Kotlin Multiplatform Crypto Library

Kotlin Multiplatform Crypto is a library for various cryptographic applications.

The library comes in two flavors multiplatform-crypto and multiplatform-crypto-delegated.

• multiplatform-crypto contains pure kotlin implementations, is not reviewed, should be considered unsafe and only for prototyping or experimentation purposes.

• multiplatform-crypto-delegated relies on platform specific implementations, mostly libsodium, but care should still be taken that the kotlin code is not reviewed or proven safe.

APIs of both variants are identical.

Table of contents

1. Supported platforms
2. API
3. TODO

Supported platforms by variant

Sample project

The library includes sample project that shows usage on different platforms

• NOTE: Currently only linux, macOs and windows are included.

Notes & Roadmap

The API will move fast and break often until v1.0

Next steps:

• Expand API (ECC, Signing ...)

Should I use this in production?

NO. The library is under HEAVY development. Until development is done it will not be reviewed and therefore it shouldn't be used. Contributions are still welcome!

Why?

This is an experimental implementation, mostly for expanding personal understanding of cryptography. It's not peer reviewed, not guaranteed to be bug free, and not guaranteed to be secure.

API for Pure and Delegated flavours

Hashing functions

• Blake2b
• SHA512
• SHA256

Key Derivation

• Argon2

Authenticated symmetric encryption (AEAD)

• XChaCha20-Poly1305

Integration

Gradle

Kotlin

implementation("com.ionspin.kotlin:multiplatform-crypto:0.1.0")

or

implementation("com.ionspin.kotlin:multiplatform-crypto-delegated:0.1.0")

Snapshot builds

repositories {
    maven {
        url = uri("https://oss.sonatype.org/content/repositories/snapshots")
    }
}
implementation("com.ionspin.kotlin:multiplatform-crypto:0.1.0-SNAPSHOT")

Usage

Helper functions

All API take UByteArray as message/key/nonce/etc parameter. For convenience when working with strings we provide String.enocdeToUbyteArray() extensions function, and UByteArray.toHexString extension function.

More convenience functions will be added.

Hashes

Hashes are provided in two versions, "stateless", usually the companion object of the hash, which takes the data to be hashed in one go, and "updatable" which can be fed data in chunks.

Blake2b

You can use Blake 2b in two modes

Stateless version

You need to deliver the complete data that is to be hashed in one go

val input = "abc"
val result = Crypto.Blake2b.stateless(input.encodeToUByteArray())

Result is returned as a UByteArray

Updatable instance version

You can create an instance and feed the data by using update(input : UByteArray) call. Once all data is supplied, you should call digest().

If you want to use Blake2b with a key, you should supply it when creating the Blake2b instance.

val test = "abc"
val key = "key"
val blake2b = Crypto.Blake2b.updateable(key.encodeToUByteArray())
blake2b.update(test.encodeToUByteArray())
val result = blake2b.digest().toHexString()

After digest is called, the instance is reset and can be reused (Keep in mind key stays the same for the particular instance).

SHA2 (SHA256 and SHA512)

Stateless version

You need to deliver the complete data that is to be hashed in one go. You can either provide the UByteArray as input or String. Result is always returned as UByteArray (At least in verision 0.0.1)

val input = "abc"
val result = Crypto.Sha256.stateless(input.encodeToUByteArray())

val input ="abc"
val result = Crypto.Sha512.stateless(input.encodeToUByteArray())

Result is returned as a UByteArray

Updateable version

Or you can use the updatable instance version

val sha256 = Crypto.Sha256.updateable()
sha256.update("abc".encodeToUByteArray())
val result = sha256.digest()

val sha512 = Crypto.Sha512.updateable()
sha512.update("abc".encodeToUByteArray())
val result = sha512.digest()

Key derivation

Argon2

NOTE: This implementation is tested against KAT generated by reference Argon2 implementation, which does not follow specification completely. See this issue https://github.com/P-H-C/phc-winner-argon2/issues/183

val argon2Instance = Argon2(
            password = "Password",
            salt = "RandomSalt",
            parallelism = 8,
            tagLength = 64U,
            requestedMemorySize = 256U, //4GB
            numberOfIterations = 4U,
            key = "",
            associatedData = "",
            argonType = ArgonType.Argon2id
        )
val tag = argon2Instance.derive()
val tagString = tag.map { it.toString(16).padStart(2, '0') }.joinToString(separator = "")
val expectedTagString = "c255e3e94305817d5e09a7c771e574e3a81cc78fef5da4a9644b6df0" +
        "0ba1c9b424e3dd0ce7e600b1269b14c84430708186a8a60403e1bfbda935991592b9ff37"
println("Tag: ${tagString}")
assertEquals(tagString, expectedTagString)

Symmetric encryption (OUTDATED, won't be exposed in next release, no counterpart in delegated flavor - 0.1.1)

AES

Aes is available with CBC and CTR mode through AesCbc and AesCtr classes/objects. Similarly to hashes you can either use stateless or updateable version.

Initialization vector, or counter states are chosen by the SDK automaticaly, and returned alongside encrypted data

Stateless AesCbc and AesCtr

AesCtr

val keyString = "4278b840fb44aaa757c1bf04acbe1a3e"
val key = AesKey.Aes128Key(keyString)
val plainText = "6bc1bee22e409f96e93d7e117393172aae2d8a571e03ac9c9eb76fac45af8e5130c81c46a35ce411e5fbc1191a0a52eff69f2445df4f9b17ad2b417be66c3710"

val encryptedDataAndInitializationVector = AesCtr.encrypt(key, plainText.hexStringToUByteArray())
val decrypted = AesCtr.decrypt(
    key,
    encryptedDataAndInitializationVector.encryptedData,
    encryptedDataAndInitializationVector.initialCounter
)
plainText == decrypted.toHexString()

AesCbc

val keyString = "4278b840fb44aaa757c1bf04acbe1a3e"
val key = AesKey.Aes128Key(keyString)

val plainText = "3c888bbbb1a8eb9f3e9b87acaad986c466e2f7071c83083b8a557971918850e5"

val encryptedDataAndInitializationVector = AesCbc.encrypt(key, plainText.hexStringToUByteArray())
val decrypted = AesCbc.decrypt(
    key,
    encryptedDataAndInitializationVector.encryptedData,
    encryptedDataAndInitializationVector.initilizationVector
)
plainText == decrypted.toHexString()

Supported native platforms

Currently supported native platforms:

Known issues:

• Using LazySodium self built variant to fix some of the bugs present in LazySodium, but Android is using directly LazySodium release which has not been updated (latest version is 4.2.0), this means that randombytes_random, basetobin and base64tohex functions are not working on Android, as well as problems with sodium_pad:

  https://github.com/terl/lazysodium-java/issues/83

  https://github.com/terl/lazysodium-java/issues/85

  https://github.com/terl/lazysodium-java/issues/86

  Also it is not clear where are the precompiled libraries in LazySodium coming from

  This will be handled by providing a new JNA libsodium wrapper library

Notes for Gitlab runners:

• At the moment all runners need to have android sdk

Mac:

Windows:

• Needs android sdk
• Git needs long file path enabled
• msys2 needs to be installed and pacman update executed