Re: Vuln in Verisign PayFlow Link payment service

[Doru Petrescu <pdoru () kappa ro>]

> Perhaps a fix for VeriSign would be to passback a secret code (configurable
> through the PayFlow Link admin panel) that does not originate from a cart
> input value, but is stored and sent from PayFlow. Then a simple 'if'
> statement in the cart software could weed out the bad along with an e-mail
> sent to the admin. That would surely slow someone down if they have to guess
> the secret code's input value.


THIS IS WRONG!!!

the "secret code" can be hijacked as well if you can afford to make a
valid payment FIRST. That will require a valid creditcard something that I
don't have so will reduce a little the nr of people that can attempt to
crackin.

The SAFE WAY is to have a SECRET PASSPHRASE shared between you and
VeriSign and use it to ENCODE THE DATA or at least to SIGN THEM.

You can use a simetric encoding scheme or a generate a MD5 signature that
can be used to verify that the response came from verisign and not someone
else. also some random data need to be inserted (like the current
timestamp cancat with a random 10 digits number) to shield from "reply"
attacks that reuse the same signature.

YES this will require some basic crypto functions to be included in the
libs they supply, but since this is pure math it is system independent, so
it should not introduce any problemes.


just my 2c ...

A HAPPY NEW YEAR TO ALL OF YOU,
------
Doru Petrescu
KappaNet - Senior Software Engineer
E-mail: pdoru () kappa ro                LINUX - the choice of the GNU generation