[tor-dev] Proposal: Merging Hidden Service Directories and Introduction Points

[Aaron Johnson]

>> That seems easy to fix. Make the number of Introduction Points the same as it was before and make them be selected in a bandwidth-weight way. There is no cost to this. You need IPs to be online, and so whatever number was used in the past will yield the same availability now. And bandwidth-weighting should actually improve both performance and security.
>> 
> 
> Is it obvious how to build a bandwidth-weighted DHT that is stable
> across changes in the consensus?  One advantage of using the hash ring
> is that the loss of an HSDir causes only local changes in the
> topology, so if the client is using a different version of the
> consensus they can still locate one of the responsible HSDirs.  (Note:
> I do not claim this cannot be done; it just seems like an important
> detail to sort out…)

You could reserve a space after each relay in the hash ring with a length equal to the relay's bandwidth, and then assign an onion service with a hash that is a fraction f of the maximum possible hash value to the relay owning the space in which the fraction f of the total hash-ring length is located. Removing or adding a relay adjusts the onion service locations by an amount that is at most the fraction that is that relay’s total bandwidth fraction. To ensure coverage for clients with older consensuses, the relay can maintain HSDir+IPs at the locations indicated by both the current and previous consensus.

Aaron