bedrock-protocol/src/transforms/encryption.js

const { PassThrough, Transform } = require('readable-stream')
const crypto = require('crypto')
const aesjs = require('aes-js')
const Zlib = require('zlib')

const CIPHER = 'aes-256-cfb8'

function createCipher(secret, initialValue) {
  if (crypto.getCiphers().includes(CIPHER)) {
    return crypto.createCipheriv(CIPHER, secret, initialValue)
  }
  return new Cipher(secret, initialValue)
}

function createDecipher(secret, initialValue) {
  if (crypto.getCiphers().includes(CIPHER)) {
    return crypto.createDecipheriv(CIPHER, secret, initialValue)
  }
  return new Decipher(secret, initialValue)
}

class Cipher extends Transform {
  constructor(secret, iv) {
    super()
    this.aes = new aesjs.ModeOfOperation.cfb(secret, iv, 1) // eslint-disable-line new-cap
  }

  _transform(chunk, enc, cb) {
    try {
      const res = this.aes.encrypt(chunk)
      cb(null, res)
    } catch (e) {
      cb(e)
    }
  }
}

class Decipher extends Transform {
  constructor(secret, iv) {
    super()
    this.aes = new aesjs.ModeOfOperation.cfb(secret, iv, 1) // eslint-disable-line new-cap
  }

  _transform(chunk, enc, cb) {
    try {
      const res = this.aes.decrypt(chunk)
      cb(null, res)
    } catch (e) {
      cb(e)
    }
  }
}

function computeCheckSum(packetPlaintext, sendCounter, secretKeyBytes) {
  let digest = crypto.createHash('sha256');
  let counter = Buffer.alloc(8)
  // writeLI64(sendCounter, counter, 0);
  counter.writeBigInt64LE(sendCounter, 0)
  // console.log('Send counter', counter)
  digest.update(counter);
  digest.update(packetPlaintext);
  digest.update(secretKeyBytes);
  let hash = digest.digest();
  // console.log('Hash', hash.toString('hex'))
  return hash.slice(0, 8);
}

function createEncryptor(client, iv) {
  client.cipher = createCipher(client.secretKeyBytes, iv)
  client.sendCounter = client.sendCounter || 0n

  // A packet is encrypted via AES256(plaintext + SHA256(send_counter + plaintext + secret_key)[0:8]).
  // The send counter is represented as a little-endian 64-bit long and incremented after each packet.

  function process(chunk) {
    const buffer =  Zlib.deflateRawSync(chunk, { level: 7 })
    // client.outLog('🟡 Compressed', buffer, client.sendCounter)
    const packet = Buffer.concat([buffer, computeCheckSum(buffer, client.sendCounter, client.secretKeyBytes)])
    client.sendCounter++
    // client.outLog('writing to cipher...', packet, client.secretKeyBytes, iv)
    client.cipher.write(packet)
  }

  // const stream = new PassThrough()

  client.cipher.on('data', client.onEncryptedPacket)


  return (blob) => {
    // client.outLog(client.options ? 'C':'S', '🟡 Encrypting', client.sendCounter, blob)
    // stream.write(blob)
    process(blob)
  }
}


function createDecryptor(client, iv) {
  client.decipher = createDecipher(client.secretKeyBytes, iv)
  client.receiveCounter = client.receiveCounter || 0n

  function verify(chunk) {
    // console.log('Decryptor: checking checksum', client.receiveCounter, chunk)
    // client.outLog('🔵 Inflating', chunk)
    // First try to zlib decompress, then see how much bytes get read
    const { buffer, engine } = Zlib.inflateRawSync(chunk, {
      chunkSize: 1024 * 1024 * 2,
      info: true
    })

    // Holds how much bytes we read, also where the checksum (should) start
    const inflatedLen = engine.bytesRead
    // It appears that mc sends extra bytes past the checksum. I don't think this is a raknet
    // issue (as we are able to decipher properly, zlib works and should also have a checksum) so 
    // there needs to be more investigation done. If you know what's wrong here, please make an issue :)
    const extraneousLen = chunk.length - inflatedLen - 8
    if (extraneousLen > 0) { // Extra bytes
      // Info for debugging, todo: use debug()
      const extraneousBytes = chunk.slice(inflatedLen + 8)
      console.debug('Extraneous bytes!', extraneousLen, extraneousBytes.toString('hex'))
    } else if (extraneousLen < 0) {
      // No checksum or decompression failed
      console.warn('Failed to decrypt', chunk.toString('hex'))
      throw new Error('Decrypted packet is missing checksum')
    }

    const packet = chunk.slice(0, inflatedLen);
    const checksum = chunk.slice(inflatedLen, inflatedLen + 8);
    const computedCheckSum = computeCheckSum(packet, client.receiveCounter, client.secretKeyBytes)
    client.receiveCounter++

    if (checksum.toString("hex") == computedCheckSum.toString("hex")) {
      client.onDecryptedPacket(buffer)
    } else {
      console.log('Inflated', inflatedLen, chunk.length, extraneousLen, chunk.toString('hex'))
      throw Error(`Checksum mismatch ${checksum.toString("hex")} != ${computedCheckSum.toString("hex")}`)
    }
  }

  client.decipher.on('data', verify)

  return (blob) => {
    // client.inLog(client.options ? 'C':'S', ' 🔵 Decrypting', client.receiveCounter, blob)
    // client.inLog('Using shared key', client.secretKeyBytes, iv)
    client.decipher.write(blob)
  }
}

module.exports = {
  createCipher, createDecipher, createEncryptor, createDecryptor
}

function testDecrypt() {
  const client = {
    secretKeyBytes: Buffer.from('ZOBpyzki/M8UZv5tiBih048eYOBVPkQE3r5Fl0gmUP4=', 'base64'),
    onDecryptedPacket: (...data) => console.log('Decrypted', data)
  }
  const iv = Buffer.from('ZOBpyzki/M8UZv5tiBih0w==', 'base64')

  const decrypt = createDecryptor(client, iv)
  console.log('Dec', decrypt(Buffer.from('4B4FCA0C2A4114155D67F8092154AAA5EF', 'hex')))
  console.log('Dec 2', decrypt(Buffer.from('DF53B9764DB48252FA1AE3AEE4', 'hex')))
}

// testDecrypt()