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I'm currently looking into ways of accessing randomness in a smartcontract.

I found oraclize random datasource https://github.com/oraclize/ethereum-examples/tree/master/solidity/random-datasource and read the paper, but I'm not fully sure what exactly I'd be trusting if using it as in their randomExample.sol

If I understand the paper correctly, they have a Ledger Nano S device connected to some machine which their smart contract interacts with.

So, if I use it, I'd have to trust the following things:

  • Their code is bug-/tamperfree
  • The device they use is bug-/tamperfree
  • They don't just switch out the device with a source they control
  • They don't just unplug the device and thereby cripple the service

Is this correct? Am I missing something?

Also, what are the cost of this service? In the example I just see that it defines

uint callbackGas = 200000; // amount of gas we want Oraclize to set for the callback function

Does the contract send this amount of gas to the random datasource contract and this contract sends the same ammount of gas back to execute the callback function? Or do they keep a part of the gas? how much? What's the right value here?

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  • Essentially yes, you are trusting on the good behavior of Oraclize. For the other question check this ethereum.stackexchange.com/questions/25008/… and their documentation. If you have more doubts about that create a separate question if you found nothing.
    – Ismael ♦
    Commented Aug 22, 2018 at 14:34
  • Who is Oraclize? Are there any sources of independent vetting?
    – matthias_buehlmann
    Commented Aug 22, 2018 at 14:39

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