80 lines
3.3 KiB
Markdown
80 lines
3.3 KiB
Markdown
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[](https://standardjs.com)
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# bigint-mod-arith
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Some extra functions to work with modular arithmetic using native JS ([ES-2020](https://tc39.es/ecma262/#sec-bigint-objects)) implementation of BigInt. 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).
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> 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).
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## Installation
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bigint-mod-arith is distributed for [web browsers and/or webviews supporting BigInt](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt#Browser_compatibility) as an ES6 module or an IIFE file; and for Node.js (>=10.4.0), as a CJS module.
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bigint-mod-arith can be imported to your project with `npm`:
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```bash
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npm install bigint-mod-arith
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```
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NPM installation defaults to the ES6 module for browsers and the CJS one for Node.js.
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For web browsers, you can also directly download the [IIFE bundle](https://raw.githubusercontent.com/juanelas/bigint-mod-arith/master/lib/index.browser.bundle.js) or the [ES6 bundle module](https://raw.githubusercontent.com/juanelas/bigint-mod-arith/master/lib/index.browser.bundle.mod.js) from GitHub.
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## Usage example
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Import your module as :
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- Node.js
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```javascript
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const bigintCryptoUtils = require('bigint-mod-arith')
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... // your code here
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```
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- JavaScript native project
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```javascript
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import * as bigintCryptoUtils from 'bigint-mod-arith'
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... // your code here
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```
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- Javascript native browser ES6 mod
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```html
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<script type="module">
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import * as bigintCryptoUtils from 'lib/index.browser.bundle.mod.js' // Use you actual path to the broser mod bundle
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... // your code here
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</script>
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import as bcu from 'bigint-mod-arith'
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... // your code here
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```
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- JavaScript native browser IIFE
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```html
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<script src="../../lib/index.browser.bundle.js"></script>
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<script>
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... // your code here
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</script>
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- TypeScript
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```typescript
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import * as bigintCryptoUtils from 'bigint-mod-arith'
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... // your code here
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```
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> BigInt is [ES-2020](https://tc39.es/ecma262/#sec-bigint-objects). In order to use it with TypeScript you should set `lib` (and probably also `target` and `module`) to `esnext` in `tsconfig.json`.
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```javascript
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/* Stage 3 BigInts with value 666 can be declared as BigInt('666')
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or the shorter new no-so-linter-friendly syntax 666n.
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Notice that you can also pass a number, e.g. BigInt(666), but it is not
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recommended since values over 2**53 - 1 won't be safe but no warning will
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be raised.
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*/
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const a = BigInt('5')
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const b = BigInt('2')
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const n = BigInt('19')
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console.log(bigintCryptoUtils.modPow(a, b, n)) // prints 6
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console.log(bigintCryptoUtils.modInv(BigInt('2'), BigInt('5'))) // prints 3
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console.log(bigintCryptoUtils.modInv(BigInt('3'), BigInt('5'))) // prints 2
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```
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## JS Doc
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{{>main}}
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