How does the random number generator work?
You set the bounds of the range and how many numbers you need, and the generation runs on the server rather than in the browser. A single run returns up to 10,000 numbers in the range from -1,000,000,000,000 to 1,000,000,000,000, and repeats can be disabled so that every number in the batch is different. There are two modes: the ordinary one, where the numbers come from the server's cryptographic generator, and the verifiable one — the "Authenticity check" switch on the form.
How can I check that the result was not tampered with?
Turn the authenticity check on. The site then picks a future round of the drand public randomness beacon and publishes the conditions of the generation before the value of that round exists: the protocol page opens right away, still without the numbers. The numbers are computed from the round value once the network publishes it, so nobody can cherry-pick the result, us included. Anyone can recompute the numbers and see it for themselves — in the browser on the protocol page or with their own script.
Is the generator suitable for prize draws and contests?
Yes, that is exactly what the generation protocol is for: it confirms that the result was produced at the stated time and has not changed since it was published. If the participants need to verify the fairness themselves, turn the authenticity check on — the protocol link can then be published before the numbers even exist. The service is not intended for lotteries or gambling, where the law requires a certified random number generator.
What is drand and why can it be trusted?
drand is a public randomness beacon: the League of Entropy, a network of independent organisations from different countries, publishes a new random value every 3 seconds. Its members include Cloudflare, Protocol Labs, EPFL, Kudelski Security and the University of Chile. No single one of them can learn a value in advance or substitute it, and every round is signed with the group's shared key — so the authenticity of a value is checked mathematically.