https://en.bitcoin.it/wiki/Contracts#Example_2%3a_Escrow_and_dispute_mediation"Trust minimization: trusted hardware
Using commodity hardware, you can use trusted computing in the form of Intel TXT or the AMD equivalent (SKINIT) to set up a sealed hardware environment and then use the TPM chip to attest that fact to a third party. That third party can verify the hardware was in the required state. Defeating this requires someone to be able to interfere with the execution of a program that may run entirely on the CPU, even in extreme cases without any data traversing the memory bus (you can run entirely using on-die cache if the program is small enough).
Trust minimization: Amazon AWS oracles
Finally, perhaps the most practical approach currently is to use Amazon Web Services. As of November 2013, the closest we have to a working oracle is this recipe for creating a trusted computing environment using AWS, built in support of this project for doing selective SSL logging and decryption. The idea is that an oracle, which can be proven trustworthy using the Amazon APIs with Amazon as the root of trust, records encrypted SSL sessions to an online banking interface in such a way that later if there is a dispute about a person-to-person exchange, the logs can be decrypted and the dispute settled."
