I need to present, for user, last 4 digits of credit card attached to our system (as skype does for example).
It should look like:

> 
> We will charge your card xxx-xxx-xxxx-1234
> 
> 
> 

For authorizing and charging CD we use some 'Payment Gateway'. Unfortunately they do not have any API which based on transaction number can return me that data. Is it legal to keep last 4 digits in my local DB, and is it ok according to PCI? 

Or maybe there is a difference way to do that.