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Réf. : Re: Encryption control of SNDU
Dear All,
I am working on layer 2 security solution for broadband satellite systems
based on the DVB-RCS standard (part 9.4 of the EN301790) and I see several
advantages for an ULE-level encryption as explained below.
Why ULE level encryption ?
1. Role Model and security requirements
Satcom systems based on DVB-S/DVB-RCS are operated by Access Network
Operators that want to provide their customers (ISP) with security
services.
Common targeted security services are : terminal authentication and data
confidentiality (for the unicast and multicast streams) between the gateway
and the terminals (also limited to the satcom system).
The objective is to provide the same level of privacy as the terrestrial
links.
Moreover, in the same time, the ISP may want to provide end-to-end security
services to the end-users (based on the well known IPSec).
As a matter, I think this is really important to understand that both
security solutions ((ANO to ISP) and (ISP to End-users)) can co-exist and
are economically viable.
2. Solutions comparison
For the end-to-end security solution between the ISP and the end-users, it
is obvious that IPSec or an application security (TLS or SSL) are largely
deployed and accepted by the telecom world.
Regarding the satcom security (between the gateway and the terminals),
different solutions were envisaged by Alcatel Space :
- DVB-S Common Scrambling (security solution deployed for the digital
broadcast television) : this solution is not compliant to the granularity
security requirement (scrambling per PID and not per unicast user!).
Moreover, key distribution techniques are one way only and does not benefit
from the interactive return link.
- IPSec has lot of drawbacks : it is not a L2 solution, it is an
end-to-end technology, it can interfere with the end-to-end security
solution, it can interfere with satellite techniques (PEP), it does not
provide encryption of multicast flows and it generates many overheads and
number of signaling messages!!!!!! Lots of comparison studies and
simulations have been performed by Alcatel leading to reject this
solution!!
- Proprietary solutions close to the DVB-S CS : same conclusion as DVB-S CS
- DVB-RCS security solution : we believe that it is the most interesting
solution regarding the intrinsic satcom security as it complies with the
ANO security requirements.
Indeed, it is a layer 2 solution (control plane defined in the DVB-RCS
standard and traffic plane below the IP layer) enabling to encrypt not only
IP streams but also Ethernet frames (PPPoE for example) or other
protocols... It can support unicast or multicast streams encryption.
Moreover, regarding the performances, It largely reduces the number of
signaling messages and overheads (main worry in satcom!).
It is currently based on the 2 bits payload_scrambling_control of the MPE
header providing the information if the packet is encrypted or not and with
which key (odd or even)...... and this essential information would be
canceled in the ULE definition.
3. Concurrent systems and standardization
As you know, the main concurrent to the european ETSI DVB-S/DVB-RCS
standards is the US DOCSIS standard that includes (in its baseline!!!) a
layer 2 security solution providing terminal authentication and
confidentiality (called BPI+).
Alcatel believes that it is really important to make the DVB-RCS standard
evolve (current Satlab contributions) to offer a complete DVB-RCS security
solution that can be compared to the US DOCSIS standard.
That would really be worrying if the ULE encapsulation could not include
this feature because it would not be compliant with the DVB-RCS security
solution.
I hope that you will understand my concern.
Regards.
Laurent Claverotte
Alain RITOUX <alain.ritoux@6wind.com>@erg.abdn.ac.uk on 26/02/2004 15:25:15
Veuillez répondre à ip-dvb@erg.abdn.ac.uk
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Pour : IPDVB <ip-dvb@erg.abdn.ac.uk>
cc :
Objet : Re: Encryption control of SNDU
Gorry Fairhurst wrote:
> So, I'm trying to build a list of "issues for ULE" and the questions I
have
> are:
>
> (i) Does the proposed ULE base header format (4/12B of header) need to be
> changed to support any required encryption/scrambling?
>
> Possible answers include:
>
> * Yes - because the ULE header must not be increased when
> link encryption is used.
>
> * No - because the ULE header can specify a TYPE that could
> indicate an encrypted payload, and hence this issue
> could be solved by using an extension header of some form.
>
> If it is YES, then this has design implications for the ULE Spec.
I would say No, because :
- I don't really understand the need for ULE level encryption
see point I)
- If needed, it can be separated from ULE base specs. see point II)
I) Why ULE level encryption ?
=============================
I still don't sse the need for an ULE-level encryption, because
I see 3 possibilities of encryption
1) At MPEG-2 level, i.e. same encryption for whole content of a PID
2) At ULE level, i.e. encryption on a per SNDU basis for the case as
Tarif said, where PID is mutli-receiver (belonging to different groups)
3) At IP level
but what can distinguish 2 SNDU ?
- IP addresses ?
- DVB Mac addr ?
But the DVB Mac addr is itself the result of IP address/prefix
resolution (which can use destination and/or sources)
So I think it can all be expresed in term of either destination and/or
source Addresses, which can perfectly be handled by IPsec. So 2) and 3)
seem to me to offer the same granularity and 3) is already defined and
working.
This is my current understanding, and a counter-example where 2) would
solve a use-case and not 3) would be very helpfull.
Anyway, I may have missed something, so :
II) Etxension Header for Encryption
====================================
*IF* an ULE encryption is needed, then some extension header can be
defined to provide it, so the SNDU would be like :
- [ULE_Header] [DVB_MAC*] [SEC_Header] [xxx SNDU Payload xxx]
|
+--> Type = sec_header
(*) if MAC addres bit is '0'
- The SEC_Header would be
+---+---+---+--// ..... // ----+
| NH | L | security params |
+---+---+---+--// ..... // ----+
with NH = Type of SNDU payload (IP, IPv6, ...)
L = Length of SEC_Header
security params will define key material, type of security
(encryption, authentication, ....), algo, whatever ...
In the extension headers I proposed, the SEC_Header would be one
of the "drop packets if unknown" type.
- The SNDU payload woul be clear/encrypt/padded accordingly to what
params will be found in SEC_Header.
With that approach, the only thing needed is to include the Extension
Headers mechanism definition in the ULE base specs. Then ALL that
SEC_Header stuff can be described in a separate doc, and good luck with
the (re)keying framework/protocols, security analysis ...
Regards.
Alain.
--
Alain RITOUX
Tel +33-1-39-30-92-32
Fax +33-1-39-30-92-11
visit our web http://www.6wind.com
Sincères Salutations / Best regards
Laurent Claverotte
ALCATEL SPACE
DSR/DRE
Tel : 33 (0)5.34.35.46.47 / Fax : 33 (0)5.34.35.61.69
E-Mail : Laurent.Claverotte@space.alcatel.fr