Re: [openssl.org #1276] [PATCH] TLS Extensions

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Hello,

Since I was pretty active in providing the current code, here are some
of our thoughts which may or may not be compatible with the core team.

In 2004, we had developped some extensions for the 0.9.7d version concern=
ing
servername and srp. We initially also had the idea and a logic where one=20
could
try to have a very generic extension mechanism.

The problem is that extensions may require modification of the internal=20
states
of openssl, or at least have to interfere with it in some cases. Or, in=20
other words,
extension doesn't mean that either all extensions are logically=20
equivalent because
they are indicated with some number in the hellos, some are extensions=20
of the
protocol which may be done with almost no interaction with the applicatio=
n.
Example, treating the maximum packet size. It would mean that an applicat=
ion
would call a SSL_set_hello_extension to set the value of the extension.=20
Well,
ok, but then openssl has to check first, whether it needs additional=20
logic to support
the required extension in any way, but how can it know this?

I also have the feeling that applications don't really want to=20
understand how
the ssl protocols happens, and neither how encodings are done, but=20
rather just
interfere as either providing parameters or being called at an=20
appropriate instance.

To me it seems too low level to allow applications to interfere with the
protocol data, I'd prefer an API for some abstract service with set/get=20
functions
and callbacks, i.e., following exactly the same logic as with=20
'normal/standard' features.

Thus, each "extension" is independant and needs support code. What has be=
en
attempted in the current snapshot is to concentrate the=20
encoding/decoding stuff
in one place where the appropriate encoding/decoding would be added for n=
ew
extensions, and then, add the required logic where it has to be added.
The global compile option of whether tls extensions are supported may not
really be necessary unless one really has a small footprint problem.

Well, this is my current state of thinking, the code in the devel snapsho=
t
is experimental, and the core team may change it at any time.

Am I right that your current patch only provides a callback for ONE=20
extension?

Regards
Peter

Jouni Malinen wrote:[color=blue]
> On Tue, Jan 31, 2006 at 09:00:04PM +0100, Dr. Stephen Henson wrote:
>
> =20[color=green]
>> As has happened previously the functionality in the HEAD is not set in=[/color][/color]
stone[color=blue][color=green]
>> and may be subject to change.
>>
>> I'm aware of the 0.9.9 TLS extension efforts but I'm not currently act=[/color][/color]
ively[color=blue][color=green]
>> involved with them. I have a shed load of other things to do.
>> =20[/color]
>
> It looks like the current implementation is going more towards adding
> each TLS extension as a separate implementation whereas the patch that
> wpa_supplicant is using for EAP-FAST support has a more generic
> mechanism that allows arbitrary TLS extensions to be added to
> ClientHello without having to modify OpenSSL for each new type.
>
> Current CVS HEAD includes support for servername and host_name
> extensions. EAP-FAST is using PAC-Opaque extension, so it would need
> additional code to add that into the ClientHello. This would likely be
> something similar to the way setting host_name extension is done.
>
> Before starting to port the patch I've used with OpenSSL 0.9.8 to 0.9.9=[/color]
,[color=blue]
> I would like to get a better understanding on the desired design for TL=[/color]
S[color=blue]
> extensions and to find out whether someone else is working on
> implementing additional extensions at the moment. Is the current design
> of separate implementation without generic support for arbitrary
> extensions the preferred way of doing this (i.e., is it likely to remai=[/color]
n[color=blue]
> in 0.9.9)? CHANGES file is marking most of the TLS extension code with
> "subject to change".
>
> If separate implementation is desired, it would probably be a
> combination of adding the PAC-Opaque extension (a.k.a. SessionTicket TL=[/color]
S[color=blue]
> extension) and taking care of a callback for fetching pre-shared secret
> for session resumption.
>
> =20[/color]

--=20
To verify the signature, see [url]http://edelpki.edelweb.fr/=20[/url]
Cela vous permet de charger le certificat de l'autorit=E9;=20
die Liste mit zur=FCckgerufenen Zertifikaten finden Sie da auch.=20

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Re: [openssl.org #1276] [PATCH] TLS Extensions - RFC 3546 (Try 2)