Hi,
Attached a patch that should close issue #197. This patch moves from
using the deprecated RSA_generate_key() to the 'new'
RSA_generate_key_ex() to generate ephemeral RSA keys. This patch does
not change OpenVPN's behaviour.
One note on the implementation though; the code generates one ephemeral
RSA key that is used during the entire lifetime of an OpenVPN process.
If OpenSSL requests a new (ephemeral) key, it will keep on returning the
same (usually rather small) key. Not the best solution.
To actually run this code, I had to force usage by selecting the
TLS-RSA-EXPORT-WITH-DES40-CBC-SHA tls-cipher. That generated a 512-bit
ephemeral RSA key, and uses the outdated DES encryption protocol.
Using this mode could lead to a false sense of security. Then again, one
should be using (Ephemeral) Diffie-Hellman anyway, and OpenVPN requires
a tls-server to supply dh parameters. A user would need to deliberately
choose a weak tls-cipher like TLS-RSA-EXPORT-WITH-DES40-CBC-SHA, which
would be aligning a gun with his foot anyway. If one would decide this
implementation is not good enough anymore, I'd suggest to just strip out
support for this completely.
-Steffan
>From 6d7d536ea52713fe230264f7798c509f37dd40c9 Mon Sep 17 00:00:00 2001
From: Steffan Karger <stef...@karger.me>
List-Post: openvpn-devel@lists.sourceforge.net
Date: Sun, 15 Dec 2013 17:58:04 +0100
Subject: [PATCH] Use RSA_generate_key_ex() instead of deprecated
RSA_generate_key()
Code has been tested using the TLS-RSA-EXPORT-WITH-DES40-CBC-SHA tls-cipher
which uses this to create ephemeral RSA keys.
This should resolve ticket #197.
---
src/openvpn/ssl_openssl.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/src/openvpn/ssl_openssl.c b/src/openvpn/ssl_openssl.c
index f41bb71..271801d 100644
--- a/src/openvpn/ssl_openssl.c
+++ b/src/openvpn/ssl_openssl.c
@@ -103,8 +103,17 @@ tmp_rsa_cb (SSL * s, int is_export, int keylength)
static RSA *rsa_tmp = NULL;
if (rsa_tmp == NULL)
{
+ int ret = -1;
+ BIGNUM *bn = BN_new();
+ rsa_tmp = RSA_new();
+
msg (D_HANDSHAKE, "Generating temp (%d bit) RSA key", keylength);
- rsa_tmp = RSA_generate_key (keylength, RSA_F4, NULL, NULL);
+
+ if(!bn || !BN_set_word(bn, RSA_F4) ||
+ !RSA_generate_key_ex(rsa_tmp, keylength, bn, NULL))
+ msg(M_SSLERR, "Failed to generate temp RSA key");
+
+ if (bn) BN_free( bn );
}
return (rsa_tmp);
}
--
1.8.3.2
