Authentication over the phone? Are there any known good methods of performing authentication over the phone in a way that's not susceptible to replay attacks?

The specific scenario that comes to mind is having an automated call centre which verifies the identity through one or more questions. Since the phone line is not guaranteed to be secure (or the user may simply be in public), the calls can be eavesdropped.

One idea that came to mind would be something akin to CHAP - the user hears a challenge, mentally hashes it (per this CryptoSE Q&amp;A, perhaps Blum's hash is a good candidate) and then speaks the solution out loud. Has something like this been attempted before and are there any known vulnerabilities?
Take a look at the military's Dryad for authentication.