@cogitojs/crypto

This package provides cryptographic primitives that are used by other Cogito packages, such as the Cogito Encryption package which provides support for encryption & decryption using keys that are managed by the Cogito mobile app.

Usage

Add @cogitojs/crypto to your dependencies:

$ yarn add @cogitojs/crypto

Initializing Sodium

Before using any of the other utilities provided in @cogitojs/crypto, you have to make sure that Sodium is initialized and ready to use. You do that by using Sodium class (also provided by the @cogitojs/crypto package):

import { Sodium } from '@cogitojs/crypto'

// IMPORTANT!!! must be called before you can use any of the sodium functions
await Sodium.wait()

You can always check if Sodium is ready by checking value of Sodium.ready. It is true when Sodium is initialized correctly.

If you try to use any function (including constructors) that depends on Sodium library when Sodium is not initialized (i.e. when Sodium.ready === false), an exception will be thrown. This currently apply to Sodium, StreamEncoder and StreamDecoder classes.

Using stream encoder and decoder

Stream encoding/decoding is provided by the means of the StreamEncoder and StreamDecoder classes.

You initialize StreamEncoder by calling its constructor:

const streamEncoder = new StreamEncoder()

Then, you push the chunks of data to be encrypted one by one, calling end for the last data chunk.

const chunk1 = Uint8Array.from({length: 10}, (v, k) => k)
console.log(`chunk1=[${chunk1}]`) // [0,1,2,3,4,5,6,7,8,9]
const chunk2 = Uint8Array.from({length: 10}, (v, k) => k)
console.log(`chunk2=[${chunk2}]`) // [0,1,2,3,4,5,6,7,8,9]

const encrypted1 = streamEncoder.push(chunk1)
// Everytime different output!
// [255,252,110,195,141,98,144,46,132,235,208,156,31,156,18,71,65,202,166,234,145,0,91,170,206,200,41]
console.log(`encrypted1=[${encrypted1}]`)
const encrypted2 = streamEncoder.end(chunk2)
// Everytime different output!
// [48,160,224,222,153,218,1,75,145,208,231,40,184,242,102,58,196,90,154,238,46,53,218,76,163,149,222]
console.log(`encrypted2=[${encrypted2}]`)

Now to decrypt, you call constructor of StreamDecoder providing it with the crypto material that you retrieved from StreamEncoder instance:

const cryptoMaterial = streamEncoder.cryptoMaterial
const streamDecoder = new StreamDecoder(cryptoMaterial)

Now you pull the decrypted chunks by calling pull with encrypted chunk as the argument:

const {message: decrypted1, tag: tag1} = streamDecoder.pull(encrypted1)
const {message: decrypted2, tag: tag2} = streamDecoder.pull(encrypted2)

console.log(`decrypted1=[${decrypted1}]`) // [0,1,2,3,4,5,6,7,8,9]
console.log(`tag1=${tag1}`) // 0
console.log(`decrypted2=[${decrypted2}]`) // [0,1,2,3,4,5,6,7,8,9]
console.log(`tag2=${tag2}`) // 3

expect(decrypted1).toEqual(chunk1)
expect(tag1).toBe(Sodium.TAG_MESSAGE)
expect(decrypted2).toEqual(chunk2)
expect(tag2).toBe(Sodium.TAG_FINAL)

The pull function returns an object {message, tag}. All the tags except for the last one should have value Sodium.TAG_MESSAGE. The tag for the last data chunk of the stream should be equal to Sodium.TAG_FINAL.

Please notice, you can only access Sodium.TAG_MESSAGE and Sodium.TAG_FINAL after Sodium has been initialized: so after you called await Sodium.wait().

Below is the complete example you can use as a jest test:

describe('Stream Encryption Decryption', () => {
  beforeAll(async () => {
    await Sodium.wait()
  })

  it('can encrypt and decrypt', () => {
    const streamEncoder = new StreamEncoder()

    const chunk1 = Uint8Array.from({length: 10}, (v, k) => k)
    console.log(`chunk1=[${chunk1}]`)
    const chunk2 = Uint8Array.from({length: 10}, (v, k) => k)
    console.log(`chunk2=[${chunk2}]`)

    const encrypted1 = streamEncoder.push(chunk1)
    console.log(`encrypted1=[${encrypted1}]`)
    const encrypted2 = streamEncoder.end(chunk2)
    console.log(`encrypted2=[${encrypted2}]`)

    const cryptoMaterial = streamEncoder.cryptoMaterial
    const streamDecoder = new StreamDecoder(cryptoMaterial)

    const {message: decrypted1, tag: tag1} = streamDecoder.pull(encrypted1)
    const {message: decrypted2, tag: tag2} = streamDecoder.pull(encrypted2)
    console.log(`decrypted1=[${decrypted1}]`)
    console.log(`tag1=${tag1}`)
    console.log(`decrypted2=[${decrypted2}]`)
    console.log(`tag2=${tag2}`)

    expect(decrypted1).toEqual(chunk1)
    expect(tag1).toBe(Sodium.TAG_MESSAGE)
    expect(decrypted2).toEqual(chunk2)
    expect(tag2).toBe(Sodium.TAG_FINAL)
  })
})

Using the tags

If you are not interested in validating the final tag, you can decide not to use end for the final data chunk in encryption, and use push for all the data chunks. In the end the only difference between push and end is the tag value.