Something like this:
- Both encrypt a seed and send it.
- Once you receive your partner's seed, send the key to decrypt your side. This is important, because your partner can't change their seed at this point, and neither can you.
- Decrypt the seeds and combine them in some agreed way (say, by multiplying or adding them together).
- Generate a random number using the combined seed.
- Discard seeds and start over to avoid look-ahead cheating.
Mokalus of Borg
PS - So far I've been unable to determine a version that allows the equivalent of both sides drawing random cards and keeping them secret.
PPS - For now, this is obviously a trusted P2P dice mechanism and nothing more.