Actually, I had been considering doing exactly that. I hadn't seen it elsewhere (I don't read blogs much) but my plan was to make the hash so that, for example, if the first three octets of the IP match, then the first three chunks of the hash would match since many have dynamic IPs (but the hashing of each octet would depend on the previous octets so the hashing wouldn't be trivial to reverse).

I suspect even a hash of the source IP being displayed on non-anonymous nodes here would be greeted by complaints from some people. But I'd also like to discourage the "registered user pretending to be anonymous" sham. But I've also posted anonymously for good reason several times. Perhaps the ability to see the hash of the IP of non-anonymous nodes could be a level power or there could be a level power that allows comparing the source IPs of two specific nodes?

In the end, it didn't make it to the top of my to-do list in part because we've banned the IPs of the two most persistent anonymous trolls so the benefit was limited for now. I somewhat envy wikipedia's position of noting IPs of anonymous contributors from the beginning.

...my plan was to make the hash so that, for example, if the first three octets of the IP match, then the first three chunks of the hash would match

That sounds like a nice goal, but one thing to be wary of is making brute force attacks too easy. If you publish a hash of only the first three octets of an IP address, that's a somewhat smaller range of numbers I have to plough through to guess what the original numbers are. I get an even bigger advantage if I check only the blocks that I know are registered to some organization and look first at blocks from English speaking countries, etc.

Just a thought.

Quite right; at worst a naive dictionary of md5s for the entire 32 bit IPv4 range would be 64G ( ( 16 * 2**32 ) / ( 2**30 ) ) which would fit on a keychain these days (not to mention winnowing out multicast and unroutable addresses would shrink it from there). You'd want to toss in some sort of not-public salt so Eve can't do a dictionary attack (and maybe the salt used for anonomonks could move periodically so that it's constant over the life of a thread but varies unpredictably month-to-month).

The cake is a lie.
The cake is a lie.
The cake is a lie.

I wasn't going to only display the first 3 octets. And if you have the resources to post anonymous nodes from any IP address you want to, then I probably have more to fear from you than you figuring out what IP addresses anonymous postings to PerlMonks come from.

- tye        

Personally I just think it is not worth the bother. If some people wish to speak to themselves, I don't mind. The sooner you leave them alone, the faster they disappear.