API: encrypt

-- I, didn't create the api so I don't take any merit for it. I post it because I use it in my programms I think it is extremely well written.
local function enc(str, key)
    if not key then return false end
    local f = ""
    local kb = {}
    for i = 1, #key do
        kb[i] = string.byte(key:sub(i,i)) - 31
    end
    local c = 1
    for i = 1, #str do
        local t1 = string.byte(str:sub(i,i))
        if t1 == 10 then
            f = f .. string.char(10)
        else
            local t2 = t1 + kb[c]
            if t2 > 126 then
                local t3 = t2 - 126
                t2 = 31 + t3
            end
        f = f .. string.char(t2)
        end
        c = c + 1
        if c > #key then
            c = 1
        end
    end
    return f
end

local function dec(str, key)
    if not key then return false end
    local f = ""
    local kb = {}
    for i = 1, #key do
        kb[i] = string.byte(key:sub(i,i)) - 31
    end
    local c = 1
    for i = 1, #str do
        local t2 = string.byte(str:sub(i,i)) - 31
        if t2 == -21 then
            f = f .. string.char(10)
        else
            local t3 = t2 - kb[c] + 31
            if t3 < 32 then
                t3 = t3 + 126 - 31
            end
            if t3 < 32 then return false, t3 end
            if t3 > 126 then return false, t3 end
            f = f .. string.char(t3)
        end
        c = c + 1
        if c > #key then
            c = 1
        end
    end
    return f
end

function encrypt(str, key)
    if not key then return false end
    if #key < 3 then return false end
    local f = str
    key = key .. key .. "#me1"
    for i = 0, #key - 1 do
        f = enc(f, key:sub(i,i + 1))
    end
    f = enc(f, key:sub(1,2) .. key:sub(#key - 1, #key) .. enc(key, key .. key))
    return f
end

function decrypt(str, key)
    if not key then return false end
    if #key < 3 then return false end
    local f = str
    key = key .. key .. "#me1"
    for i = 0, #key - 1 do
        f = dec(f, key:sub(i,i + 1))
    end
    f = dec(f, key:sub(1,2) .. key:sub(#key - 1, #key) .. enc(key, key .. key))
    return f
end