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Re: [AVTCORE] New Version Notification for draft-rescorla-avtcore-6222bis-00.txt

"Ali C. Begen (abegen)" <abegen@cisco.com> Thu, 07 March 2013 04:03 UTC

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From: "Ali C. Begen (abegen)" <abegen@cisco.com>
To: Kevin Gross <kevin.gross@avanw.com>
Thread-Topic: [AVTCORE] New Version Notification for draft-rescorla-avtcore-6222bis-00.txt
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Date: Thu, 07 Mar 2013 04:03:45 +0000
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Subject: Re: [AVTCORE] New Version Notification for draft-rescorla-avtcore-6222bis-00.txt
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Picking up this old thread.

On Jan 13, 2013, at 7:14 AM, Kevin Gross <kevin.gross@avanw.com> wrote:

> Sorry for the delay responding. I do think otherwise. (a) is fine because OUI registration prevents collisions. (b) relies on statistics to prevent collisions. There's not enough entropy in 48-bit number to statistically prevent collisions in a larger population of participants. See http://en.wikipedia.org/wiki/Birthday_problem. 96-bits is where things are workable.
> 

What about this:

... After obtaining an identifier in case of (a), the 48 bits are converted to the standard colon-separated hexadecimal format [RFC5342], e.g., "00:23:32:af:9b:aa", resulting in a 17-octet printable string representation. In case of (b), the least significant 96 bits are converted to ASCII using Base64 encoding [RFC4648], resulting in a 16-octet string representation.

-acbegen

> Kevin
> 
> On Sat, Dec 29, 2012 at 2:48 PM, Ali C. Begen (abegen) <abegen@cisco.com> wrote:
> Kevin,
> 
> -----Original Message-----
> From: "Ali C. Begen" <abegen@cisco.com>
> Date: Monday, November 5, 2012 7:02 PM
> To: Kevin Gross <kevin.gross@avanw.com>
> Cc: "avt@ietf.org" <avt@ietf.org>
> Subject: Re: [AVTCORE] FW: New Version Notification for
> draft-rescorla-avtcore-6222bis-00.txt
> 
> >>Second bullet point in section 4.2 Item (b): Proposes truncating our nice
> >>96-bit random CNAME to 48 bits. I think we have an unacceptable
> >>opportunity for duplication with this approach. This CNAME should
> >>probably use RFC 4648 in which case these CNAMEs
> >>take the same form as the per-session CNAMES but differ in the
> >>requirement to create once at software initialization. Is it necessary
> >>for the different types of CNAMEs to have different appearance?
> >
> >I don¹t think there is such a requirement and your suggestion makes sense.
> 
> Thinking more about this, I think the current text is good. Item (a) uses
> 48-bit MAC addresses. So, even if we use truncating in item (b), its
> collision probability will not be any worse than item (a)'s. Note that
> both item (a) and (b) use 17-octet string representation whereas the
> per-session CNAME uses 16-octet string representation.
> 
> Let me know if you think otherwise.
> 
> -acbegen
> 
>

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