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Basic methods of Audio Steganography (spectrograms)

Couple days ago, a video, ad hoc named 11B-X-1371, containing some hidden puzzles, went viral. See original source or Reddit thread for more information on that. Most of these puzzles aren’t very sophisticated (some seems to be), but never mind. Some of them were hidden within an audio track and that’s pretty neat. It could be done better though. And it’s something I’d like to cover here.

45kB RAM? I can be a server too!

About two weeks ago, with a help of Reddit and Hacker News users, we tested if ESP8266 chip is capable of serving webpages for the outside world. And pretty much it was. See

DS18B20 in two-wire mode on Raspberry Pi

Since recently Raspberry Pi used Device Tree for deciding which kernel modules should be loaded. This makes most instructables on the Internet outdated.

I wanted to connect DS18B20 thermometer using only two wires. This circut use 1-wire protocol to communicate, so it has to be connected with three lines for normal operation: VCC, GND and DATA.

Geovision camera streaming to Linux machine via RTSP

For a while, I used an ftp connection to download videos from my geovision camera (model GV-MFD520, I use it for home surveillance). But due to often power outages in place where I live, I had constantly repeating problems with the sd card which was used as an intermediary between camera and linux-powered station. It made me to look for other solutions. I switched to RTSP protocol and now it works flawless.

Own DDNS service powered by Digital Ocean

Although Digital Ocean provide its own DNS servers, it’s possible to set a simple DDNS, since they provide a handy api for domain settings manipulation. I’ve written a small script that has to be installed on every machine, which IP we want to track. Remember to modify token, domain_name and record_name variables.

Compiling Postfix with PostgreSQL support on Centos 7

I finally decided to move my server to Centos 7. One of the most important services that I hosted was my mail server based on Postfix and Dovecot. I also decided to migrate from MySQL to PostgreSQL, which finally proved to be not so easy. This is because Postfix in Centos 7 repositories is being provided without Postgres support. So I needed to compile one on my own. This tutorial is based on Centos 7 that is being installed on Digital Ocean droplets.

Secure semi-automatic Postfix config

Setting Postfix isn’t especially hard, but for sure is tedious. To make this process less inconvinient, I created a simple shell script for Debian 7 that takes care of basic system configuration. After some minor changes it should be usable for other Linux distributions.

That configuration supports most secure solutions: SMTPS with STARTTLS on port 587 and SSL secured IMAP on port 993. I also decided to use PostgreSQL instead of MySQL which is used in most configurations you can find on the Internet. So this is virtual mail system based on Dovecot, managed by Postfix Admin, with web frontend Roundcube.