Schneier on Security

Steven Murdoch • August 30, 2005 2:01 PM

"Interestingly, they can see through scratch-here type protections too. I wonder if the same thing applies to national lottery scratch cards or not..."

The mailers we looked at all worked on a similar principle: you print on the top of transparent plastic and have a "scrambling pattern" on the other side. Then to reveal the PIN, you remove the plastic from the scrambling pattern, either by scratching it off or peeling the two apart. Even though you can still see the toner which makes up the PIN, the idea is that the scrambling pattern will make it hard to read. This system has the advantage of being one-pass and needing only a standard laser printer. However, you can attack them by using some, non-intrusive method to visually separate the toner from the scrambling pattern, for example angled light or image processing.

Lottery scratch-cards generally have the scratch off coating put over the top of the printed message, rather than on the other side, requiring two passes and special machinery at the printing site. This means you have to see through it, instead of just needing to separate two layers which you can both see. So I don't think the techniques mentioned in the report will work.

However, discussion of this report did trigger someone to describe a fairly high-tech, but feasible technique for reading lottery scratch-cards: http://www.mail-archive.com/...

Steven Murdoch • August 30, 2005 2:13 PM

"One peripheral comment I would make on this subject - it's far safer for someone to have their cards / cheque book / pin number sent to their local bank branch rather than their home address."

Indeed, and I know of some banks who do this, particularly in the US and continental Europe. However in the UK, I don't know of any banks who do this as standard. Though banks in the UK sometimes require customers to pick their cards/PIN up from the bank, because the customer lives in an area where there is an unusually high rate of mail non-receipt fraud, generally believed to happen in the local mail sorting office.

Steven Murdoch • August 30, 2005 8:20 PM

"This didn't (to my knowledge) happen with the older style PIN mailers which contained some sort of carbon-paper analogue, imprinted upon by a dot-matrix or line printer. However, I understand those mailers cost over $1 each, so it's clear that finding savings was big business."

We also found similar techniques effective at reading these types of mailer (multipart stationary) and a similar technology where the PIN is printed and the sheet is folded over and glued closed (pressure sealed). These aren't mentioned in the report since the techniques to read these are well known and their use in the UK declining.

The cost of the raw stationary isn't the only factor (although I don't know about the relative costs), there is also the printing costs. Laser-printed PIN mailers need only a laser printer, which the banks already have, whereas the other technologies require printers dedicated to this task.

Also, I think there are significant security considerations, in addition to the tamper evidence. For example, multipart stationary and pressure seal mailers look very different from normal bank mail, so a criminal could easily pick these out. Whereas the laser-printed PIN mailers just look like ordinary letters from the outside.

Another problem is that with multipart/pressure sealed mailers, they are not secure out of the printer, either a sheet has to be torn off or the letter sealed. This means someone with access to the intermediate stage could read the PINs. With the laser-printed PIN mailers, there is no second step.