bigint-mod-arith/src/doc/readme-template.md

bigint-mod-arith

Some extra functions to work with modular arithmetic using native JS (ES-2020) implementation of BigInt. It can be used by any Web Browser or webview supporting BigInt and with Node.js (>=10.4.0).

The operations supported on BigInts are not constant time. BigInt can be therefore unsuitable for use in cryptography. Many platforms provide native support for cryptography, such as Web Cryptography API or Node.js Crypto.

Installation

bigint-mod-arith is distributed for web browsers and/or webviews supporting BigInt as an ES6 module or an IIFE file; and for Node.js (>=10.4.0), as a CJS module.

bigint-mod-arith can be imported to your project with npm:

npm install bigint-mod-arith

NPM installation defaults to the ES6 module for browsers and the CJS one for Node.js.

For web browsers, you can also directly download the IIFE bundle or the ES6 bundle module from GitHub.

Usage example

Import your module as :

• Node.js

  const bigintModArith = require('bigint-mod-arith')
  ... // your code here
  

• JavaScript native project

  import * as bigintModArith from 'bigint-mod-arith'
  ... // your code here
  

• JavaScript native browser ES6 mod

  <script type="module">
    import * as bigintModArith from 'lib/index.browser.bundle.mod.js'  // Use you actual path to the browser mod bundle
    ... // your code here
  </script>
  

• JavaScript native browser IIFE

  <script src="../../lib/index.browser.bundle.js"></script> <!-- Use you actual path to the browser bundle -->
  <script>
    ... // your code here
  </script>
  

• TypeScript

  import * as bigintModArith from 'bigint-mod-arith'
  ... // your code here
  

  BigInt is ES-2020. In order to use it with TypeScript you should set lib (and probably also target and module) to esnext in tsconfig.json.

/* Stage 3 BigInts with value 666 can be declared as BigInt('666')
or the shorter syntax 666n.
Notice that you can also pass a number, e.g. BigInt(666), but it is not
recommended since values over 2**53 - 1 won't be safe but no warning will
be raised.
*/
const a = BigInt('5')
const b = BigInt('2')
const n = 19n

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

console.log(bigintModArith.modInv(2n, 5n)) // prints 3

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

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