Practical Public Key Cryptography

October 18, 2017 by 25 Comments

Encryption is one of the pillars of modern-day communications. You have devices that use encryption all the time, even if you are not aware of it. There are so many applications and systems using it that it’s hard to begin enumerating them. Ranging from satellite television to your mobile phone, from smart power meters to your car keys, from your wireless router to your browser, and from your Visa to your Bitcoins — the list is endless.

One of the great breakthroughs in the history of encryption was the invention of public key cryptography or asymmetrical cryptography in the 70’s. For centuries traditional cryptography methods were used, where some secret key or scheme had to be agreed and shared between the sender and the receiver of an encrypted message.

Asymmetric cryptography changed that. Today you can send an encrypted message to anyone. This is accomplished by the use of a pair of keys: one public key and one private key. The key properties are such that when something is encrypted with the public key, only the private key can decrypt it and vice-versa. In practice, this is usually implemented based on mathematical problems that admit no efficient solution like certain integer factorization, discrete logarithm and elliptic curve relationships.

But the game changer is that the public key doesn’t have to be kept secret. This allows cryptography to be used for authentication — proving who someone is — as well as for encryption, without requiring you to have previously exchanged secrets. In this article, I’ll get into the details of how to set yourself up so that anyone in the world is able to send you an e-mail that only you can read.
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Rescuing An Antique Saw Set

October 18, 2017 by 16 Comments

Who doesn’t like old tools? Even if they aren’t practical to use for production, plenty of old tools still have a life to offer the hobbyist or home worker.  Some tools might seem a bit too far gone – due to age, rust, or practicality, to use. That’s where [Hand Tool Rescue] comes in. [HTR] finds rusty, dirty old tools, and brings them back to life. Sometimes they’re practical tools, other times, they’re a bit out there. In a recent video, he restored a BeMaCo automatic saw set from the 1940’s. Saw sets are tools which bend each tooth of a saw blade slightly. Typically they are pliers-like devices.

The slight bend of each tooth on the blade widens the saw’s kerf and prevents binding. Typically these tools are pliers-like devices. The BeMaCo set is something else — it pulls the blade through tooth by tooth, while a spring-loaded head pecks away, bending each tooth. It’s something Rube Goldberg would have loved.

[HTR’s] filming style borrows a lot from [Jimmy DiResta], who we’ve covered here before. There are no words, and most of the video is sped up. Even with the fast video, [HTR] probably has many hours of footage to pare down to a 20-minute video.

The restoration begins with tearing the saw set apart. Every nut and bolt is removed. All the parts are cleaned, chemically de-rusted, and wire-wheeled. Even the motor is torn down, cleaned, and wired up. Then come the re-assembly. [HTR] gets every piece back in its proper place. We’re wondering how many times he had to refer to the teardown video to get everything right. Finally, the saw set is complete — ready for another 70 years of work.

Testing Brushless Motors With A Scope (or A Meter)

October 18, 2017 by 18 Comments

Brushless motors have a lot of advantages over traditional brushed motors. However, testing them can be a bit of a pain. Because the resistance of the motor’s coils is usually very low, a standard resistance check isn’t likely to be useful. Some people use LC meters, but those aren’t as common as a multimeter or oscilloscope. [Nils Rohwer] put out two videos — one two years ago and one recently — showing how to test a brushless motor with a multimeter or scope. Oh, you do need one other thing: a drill.

You don’t have to drill into the motor, instead you use the drill to spin the motor’s shaft. Since a motor and a generator are about the same thing, you can read the voltages produced by the spinning motor and determine if it is good or not. The first video shows the technique and the second, more recent video shows a scope reading a bad motor. You can see both videos, below.

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Control System Fundamentals By Video

October 17, 2017 by 17 Comments

If you’ve had the classic engineering education, you probably have a hazy recollection of someone talking about control theory. If you haven’t, you’ve probably at least heard of PID controllers and open loop vs closed loop control. If you don’t know about control theory or even if you just want a refresher, [Brian Douglas] has an excellent set of nearly 50 video lectures that will give you a great introduction to the topic. You can watch the first lecture, below.

You might think that control systems are only useful in electronics when you are trying to control a process like a chemical plant or a temperature. However, control theory shows up in a surprising number of places from filters to oscillators, to the automatic gain control in a receiver. You’ll find the background behind many familiar results inside control theory. Sort of like when you take calculus and you discover how they came up with all the formulas you memorized in geometry.

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Sacrificial Bridge Avoids 3D Printed Supports

October 17, 2017 by 25 Comments

[Tommy] shares a simple 3D printing design tip that will be self-evident to some, but a bit of a revelation to others: the concept of a sacrificial bridge to avoid awkward support structures. In the picture shown, the black 3D print has small bridges and each bridge has a hole. The purpose of these bits is to hold a hex nut captive in the area under the bridge; a bolt goes in through the round hole in the top.

Readers familiar with 3D printing will see right away that printing the bridges might be a problem. When a printer gets to the first layer of the bridge, it will be trying to lay filament in empty space. By itself this is not usually a problem as long as a bridge is short, flat, and featureless. Unfortunately this bridge has a hole in it, and that hole means the printer will be trying to draw circles in mid-air, rather than simply stretching filament point-to-point across a gap. One solution would be to add a small amount of support structure, but that just moves the problem. Removing small supports from enclosed spaces can be a real hassle.

To solve this [Tommy] added what he calls a “sacrificial bridge”, shown as blue in the CAD image. He essentially gives the hole a flat bottom, so that the printer first lays down a thin but solid bridge as a foundation. Then, the portion with the round hole is printed on top of that. With this small design change, the print becomes much more reliable with no support structure required.

There is a bit of post-work involved since each hole needs to be drilled out to punch through the thin sacrificial bridge underneath, but it definitely beats digging out little bits of support structure instead.

Click Your Heels Thrice, Hail A Cab Home

October 17, 2017 by 21 Comments

If Dorothy from The Wizard of Oz were to wake up in 2017, with her magic Ruby Slippers on her feet, she’d probably believe she had woken up in a magical world. But modern folks will need a little more magic to impress them. Like Clicking your heels thrice to get home with these Uber ruby slippers. [Hannah Joshua] was tasked by her employer to build a quirky maker project. She got an idea when a friend complained about having trouble hailing a cab at the end of a hard day at work.

[Hannah] started with ruby colored slippers with a platform toe and high heels to allow space to stuff in all the magic dust, err, electronic bits. The initial plan was to use an Arduino with a GSM/GPS shield but that would have needed a separate SIM card and data plan for the shoes. Instead, she opted for the 1Sheeld which connects to a smart phone over Bluetooth. The 1Sheeld gets access to all of the smart phone’s sensors including the GPS as well as the data connection. The Arduino and 1Sheeld are put in a cavity carved out in the toe section. The 9 V battery goes inside another cavity in the heel, where an activation switch is also installed. Three LED’s indicate when the shoe is active, the cab request is accepted, and when the cab is on its way.

The code is basic since this one of her first Arduino projects, but it gets the job done. It sends an http request to Uber’s API to request a cab. The destination is hard-coded, so the slippers only allow you to get from your current location to whatever destination is programmed. The GitHub repository provides code, as well as some additional information on construction. [Hannah] has also added notes explaining some of the design choices and things to take care about if you plan to build one of these magic slippers.

We covered the 1Sheeld when it was introduced several years back, and if you get your hands on one, try building this Hand Waving Door Unlocker.

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Spare RPi? You Have A Currency Trading Platform

October 17, 2017 by 29 Comments

While Bitcoin and other altcoins are all the rage these days, there is still a lot of activity in the traditional currency exchanges. Believe it or not, there’s money to be made there as well, although it rarely makes fanciful news stories like cryptocurrency has been. Traditional currency trading can be done similar to picking stocks, but if you’d rather automate your particular trading algorithm you can set up a Raspberry Pi to make money by trading money.

This particular project by [dmitry] trades currency on the Forex exchange using an already-existing currency trading software package called MetaTrader. This isn’t an ARM-compatible software suite though, so some auxiliary programs (Wine and ExaGear Desktop) need to be installed to get it working properly. From there, its easy enough to start trading in government-backed currency while reaping all of the low-power-usage benefits that the Pi offers.

[dmitry] does note that you can easily use MetaTrader on a standard laptop, but you might be tempted to go against your trading algorithms and even then you won’t be reaping the power benefits of the ARM processor. We don’t see too many traditional currency or stock trading tips around here, but don’t forget that it’s still possible to mine some types of cryptocurrency even if BitCoin is out of reach of most now.