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# {{PKG_NAME}}
Arbitrary precision modular arithmetic, cryptographically secure random numbers and strong probable prime generation/testing.
It relies on the native JS implementation of ([BigInt](https://tc39.es/ecma262/#sec-bigint-objects)). It can be used by any [Web Browser or webview supporting BigInt](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt#Browser_compatibility) and with Node.js (>=10.4.0). The bundles can be imported directly by the browser or in Angular projects, React apps, Node.js, etc.
Secure random numbers are generated using the native crypto implementation of the browsers ([Web Cryptography API](https://w3c.github.io/webcrypto/)) or [Node.js Crypto](https://nodejs.org/dist/latest/docs/api/crypto.html)). Strong probable prime generation and testing use Miller-Rabin primality tests and are automatically sped up using parallel workers both in browsers and Node.js.
> 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 [Web Cryptography API](https://w3c.github.io/webcrypto/) or [Node.js Crypto](https://nodejs.org/dist/latest/docs/api/crypto.html).
## Installation
{{PKG_NAME}} can be imported to your project with `npm`:
```bash
npm install {{PKG_NAME}}
```
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 {{ESM_BUNDLE}} from the repository.
## Usage examples
Import your module as :
- Node.js
```javascript
const bigintCryptoUtils = require('bigint-crypto-utils')
... // your code here
```
- JavaScript native or TypeScript project (including React and Angular JS)
```javascript
import * as bigintCryptoUtils from 'bigint-crypto-utils'
... // your code here
```
`{{PKG_NAME}}` **CANNOT BE POLYFILLED** to suport older browsers. If you are using webpack/babel to create your production bundles, you should target only the most modern browsers. For instance, for **React** apps created with [`create-react-app`](https://create-react-app.dev/), you should edit your `package.json` and modify the `browserList` so that it only targets the latest browsers (supporting the latest features):
```json
"browserslist": {
"production": [
"last 1 chrome version",
"last 1 firefox version",
"last 1 safari version"
],
"development": [
"last 1 chrome version",
"last 1 firefox version",
"last 1 safari version"
]
}
```
Also, notice that [BigInt implementation is quite recent](https://tc39.es/ecma262/#sec-bigint-objects). In order to use it with TypeScript you will probably need to set `lib`, `target` and/or `module` to `esnext` in your project's `tsconfig.json`.
- JavaScript native browser ES module
```html
```
- JavaScript native browser IIFE
```html
...
...
```
An example of usage could be:
```javascript
/* A BigInt with value 666 can be declared calling the bigint constructor as
BigInt('666') or with the shorter 666n.
Notice that you can also pass a number to the constructor, e.g. BigInt(666).
However, 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(bigintCryptoUtils.modPow(a, b, n)) // prints 6
console.log(bigintCryptoUtils.modInv(2n, 5n)) // prints 3
console.log(bigintCryptoUtils.modInv(BigInt('3'), BigInt('5'))) // prints 2
console.log(bigintCryptoUtils.randBetween(2n ** 256n)) // Prints a cryptographically secure random number between 1 and 2**256 bits.
async function primeTesting () {
// Output of a probable prime of 2048 bits
console.log(await bigintCryptoUtils.prime(2048))
// Testing if a number is a probable prime (Miller-Rabin)
const number = 27n
const isPrime = await bigintCryptoUtils.isProbablyPrime(number)
if (isPrime) {
console.log(`${number} is prime`)
} else {
console.log(`${number} is composite`)
}
}
primeTesting()
```
You can find examples in the [examples folder of the repository](https://github.com/juanelas/bigint-crypto-utils/tree/master/examples).
## API reference documentation
{{>main}}