<script type="text/javascript">  
  passGen({num:10, len:10});  
  </script>

<textarea col="4" id="inp" onfocus="this.select();"></textarea></br />  
  <script type="text/javascript">  
  passGen({id:'inp', num:10, len:10});  
  </script>

<div style="width:450px;background:#C4C64D;padding:5px;border:2px solid #579579;border-radius:5px;">
<textarea style="width:100%;height:150px;max-width:100%;" id="inp" onfocus="this.select();"></textarea></br />
<label><input type="checkbox" id="check" style="margin-top:5px;" />Символы</label>
<div style="float:right;background:#C9C44D;padding:0px 2px 0px 2px;">
<label>Длина: <input type="text" id="len" style="width:25px;height:20px;"value="10" /> </label>
<label>Количество: <input type="text" id="num" style="width:25px;height:20px;"value="10" /> </label>
<input type="button" value="Сгенерировать" onclick="runDemo()" />
</div>
<script type="text/javascript">
function runDemo () {
var _sym = document.getElementById('check').checked;
var _len = document.getElementById('len').value;
var _num = document.getElementById('num').value;
passGen({id:'inp', num:_num, len:_len, symbol: _sym})
}
function passGen (a) {
  var b = '1234567890qwertyuiopasdfghjklzxcvbnm';
  var c = [], d, e = '', k = 1;
  var f = '!@#$%^&*';
  if (a.symbol == true ) b += f;
  while (k <= a.num) { d = '';
  for (var i=0; i<a.len; i++) {
  c[0] = Math.floor(Math.random() * b.length);
  c[1] = Math.floor(Math.random() * 2);
  if (c[1] == 1) d += b[c[0]].toUpperCase(); else d += b[c[0]];
  } if (a.num == 1) e += d; else e += String(d + (a.id ? '\n' : '<br>'));
  k++;
  } if (a.id) {
  var id = document.getElementById(a.id);
  if (/text|textarea/g.test(id.type)) id.value = e;  
  } else return document.write(e);
}
</script>