# Is there an escrow-like mechanism that doesn't involve a trusted 3rd party?

We know that escrow mechanisms are easy to implement when it involves a trusted 3rd party. For example if A and B don't trust each other they can simply send their goods to C whom they both trust. Then C can distribute the goods to them fairly.

However, is there a primitive that achieves the same when there isn't a trusted 3rd party? Basically, A and B don't trust each other and they want to exchange something. Can they do this without involving any trusted party?

• Only for some specific goods. I heard about protocols to exchange crypto-currency across chain boundaries. Even fairly exchanging information is only possible with severe limitations. – CodesInChaos Oct 13 '17 at 9:38
• What is often possible is designing the exchange so that C can choose to award the reward to either A or B, but not take it for themselves, scamming both A and B. – CodesInChaos Oct 13 '17 at 9:39

• These would enable both parties to send their goods. But how do one party knows the other has sent his tx to the chain? If say, I send the amount to the blockchain and the vendor doesn't then I will just lose money, right? – SpiderRico Oct 13 '17 at 8:52