Au hasard

Au hasard is a random number generator and list picker app for Android (10+). It works fully offline, needs no permissions and collects no data.

The Numbers tab: the number 52 drawn from the range 1 to 100 The Lists tab: “Burger” drawn from a list of three items

Installation

The app is available as an APK.

It’s not currently on F-Droid or Google Play; just get it here, and if you like it, drop me a line.

Certificate SHA-256 fingerprint: 58f0ab46927fe6f188d4d2e4786173c1457cbccb5a346cddfab576c33bf923c9.

Source code (GNU GPL v3+): github.com/UnkindPartition/au-hasard.

What does Au hasard mean?

It’s French for “at random”, pronounced “oh ah-ZAR” (/o a.zaʁ/).

How does it work, exactly?

When the app starts, a 256-bit key is read from the kernel’s random number generator, /dev/urandom. Before each draw or shuffle, the key is replaced with the SHA-256 hash of the previous key and the precise time of your tap. From the current key, the ChaCha20 cipher produces a stream of random 64-bit numbers from which the draws and shuffles below are made:

Drawing numbers: rejection sampling (reject the \(2^{64} \bmod n\) smallest values to avoid modulo bias);
Shuffling lists: the Fisher–Yates algorithm;
Shuffling numbers: up to 100 numbers are chosen with Floyd’s sampling algorithm, then put in random order with Fisher–Yates.