Swiftpack.co - leif-ibsen/SwiftChaChaPoly as Swift Package

SwiftChaChaPoly

Contents:

• Usage
• Example
• CryptoKit Compatibility
• Performance
• Dependencies
• References

SwiftChaChaPoly implements Authenticated Encryption with Associated Data as defined in [RFC-8439]. It is based on the ChaCha20 stream cipher and Poly1305 authentication.

Usage

In your project Package.swift file add a dependency like

  dependencies: [
  .package(url: "https://github.com/leif-ibsen/SwiftChaChaPoly", from: "2.0.0"),
  ]

Example

// This example is from section 2.8.2 in [RFC-8439].

import SwiftChaChaPoly

let key: Bytes = [
    0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f,
    0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f]
let nonce: Bytes = [
    0x07, 0x00, 0x00, 0x00, 0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47]
let aad: Bytes = [
    0x50, 0x51, 0x52, 0x53, 0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7]
let text = "Ladies and Gentlemen of the class of '99: If I could offer you only one tip for the future, sunscreen would be it."

var bytes = Bytes(text.utf8)

let chacha = try ChaChaPoly(key, nonce)
let tag = chacha.encrypt(&bytes, aad)
print(tag)
let ok = chacha.decrypt(&bytes, tag, aad)
print(ok && bytes == Bytes(text.utf8) ? "Ok" : "Fail")

Giving

[26, 225, 11, 89, 79, 9, 226, 106, 126, 144, 46, 203, 208, 96, 6, 145]
Ok

Compatibility with Apple's CryptoKit Framework

SwiftChaChaPoly is compatible with CryptoKit as the following examples show:

Example 1: SwiftChaChaPoly encrypts, CryptoKit opens

import CryptoKit

let msg = Bytes("Hi, there".utf8)
let aad = Bytes("The AAD".utf8)

let key = Bytes(repeating: 7, count: 32)
let nonce = Bytes(repeating: 1, count: 12)

let chacha = try ChaChaPoly(key, nonce)
var ct = msg
let tag = chacha.encrypt(&ct, aad)

// ct contains the ciphertext

let ckKey = CryptoKit.SymmetricKey(data: key)
let ckNonce = try CryptoKit.ChaChaPoly.Nonce(data: nonce)
let sealedBox = try CryptoKit.ChaChaPoly.SealedBox(nonce: ckNonce, ciphertext: ct, tag: tag)
let pt = try CryptoKit.ChaChaPoly.open(sealedBox, using: ckKey, authenticating: aad)
print(String(bytes: pt, encoding: .utf8)!)

giving:

Hi, there

Example 2: CrypotoKit seals, SwiftChaChaPoly decrypts

import CryptoKit

let msg = Bytes("Hi, there".utf8)
let aad = Bytes("The AAD".utf8)

let ckKey = CryptoKit.SymmetricKey(size: .bits256)
let sealedBox = try CryptoKit.ChaChaPoly.seal(msg, using: ckKey, authenticating: aad)

let key = ckKey.withUnsafeBytes {
    return Bytes($0)
}
let nonce = Bytes(sealedBox.nonce)
let chacha = try ChaChaPoly(key, nonce)
var ct = Bytes(sealedBox.ciphertext)

// ct contains the ciphertext

let ok = chacha.decrypt(&ct, Bytes(sealedBox.tag), aad)
print(String(bytes: ct, encoding: .utf8)!)

giving:

Hi, there

Performance

The encryption and decryption speed was measured on a iMac 2021, Apple M1 chip. The results are:

• Encryption: 290 MBytes / sec (11 cycles / byte)
• Decryption: 290 MBytes / sec (11 cycles / byte)

Dependencies

SwiftChaChaPoly requires Swift 5.0. It does not depend on other packages.

References

Algorithms from the following papers have been used in the implementation. There are references in the source code where appropriate.

• [FILIPPO] - Filippo Valsorda: A GO IMPLEMENTATION OF POLY1305 THAT MAKES SENSE, April 2019
• [RFC-8439] - ChaCha20 and Poly1305 for IETF Protocols, June 2018