Scramblepad Teardown Reveals Complicated, Expensive Innards

What’s a Scramblepad? It’s a type of number pad in which the numbers aren’t in fixed locations, and can only be seen from a narrow viewing angle. Every time the pad is activated, the buttons have different numbers. That way, a constant numerical code isn’t telegraphed by either button wear, or finger positions when punching it in. [Glen Akins] got his hands on one last year and figured out how to interface to it, and shared loads of nice photos and details about just how complicated this device was on the inside.

Just one of the many layers inside the Scramblepad.

Patented in 1982 and used for access control, a Scramblepad aimed to avoid the risk of someone inferring a code by watching a user punch it in, while also preventing information leakage via wear and tear on the keys themselves. They were designed to solve some specific issues, but as [Glen] points out, there are many good reasons they aren’t used today. Not only is their accessibility poor (they only worked at a certain height and viewing angle, and aren’t accessible to sight-impaired folks) but on top of that they are complex, expensive, and not vandal-proof.

[Glen]’s Scramblepad might be obsolete, but with its black build, sharp lines, and red LED 7-segment displays it has an undeniable style. It also includes an RFID reader, allowing it to act as a kind of two-factor access control.

On the inside, the reader is a hefty piece of hardware with multiple layers of PCBs and antennas. Despite all the electronics crammed into the Scramblepad, all by itself it doesn’t do much. A central controller is what actually controls door access, and the pad communicates to this board via an unencrypted, proprietary protocol. [Glen] went through the work of decoding this, and designed a simplified board that he plans to use for his own door access controller.

In the meantime, it’s a great peek inside a neat piece of hardware. You can see [Glen]’s Scramblepad in action in the short video embedded below.

28 thoughts on “Scramblepad Teardown Reveals Complicated, Expensive Innards

  1. Been doing work in a building for a few weeks that has one of these mounted in the elevator, it’s long-disused from the looks of it, but the nasa spaghetti logo font and menacing robocop corporate design is pretty striking. Nice to know what it’s called and that is has such interesting behavior!

    1. It’s a Hisrch ScramblePad (Hirsch is now Identive). Hirsch is an Access Control system. I have installed hundreds of these over the years. They are built like tanks. Short of vandalism, I have never seen one fail on its own or thru normal use.

  2. The only place I’ve seen one of these in the wild, vandalism wasn’t an issue. It was already inside a secure facility, this was just another layer on top of the armed guards and razor fence.

    1. Identiv is the original maker of these (well technically Hirsch but they merged with 2 other companies to form identiv). As much as I love hackaday it would be nice if some of the stories weren’t just summaries of whatever webpage they are linking to. A 5 minute google search would have let everyone know that this isn’t some bygone product but instead an old version of what is still being made.

    1. Looks like they used off-the-shelf 7-segment displays, which are almost always slightly slanted, but they wanted upright digits, so they rotated the units. The resulting digits are upright but they have slightly unlevel horizontal segments, which i guess is less noticeable behind the lenses.

  3. Interesting how they tilted the angled numbers towards vertical. Going back to the 70’s I always wondered at why seven segment numbers had to be slanted. How many tilted fonts do we have out of hundreds of perfectly fine straight normal fonts. Italics, one.

    Next Captcha tests for each digit. No robot entry.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.