It seems like when I give the Oraclize query a N of 4, it always returns a 19 digit number, this might be a coincidence but I think not. What if I actually want a number between lets say 0 and 10 * 10^18?

Is this possible? This is how how my Oraclize looks now:

    oraclize_setProof(proofType_Ledger); // sets the Ledger authenticity proof
    uint N = 4; // number of random bytes we want the datasource to return
    uint delay = 0; // number of seconds to wait before the execution takes place
    uint callbackGas = 200000; // amount of gas we want Oraclize to set for the callback function
    bytes32 queryId = oraclize_newRandomDSQuery(delay, N, callbackGas);

And in the __callBack

        uint maxRange = totalEth -1; // deduct one so that when one gets added later it cant be bigger than the total eth.
        randomNumber = (uint(sha3(_result)) % maxRange) + 1 // this is an efficient way to get the uint out in the [1, maxRange] range

1 Answer 1


It looks like you're using the random bytes to generate a number between 1 and maxRange, inclusive. If you want a number between 0 and 10**18, set maxRange to 10**18 and drop the + 1 in your code.

But note that 4 random bytes is not enough entropy to generate numbers in that range. 4 bytes gives you only 2**32 different values, which is 4,294,967,296. This is much smaller than 10**18. You'll need to use 8 bytes. (log2(10^18) ~= 60 bits.)

  • Thanks for your answer, and yes the 0 to 10^18 was a mistake It's meant to be 1 to 10^18, so an outcome of this random number could be for example 67? Ive only seen really high numbers but the testing is so slow that it could be a coincidence.
    – jasper
    Jun 1, 2018 at 17:28
  • Yes, but a number that small would be extraordinarily unlikely. If you picked numbers between 0 and 999, 90% of them would be three digits. (100/1000 are two digits or fewer.)
    – user19510
    Jun 1, 2018 at 18:58

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