StreamKit/ChaCha20Stream.md

ChaCha20 Stream

ChaCha20 is a stream cipher with symmetric secret key. It works on data blocks of size 64 bytes. Key length is 32 bytes.
Initialization vector(iv) is required of 12 bytes length.
The stream cipher algorithm performs 20 rounds of computations in its hash function.

Create output(encrypting) stream

let encryptingStream = ChaCha20OutputStream(writingTo: dataOutputStream,
                                            key: key,
                                            iv: iv)
try encryptingStream.open()
try encryptingStream.write(buffer, length: len)
try encryptingStream.close()

Create input(decrypting) stream

let decryptionStream = ChaCha20InputStream(readingFrom: dataInputStream,
                                                   key: key,
                                                   iv: iv)
try decryptingStream.open()
        
var decryptedBytes = [UInt8]()
while decryptingStream.hasBytesAvailable {
  let tmpBufferLen = 1<<16 // 65KB buffer
  var tmpBuffer = Array<UInt8>(repeating: 0, count: tmpBufferLen)
  let readLen = try decryptingStream.read(&tmpBuffer, maxLength: tmpBufferLen)
  decryptedBytes.append(contentsOf: tmpBuffer.prefix(readLen))
}

let decryptedData = Data(decryptedBytes)