Firewall Wizards: Re: "Who else picked this one up?"

[Adam Shostack <adam () homeport org>]

If you use a long salt (say a block) for each IP before hashing, then
its easy to see, when submitting an entry, if that entry is already
present (2 hash operations), but brute forcing the space becomes
impractical.

I don't have any thoughts on the reputational or other deep issues,
but wanted to toss in a way to effectively privatize the addresses
while allowing 'good contributers' to check that their data either
matches or doesn't match existing entries.

Adam


On Fri, Apr 30, 1999 at 08:52:17PM -0400, Marcus J. Ranum wrote:
| Paul Robertson writes:
| >A hashed IP address isn't going to be really useful as a cover if it's 
| >easily recreated, and not so useful as a tool if it isn't.  I'd rather 
| >see heavy disclaimers that packets may be spoofed and real addresses.
| 
| True. This is a Hard Problem(tm) - I was toying with 3 choices:
|       1) Send up hashed addresses
|       2) Send up keyed hashed addresses
|       3) Send up actual addresses
| 
| Hashed addresses has the advantage that we're not publishing a
| "black list" of addresses. It has the disadvantage that someone
| can pretty easily brute force the hashes.
| 
| Using keyed hashed addresses has the advantage that only the
| person who submits the address can verify that it matches
| previous/other entries. So groups of network managers who are
| cooperating could share the keys and generate useful information
| without sharing it. It has the disadvantage that correlation
| across addresses would then be impractical/useless.

-- 
"It is seldom that liberty of any kind is lost all at once."
                                                       -Hume