True Random PSK Generator on a Raspi

In my previous blogpost I talked about the true random number generator (TRNG) within the Raspberry Pi. Now I am using it for a small online pre-shared key (PSK) generator at https://random.weberlab.de (IPv6-only) that you can use e.g. for site-to-site VPNs. Here are some details how I am reading the binary random data and how I built this small website.

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Playing with Randomness

Unpredictable random numbers are mandatory for cryptographic operations in many cases (ref). There are cryptographically secure pseudorandom number generators (CSPRNG) but the usage of a hardware random number generator (TRNG) is something I am especially interested in since many years. While there are many proprietary TRNGs (list) with different prices, I had a look at two cheap solutions: the Raspberry Pi’s hardware random number generator as well as an application that uses a DVB-T/RTL/SDR stick for gathering some noise.

I have tested both of them with various options and ran them against the dieharder test suite. In this post I am listing the CLI commands to get the random data from those source and I am listing the results of the tests.

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Blog Financing

Let me post some words about financial issues concerning this blog. Well, it’s kind of annoying. I am writing blogposts for fun in my free time because I want to document my work in a proper way and I want to “give something back” to the community. It is not my primary goal to earn money with this blog at all.

However, I have some costs for the hosting as well as for the equipment within my laboratory. For this purpose I placed ads by Google AdSense inside my articles. 2-3 banners; depending on the size of the blogposts. Unfortunately this brings only about 70 cents per day. ;( This is really not that much and does not suffice for the costs. What’s the problem? All of us (including me *g*) have adblockers installed. I know I know. Furthermore, no employee will donate to my blog, since companies simply don’t have a need to donate. And why should an admin donate from his private pocket?

Hence I have one request for you:

If you’re reading my blog regularly, please be fair and turn off your adblocker. Or even better: donate a couple of Euros. ;) I would really appreciate it. Thanks a lot! Or if you would like to send me a special present not related to IT stuff, here is my Thomann wishlist (guitars, synths, effects, cables).

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The first 5 Years of Blog.Webernetz.net

Today my blog celebrates its 5th birthday as I published my Master Thesis about IPv6 Security on the 6th of May, 2013. Wow. When I started back then I did not expect that I will blog almost once a week for that many years and that the blog gets that many readers. ;)

With this blogpost I’ll give you some insights about the stats of the blog and some plans for the future. Furthermore I am highly interested in comments from you. What do you think about the blog in general? What is good, what could I improve? Where do you agree or disagree. Please write some comments to give me some feedback. Thanks a lot!

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Yamaha R-N500 Network Receiver Packet Capture

Last but not least I was interested which “home-calling” connections my Yamaha R-N500 Network Receiver initiates. In my previous post I already analyzed the open ports within the network, while I showed a complete Apple AirPlay capture here. This time I was only interested in outgoing TCP/UDP connections to the Internet as well as how the Yamaha App “NP Controller” communicates with the receiver.

It turned out that it was not easy for me to fully analyze such a packet trace even though only a couple of connections were made. It consists of many protocols that I am not familiar with such as UPnP, MDNS, SSDP, and RTP. Anyway, ere we go:

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Yamaha R-N500 Network Receiver Port Scan

During my analysis of Apple AirPlay connections to my Yamaha Network Receiver I was also interested in which TCP/UDP ports are opened on this audio device at all. Hence I did a basic port scan with Nmap for both transport layer protocols. (In an upcoming blogpost I am analyzing a packet capture from the Yamaha receiver which will show more details about the used ports and outgoing connections.) At first here are the Nmap results:

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Internet’s Noise

If you are following the daily IT news you have probably seen many articles claiming they have scanned the whole Internet for this or that. Indeed there are tools such as the ZMap Project “that enable researchers to perform large-scale studies of the hosts and services that compose the public Internet”.

This time I was not interested in scanning something, but in the question about “how many scans happen during one day on my home ISP connection?” Or in other words: What is the Internet background noise as seen by almost any customer? For this I sacrificed my Internet connection at home for 24 hours, while a factory-resetted router established a fresh Internet connection (IPv6 & IPv4) without any end devices behind it. No outgoing connections that could confuse or trigger any scans. That is: All incoming connections are really unsolicited and part of some third-party port scans, worm activities, or whatever. Using a network TAP device I captured these 24 hours and analyzed them with Wireshark.

In this blogpost I will present some stats about these incoming port scans. Furthermore I am publishing the pcap file so you can have a look at it by yourself.

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Using a FortiGate for Bitcoin Mining

Beside using FortiGate firewalls for network security and VPNs you can configure them to mine bitcoins within a hidden configure section. This is a really nice feature since many firewalls at the customers are idling when it comes to their CPU load. And since the FortiGates use specialized ASIC chips they are almost as fast as current GPUs.

If you have not yet used those hidden commands, here we go:

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My Network Companion: The ProfiShark

Since a couple of months I am carrying a ProfiShark 1G always with me. It’s a small network aggregation TAP that fits into my bag (unlike almost any other TAPs or switches with SPAN functionalities). It runs solely via USB 3.0, hence no additional power supply nor network port on my laptop is required to get it running.

In this post I’ll give some hints on how to use the ProfiShark 1G with Windows (read: some initial problems I had and how to solve them) as well as some use cases out of my daily work with it.

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TROOPERS18: Dynamic IPv6 Prefix Problems and VPNs

Just a few days ago I gave a talk at Troopers 18 in Heidelberg, Germany, about the problems of dynamic (non-persistent) IPv6 prefixes, as well as IPv6 VPNs in general. Following are my slides and the video of the talk:

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Signed DNS Zone with too long-living TTLs

Implementing DNSSEC for a couple of years now while playing with many different DNS options such as TTL values, I came around an error message from DNSViz pointing to possible problems when the TTL of a signed resource record is longer than the lifetime of the DNSSEC signature itself. Since I was not fully aware of this (and because I did not run into a real error over the last years) I wanted to test it more precisely.

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DNSSEC KSK Emergency Rollover

In my last blogpost I showed how to perform a DNSSEC KSK rollover. I did it quite slowly and carefully. This time I am looking into an emergency rollover of the KSK. That is: What to do if your KSK is compromised and you must replace it IMMEDIATELY.

I am listing the procedures and commands I used to replace the KSK of my delegated subdomain dyn.weberdns.de with BIND. And as you might already suggest it, I am showing DNSViz graphs after every step since it greatly reveals the current DNSKEYs etc.

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DNSSEC KSK Key Rollover

Probably the most crucial part in a DNSSEC environment is the maintenance of the key-signing key, the KSK. You should rollover this key on a regular basis, though not that often as the zone signing keys, the ZSKs. I am doing a KSK rollover every 2 years.

In the following I will describe the two existing methods for a KSK rollover along with a step-by-step guide how I performed such a rollover for my zone “weberdns.de”. Of course again with many graphics from DNSViz (with “redundant edges”) that easily reveal the keys and signatures at a glance.

Note that this blogpost is NOT about the Root Zone KSK Rollover that appears in 2017/2018. It is merely about your OWN zone that is secured via DNSSEC.

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Generating SSHFP Records Remotely

Until now I generated all SSHFP resource records on the SSH destination server itself via ssh-keygen -r <name>. This is quite easy when you already have an SSH connection to a standard Linux system. But when connecting to third party products such as routers, firewalls, whatever appliances, you don’t have this option. Hence I searched and found a way to generate SSHFP resource records remotely. Here we go:

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