karger.me>
URL: http://article.gmane.org/gmane.network.openvpn.devel/8152
Signed-off-by: Gert Doering <gert@greenie.muc.de>

diff --git a/src/openvpn/ssl_openssl.c b/src/openvpn/ssl_openssl.c
index 1c6291fc4d538c2c6b24b47d67636d5be3c9f34c..08327a1cb2fa62602b8caa8cda9f7b6729fd945a 100644 (file)
--- a/src/openvpn/ssl_openssl.c
+++ b/src/openvpn/ssl_openssl.c
@@ -93,22 +93,6 @@ tls_clear_error()
   ERR_clear_error ();
 }
 
-/*
- * OpenSSL callback to get a temporary RSA key, mostly
- * used for export ciphers.
- */
-static RSA *
-tmp_rsa_cb (SSL * s, int is_export, int keylength)
-{
-  static RSA *rsa_tmp = NULL;
-  if (rsa_tmp == NULL)
-    {
-      msg (D_HANDSHAKE, "Generating temp (%d bit) RSA key", keylength);
-      rsa_tmp = RSA_generate_key (keylength, RSA_F4, NULL, NULL);
-    }
-  return (rsa_tmp);
-}
-
 void
 tls_ctx_server_new(struct tls_root_ctx *ctx)
 {
@@ -118,8 +102,6 @@ tls_ctx_server_new(struct tls_root_ctx *ctx)
 
   if (ctx->ctx == NULL)
     msg (M_SSLERR, "SSL_CTX_new SSLv23_server_method");
-
-  SSL_CTX_set_tmp_rsa_callback (ctx->ctx, tmp_rsa_cb);
 }
 
 void