Basic Lua Encryption

--[[
        Key Encryption/Decryption       PaymentOption
                                        26 November 2012
                                        Black Wolf Server

        This program employs a method of encrypting strings using
        an algorithm that will behave differently given a specific
        string, or key.

        In respect, the decryption of a string will yield different
        results depending on the key given.

        Key model: 10 letter alpha-numeric key generated randomly
                   by using a random number between 0 and 9 and a
                   random character between a and z.
]]--

-- Generates a random 10 character alpha-numeric key using a random
-- number between 0 and 9, and a random letter between a and z.
-- Params : nil
-- Returns: key - The key of type string that is generated.
function generateKey()
        -- Reseed the generator.
        math.randomseed(math.random(1, 100000000))

        -- Reseed the generator with the current time so the key generation
        -- should be even more difficult to recreate.
        local characters = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
                            'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
                            'u', 'v', 'w', 'x', 'y', 'z'
                           }
        local key = ""
        for index = 1, 5 do
                key = key .. math.random(0, 9) .. characters[math.random(1, 26)]
        end

        return key
end

-- Encrypts a given string based on the key given. Remember, the encryption
-- algorithm will behave differently based on what key is passed as a
-- parameter.
-- Params : text, key - The text to encrypt and the key to encrypt it with.
-- Returns: encryptedText - The text that will have been encrypted.
function encrypt(text, key)
        text = tostring(text)
        local encryptedText = ""
        local randomSeed = 0

        for index = 1, key:len() do
                if tonumber(key:sub(index, index)) then
                        randomSeed = randomSeed + tonumber(key:sub(index, index)) * index
                end
        end
        math.randomseed(randomSeed)

        local randomNumber = math.random(1, 20) * 5
        for index = 1, text:len() do
                encryptedText = encryptedText .. string.char(math.floor(text:byte(index) + randomNumber))
        end

        -- Reseed the generator.
        math.randomseed(math.random(1, 100000000))
        return encryptedText
end

-- Decrypts a given encrypted string based on the key given. The decryption
-- will vary depending on what key was passed as well, so the decryption
-- will rely on the fact that you have the correct key for decryption.
-- Params : text, key - The text to decrypt and the key to decrypt it with.
-- Returns: decryptedText - The text that will have been decrypted.
function decrypt(text, key)
        local text = tostring(text)
        local decryptedText = ""
        local randomSeed = 0

        for index = 1, key:len() do
                if tonumber(key:sub(index, index)) then
                        randomSeed = randomSeed + tonumber(key:sub(index, index)) * index
                end
        end
        math.randomseed(randomSeed)

        local randomNumber = math.random(1, 20) * 5
        for index = 1, text:len() do
                decryptedText = decryptedText .. string.char(text:byte(index) - randomNumber)
        end

        -- Reseed the generator.
        math.randomseed(math.random(1, 100000000))
        return decryptedText
end