local function convert( chars, dist, inv )
    return string.char( ( string.byte( chars ) - 32 + ( inv and -dist or dist ) ) % 95 + 32 )
end
 
local function crypt(str,k,inv)
    local enc= "";
    for i=1,#str do
        if(#str-k[5] >= i or not inv)then
            for inc=0,3 do
                if(i%4 == inc)then
                    enc = enc .. convert(string.sub(str,i,i),k[inc+1],inv);
                    break;
                end
            end
        end
    end
    if(not inv)then
        for i=1,k[5] do
            enc = enc .. string.char(math.random(32,126));
        end
    end
    return enc;
end
 
local enc1 = {29, 58, 93, 28, 27};
local str = "This is an encrypted string.";
local crypted = crypt(str,enc1)
print("Encryption: " .. crypted);
print("Decryption: " .. crypt(crypted,enc1,true));
 
-- returns: 
-- Encryption: /f&1Zg0=<l<#Ia/7Kr""Zq10Dl$KT)8b>%*JbV>Z^Ik!p=B@'7cHMY<
-- Decryption: This is an encrypted string.