Re: Advantages and disadvantages of using CB64 type of identifiers

Hi Christian,

El 02/07/2004, a las 19:21, Christian Huitema escribió:

>> My understanding is that SeND chose different IIDs for different
> prefixes
>> but that might be overkill. If the IID is not a function of the prefix
>> it would enable redirection by a resourceful attacker
>> by precomputing 2^64 public/private keys that hash to all 2^64 IIDs.
>> If the content of the packets are encrypted the redirection would not
>> provide access to the content; it could only be used for DoS or for
>> gathering the content for cryptoanalysis.
>
> There are two issues: catalog attacks and privacy implications. I have
> already expressed my reservations about the privacy effects of having
> unique identifiers in addresses. I would certainly not recommend that 
> my
> company ships anything like that.
>

i don't fully understand why do you think that having an identifier in 
the address is worse than current IPv4 situation (where the id and 
locator are one, and multihomed sites have a single address) or the 
current IPv6 situation (i guess that something similar to privacy 
extensions could be achieved by periodically creating new keys hence 
new identifiers)

>> A while back Jari Arkko computed the amount of space needed to store
>> 2^64 precomputed keys, and the storage space was a few buildings the
> size
>> of the former world trade center buildings I think.
>
> You do not need to compute 2^64 keys to start having an effect. Suppose
> that there are N users in the system, and that the bad guys have
> computed a catalog of M keys. The average number of hits that a catalog
> of size N will achieve is approximately NxM/2^64. There are currently 
> at
> least 500M Internet users, it is reasonable to expect some growth, so 
> we
> can set N to about 1 billion -- 2^30. This means you need M=2^34 to get
> at least one hit.

Yes but how useful would this single hit be?
i mean this hit is likely to correspond with an identifier of an 
unknown host.
i guess that an attacker would be interested in knowing the identifier 
of a specific victim, right?

perhaps we need (at least i need) to understand the potential attacks a 
bit more...

>  That is probably less than a Terabyte of data, i.e.
> pretty soon a single hard disk.
>
> Everybody should be convinced that, when it comes to cryptography, 2^64
> is actually a small number. SEND alleviates this risk by
> cryptographically link a public key to the entire 128 bits of the
> address. This is NOT overkill.

i still don't have an opinion about this being an overkill or not.

regards, marcelo

>
> -- Christian Huitema
>