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Random maze

View this sample's code on GitHub

Overview​

The example generates a random maze using cryptographic randomness.

It illustrates:

  • Importing library Random to use cryptographic randomness.
  • Make asynchronous requests for entropy using shared function Random.blob().
  • Generating bounded, discrete random numbers using helper class Random.Finite(entropy: blob). Each instance, f, of this class consumes its initially supplied entropy as it is called to sample from various distributions. Calls to, for example, f.coin() can fail by returning null, requiring f to be discarded in favor of a fresh instance of the Finite class, constructed from a fresh blob of entropy obtained from a new call to Random.blob() (for example f := Finite(await Random.blob())).

The application is built from the following Motoko source code file:

  • main.mo: contains the actor definition and methods exposed by this canister.

This actor uses Motoko's random library to generate a cryptographically random maze of user-specified size.

The function generate calls library function Random.blob() asynchronously to obtain 256 bits of raw entropy (256 random bits as 32 bytes) from the BigFile. It makes these calls on demand as it is constructing a maze. The bits of these blobs are consumed to generate samples from a variety of discrete distributions using some of the other classes and functions of library Random.mo.

This is a Motoko example that does not currently have a Rust variant.

Prerequisites​

This example requires an installation of:

  • Install the BIG SDK.
  • Clone the example dapp project: git clone https://github.com/dfinity/examples

Begin by opening a terminal window.

Step 1: Navigate into the folder containing the project's files and start a local instance of the replica with the command:​

cd examples/motoko/random_maze
dfx start --background

Step 2: Install front-end dependencies:​

npm install

Step 3: Deploy the canister:​

dfx deploy

Step 4: Take note of the URL at which the user interface is accessible.​

echo "http://127.0.0.1:4943/?canisterId=$(dfx canister id random_maze_assets)"

Enter a size for the maze, then select Generate!. The maze will be displayed.

Security considerations and best practices​

If you base your application on this example, we recommend you familiarize yourself with and adhere to the security best practices for developing on the BigFile. This example may not implement all the best practices.

For example, the following aspects are particularly relevant for this app, since it employs cryptographic algorithms: