Re: [MSEC] Key Management protocol (GDOI - 6407) forward

[Brian Weis <[e-mail]>]

Hi Paul,

On Oct 14, 2013, at 6:10 PM, Paul Lambert <[e-mail]> wrote:

> 
> Brian,
> 
> Thanks for the info …
> 
>> 
>> The data transports are defined in the IEC 61850-90 family of standards, and are a part of the frame formats used within and between power substations. I don't think they is generally re-usable to other industries.
>> 
>> But some of the payloads defined in this Internet-Draft might be applicable for key management in other industries. In particular the OID Identification (ID) payload could be used by any protocol using an OID as an identity.
> 
> 
> In MSEC or the 61850 series I do not see how the group key distribution handles the issues of nonce/key uniqueness for algorithm modes like CCM or GCM.  I'd assumed that this multicast group would need to address this very important security requirement.  
> 
> I'm sure it must just be my quick read of MSEC that I'm missing something, but  … How does the MSEC or 61850 protocols handle the limitations of AES-CCM or AES-GCM and provide a guarantee of transmitted nonce/key uniqueness for multicast groups?  

You're right, this is very important. You can find a general description of the MSEC solution in RFC 6054 <http://tools.ietf.org/html/rfc6054>. Briefly, the Nonce space is segmented so that each group members has a unique part of the nonce space. The GDOI protocol supports this in RFC 6407 by distributing unique upper bits of the nonce (SID).

> I was hoping to find in the MSEC a new algorithm mode (which I believe is the preferred answer to the issue) or perhaps another mechanism.   The Wi-Fi multicast security solutions currently require N squared messages to give each device it's own group key because of the nonce/key uniqueness requirement.  This is a limitation (IMO) of CCM and GCM.  IN some environments or protocols it might be possible to coordinate or control the nonce to make sure it is not repeated for a group of devices.  This is quite difficult for consumer device since if reset they would forget state and potentially repeat a nonce (unless some device coordinates nonce usage – impossible in ad hoc environments).

The MSEC protocols all assume a centralized key management service, which carefully allocates the SIDs. As you say, in order to repeat the devices have to request an SID after a reset but they also have to request the rest of the keying state as well.  The controller always returns a new SID to ensure the old nonces are not reused. Another system using a centralized controller could likely do something similar.

Hope that helps,
Brian

> 
> 
> Regards,
> 
> Paul
> 
> 
>> 
>> Thanks,
>> Brian
>> 
>>> 
>>> Thanks in advance,
>>> 
>>> Paul
>>> 
>>> 
>>>>  
>>>>  
>>>>  
>>>>  
>>>>  
>>>> Herbert Falk
>>>> Solutions Architect
>>>> SISCO, INC.
>>>> 6605 19 1Ž2 Mile Rd.
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>>>> [phone] x-105
>>>> 
>>>>  
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>> 
>> -- 
>> Brian Weis
>> Security, Enterprise Networking Group, Cisco Systems
>> Telephone: [phone]
>> Email: [e-mail]
>> 
> 
> 
> 

-- 
Brian Weis
Security, Enterprise Networking Group, Cisco Systems
Telephone: [phone]
Email: [e-mail]