More comments and questions on OSPFv3 security draft

[Mike Fox <[e-mail]>]

Back in Feburary and March I had a dialog with Vishwas involving some 
questions on the OSPFv3 security draft.  Our security expert has asked for 
some additional clarification, here is his comment: 

My comment is based on the following from RFC 2401 (section 4.1): 

A security association is uniquely identified by a triple consisting
   of a Security Parameter Index (SPI), an IP Destination Address, and a
   security protocol (AH or ESP) identifier.  In principle, the
   Destination Address may be a unicast address, an IP broadcast
   address, or a multicast group address.  However, IPsec SA management
   mechanisms currently are defined only for unicast SAs.  Hence, in the
   discussions that follow, SAs will be described in the context of
   point-to-point communication, even though the concept is applicable
   in the point-to-multipoint case as well.

As noted above, two types of SAs are defined: transport mode and
   tunnel mode.  A transport mode SA is a security association between
   two hosts.

Comment: Certainly an SPD can have a ranged address that points to the 
same SA. This is how you would set up an SPD in a firewall for tunnel mode 
traffic. That is, a range of addresses for a network (not on the firewall) 
can use a single SA. The destination IP address is an IPSec SA endpoint. 
However, the SA must adhere to the definition above. For unicast transport 
mode, I read this to be that the destination address is a single IP 
address not a range. I suggest that the OSPFv3 security draft specify 
exactly how the manual SAs would need to be set up to be compliant. I 
don't think there is anything in RFC 2401 that allows a range of unicast 
IP addresses to be "a unicast address". 

And since it has been a while, here is the string of notes he is 
commenting on: 






Vishwas Manral <[e-mail]>
Sent by: Mailing List <[e-mail]>
03/01/2005 05:59 AM
Please respond to Mailing List
 
        To:     [e-mail]
        cc: 
        Subject:        Re: Questions about OSPF v3 security draft


Hi Mike,

Sorry for the delay. I may be wrong as I have not implemented this myself, 
however my views are as follows: -

If you see the SPD entry the Remote IP Address can be 
      "- Remote IP Address(es) (IPv4 or IPv6): this is a list of ranges
        of IP addresses (unicast, anycast, broadcast (IPv4 only), or
                multicast group). "
So for OSPF the Multicast as well as the unicast addresses will be used to 
refer to an SA.

Next Layer Protocol would say OSPF.

That way we will have just one entry for all OSPF packets out of an 
interface, just as we want it and a similar entry for inbound traffic. I 
do not see a case of Full Mesh at all. I may be missing the point.

Thanks,
Vishwas
________________________________________
From: Mailing List [mailto:[e-mail]] On Behalf Of Mike 
Fox
Sent: Friday, February 25, 2005 2:58 AM
To: [e-mail]
Subject: Re: Questions about OSPF v3 security draft


Vishwas, 

I shared your response with our security expert and here is his response: 

What we need to know is whether the paragraph is referring to unicast. " 
What it means is we will use the same crypto-algorithm and keys for all 
traffic to a neighbor over an interface." If this comment is referring to 
unicast, the point remains is that there will be multiple SAs. We will not 
be able to adhere to the figure 3 requirements for unicast, and there will 
be full meshing of SAs required between all communicating OSPFs. Not so 
bad if using IKE. Really bad if using manual SAs.   

Here is the thread of notes being referred to (since it's been a couple of 
weeks): 

Vishwas Manral <[e-mail]> 
Sent by: Mailing List <[e-mail]> 
02/15/2005 12:01 AM 
Please respond to Mailing List 
        
        To:        [e-mail] 
        cc:         
        Subject:        Re: Questions about OSPF v3 security draft



Hi Mike, 
  
I think both the authors are on leave, so they will probably reply later. 
  
However regarding the first point, I agree the wording should be clearer. 
However what it means is we will use the same crypto-algorithm and keys 
for all traffic to a neighbor over an interface. 
  
Regarding the second point, I think I too have brought the issue on this 
list and the reply I think was that the draft does not prohibit the use of 
IKE for unicast flows. 
                                                                          
                                                                          
      
Thanks, 
Vishwas 
________________________________________

From: Mailing List [mailto:[e-mail]] On Behalf Of Mike 
Fox
Sent: Friday, February 11, 2005 8:04 PM
To: [e-mail]
Subject: Questions about OSPF v3 security draft 
  

Regarding 
http://www.ietf.org/internet-drafts/draft-ietf-ospf-ospfv3-auth-07.txt, 
and the previous drafts, a couple of questions have come up in our shop. 

1) Section 7, 2nd paragraph says "the implementations MUST use manually 
configured keys with same SA for inbound and outbound traffic (as shown in 
figure 3).  I assume the "same SA" MUST rule applies to multicast traffic 
only and not unicast traffic. This is because an SA is defined as an SPI, 
security protocol (AH or ESP), and destination IP address. For unicast 
addresses, by definition there will be as many SAs as there are unicast 
destination addresses. Therefore, I don't think it is possible to apply 
this MUST rule given the current IPSec definition (RFC 2401 section 4.1) 
of an SA for unicast. Assuming the intention of the draft was to apply 
only to multicast and given the number of potential SAs carrying unicast 
traffic, it would seem that using IKE to setup the SAs dynamically would 
be a reasonable alternative to manual keying.     
 
2)Section 9, 2nd paragraph discusses setting up a "secure IPSec channel 
dynamically once it acquires the required information".  Since this 
traffic is unicast only, IKE could easily set up the required SAs without 
knowing the specific IP addresses in advance. Creating SAs dynamically do 
not fit easily within scope of manual SA functional capabilities. Why not 
use IKE for this traffic? Is this an acceptable option?   

Mike 


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