AndroidDoubleRatchet

Implementation of the Double Ratchet protocol in Kotlin for Android. The cryptographic operations are provided by Lazysodium entirely.

Installation

Jitpack

To integrate the library via jitpack add the jitpack repository to your root build.gradle file:

allprojects {
  repositories {
    ...
    maven { url  "https://dl.bintray.com/terl/lazysodium-maven" }
    maven { url 'https://jitpack.io' }
  }
}

You can then add the dependency to your app's build.gradle file where $VERSION specifies the specific version of the library:

dependencies {
  implementation 'com.github.TICESoftware:AndroidDoubleRatchet:$VERSION'
  implementation "com.goterl:lazysodium-android:4.1.0@aar"
  implementation 'net.java.dev.jna:jna:5.5.0@aar'
}

Usage

Alice and Bob calculate a shared secret using a secure channel. After that one party can start the conversation as soon as she gets to know the public key of the other one.

import com.ticeapp.androiddoubleratchet.DoubleRatchet

val sharedSecret: ByteArray = ...
val info = "DoubleRatchetExample"

val bob = DoubleRatchet(keyPair = null, remotePublicKey = null, sharedSecret = sharedSecret, maxSkip = 20, maxCache = 20, info = info)

// Bob sends his public key to Alice using another channel
// sendToAlice(bob.publicKey)

val alice = DoubleRatchet(keyPair = null, remotePublicKey = bob.publicKey, sharedSecret = sharedSecret, maxSkip = 20, maxCache = 20, info = info)

// Now the conversation begins
val message = "Hello, Bob!".encodeToByteArray()
val encryptedMessage = alice.encrypt(message)
val decryptedMessage = bob.decrypt(encryptedMessage)

println(decryptedMessage.decodeToString()) // Hello, Bob!