Re: Giving up security & privacy when manually configuring addresses - rfc4291bis text (Re: draft-bourbaki-6man-classless-ipv6-00)

[Fernando Gont <[e-mail]>]

On 06/09/2017 03:20 AM, Lorenzo Colitti wrote:
> On Fri, Jun 9, 2017 at 2:17 AM, Fernando Gont <[e-mail]
> <mailto:[e-mail]>> wrote:
> 
>     > I don't think you have measurements that prove this. You almost
>     > certainly can make a statement that there are a number of low-entropy
>     > addresses where the top bytes are all zeros, and that those are *likely*
>     > statically configured.
> 
>     Are you assuming that such low-byte addresses are the result of
>     automatic configuration? How come?
> 
> 
> No, what I'm saying is: I don't think you can prove that high-entropy
> addresses are *not* the result of manual configuration or DHCPv6 address
> assignment.

Look at the percentage of addresses with high entropy in the
measurements in RFC7707: they are marginal.



>     That's the point: there are not a lot of high-entropy addresses. See the
>     measurements in RFC7707.
> 
>  
> Oh, I see. You're talking about publicly-accessible servers, not clients. 

Exactly. I doubt clients do manual configuration.



>     we have similar measurements in RFC7707. However, using the low-order 32
>     bits in such way is equivalent to simply setting the low byte of the
>     addresses.
> 
> 
> Equivalent in what way? It provides 4 times more nonzero bits, does it not?

Equivalent in terms of entropy. If you do low-byte addresses, th entropy
is 8-16 bits. If you embed IPv4 addresses in the IID, and the IPv4
prefix is known or guessable, you get roughly the same number of bits of
entropy. In both cases, you'd have got the same entropy if you ha been
using a /120 prefix or the like.




>     The point is that when employing manual configuration, addresses always
>     have small entropy. Hence employing a lot of bits doesn't buy much,
>     because folks simply do not use them for additional entropy.

> But they could. If the server had a /64 prefix, then it could store
> useful information in the 64 bits. For example, SNI (which sends
> information in the clear) might not be necessary any more.

We're talking about entropy here. If you want entropy, randomize your
IPv6 address (RFC7217), rather than set it manually.



-- 
Fernando Gont
SI6 Networks
e-mail: [e-mail]
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