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

[Paul Lambert <[e-mail]>]

Brian,

Thanks for the help below.  It's a bit confusing trying to find how the SID is set, but I'll keep keep looking.

Are there any reference implementations of test vectors for MSEC?

Paul


Hi Paul,

On Oct 14, 2013, at 6:10 PM, Paul Lambert <[e-mail]<mailto:[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
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Brian Weis
Security, Enterprise Networking Group, Cisco Systems
Telephone: [phone]
Email: [e-mail]<mailto:[e-mail]>




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