From: Hal <hfinney@shell.portal.com>
I was just reading RFC1034 about DNS, and one thing I noted was that there is a "reverse lookup" feature. This allows you to go from, say, 156.151.1.101 to portal.com. This problem seems similar in some ways to the key lookup problem since you have a relatively unstructured number and you want to use it as a lookup key. [...] According to the RFC, if you want to know what host machine is at address 156.151.1.101, you do a lookup of 156.151.1.101.IN-ADDR.ARPA. The RFC did not make it very clear how this is done. [...]
Actually you do a lookup on 101.1.151.156.in-addr.arpa, it is reversed because of the way addresses are structured. This is part of the problem with PGP keys and DNS: PGP key IDs are unstructured and randomly distributed, IP addresses are not really unstructured and thier distribution is not random. A reverse lookup (aka "pointer query") happens the same way as a regular name lookup, it just reverses the order of the bytes in the IP address and then resolves it in the same method as a regular name, from the least specific to most specific parts of the address. With a PGP key ID there is no order to the distribution of the IDs, so it is not like one could delegate authority for bits in a key ID the same way taht one can with bits/bytes in an IP address. The inability to delgate chunks of the key ID space is what will prevent lookups by keyID; no one can run a single server that has all the IDs and the organizational problems with delegating random chunks of the keyID-space are fairly obvious (e.g. in the DNS model you are responsible for your own address space and it is in your own self-interest to make sure that it works, the same cannot be said of keyID-space) jim