ChaCha20-Lua

-- Chacha20 cipher in ComputerCraft
-- By Anavrins
-- MIT License
-- Pastebin: https://pastebin.com/GPzf9JSa
-- Last updated: March 27 2020

local mod32 = 2^32
local bor = bit32.bor
local bxor = bit32.bxor
local band = bit32.band
local blshift = bit32.lshift
local brshift = bit32.arshift

local tau = {("expand 16-byte k"):byte(1,-1)}
local sigma = {("expand 32-byte k"):byte(1,-1)}
local null32 = {("A"):rep(32):byte(1,-1)}
local null12 = {("A"):rep(12):byte(1,-1)}

local function rotl(n, b)
    local s = n/(2^(32-b))
    local f = s%1
    return (s-f) + f*mod32
end

local function quarterRound(s, a, b, c, d)
    s[a] = (s[a]+s[b])%mod32; s[d] = rotl(bxor(s[d], s[a]), 16)
    s[c] = (s[c]+s[d])%mod32; s[b] = rotl(bxor(s[b], s[c]), 12)
    s[a] = (s[a]+s[b])%mod32; s[d] = rotl(bxor(s[d], s[a]), 8)
    s[c] = (s[c]+s[d])%mod32; s[b] = rotl(bxor(s[b], s[c]), 7)
    return s
end

local function hashBlock(state, rnd)
    local s = {unpack(state)}
    for i = 1, rnd do
        local r = i%2==1
        s = r and quarterRound(s, 1, 5,  9, 13) or quarterRound(s, 1, 6, 11, 16)
        s = r and quarterRound(s, 2, 6, 10, 14) or quarterRound(s, 2, 7, 12, 13)
        s = r and quarterRound(s, 3, 7, 11, 15) or quarterRound(s, 3, 8,  9, 14)
        s = r and quarterRound(s, 4, 8, 12, 16) or quarterRound(s, 4, 5, 10, 15)
    end
    for i = 1, 16 do s[i] = (s[i]+state[i])%mod32 end
    return s
end

local function LE_toInt(bs, i)
    return (bs[i+1] or 0)+
    blshift((bs[i+2] or 0), 8)+
    blshift((bs[i+3] or 0), 16)+
    blshift((bs[i+4] or 0), 24)
end

local function initState(key, nonce, counter)
    local isKey256 = #key == 32
    local const = isKey256 and sigma or tau
    local state = {}

    state[ 1] = LE_toInt(const, 0)
    state[ 2] = LE_toInt(const, 4)
    state[ 3] = LE_toInt(const, 8)
    state[ 4] = LE_toInt(const, 12)

    state[ 5] = LE_toInt(key, 0)
    state[ 6] = LE_toInt(key, 4)
    state[ 7] = LE_toInt(key, 8)
    state[ 8] = LE_toInt(key, 12)
    state[ 9] = LE_toInt(key, isKey256 and 16 or 0)
    state[10] = LE_toInt(key, isKey256 and 20 or 4)
    state[11] = LE_toInt(key, isKey256 and 24 or 8)
    state[12] = LE_toInt(key, isKey256 and 28 or 12)

    state[13] = counter
    state[14] = LE_toInt(nonce, 0)
    state[15] = LE_toInt(nonce, 4)
    state[16] = LE_toInt(nonce, 8)

    return state
end

local function serialize(state)
    local r = {}
    for i = 1, 16 do
        r[#r+1] = band(state[i], 0xFF)
        r[#r+1] = band(brshift(state[i], 8), 0xFF)
        r[#r+1] = band(brshift(state[i], 16), 0xFF)
        r[#r+1] = band(brshift(state[i], 24), 0xFF)
    end
    return r
end

local mt = {
    __tostring = function(a) return string.char(unpack(a)) end,
    __index = {
        toHex = function(self) return ("%02x"):rep(#self):format(unpack(self)) end,
        isEqual = function(self, t)
            if type(t) ~= "table" then return false end
            if #self ~= #t then return false end
            local ret = 0
            for i = 1, #self do
                ret = bor(ret, bxor(self[i], t[i]))
            end
            return ret == 0
        end
    }
}

local function crypt(data, key, nonce, cntr, round)
    assert(type(key) == "table", "ChaCha20: Invalid key format ("..type(key).."), must be table")
    assert(type(nonce) == "table", "ChaCha20: Invalid nonce format ("..type(nonce).."), must be table")
    assert(#key == 16 or #key == 32, "ChaCha20: Invalid key length ("..#key.."), must be 16 or 32")
    assert(#nonce == 12, "ChaCha20: Invalid nonce length ("..#nonce.."), must be 12")

    local data = type(data) == "table" and {unpack(data)} or {tostring(data):byte(1,-1)}
    cntr = tonumber(cntr) or 1
    round = tonumber(round) or 20

    local out = {}
    local state = initState(key, nonce, cntr)
    local blockAmt = math.floor(#data/64)
    for i = 0, blockAmt do
        local ks = serialize(hashBlock(state, round))
        state[13] = (state[13]+1) % mod32

        local block = {}
        for j = 1, 64 do
            block[j] = data[((i)*64)+j]
        end
        for j = 1, #block do
            out[#out+1] = bxor(block[j], ks[j])
        end

        if i % 1000 == 0 then
            os.queueEvent("")
            os.pullEvent("")
        end
    end
    return setmetatable(out, mt)
end

local function genNonce(len)
    local nonce = {}
    for i = 1, len do
        nonce[i] = math.random(0, 0xFF)
    end
    return setmetatable(nonce, mt)
end

local obj = {}
local mtrng = {['__index'] = obj}
local function newRNG(seed)
  local objVars = {}
  objVars.seed = seed
  objVars.cnt = 0
  objVars.block = {}
  return setmetatable(objVars, mtrng)
end

-- Specify how many bytes to return
-- 1 Byte is 8 bits, returns int between 0 and 255
-- 2 Bytes is 16 bits, returns int up to 65535
-- 4 Bytes is 32 bits, returns int up to 4294967295
-- Max of 6 Bytes is 48 bits, returns int up to 281474976710655
function obj:nextInt(byte)
  if not byte or byte < 1 or byte > 6 then error("Can only return 1-6 bytes", 2) end
  local output = 0
  for i = 0, byte-1 do
    if #self.block == 0 then
      self.cnt = self.cnt + 1
      self.block = crypt(null32, self.seed, null12, self.cnt)
    end
    local newByte = table.remove(self.block)
    output = output + (newByte * (2^(8*i)))
  end
  return output
end

return {
    crypt = crypt,
    genNonce = genNonce,
    newRNG = newRNG
}