[vlc-devel] [PATCH 1/2] gnutls: show a dialog allowing the user to bypass certificate issues

Rémi Denis-Courmont remi at remlab.net
Thu Jun 28 15:07:47 CEST 2012

On Thu, 21 Jun 2012 10:34:48 +0200, Ludovic Fauvet <etix at videolan.org>
> On Thu, Jun 21, 2012 at 5:13 AM, Rémi Denis-Courmont <remi at remlab.net>
> wrote:
>> Le jeudi 21 juin 2012 02:35:58 Ludovic Fauvet, vous avez écrit :
>>> ---
>>>  include/vlc_tls.h     |    2 +-
>>>  modules/access/http.c |    4 +++-
>>>  modules/misc/gnutls.c |   37 ++++++++++++++++++++++++++++++++++---
>>>  src/network/tls.c     |    9 +++++----
>>>  4 files changed, 43 insertions(+), 9 deletions(-)
>> I don't understand why you export the trust bit. If the certificate is
>> not
>> trustworthy, the connection should fail anyway.
> The reason is that the GNU TLS module is loaded 5 times for a single
> connection,

That would be a bug, and it should be fixed rather than worked around.

You cannot negotiate TLS more than once per TCP connection, at least not
for any of the few protocols that VLC actually implements.

> thus asking the user's authorization 5 times in a row

...would be The Right Thing.

Just because the user agreed to use one particular untrusted certificate
does not imply that (s)he would agree to use any other untrusted
certificate. Definitely not so.

> and AFAIK exporting the trust bit to the http module is the most obvious
> way to keep the state for the whole http session.

Doing it like every body else is obvious to me. And that is not what
everybody else does. This proposal strikes me as obviously stupid rather
than obvious.

For the reference, "everybody else" remembers which certificates have been
permitted under which circumstances, e.g. certificate X is permitted for
host "streaming.example.com." even though its CN is "www.example.com.".

There is no deying that this is not a simple development task. If it were
as simple as you make it, it would have been implemented a long time ago.
But TLS, just like HTTP cookies, is a security-sensitive feature. You
cannot take many shortcuts when it comes to security.

>> I think the messages are way too simplistic for normal people to
>> understand.
>> Conversely, for expired certificates, the dates are needed. For
>> mismatched
>> namse, the names are needed. And for untrusted roots, the certificates
>> need to
>> be shown. Otherwise there is no way to determine whether the situation
>> is safe
>> or not.
> A question dialog won't suffice then.

A VLC question dialog in the current form might be too primitive to
present the needed data. Nevertheless, it is very much a Yes/No question.

>> I am also not sure this works very well with streaming output cases.
> This code is for the TLS client only. Shouldn't be an issue for
> streaming output cases.

You can use a secure input when streaming, can't you?

Rémi Denis-Courmont
Sent from my collocated server

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