Does OpenVPN support TLSv1.2?

anthonyl

To get to the point, does anyone know if openvpn version 2.3.2 support TLSv1.2? My investigations lead me to believe the answer is "no, only TLSv1", but I'm hoping to get some confirmation. Can anyone help, please?

The long version:

I'm trying to narrow down a set of cipher suites to use with the --tls-cipher parameter. I ran "openvpn --show-tls" to get the list of available ciphers have been trying them out. What I've found is that any suites that specify SHA256 (eg TLS-DHE-RSA-WITH-AES-256-CBC-SHA256) fail to work, while similar suites with SHA (eg TLS-DHE-RSA-WITH-AES-256-CBC-SHA) do work.

On the client, if I used the following configuration:
openvpn --remote 192.1.1.1 --dev tap --auth-user-pass /flash/openvpn.pass --pull --tls-client --ca /flash/cacert.pem --tls-cipher TLS-DHE-RSA-WITH-AES-256-CBC-SHA256

I get the following errors:
Fri Jun 14 04:35:48 2013 UDPv4 link local (bound): [undef]
Fri Jun 14 04:35:48 2013 UDPv4 link remote: [AF_INET]192.1.1.1:1194
Fri Jun 14 04:35:48 2013 TLS_ERROR: BIO read tls_read_plaintext error: error:140830B5:SSL routines:SSL3_CLIENT_HELLO:no ciphers available
Fri Jun 14 04:35:48 2013 TLS Error: TLS object -> incoming plaintext read error
Fri Jun 14 04:35:48 2013 TLS Error: TLS handshake failed

After a bit of digging I found that SHA256 is part of TLSv1.2. After a bit more digging I found that in src/openvpn/ssl_openssl.c, tls_ctx_client_new(), TLSv1_client_method (an openssl call) is specified. I tried changing this to TLSv1_2_client_method in tls_ctx_client_new() and the equivalent in tls_ctx_server_new(). With these changes on my client and server everything seems to work.

I was hoping that I might just be able to make this modification on my server only so that it rolls back to TLSv1 if the client doesn't support 1.2. Sadly there seems to be no such roll back.

Does anyone have any idea if TLSv1.2 is on the roadmap?

Any information regarding any of this would be greatly appreciated.

Thanks

lalamper

Thanks, you are right!

At the moment OpenVPN is unable to use ciphersuites needing TLS v1.2

How should developers be forced to correct this issue?

Wheelz

After a bit of digging I found that SHA256 is part of TLSv1.2. After a bit more digging I found that in src/openvpn/ssl_openssl.c, tls_ctx_client_new(), TLSv1_client_method (an openssl call) is specified. I tried changing this to TLSv1_2_client_method in tls_ctx_client_new() and the equivalent in tls_ctx_server_new(). With these changes on my client and server everything seems to work.

Do you have a patch file that shows how you made this change?

Thanks!

JoshC

Git commit 4b67f98 (currently on the master branch,) is slated to be included in the next official release. This patch includes support for the cipher-suites in TLSv1.2, as well as a new option to restrict the TLS negotiation to a minimum version.

The solution propsed earlier in this thread of replacing the TLSv1_method() with TLSv1_2_method() will require a TLSv1.2 negotiation, failing when connecting to any <=2.3.2 version peer that can only speak TLSv1.0. The git master status with the referenced commit uses SSLv23_method() which is more flexible by allowing TLSv1.2 when both peers support it, can fall back to TLSv1.0, and can support a mandatory minimum version with the --tls-version-min option.