If the random numbers can be 1-6, then yes, it would be trivial to attack. If the numbers are 300 bytes long, then it's impossible to predict.
> "I can try to be lucky and find your number by hashing random ones,"
If we were using sha-256, then you would be very impossibly lucky. There are 2^256 possible hash values for sha-256. It's extremely unlikely, that you would find a collision in the lifetime of the universe.
> "I can try to be lucky and find your number by hashing random ones," If we were using sha-256, then you would be very impossibly lucky. There are 2^256 possible hash values for sha-256. It's extremely unlikely, that you would find a collision in the lifetime of the universe.