Encer

local alpha = "pqowieurytlaksjdhfgmznxbcvPLOKIJUHYGTFRDESWAQMNBVCXZ|\\/.,?><#';[]~@:{}=+-_0)9(8*7&6^5%4$3£21! ¬"
alpha = alpha..'"'

local function getNum(ch)
    local num = 1
    for i=1,string.len(alpha) do
        if string.sub(alpha, i, i) == ch then num = i end
    end
    return num
end

local function getCh(num)
    if num > string.len(alpha) then num = 1 end
    return string.sub(alpha, num, num)
end

local cur = 1
local function getRand(pass)
    cur = cur + 1
    if cur > string.len(pass) then cur = 1 end
    local letter = string.sub(pass, cur, cur)
    local num = getNum(letter)
    if (num + cur) <= string.len(alpha) then num = num + cur
    elseif (num - cur) > 1 then num = num - cur else
        if (num + string.len(pass)) <= string.len(alpha) then num = num + string.len(pass)
        elseif (num - string.len(pass)) > 1 then num = num - string.len(pass) end
    end

    return num
end

local function getRCh(pass, ch, index)
    local i = index * 2
    while i > string.len(pass) or (string.len(pass) > string.len(alpha) and i > string.len(alpha)) do
        i = i - string.len(pass)
    end
    local mod = getRand(pass)
    local n = getNum(ch)
    local r = n + mod
    local omd = mod
    if r > string.len(alpha) then
        r = r - string.len(alpha)
        omd = mod - string.len(pass)
        while omd < 1 do omd = omd + r end
        if omd == mod then omd = omd - 1 end
        if omd > string.len(alpha) then omd = string.len(alpha)-1 end
        if omd == mod then omd = omd - 1 end
    end
    if omd ~= mod and omd > string.len(alpha) then omd = 1 end
    if omd < 1 and omd ~= mod then omd = string.len(alpha) end
    return getCh(r)..getCh(omd)
end

local function revRCh(pass, ch1, ch2, index)
    local i = index * 2
    while i > string.len(pass) or (string.len(pass) > string.len(alpha) and i > string.len(alpha)) do
        i = i - string.len(pass)
    end
    local mod = getRand(pass)
    local omod = getNum(ch2)
    local r = getNum(ch1)

    if omod ~= mod then
        r = r + string.len(alpha)
    end

    local n = r - mod

    local ch = getCh(n)
    return ch
end

local function gen(pass)
    local sp = 1
    for i=1,string.len(pass) do
        local ch = string.sub(pass, i, i)
        local num = getNum(ch)
        if num <= string.len(pass) then sp = num end
    end
    local key = ""
    for i=sp,string.len(pass) do
        local ch = string.sub(pass, i, i)
        local num = getRand(pass)
        num = num + sp
        local num2 = getNum(ch)
        num2 = num2 + sp

        key = key..getCh(num)..getCh(num2)
    end
    return key
end

local function enc(pass, str)
    local nstr = ""
    for i=1,string.len(str) do
        local ch = string.sub(str, i, i)
        local nch = getRCh(pass, ch, i)
        nstr = nstr..nch
    end
    return nstr
end

local function unenc(pass, str)
    local nstr = ""
    for i=1,string.len(str)/2 do
        local i1 = (i*2)-1
        local i2 = (i*2)

        local ch1 = string.sub(str, i1, i1)
        local ch2 = string.sub(str, i2, i2)

        local fch = revRCh(pass, ch1, ch2, i)
        nstr = nstr..fch
    end
    return nstr
end

local function unencfile(pass, lines, fname)
    if fs.exists(fname) then fs.delete(fname) end
    local file = fs.open(fname, "a")
    for i=2,#lines do
        local line = lines[i]
        local eline = unenc(pass, line)
        file.writeLine(eline)
    end
    file.close()
end

local function encfile(pass, lines, fname, key)
    if fs.exists(fname) then fs.delete(fname) end
    local file = fs.open(fname, "a")
    file.writeLine(key)
    for i=1,#lines do
        local line = lines[i]
        local eline = enc(pass, line)
        file.writeLine(eline)
    end
    file.close()
end


local function getInput()
    local input = read()
    while input == nil or input == "" do
        input = read
    end
    return input
end

print("Enter file directory:")
local fname = getInput()
print("Enter password:")
local pass = getInput()
print("Open/Close:")
local cmd = string.lower(getInput())

if fs.exists(fname) then
    local file = fs.open(fname, "r")
    local lines = {}
    local line = file.readLine()
    while line ~= nil do
        lines[#lines + 1] = line
        line = file.readLine()
    end
    file.close()

    local key = lines[1]
    local gkey = gen(pass)
    print(gkey)
    if cmd == "open" then
        if gkey == key then
            unencfile(pass, lines, fname)
        else
            print("Incorrect password!")
        end
    elseif cmd == "close" then
        encfile(pass, lines, fname, gkey)
    else
        print("Unkown command!")
    end
else
    print("Non existant file!")
end