# bigint-utils 

Some extra functions to work with modular arithmetics along with secure random numbers and probable prime (Miller-Rabin primality test) generation/testing using native JS (stage 3) implementation of BigInt. It can be used with Node.js (>=10.4.0) and [Web Browsers supporting BigInt](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt#Browser_compatibility).

_The operations supported on BigInts are not constant time. BigInt can be therefore **[unsuitable for use in cryptography](https://www.chosenplaintext.ca/articles/beginners-guide-constant-time-cryptography.html)**_

Many platforms provide native support for cryptography, such as [webcrypto](https://w3c.github.io/webcrypto/Overview.html) or [node crypto](https://nodejs.org/dist/latest/docs/api/crypto.html).

## Installation
bigint-utils is distributed as both an ES6 and a CJS module.

The ES6 module is built for any [web browser supporting BigInt](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt#Browser_compatibility). The module only uses native javascript implementations and no polyfills had been applied.

The CJS module is built as a standard node module.

bigint-utils can be imported to your project with `npm`:
```bash
npm install bigint-utils
```

For web browsers, you can also [download the bundle from GitHub](https://raw.githubusercontent.com/juanelas/bigint-utils/master/dist/bigint-utils-latest.browser.mod.min.js).

## Usage example

With node js:
```javascript
const bigintUtils = require('bigint-utils');

// Stage 3 BigInts with value 666 can be declared as BigInt('666')
// or the shorter new no-so-linter-friendly syntax 666n
let a = BigInt('5');
let b = BigInt('2');
let n = BigInt('19');

console.log(bigintModArith.modPow(a, b, n)); // prints 6

console.log(bigintModArith.modInv(BigInt('2'), BigInt('5'))); // prints 3

console.log(bigintModArith.modInv(BigInt('3'), BigInt('5'))); // prints 2

// Generation of a probable prime of 2048 bits
const prime = await bigintUtils.prime(2048);

// Testing if a prime is a probable prime (Miller-Rabin)
if ( await bigintUtils.isProbablyPrime(prime) )
    // code if is prime

// Get a cryptographically secure random number between 1 and 2**256 bits.
const rnd = bigintUtils.randBetween(BigInt(2)**256);

```

From a browser, you can just load the module in a html page as:
```html
  <script type="module">
    import * as bigintUtils from 'bigint-utils-latest.browser.mod.min.js';

    let a = BigInt('5');
    let b = BigInt('2');
    let n = BigInt('19');

    console.log(bigintModArith.modPow(a, b, n)); // prints 6

    console.log(bigintModArith.modInv(BigInt('2'), BigInt('5'))); // prints 3

    console.log(bigintModArith.modInv(BigInt('3'), BigInt('5'))); // prints 2

    (async function () {
      // Generation of a probable prime of 2018 bits
      const p = await bigintSecrets.prime(2048);

      // Testing if a prime is a probable prime (Miller-Rabin)
      const isPrime = await bigintSecrets.isProbablyPrime(p);
      alert(p.toString() + '\nIs prime?\n' + isPrime);

      // Get a cryptographically secure random number between 1 and 2**256 bits.
      const rnd = await bigintSecrets.randBetween(BigInt(2)**256);
      alert(rnd);
    })();
  </script>
```

# bigint-utils JS Doc

{{>main}}

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