Re: [PEN-TEST] IE Cookie Crypt-Analysis - Good or Bad

[Ryan Russell <ryan () SECURITYFOCUS COM>]

On Mon, 18 Dec 2000, Ruso, Anthony wrote:

>       What are common methods used in decrypting/encrypting cookies. Would
> many of you trust the use of cookies to store - lets say - passwords and
> personal information.

Only to the extent that I trust the machine I leave the cookies lying
around on.  Do I have the option to not use cookies?  Is this something
the user would normally want to protect (i.e. many users are not
interested in keeping their authentication information for porn sites
secret, but they want their bank login secret.)

> I'm trying to extract passwords from a clients website
> through the use of cookies. They used to store website passwords in clear
> text. I managed to convince them to encrypt them but how can I test their
> encryption choice and methods. My crypt-analysis experience is very basic.

Look at these items: Is the cookie the same size as the password?  Does
the size appear to be a function of the size of the password?  Does it
change each time it's set (i.e. is there salt?)  Does it work if you drag
it from machine to machine?  If you change IP addresses?  When does it
expire?

If it can be used as-is on a different machine, then it's just as good as
a plain-text password, and you've probably bought very little by getting
them to do this (warm fuzzies, really.)  it boils down to the fact that
there isn't a good way to store passwords on a client securely, short of
another password to protect those.

Probably the best you can do as a trade-off is see if there's a way to
encode something special about the client... dunno, perhaps browser
version and OS?  Make sure the cookies expire after a reasonably short
amount of time.. and make sure that the time info or a pointer to it at
the server is included in the cookie, crypted as well.

                                        Ryan