Fortinet

The French Post Office now offers a new online Web service for end-users to print their own stamps, on their own printers.* Although I hate lining up for stamps at the post office, I just wonder if they really have thought it through.

The stamps are issued for a 60-day period, and they contain a small 2D barcode on the right proving their authenticity. This code probably contains a signature of the expiration date (of course) and the stamp’s value (otherwise a given authenticity code could be re-used on a stamp with a greater value). By the way, I hope the authenticity code’s signature does not use the MD5 hash function ;-). In addition, when you send your mail, the
code is scanned by the post office and memorized so it can only be used once (actually, this probably explains why the stamp is only valid for a period of 60 days). Ok, so the replay attack is detected. But what about other attacks ?

Fault Injection: what happens if an attacker intentionally prints the stamp on a poor-quality printer, ink dripping all over the 2D code ? The automatic scan process probably fails and it falls back to manual check. But how on earth
can we expect a human eye to tell the difference between an intentionally badly printed stamp and an end-user’s whose printer is just slightly dusty or old ? The French Post Office can’t expect users to own high quality laser
printers at home. As long as the fraud isn’t obvious, I bet the French Post Office will decide it costs less to accept a few cents stamp than work for hours on it trying to prove or not its validity.

Privacy: the French Post Office does not provide any detail on the content of the corresponding database. It is however likely to include private data: credit card information, account holder information… Is Big Brother watching
you and storing the names of all recipients you send mail to?

Infection: is it possible to get infected by a stamp ? 2D codes may be tied to additional information, such as URLs. The marketing idea behind this feature is to have the user read a 2D code with his/her mobile phone and automatically open the attached URL. I hope it is impossible to link 2D codes to malware or to URLs that contain malware, otherwise Fortinet is going to need to work on Forti…stamps very soon ;-)

– The Crypto Girl

* Side note: some employees of the French Post Office seem unaware of this service… and actually refused a perfectly authentic stamp, threatening to sue the sender.