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While implementing a generic POP3/SMTP Web-Interface (see a German language version at http://webmail.zf2.de) I thought about storing sensible user data (like passwords) over the session. After dropping my first idea to store that data on the server (which is possible but unwanted by our customers), I decided to store those passwords in the Cookie.

As it may be possible (in this case even most probably) that a user will use that interface from a foreign computer (maybe in an internet cafe) I needed to ensure that nobody else could read this information (from the cookie).

The final approach is:

Encrypt the password with any Crypt::CBC enabled encryption scheme.
Store the encrypted password in the Cookie together with a session id and other values (POP3 server et. al.)
Store the encryption key together with the session id on the server.
In short: the user get the cipher, we get the key.

I think this procedure is fine to ensure client security and some server security by not storing the password server-side. I know that the script itself knows the password, but I don't consider this too risky.

I would like to have some comments on this approach. Did I miss something? Did I oversize the problem? Please give me some feedback

alex pleiner <alex@zeitform.de>
zeitform Internet Dienste

use Crypt::CBC;
use CGI;
my $q = new CGI;
my $encryption_method = "Blowfish";

# get cookie
my ($login, $password, $pophost, $smtphost, $session) = getcookie();

## do something here such as fill template et. al.

# set cookie
my $cookie = setcookie($login, $password, $pophost, $smtphost, $sessio
+n);

print $q->header(-cookie=>$cookie, -expires => "now");
print $template->output;



############################################
sub setcookie {
############################################

  my $login    = shift;
  my $password = shift;
  my $pophost  = shift;
  my $smtphost = shift;

  my $session  = shift;

  my $key = $ENV{UNIQUE_ID};

  my $ciphertext;
  my $cipher = new Crypt::CBC($key, $encryption_method);
  $ciphertext = $cipher->encrypt($password);

  open ID, ">$Conf::tmp_dir/$session" or print_error("write_error");
  print ID $key;
  close ID;

  my $cookie = $q->cookie(
          -name    => "zf_webmail",
          -value   => {
                       pop3     => $pophost,
                       smtp     => $smtphost,
                       login    => $login,
                       password => $ciphertext,
                       id       => $session,
                      },
          -expires => '+10m');

  return $cookie;

}

###########################################
sub getcookie {
###########################################

  my %cookies = $q->cookie(-name => "zf_webmail");
  my $login = $cookies{login};

  unless ($login) { # no cookie -> no session

    # print error

  } else {

    my $ciphertext = $cookies{password} or print_error("no_cook_passwo
+rd");
    my $pophost    = $cookies{pop3}     or print_error("no_cook_pop3")
+;
    my $smtphost   = $cookies{smtp}     or print_error("no_cook_smtp")
+;
    my $session    = $cookies{id}       or print_error("no_cook_sessio
+n");

    my $password;
    open ID, "$Conf::tmp_dir/$session" or print_error("read_error");
    my $key = <ID>;
    close ID;

    my $cipher = new Crypt::CBC($key, $encryption_method);
    $password = $cipher->decrypt($ciphertext);
    return ($login, $password, $pophost, $smtphost, $session);
  }

}
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In reply to Encrypted Storage of sensible Data in a Cookie by projekt21

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