Encryption / Decryption API

--[[
MDCrypt 1.0

MDCrypt is a simple and fast encryption/decryption API which allows data to be saved and transferred with an encryption key.

Copyright (C) 2012 MetaDark

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
]]--

local charSize = 255
local amplitude = charSize/math.pi
local frequency = math.pi/charSize*8

-- MetaDark Offset Algorithm 1 (Not complicated but very hard to crack) --
function MDOA1(x)
    return math.ceil(amplitude * math.sin(frequency * x) + (amplitude*(math.cos(x) % 9)))
end

-- Convert letters into numbers --
function stringToInt(input)
    if type(input) == "number" then
        return input
    elseif type(input) == "string" then
        output = 0
        for x = 1, #input do
            output = output + input:byte(x)
        end

        return output
    else
        return 0
    end
end

-- Encrypt String --
function encrypt(input, key)
    key = stringToInt(key)

    local output = ""
    for x = 1, #input do
        output = output .. string.char((input:byte(x) + MDOA1(x + key)) % charSize)
    end

    return output
end

-- Decrypt String --
function decrypt(input, key)
    key = stringToInt(key)

    local output = ""
    for x = 1, #input do
        output = output .. string.char((input:byte(x) - MDOA1(x + key)) % charSize)
    end

    return output
end