2FA SSH aka OpenSSH OATH, Two-Factor Authentication

prologue

Good security is based on layers of protection. At some point the usability gets in the way. My thread model on accessing systems is to create a different ssh pair of keys (private/public) and only use them instead of a login password. I try to keep my digital assets separated and not all of them under the same basket. My laptop is encrypted and I dont run any services on it, but even then a bad actor can always find a way.

Back in the days, I was looking on Barada/Gort. Barada is an implementation of HOTP: An HMAC-Based One-Time Password Algorithm and Gort is the android app you can install to your mobile and connect to barada. Both of these application have not been updated since 2013/2014 and Gort is even removed from f-droid!

Talking with friends on our upcoming trip to 34C4, discussing some...

How to install Signal dekstop to archlinux

Download Signal Desktop

eg. latest version v1.0.41

$ curl -s https://updates.signal.org/desktop/apt/pool/main/s/signal-desktop/signal-desktop_1.0.41_amd64.deb \
    -o /tmp/signal-desktop_1.0.41_amd64.deb

Verify Package

There is a way to manually verify the integrity of the package, by checking the hash value of the file against a gpg signed file. To do that we need to add a few extra steps in our procedure.

Download Key from the repository

$ wget -c https://updates.signal.org/desktop/apt/keys.asc

--2017-12-

Autonomous by Annalee Newitz

The year is 2144. A group of anti-patent scientists are working to reverse engineer drugs in free labs, for (poor) people to have access to them. Agents of International Property Coalition are trying to find the lead pirate-scientist and stop any patent violation by any means necessary. In this era, without a franchise (citizenship) autonomous robots and people are slaves. But only a few of the bots have are autonomous. Even then, can they be free ? Can androids choose their own gender identity ? Transhumanism and extension life drugs are helping people to live a longer and better life.

A science fiction novel without Digital Rights Management (DRM).

Fighting Spam

Fighting email spam in modern times most of the times looks like this:

Rspamd

Rspamd is a rapid spam filtering system. Written in C with Lua script engine extension seems to be really fast and a really good solution for SOHO environments.

In this blog post, I'’ll try to present you a quickstart guide on working with rspamd on a CentOS 6.9 machine running postfix.

DISCLAIMER: This blog post is from a very technical point of view!

Installation

We are going to install rspamd via know rpm repositories:

Epel Repository

...

Walkaway by Cory Doctorow

Are you willing to walk-away without anything in the world to build a better world ?

In many companies, nagios is the de-facto monitoring tool. Even with new modern alternatives solutions, this opensource project, still, has a large amount of implementations in place. This guide is based on a “clean/fresh” CentOS 6.9 virtual machine.

Epel

An official nagios repository exist in this address: https://repo.nagios.com/
I prefer to install nagios via the EPEL repository:

# yum -y install http://fedora-mirror01.rbc.ru/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm

# yum info nagios | grep Version
Version   ...

SCAM

Τον τελευταίο καιρό, όλο και περισσότερα email με το παρακάτω (ή παρόμοιο) body φτάνουν στο mailbox μου.
Οι περισσότεροι από εσάς, εύκολα θα διαπιστώσετε πως το παρακάτω είναι google translate, άλλοι πάλι όχι με μια πρώτη ματιά.

Be careful

Είναι, λοιπόν, ένα SCAM email, που προσπαθεί να σας ψαρέψει τα στοιχεία.

Π Ο Τ Ε καμία εταιρεία (πάροχος ή τράπεζα) δεν πρόκειται να σας ζητήσει μέσω email τα στοιχεία σας.

για αυτό Μ Η Ν απαντάτε ΠΟΤΕ σε emails της παρακάτω μορφής.

Actions

Το καλύτερο που έχετε να κάνετε, είναι να προωθήσετε ΑΜΕΣΩΣ το παρακάτω email στο abuse department της εταιρείας σας.

Μπορείτε να βοηθήσετε στην καταπολέμηση της εξάπλωσης αυτού του scam.

Abuse

Τα εκάστοτε abuse departments έχουν εργαλεία που καταγράφουν αυτές τις απόπειρες “ψαρέματος” κι εντοπίζουν τα μολυσμένα PC ή compromised ac...

Let’s Encrypt

I’ve written some posts on Let’s Encrypt but the most frequently question is how to auto renew a certificate every 90 days.

Disclaimer

This is my mini how-to, on centos 6 with a custom compiled Python 2.7.13 that I like to run on virtualenv from latest git updated certbot. Not a copy/paste solution for everyone!

Cron

Cron doesnt not seem to have something useful to use on comparison to 90 days:

Modification Time

The most obvious answer is to look on the modification time on lets encrypt directory :

eg. domain: balaskas.gr

To see the entire article, click uppon article's title/link. 
Thank you.

How to install slack dekstop to archlinux

Download Slack Desktop

eg. latest version

https://downloads.slack-edge.com/linux_releases/slack-2.6.3-0.1.fc21.x86_64.rpm

Extract under root filesystem

# cd /

# rpmextract.sh slack-2.6.3-0.1.fc21.x86_64.rpm

Done

Actually, that’s it!

Run

Run slack-desktop as a regular user:

$ /usr/lib/slack/slack

Slack Desktop

Proxy

Define your proxy settings on your environment:

declare -x ftp_proxy="proxy.example.org:8080"
declare -x http_proxy="proxy.example.org:8080"
declare -x https_proxy="proxy.example.org:8080"

Slack

Iterator

a few months ago, I wrote an article on RecursiveDirectoryIterator, you can find the article here: PHP Recursive Directory File Listing . If you run the code example, you ‘ll see that the output is not sorted.

Object

Recursive Iterator is actually an object, a special object that we can perform iterations on sequence (collection) of data. So it is a little difficult to sort them using known php functions. Let me give you an example:

$Iterator = new RecursiveDirectoryIterator('./');
foreach ($Iterator as $file)
    var_dump($file);

object(SplFileInfo)

Prologue

Part of my day job is to protect a large mail infrastructure. That means that on a daily basis we are fighting SPAM and try to protect our customers for any suspicious/malicious mail traffic. This is not an easy job. Actually globally is not a easy job. But we are trying and trying hard.

ReplyTo

The last couple months, I have started a project on gitlab gathering the malicious ReplyTo from already identified spam emails. I was looking for a pattern or something that I can feed our antispam engines with so that we can identify spam more accurately. It’s doesnt seem to work as i thought. Spammers can alter their ReplyTo in a matter of minutes!

TheList

Here is the list for the last couple months: ReplyTo
I will -from time to time- try to update it and hopefully someone can find ...

Prologue

I should have written this post like a decade ago, but laziness got the better of me.

I use TLS with IMAP and SMTP mail server. That means I encrypt the connection by protocol against the mail server and not by port (ssl Vs tls). Although I do not accept any authentication before STARTTLS command is being provided (that means no cleartext passwords in authentication), I was leaving the PLAIN TEXT authentication mechanism in the configuration. That’s not an actual problem unless you are already on the server and you are trying to connect on localhost but I can do better.

LDAP

I use OpenLDAP as my backend authentication database. Before all, the ldap attribute password must be changed from cleartext to To see the entire article, click uppon article's title/link.
Thank you.

This is my basic home setup for a nice cup of coffee:

You can find my posts regarding coffee here: coffee

I’ve tried to clean up my graef coffee grinder with a small cup of instant rice.
and the results are pretty good:

(click on images for more detail)

When traveling, I make an effort to visit the local hackerspace. I understand that this is not normal behavior for many people, but for us (free / opensource advocates) is always a must.

This was my 4th week on Bratislava and for the first time, I had a couple free hours to visit ProgressBar HackerSpace.

For now, they are allocated in the middle of the historical city on the 2nd floor. The entrance is on a covered walkway (gallery) between two buildings. There is a bell to ring and automated (when members are already inside) the door is wide open for any visitor. No need to wait or explain why you are there!

Entering ProgressBar there is no doubt that you are entering a hackerspace.

You can view a few ...

An Amazing Book!!!

Must Read !!

I’ve listened to the audiobook like in two days.
Couldnt leave it down.

Then organize a CryptoParty to your local hackerspace

Failures

Every SysAdmin, DevOp, SRE, Computer Engineer or even Developer knows that failures WILL occur. So you need to plan with that constant in mind. Failure causes can be present in hardware, power, operating system, networking, memory or even bugs in software. We often call them system failures but it is possible that a Human can be also the cause of such failure!

Listening to the stories on the latest episode of stack overflow podcast felt compelled to share my own oh-shit moment in recent history.

I am writing this article so others can learn from this story, as I did in the process.

Rolling upgrades

I am a really big fun of rolling upgrades.

I am used to work with server farms. In a nutshell that means a lot of servers connected to their...

CAA

Reading RFC 6844 you will find the definition of “DNS Certification Authority Authorization (CAA) Resource Record”.

You can read everything here: RFC 6844

So, what is CAA anyhow?

Certificate Authority

In a nutshell you are declaring which your Certificate Authority is for your domain.

It’s another way to verify that the certificate your site is announcing is in fact signed by the issuer that the certificate is showing.

So let’s see what my certificate is showing:

DNS

Now, let’s find out what my DNS is telling us:

# dig caa balaskas.gr 

;; ANSWER SECTION:
balaskas.gr.        5938    IN  CAA 1 issue "letsencrypt.org"

Testing

You can also use the Qualys ssl server test:

https://www.ssllabs.com/ssltest/

Postfix

smtp Vs smtpd

• postfix/smtp
  • The SMTP daemon is for sending emails to the Internet (outgoing mail server).
• postfix/smtpd
  • The SMTP daemon is for receiving emails from the Internet (incoming mail server).

TLS

Encryption on mail transport is what we call: opportunistic. If both parties (sender’s outgoing mail server & recipient’s incoming mail server) agree to exchange encryption keys, then a secure connection may be used. Otherwise a plain connection will be established. Plain as in non-encrypted aka cleartext over the wire.

SMTP - Outgoing Traffic

In the begging there where only three options in postfix:

• none
• may
• encrypt

The

What is the time?

Time offset is the amount of time that is off (or drift) from a specific value. In Linux systems, date is been calculating from the beginning of time. That is 00:00:00 1 January 1970 or as it called Unix Time and systems define date (time) as the number of seconds that have elapsed from 01.01.1970.

It is so important that even a few seconds off can cause tremendous disaster in data centers and applications.

Network Time

To avoid problems with time, systems must and should synchronize their time over the Internet every now and then. This is being done by asking a central NTP server via Network Time Protocol. The most common scenario for infrastructures is to have one or two NTP servers and then all the systems inside this infrastructure can synchronize their time from those machines.

Nagios - NRPE

In my case, I have a centralized NTP Daemon that...

The problem

The last couple weeks, a backup server I am managing is failing to make backups!

The backup procedure (a script via cron daemon) is to rsync data from a primary server to it’s /backup directory. I was getting cron errors via email, informing me that the previous rsync script hasnt already finished when the new one was starting (by checking a lock file). This was strange as the time duration is 12hours. 12 hours werent enough to perform a ~200M data transfer over a 100Mb/s network port. That was really strange.

This is the second time in less than a year that this server is making problems. A couple months ago I had to remove a faulty disk from the software raid setup and check the system again. My notes on the matter, can be found here:

https://balaskas.gr/blog/2016/10/17/linux-raid-mdadm-md0/

Identify the problem

To see the entire article, click uppon article's title/link.
Thank you.