The tough part here is figuring out how to have the software open the file, but ensure that the contents are in fact inaccessible without the smart card. In particular, securely handling the data after opening to ensure that the data can't be saved in an unencrypted form is fiendishly difficult, as every single DRM scheme to date has demonstrated....
3) Key management - more actual implementations manage to get this wrong than do the actual crypto wrong. You can do the crypto in a totally secure manner, but it's still total security manure suitable for fertilizing the flower garden if a keystroke logger can easily sniff the passphrase....
~Mike. _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.grok.org.uk/full-disclosure-charter.html Hosted and sponsored by Secunia - http://secunia.com/