Adding machineKey to web.config on web-farm sites

We (our IT partner really) recently changed some DNS for a web farmed site we have, so that the two production server have round-robin DNS switching between them. Prior to this switch we didn't really have problems with WebResource.axd files. Since the switch, when we hit the live public URL, we get an error:

CryptographicException

Padding is invalid and cannot be removed.

When we hit the specific servers themselves, they load fine. I've researched the issue and it seems since they're sharing assets between two servers, we need to have a consistent machineKey in the web.config for each server so they can encrypt and decrypt consistently between the two. My questions are:

1. Can I generate a machineKey via a tool on the server, or do I need to write code to do this?
2. Do I just need to add the machineKey to the web.config on each server or do you think I'll need to do anything else to make the two server work together? (Both web.config's currently do not have a machineKey)