function decrypt(email, nb, id) {

 var newemail = '', i, val, pre = 0;
 var taille = email.length/2;
 
 for(i=0; i < taille; i++) {
  pre = parseInt(email.substr(i*2,2),16)-(nb+pre);
  newemail = String.fromCharCode(pre) + newemail;
 }
 
 document.getElementById("i" + id).innerHTML = newemail;
}