[Hidden-tech] Shopping cart security

[Robert Heller]

At Thu, 21 Feb 2008 07:10:00 -0500 Peter Hutchins <peter at litmusdesigns.com> wrote:

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> 
> I'd like to run a development concept past the security minded folks  
> out there for some critical feedback:
> 
> I'm setting up a shopping cart for a client who wants to process  
> credit card purchases "offline", i.e.: run the transaction through  
> their credit card terminal as though it were a phone order without a  
> web-based payment gateway or merchant account. This obviously requires  
> collecting and storing critical credit card data until the store owner  
> processes the transaction, at which point the critical data can be  
> deleted.
> 
> Here's my proposed solution for securely handling the data:
> 1. CC info is gathered in a SSL encrypted form
> 2. expiration data and ccv are written to a database and encrypted via  
> mysql's AES_ENCRYPT() (this DB is separate from the regular store DB  
> providing separate password protection, in case the first DB is  
> compromised)
> 3. credit card number is split into two parts, with one half being  
> encrypted and written to the database with the transaction above
> 4. the other half of the credit card number is written to a file that  
> is encrypted with GnuPG and emailed to the store owner (protecting it  
> with a Private/Public key and passphrase).
> 5. when the store owner gets the email, he logs into the store admin,  
> views the online credit card info, processes the order and deletes the  
> online data from the database and the email from his inbox.
> 
> - One issue I see is that the database login and encryption key for  
> that half of the process must be stored on the server, rendering it  
> vulnerable to compromise, but the other half of the CC info is still  
> protected.
> 
> So, my questions are:
> - Is this secure "enough"?

I'm not sure -- probably not.  The entire CC number should be encrypted
and none of it sent via E-Mail (even using encryption) -- the E-Mail
should just notify that a transaction has occurred and needs attending
to.  Anything stored on your server can be compromised, unless you
spend essentially a full time effort to protect it. 

The database login should also use SSL (or use SSH).  The passphrase
should not be stored on the server in any form -- if anything, just a
one-way cypher should be used.

> - Is there a better way?

Your client should just 'upgrade' his/her CC processing to include a
direct on-line CC processing system.  Is there some reason NOT to do
this? There are basically two main options (both are secure): 

1) Your client collects the CC info (using a SSL connection) and connects
to the CC processing service (also with https (SSL)).  Your client's web
server discards the original CC info and only stores the transaction id
returned by the CC processing service.

2) The 'go to checkout' button re-directs to the CC processing
service's SSL web site, passing the shopping cart as a pile of 'hidden'
CGI variables (along with things like client id and so on).  Your
client's shopping cart software (CGI/PHP script) never sees any
sensitive info -- the CC info is collected by the CC processing
service.  Again your client just has a transaction code.

Essentially, the cost in time/effort to protect the CC info, might exceed
the 'cost' of going to an on-line CC processing service.  PayPal
provides such services -- no monthly fees and a fairly modest fee for
each transaction. And no, your client's customers don't need a PayPal
account to make a purchase.

> 
> Thanks!
> -Peter Hutchins
> 
> 
> : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :
> Peter Hutchins
> Litmus Designs
> 505 S. Albany St.
> Ithaca, NY 14850
> 413.582.7038 voice
> 413.517.0596 fax
> www.litmusdesigns.com
> 
> web design, custom programming & graphic design
> : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :
> 
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Robert Heller             -- Get the Deepwoods Software FireFox Toolbar!
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