Polarized Screens to Hide Sensitive Data

NiugMan writes "NewScientist.com reports that Iizuka Denki Kogyo, a Tokio-based tech company has developed a monitor which appears to be blank if you stare at it with your eyes. Only by wearing a pair of polarised glasses you see stuff on it. The idea is to protect sensitive data from unauthorised personnel. Please take your special glasses with you when you take a coffee-break."

Comments

Effective ? Nah

[XPulga]

First, if you're leaving for a coffee break, you should lock your terminal, which will prevent others from seeing your screen contents while you're out anyway.

Second, how many different polarizations are there ? Last time I studied optics, one pair of glasses will work on any of these monitors (maybe needing some rotation/tilting). Unless you can assure polarizing glasses will always be bright red so you recognize "people with bright red glasses coming near my computer", and you can't assure that - it's quite easy to make polarizing lenses - the protection is senseless.

I can hardly wait until some company buys monitors and glasses to all their employees and then put several monitors in the same room, all people with polarizing glasses, making the whole buy futile. (Hmm, ok, will prevent the floor sweeper from reading your screen. Great.)

Laptops on airplanes...

[ClayJar]

I read about this a long, long time ago (I can't remember when, but it is on the order of years). It was a mod that a company was selling for business people's laptops. They'd strip off the polarizing film from the laptop's LCD panel, and then you could only see what was on the screen through polarizing glasses.

I'm not sure whether the glasses required were vertically polarized of horizontally polarized. If they were vertically polarized, anyone with a pair of sunglasses could quite easily read the screen (but wouldn't you look odd wearing sunglasses on a plane while staring at a business person's apparently blank laptop screen).

On the other hand, if the required glasses were horizontally polarized, you'd have to rotate the sunglass lenses 90 degrees (which, since most sunglass lenses do not posess rotational symmetry, would mean you either would have a serious mod coming, or else you'd just have to tip your head 90 degrees... Actually, this might just work, but only if you were pretending to sleep and laying your head on the business person's shoulder, and that's likely to just make them upset. ;)

Only one kind works.

[Ungrounded Lightning]

Second, how many different polarizations are there?

There are more kinds, circular for example. It means the electric field is rotating, either clockwise or counterclockwise.

But that won't work for screens. The liquid crystal will ROTATE a LINEAR polarization but won't reverse a circular polarization. The screen starts with a light source, linear-polarizes it, selectively rotates the polarization, then linear-polarizes again. Depending on the amount of rotation you get more or less light.

This ancient hack consists of taking the final linear polarizer off the front of the screen and wearing it as a pair of glasses. The screen now emits a constant-brightness, varying-LINEAR-polarization light, which isn't translated into variable intensity until it hits the polarized glasses.

But that means that if you get the polarization right you get the image, if you're off by 90 degrees you get a negative image, and at other angles you get an image that has an intended-versus-perceived intensity graph something like a check-mark. Unless you happen to be at the angle where the letters and the background match exactly it's still readable, and if you're at exactly that wrong angle just tilt your head a LITTLE bit and they reappear.

So stock polarizing sunglasses read all these screens, no problem.

If you could come up with a final filter for the screen that converted, say, the vertical component of linearly-polarized light into right-circular and the horizontal into left-circular, you could then use circularly polarized glasses and defeat linearly-polarized. But I don't know of any physical mechanism (let alone one that could be turned into a cheap thin film) that would do this, even for monochrome, let alone the near-octave of light used by color displays or the full-octave for black-and-white.

Even if you DID come up with a circularly-polarized hack you'd only have TWO possibilities for the glasses - and viewing the display with the wrong one would just give you a negative, but readable, image.