To celebrate Cosmonautics Day on April 12th, the International Space Station began transmitting slow scan tv images related to the Interkosmos project from April 11th-14th, using a Kenwood TM-D710 transceiver located in the Russian ISS Service module which broadcasted on the frequency 145.800 MHz. I found out about this event from an amateur satellite radio organization called amsat; and with my new interest in radio image reception, I planned to attempt to make contact with the ISS and decode some of these images.

I purchased a Baofeng UV-5R handheld radio capable of receiving radio transmissions on the specified frequency (which my SDR / antenna combo from part 1 of “Selfies from Space” could also receive, but was more unwieldy to use), and used a Sony voice recorder to record the transmissions. I could then  play back and decode the transmissions with a program on my PC called mmstv, or an app on my phone called Robot36. While it is possible to decode the recorded transmissions in realtime, I preferred to record the transmission and then try different programs/settings to decode the recording. I also used a website called satview to look up times when the International Space Station would be overhead, as these intervals would be short in duration (around 6-8 minutes) and the transmission equipment on the ISS required a minute or two of rest time between sending images. This meant that I might have only captured part of one image and then the whole of another image, or the whole of one image then part of another one, depending on timing. Finally, I also struggled with radio interference, which resulted in some of the images I captured being fuzzy.

Below are some examples of images I decoded from the ISS during this radio event:

Finally, here is a video demonstrating decoding of one of these image transmissions using the App Robot36 on my phone (Note: you may want to turn your sound down if you are sensitive to certain noises).

I look forward to future events like this, and – if I set up a radio transmitter – maybe even getting the chance to talk to an astronaut!

Picture credits:

All photos provided and owned by Gary Dewey.

I’ve always been a space geek, interested in astronomy and cosmic travel.  Recently I’ve become obsessed with a new space-related hobby – downloading images of the Earth as signals from weather satellites! I call this hobby “selfies from space” because the images are created in real-time; if the images’ resolution were greater and you had the ability to zoom in sufficiently, then you could see me standing outside with my antenna capturing the images.

I first became interested in this hobby because I had purchased a $20 RTL-SDR (Software Defined Radio) on a whim many months ago, and decided to finally make some use of it. I did some research online and found that it was possible to capture satellite downlink data using my radio with an antenna tuned to receive the correct radio frequency. This means that the legs or poles of the antenna must have a specific length in order to resonate or vibrate at the desired radio frequency. The principle behind this resonance is similar to the phenomena of a tuning fork: when a vibrating tuning fork is placed near a stationary fork, the stationary fork begins to vibrate at the same frequency as the vibrating fork. A simple antenna design I found online which would work for this purpose is called a V-dipole antenna (https://www.rtl-sdr.com/simple-noaameteor-weather-satellite-antenna-137-mhz-v-dipole/).

This antenna is a half wavelength design, which means each pole is as long as the quarter wavelength of the desired frequency. If we take the speed of light (300,000,000 meters/sec) and divide by the desired frequency (137,000,000 hertz), we get 2.1898 meters as the wavelength and .54 meters / 54 centimeters as the quarter wavelength. I bought some aluminum rods at the local Home Depot and cut them to the quarter wavelength in the TCMS metal shop; I couldn’t find a “Choc block” at Home Depot to tie the rods together, but I did find some aluminum grounding bars which worked as an acceptable substitute. I then mounted the grounding bars to a 2″x4″ piece of wood with 120º angle between each bar, inserted the cut rods into the bars, and attached a stripped piece of 50Ω coaxial cable between the grounding bars and my radio.

Finished Antenna:

The software which I use to control the radio and record the signals is called SDR#. You can download SDR# here as one package, complete with many useful plugins; you will also need to install drivers for the radio, using the installation guide linked here.

Most of the weather satellites that are available in our geographic region are sun-synchronous or polar orbiting, which means that the satellites “pass by” our location from horizon to horizon. There are also some geosynchronous weather satellites (synced with Earth’s rotation to seem stationary), but most of these are located near the equator and are out of range of my antenna. There is a very limited time to download signals from sun-synchronous satellites, as they are moving very quickly and are very far away – about 8-15 minutes per pass, and at an altitude of 520 miles above sea level. Therefore, we need to be able to predict when satellites will pass by our location so that we can be prepared to capture data from them ahead of time. There are several websites with satellite time/location data, as well as a program called Orbitron which has a few other useful features, such as frequency correction for the Doppler effect caused by the satellites moving across the sky relative to me as I receive data from it.

I have used this antenna and radio to download images from the following satellites: NOAA-15 (@ 137.620 Mhz), NOAA-18 (@ 137.9125 Mhz),  NOAA-19 (@ 137.100 Mhz), and Russia’s Meteor M2 (@ 137.900 Mhz). The NOAA satellites use an AM (amplitude modulation)-based system called APT (Automated Picture Transmission) to encode its data transmissions. If you were to attach a speaker to my radio, you could hear beeping and clicking as the transmissions are received, similar to the way in which fax machines sound/work. APT data can be decoded with many programs, including APT decoder and WXtoIMG. These programs convert the APT data into line by line pictures, and also have various enhancement / filtering tools which can be used to manipulate or add additional data to the newly-generated APT photos, such as map overlays. These photos have 2 channels, one with an data from an infrared camera or filter, and another with data from a regular spectrum camera; they also contain telemetry data on the sides of each picture.

Here are a sampling of APT photos taken by the NOAA satellites whose transmissions I captured:

The Russian Meteor M2 satellite uses the LRPT (Low Rate Picture Transmission) method of data transmission. LRPT is modulated with something called quadrature phase shift keying (QPSK), which uses differences of phases in the carrier wave (0º, 90º, 180º, or 270º) in order to send 2 bits of data at a time. It can transmit photo data with higher resolution than can be accomplished with APT, but it also requires a larger frequency bandwidth and generates larger raw files. The signal doesn’t sound like anything intelligible, just a bunch of static. Nevertheless, when demodulated with a plugin for SDR#  (which generates a .s file) and then decoded with an LRPT offline decoder, a higher resolution photo is created – as seen in the photos below. You’ll note that I get images only of geographic locations that have radio contact with the satellite (realtime scanning), and that there appears to be some black lines from missing data; some these are from signal loss, but some are caused by transmitter malfunctions from the satellite.

The meteor M2 photos are from 3 channels which, when combined, create a color photo (red, green, blue); but during night time passes, only black and white photos can be rendered (probably due to the lack of sunlight).

This project has been a fun way for me to learn more about space, satellites, weather, and radio. I was given the opportunity to give a speech at Rutger’s University for their Space Technology Association at Rutgers Club, which can be viewed at  https://youtu.be/qZ1JNfDFjqo. At the end of the speech, I gave the club 2 antennas, 2 USB software-defined radios, and DVDs containing the software they’ll need to record and decode images on their own.

I’ve also started working on a related project: using a Raspberry Pi with an SDR, antenna, and some scripts to automate the data recording process so that I can capture and create satellite images while I’m at work or sleeping. I’m also researching methods of uploading the images to Twitter automatically – because capturing and creating images is cool, but doing that while getting sleep is awesome! ?

Picture credits:

All photos provided and owned by Gary Dewey, except for “Adam’s v-dipole.” Admin. RTL-SDR.com. 1 March 2017. Web. 18 April 2018.

Encryption has been a buzzword in the technical world for the past few decades; but in light of recent events, such as the San Bernardino terrorism case, encryption has become important to the average person as well. Encryption is a procedure for taking ordinary information (known as plaintext) and converting it into an unrecognizable format (known as ciphertext). The history of encryption can be traced back as far as Julius Caesar, who used a substitution cipher (as shown in picture 1, below). A cipher is a pair of algorithms used to encrypt and decrypt data, like an equation. In a substitution cipher, you substitute characters in your message with other characters using some sort of scheme. In this way, Caesar would send encrypted messages to his army. For example, let’s say the substitution key is 3, so each letter is shifted to the right by 3. Using this key, “hello reader” becomes “fcjjm pcybcp”.

As you may be able to tell, this cipher is vulnerable to an attack known as frequency analysis or pattern words. In this attack, the most frequent letters are tallied and matched up with the most frequently used letters in the alphabet; with enough pattern-matching, the substitution key can usually be derived.

Another classical cipher used was the transposition cipher, where the letters are rearranged somehow to jumble the plaintext. A modern example of this which you may know is “pig latin”, where you take the first syllable of a word and move it to the back to form a new word.

The Greek military is also thought to have used stenography, which is hiding a message in plain sight. They did this using something called a scytale: they would wrap a parchment around a wooden rod, write their message on the parchment, then unwrap the parchment and add letters in between those already written (see picture 2, below). Only someone with an identical wooden rod would be able to decipher the message. Another example of early stenography was tattooing a message on a slave’s shaved head and waiting for the hair to grow back to cover up the message.

Stenographic methods have become increasingly complex over the past couple of millennia, with forms like invisible ink, microdots, and hiding information in the compressed space of music files (as seen in the tv show Mr. Robot) becoming popular. Another common method is to store your secret information in a photo file, since these files are also compressed and do not require all the bits to recreate the photo.

These methods of concealing information for secure communications are apart of a larger family of study called cryptography, which in Greek translates to hidden or secret writing. A fairly famous example of cryptography is the Enigma device, used by the German military during WWII to send secret messages. The large computer systems developed to help crack the Enigma code helped usher in the modern age of computers. Fast forward to today, and cryptography is used every day by ordinary people, not just spies and military personnel. Online banking and credit card transactions, email, electronic voting, anonymous web surfing, regular web surfing and social media are all areas where modern cryptography is used without many people ever realizing it.

In the information security world, there is a principle known as the C.I.A. triad, which stands for Confidentiality, Integrity, and Availability. Confidentiality is the ability to keep your information safe and secure from unauthorized entities, which can be equated with privacy. Integrity deals with the consistency, accuracy, and confidentiality of your data. Availability is just what it sounds like: having your data or services available to you and whoever else needs access at all times.  Cryptography can aid in confidentiality and integrity. As we have discussed earlier, encryption supports confidentiality by ensuring your message/data is not readable by an unauthorized party. Integrity is supported by using various cryptographic algorithms to ensure data has not been tampered with or altered; i.e., the original data is put through an equation to derive an ‘answer’, which you receive a copy of. If you then receive a copy of the data, put it through the same equation, and receive a different ‘answer’, your integrity check fails. These checks are sometimes known as hashes, of which there are various types depending on the algorithm used. They are used in a wide variety of applications, e.g. proving the integrity (lack of tampering or file corruption) of files downloaded from the Internet by checking them against their authenticated hashes or checksums.

Modern cryptography for confidentiality can be divided into two categories: symmetric key cryptography and public key cryptography. Symmetric key cryptography uses the same password or passcode to encrypt and to decrypt the data. This can be a security concern because of low confidence regarding secure sharing of the password. It may be a decent algorithm / scheme to use to encrypt data for your own use, which is what most full-disk or file system encryption systems use, but it’s not recommended for use when sharing data among multiple users. This scheme may be used to encrypt multiple kinds of devices: laptop hard drives, phones, tablets, flash/thumb drives, individual files, and so on.

The preferred method used to encrypt data shared among multiple users is public key encryption, which uses two different keys: a public key and a private key. The public key is just that, public; it’s the key you give to any other user, and can be publicly known. The private key is also just that, private, and is related to the public key in a way such that it can decrypt something encrypted with the public key. Anyone can encrypt a message for you using your public key, which you can then decrypt with your private key, which nobody should know except for you. Public keys can be also digitally signed by other users with their private keys, which means the people that have signed the key have verified the key owner’s identity. This creates a web of trust. Let’s say Don trusts/knows Bob but not Alice; since Bob trusts/knows Alice, Don inherently trusts Alice’s key/identity due to his trust of Bob.

A good example of a public key encryption system is GPG (GNU Privacy Guard), a free replacement for PGP (Pretty Good Privacy), as PGP used to be free but was bought by Symantec. GPG public key encryption can be used to encrypt email messages and files, and also has some built in features for integrity (verification of user identity). For example, let’s say Alice wants to email Bob a secure message. Alice could look up Bob’s public key from a public key server, or get it directly from Bob and use it to encrypt her email to Bob. She then digitally signs her message using her private key. When Bob receives the email, he decrypts the message using his private key, and verifies her digital signature using Alice’s public key.

Thank you for joining me for a brief history and overview of cryptography and encryption! Stay tuned for future blog posts where I hope you will join me as we explore cryptography and encryption in more detail. You will learn how to better protect yourself and your data in today’s computer age.

Text References and Resources:

“Cryptography: History of cryptography and cryptanalysis.” Wikipedia.org. Wikipedia, 25 July 2016. Web. 1 Sept. 2016.

“GNU Privacy Guard.” Wikipedia.org. Wikipedia, 15 Aug. 2016. Web. 1 Sept. 2016.

“Outline of cryptography.” Wikipedia.org. Wikipedia, 21 July 2016. Web. 1 Sept. 2016.

Picture References:

Skytala. Digital Image. Wikimedia Commons. Wikimedia Commons. 16 Feb. 2007. Web. 1 Sept. 2016.

Resources:

The Electronic Frontier Foundation, https://www.eff.org.