String encryption in GS3

[Gunderak]

My last attempts weren't very secure, so I thought of a new method.
Personally I think this is semi-secure, or at least harder to crack than my last method.
The only flaw of it, the key must be at least 10 in length and can't have any repeated characters.
From what I can tell, this method is called "hashing".

PHP Code:

//#GS3
function onCreated():void{
  var str:string = "abcdefghijklmnopqrstuvwxyz";
  var cat:string = this.Enc(str, "!:#$%^&*()");
  echo("Encrypted: "@cat);
  var dog:string = this.Dec(cat, "!:#$%^&*()");
  echo("Decrypted: "@dog);
}
function Enc(txt:string, key:string):string{
  var str:string = "";
  var i:number;
  var j:number;
  for(i = 0; i < txt.length(); i ++){
    var letter:string = txt.charat(i);
    var char:string = getascii(letter);
    char = (char.length()>2?char:0@char);
    var enc:string = "";
    for(j = 0; j < 3; j ++){
      var l:string = char.charat(j);
      var e:string = key.charat(l);
      enc @= e;
    }
    str @= enc;
  }
  return (str);
}
function Dec(txt:string, key:string):string{
  var txt:string = (txt);
  var str:string = "";
  var i:number;
  var j:number;
  for(i = 0; i < txt.length(); i += 3){
    var group:string = txt.substring(i, +3);
    var dec:string = "";
    for(j = 0; j < 3; j ++){
      var letter:string = group.charat(j);
      var num:number = key.pos(letter);
      dec @= num;
    }
    str @= char(dec);
  }
  return str;
} 


Encrypting the alphabet using this method produces the string:
!)*!)(!)):!!:!::!#:!$:!%:!^:!&:!*:!(:!)::!:::::#:: $::%::^::&::*::(::):#!:#::##
The last method, you could crack by trying 30 or so possible combinations, where as this one would require you to try a mass amount of combinations that you wouldn't want to have to go through and try and find the one that looks like something useful.
Also I think due to the maxlooplimit, the maximum length of the string would be 3,333.