59 lines
2.9 KiB
Markdown
59 lines
2.9 KiB
Markdown
[](https://opensource.org/licenses/MIT)
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[](https://standardjs.com)
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[](https://github.com/juanelas/bigint-mod-arith/actions?query=workflow%3A%22Node+CI%22)
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[](https://coveralls.io/github/juanelas/bigint-mod-arith?branch=master)
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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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## Usage
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`bigint-mod-arith` can be imported to your project with `npm`:
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```console
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npm install bigint-mod-arith
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```
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Then either require (Node.js CJS):
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```javascript
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const bigintModArith = require('bigint-mod-arith')
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```
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or import (JavaScript ES module):
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```javascript
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import * as bigintModArith from 'bigint-mod-arith'
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```
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The appropriate version for browser or node is automatically exported.
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You can also download the [IIFE bundle](https://raw.githubusercontent.com/juanelas/bigint-mod-arith/master/dist/bundles/bigint-mod-arith.iife.js), the [ESM bundle](https://raw.githubusercontent.com/juanelas/bigint-mod-arith/master/dist/bundles/bigint-mod-arith.esm.js) or the [UMD bundle](https://raw.githubusercontent.com/juanelas/bigint-mod-arith/master/dist/bundles/bigint-mod-arith.umd.js) and manually add it to your project, or, if you have already imported `bigint-mod-arith` to your project, just get the bundles from `node_modules/bigint-mod-arith/dist/bundles/`.
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An example of usage could be:
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```typescript
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/* Stage 3 BigInts with value 666 can be declared as BigInt('666')
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or the shorter 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 = 19n
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console.log(bigintModArith.modPow(a, b, n)) // prints 6
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console.log(bigintModArith.modInv(2n, 5n)) // prints 3
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console.log(bigintModArith.modInv(BigInt('3'), BigInt('5'))) // prints 2
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```
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## API reference documentation
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[Check the API](./docs/API.md)
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