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Password Protect: Secure?

Everyone knows about passwords. Most people I've met usually react to creating a new account with a variety of negative reactions - mainly due to the annoying issue of having to create a new password (or even worse, re-use an old one!). Most people I've met also reuse at least one password several times, too!

This is obviously a bad thing, but what can we do about it? Perhaps, while we're at it we can solve that awkward problem of forgetting which password you've used too.

Before we tackle those questions, it's important to discuss what makes a good password. Perhaps you think of some of these rules:

A laughably bad password policy that demands a password between 8 and 10 characters in length.

(Source: this post on Password Shaming)

  • It has to contain a number (not always)
  • Some symbols make it more secure (it depends)
  • Changing it often is a good security measure (not as good as you'd think)
  • It shouldn't be longer than 32 characters long (no! If longer is an option, take it! )
  • Change out letters makes it more secure (this can be guessed by attackers)

Here's the big question though: What do any of these password rules achieve? Well, we want to ensure that only the owner of an account can access it.

What could be so bad?

Ok, so we've got our goal. Make sure only the owner of an account can access it. Sounds simple, right? Just let the user enter a secret that only they know, and then we can check if they still know that secret in the future in order to verify that they are the right person attempting to access the account.

This brings a number of problems:

  1. The user has to remember their password (more on this later)
  2. As a service provider, we have to store their password securely so that a hacker can't steal it

Point #1 here is bad enough (more on this later and what you can do about it though), but #2 is a real issue. A safe is only as secure as its lock, so how to we makes sure we keep passwords stored so that nobody can steal them?

The answer: Make it so that even we can't read them! This sounds silly, but it really does work. By using a process called hashing, we can apply a process of complicated transformations to an input string - leaving us with an unintelligible output string.

Why is this useful? Because it's repeatable. By hashing the same string twice, we can get exactly the same output - allowing us to check if a user has entered their password correctly without actually storing it in plain-text! Very cool.

We're not out of the woods yet though. Picking the right hashing algorithm can be tricky. No doubt you've heard about sha1 - and maybe even sha2 and sha3. They stand for secure hashing algorithm, right? What if we used one of those?

More problems, unfortunately. It's too fast. Yep! My laptop upon which I'm writing this blog post can hash 157 Megabytes of data per second per core. I've got 4 cores, so that's 628MiB if I maxed them all out. If I manage to steal the hash of your password, then I could try every single combination of characters (including non-printable ones) in the following amount of time:

Length (chars) Time to crack
1 ~0.04µs
2 ~12µs
3 ~3ms
4 ~803ms
5 ~204s
6 ~14.5 hours
7 ~154 days
8 ~107.5 years
9 ~27423 years
10 ~7 million years

It gets worse. With new innovations, hashing algorithms such as the SHA series (don't even start on MD5) can now be run in massive parallel on a (or several) graphics card, slashing these times by several orders of magnitude:

Length (chars) Time to Crack
8 1 minute
9 2 hours
10 1 week
11 2 years
12 2 centuries

(Source: This Coding Horror Blog Post)

I don't even have to buy a top-of-the-range card any more, either. I can rent one for as little as ~35p per hour from Google Cloud Compute - well within the reach of almost any script kiddie or wannabe hacker.

Many people also use the same password for several different accounts - and attackers exploit this mercilessly. If they've gained access to one of your accounts, they'll also try using the same password against other online services to see if they can gain access to any other accounts they may belong to you.

(If you're wondering, SHA2 and SHA3 are actually secure - they just aren't for hashing passwords :P)

Furthermore, the particularly determined have gone to the trouble of pre-generating what we call rainbow tables. These table contain pre-generated hashes for millions and millions of different combinations of characters - reducing the time required to crack a password to almost nothing!

Doing something about it

Obviously, if there wasn't anything we can do about it then everyone's accounts would be hacked by now. Thankfully though, this isn't the case. We can combat the threat by using longer passwords (at least 12 characters - and preferable 16+), and that of a rainbow table by utilising a salt.

Basically, it's a long and unintelligible string that's added to the password before it's hashed - and is different for every password. Then in order to check that whether an entered password is identical to the stored one, we simply re-read the plain-text salt from storage and hash the new password with the salt.

Over the Rainbow

Pretty good right? Not so fast. Even though we've prevented attackers from using a rainbow table against our password hashes, we still have to store the salt in plain text, so our attacker can still try millions of different passwords a second if they manage to steal our password hashes.

The solution: Slow them down! Using bcrypt, we can specify a work factor when hashing a password. Higher work factors mean that it takes longer to hash a password. By making it so that it takes a consistent ~1 second to hash passwords, we can limit our attacker to trying 1 password per second instead of a few million. Furthermore, the bycrypt algorithm doesn't translate onto graphics cards very well at all - further increasing the amount of time it takes to crack our password hashes!

Combined with a salt from earlier, this is a pretty good way of storing passwords. There are other variants of this general algorithm too - including the newer Argon2 algorithm whose work factor increases the amount of memory required to calculate a hash as well as the amount of CPU power.

Still others include scrypt and PBKDF2 - the likes of which are discussed here (also see this answer).

Just getting started

This isn't the end of the road though. Far from it - we're just getting started. Next, the best hashing algorithm in the world doesn't help you if your password is terrible. There are many lists of common passwords extracted from data breaches from around the world - so if your password is in that list, you can expect your account to be hacked in seconds!

If you're unsure if your password is good enough, then there are online tools available that you can use to measure the strength of your passwords. It will even tell you if your password is on any of the common password lists.

Even so, there are other methods employed by those with questionable intent to gain access to your account. For example, why bother cracking your password when the can install a keylogger on your computer or look over your shoulder to pull out your password as you're typing it?

Some simple steps are all that's required to keep keyloggers at bay. Firstly, keeping your computer (and all the software you have installed) up-to-date is critical for patching security holes. If you're using Linux, then you've already got a brilliant way of doing this - so long as you install all your software through your package manager.

If you're on Windows, making sure any auto-update options are turned on and installing updates when prompted is very important. Though it's not installed by default, Chocolatey brings Linux-style package management to your computer - allowing you to mass-update all the software you've got installed at once.

Secondly, Windows users should make sure they have an anti-virus program installed (Windows 10 comes with one built in, so no need to worry there) with up-to-date virus definitions. If you're not on Windows 10 yet, then Windows Defender can be installed and enabled. Alternatively, Avast does the job well enough (though somewhat noisily with lots of notifications). Both are free, so there's no excuse :P

Password Management

As I mentioned earlier in this post, re-using passwords is a very bad idea. According to dashlane, the average number of accounts registered against a single email address is a staggering 118! Having to remember a different password for all 118 accounts is clearly not sustainable (dashlane also notes that the average number of 'forgot password' emails per inbox in 2020 is estimated to be 22), so is there anything we can do about it?

Yes, as it turns out. With the rise in the number of online accounts people have, so have the ways at your disposal to manage them. The best way I've found to manage my passwords is with a password manager. The general idea is that you create a password database that's encrypted with a (super-secure) master password, and then you store all of your credentials all of your different accounts inside it.

Many password managers come with helper tools that automagically type them into a box at the touch of a button - eliminating the need to remember them at all. This means that you can use much longer and more secure passwords - protecting your online accounts from intrusion.

Personally, my preference is Keepass 2 - as it lets me save my password database to disk - so that I can set up my own automatic backup system (don't forget this step!) against my own infrastructure. Many others exist though too. This article has a great discussion on the merits (and dangers) of using one, along with recommendations at the end.

Of course, it's a trade-off. In using a password database all of your passwords will be in one place (albeit encrypted with your master password). If an attacker gets hold of it and cracks the password, then it's game over! Thankfully, there are several techniques that are employed to ensure the security of such a database, such as utilising a password hashing algorithm (as discussed above) to transform the master password before encrypting the database, adding a work factor. Secondly, keeping your database stored in a secure location (such as flash drive in a safe place, or a secure remote server that you own) can also help.

Given that the chance of being burgled in the UK is about 2.5% (source), but the chance of being hacked is about 1 in 3 (source), I think I'd rather take my chances with a password database to keep my online accounts secure.

If you aren't comfortable with storing your passwords digitally yet though, fear not! You could buy a password book from loads of different online stores - and even most good high-street stationers such as W.H. Smith for under £10. Although storing really long and unintelligible passwords isn't really viable, you can still have a different one for each site - making your online accounts much more secure.

Beyond the Password

Having a good password is a great start, but is there anything else we can do? Well yes, as it turned out. Enter stage left: 2-factor authentication.

Given those statistics about burglary and hacking, ideally we want to tie our account security to the burgalry statistic rather than the hacking one. 2-factor authentication does just this: it makes it such that you require not only something that you know (your password) to access your account, but also something that you have, such as your phone - or a small flash-drive like device called a hardware-security key.

Linking the two is a system of 6-digit codes. Basically, on your phone you scan a QR code representing a lump of data. This data is then used to generate a 6-digit code that you enter into the online service after entering your password. This code changes every 20 or so seconds according to a complicated algorithm, so the server can also generate a code to see if it matches the one you entered.

In this fashion, attackers are prevented from accessing your account unless they not only crack your password, but also actively infect your phone.

(Above: A few hardware security keys. Onlykey is featured on the left, whilst a selection of Yubikeys are on the right.)

If you're really paranoid, special 'security keys' exist that can store your 2nd-factor information - and generate the codes securely without the source data ever leaving your device (though those are a separate topic for a different post - comment below if you'd like me to do a writeup on them on something!)

Conclusion

Phew. If you've reach the end of this post, then congratulations! We've covered a lot of content in this post. We've looked a little at what makes a good password, and why that is. We've investigated how attackers attempt to gain access to your account, and what you can do to protect yourself. Also also considered the merits of various password management strategies. Finally, we've looked at 2-factor authentication, and how it is far more secure than even the strongest password.

As always, this post is a starting point - not an ending point! I'll list some useful articles below for further reading. I'd also recommend you consider taking the time to secure your online accounts better - for example changing their passwords, enabling 2-factor authentication, and implementing a password management strategy.

Found this interesting? Spotted a mistake? Got a great tip of your own? Comment below!

Sources and Further Reading

Securing a Linux Server Part 2: SSH

Wow, it's been a while since I posted something in this series! Last time, I took a look at the Uncomplicated Firewall, and how you can use it to control the traffic coming in (and going out) of your server. This time, I'm going to take a look at steps you can take to secure another vitally important part of most servers: SSH. Used by servers and their administrators across the world to talk to one another, if someone manages to get in who isn't supposed to, they could do all kinds of damage!

The first, and easiest thing we can do it improve security is to prevent the root user logging in. If you haven't done so already, you should create a new user on your server, set a good password, and give it superuser privileges. Login with the new user account, and then edit /etc/ssh/sshd_config, finding the line that says something like

PermitRootLogin yes

....and change it to

PermitRootLogin no

Once done, restart the ssh server. Your config might be slightly different (e.g. it might be PermitRootLogin without-password) - but the principle is the same. This adds an extra barrier to getting into your server, as now attackers must not only guess your password, but your username as well (some won't even bother, and keep trying to login to the root account :P).

Next, we can move SSH to a non-standard port. Some might argue that this isn't a good security measure to take and that it doesn't actually make your server more secure, but I find that it's still a good measure to take for 2 reasons: defence in depth, and preventing excessive CPU load from all the dumb bots that try to get in on the default port. With that, it's make another modification to /etc/ssh/sshd_config. Make sure you test at every step you take, as if you lock yourself out, you'll have a hard time getting back in again....

Port 22

Change 22 in the above to any other number between about 1 and 65535. Next, make sure you've allowed the new port through your firewall! If you're using ufw, my previous post (link above) gives a helpful guide on how to do this. Once done, restart your SSH server again - and try logging in before you close your current session. That way if you make a mistake, you can fix through your existing session.

Once you're confident that you've got it right, you can close port 22 on your firewall.

So we've created a new user account with a secure password (tip: use a password manager if you have trouble remembering it :-)), disabled root login, and moved the ssh port to another port number that's out of the way. Is there anything else we can do? Turns out there is.

Passwords are not the only we can authenticate against an SSH server. Public private keypairs can be used too - and are much more secure - and convenient - than passwords if used correctly. You can generate your own public-private keypair like so:

ssh-keygen -t ed25519

It will ask you a few questions, such as a password to encrypt the private key on disk, and where to save it. Once done, we need to tell ssh to use the new public-private keypair. This is fairly easy to do, actually (though it took me a while to figure out how!). Simply edit ~/.ssh/config (or create it if it doesn't exist), and create (or edit) an entry for your ssh server, making it look something like this:

Host bobsrockets.com
    Port            {port_name}
    IdentityFile    {path/to/private/keyfile}

It's the IdentityFile line that's important. The port line simply makes it such that you can type ssh bobsrockets.com (or whatever your server is called) and it will figure out the port number for you.

With a public-private keypair now in use, there's just one step left: disable password-based logins. I'd recommend trailing it for a while to make sure you haven't messed anything up - because once you disable it, if you lose your private key, you won't be getting back in again any time soon!

Again, open /etc/ssh/sshd_config for editing. Find the line that starts with PasswordAuthentication, and comment it out with a hash symbol (#), if it isn't already. Directly below that line, add PasswordAuthentication no.

Once done, restart ssh for a final time, and check it works. If it does, congratulations! You've successfully secured your SSH server (to the best of my knowledge, of course). Got a tip I haven't covered here? Found a mistake? Let me know in a comment below!

Signing email with GPG/PGP in Evolution

Recently I've moved to a new laptop, and for the longest time I haven't been able to figure out why I couldn't sign my messages with gpg any more (I'm on keybase as sbrl). Turns out the problem was that gpg didn't 'trust' my private key. This post documents how I fixed it:


# First, import your private key into gpg (you've probably done this already)
gpg --import <secret_key.priv
# Then, get gpg to edit your private key, and ask it to trust your private key
gpg --edit-key toaster5@waffletoast.net
> trust
> 5
> y

Once done, you can then select your private key in evolution in the preferences (SHIFT + CTRL + S).

Did this help you out? Still having issues? Let me know in the comments below!

UFW and Samba

Today I have another post for you about Samba. Today I found that people couldn't actually access the samba shares I set up (I must have forgotten to test them). They were getting a weird "The Network Path was not found" error. Strange. After looking into it, I found that I didn't unblock the right ports in ufw. You see, Samba operates using two listeners, one called smbd, and the another called nmbd. I had forgotten to read the output of netstat -peanut correctly, and I missed a few ports.

For future reference (and for others having the same problem), here's the list of commands you need to enter in order to use shared folders with Samba correctly:

sudo ufw allow 139/tcp
sudo ufw allow 445/tcp
sudo ufw allow 137/udp
sudo ufw allow 138/udp

Hopefully it doesn't take you as long to fix your problem as it did mine...!

Protecting your Privacy Online: Reviewing which Advertisers Track your Interests

This is a different kind of post about privacy on the web.

The youronlinechoices.com website

Protecting your privacy whilst browsing online is important. Most if not all advertisers will track you and the websites you visit to try and work out what you are interested in - The amount of information that advertising networks can accumulate is astonishing! I currently have an AdBlocker installed with a tracking prevention list enabled, but that isn't always enough to stop all the advertising networks from tracking you all the time.

Recently I have come across a website called youronlinechoices.com - a website for people in the EU that allows you to review and control which out of 96(!) advertising networks are currently tracking you and your interests. I found that about two dozen advertisers were tracking me and was able to stop them.

The Internet needs adverts in order for it to stay free for all (disable your adblocker on the sites you want to support), but one also needs to prevent ones personal information from falling into the wrong hands.

Securing a Linux Server Part 1: Firewall

Welcome to a new tutorial series, where I will show you what I have learnt so far about making sure that your linux server (and desktop too!) are secure so that nobody can get in (easily) and assume control.

Disclaimer: This tutorial series will not cover everything, and should not be taken to. There probably will be some mistakes in this post too. Check other guides online or consult a professional to make sure that your machine is secure. Please suggest improvements or point out mistakes in the comments.

To start this tutorial session off, I will talk about firewalls. Firewalls control how data is allowed to travel in and out of your computer. In Ubuntu, a firewall called ufw, the 'uncomplicated firewall' is already present. It acts as a nice frontend to iptables, which I find to be difficult to understand and use. We will be using that as our firewall.

I have done an asciinema recording on a virtual machine of this whole process:

Enabling the firewall

Ufw by default allows all outgoing connections and denys all incoming connections. This means that if you are using ssh to connect to your server, you will need to open the appropriate ports first before enabling ufw. Do that like this:

~$ sudo ufw allow 22/tcp

Ufw will automatically configure iptables to allow incoming connections on port 22 that use tcp. I will talk more about allowing and denying different connections later.

Just in case ufw blocks your ssh connection and you are unable to get back in, you can use another program called at to schedule the disabling of the ufw so that you can get back in again. If you don't have it installed, you can install it with sudo apt-get install at.

~$ sudo at -vM now +10 minutes
ufw disable
^D

Where ^D stands for CTRL + D. Now that you have it set such that ufw will disable itself in 10 minutes time, we go ahead and turn ufw on:

~$ sudo ufw enable

It will warn you that this may disrupt any existing ssh connections you have open. Reply yes to this. Once it have been enabled successfully, you should check that you can still ssh into your server (if that is the method that you are using to control it). If yes, great! If not, ufw will disable itself in 10 minutes and then you can try again.

Now that we have ufw enabled, we can cancel the at job we created to disable ufw. Type sudo atq to list the jobs you have schedules, and sudo atrm <number> to remove it, where <number> is the number of the jobs that you want to delete.

You may also want to cheeck the status of ufw to make sure that it is enabled, or to get a list of the rules that are currently in force. You can do that like this:

~$ sudo ufw status
Status: active

To                         Action      From
--                         ------      ----
80/tcp                     ALLOW       Anywhere
80/tcp (v6)                ALLOW       Anywhere

Allowing connections

Allowing connections through the firewall is easy. Simply type something like this:

~$ sudo ufw allow 80/tcp

Ufw will automatically configure iptables, in this example, to allow all connections on port 80 that use tcp. It will also configure it appropriately for both ipv4 and ipv6. Replace 80 with the port number you want to allow, and tcp with udp if needed. Ufw also understands several protocol names, and can configure itself accordingly:

~$ sudo ufw allow http
~$ sudo ufw allow imap

Denying connections

Denying all connections on a given port is very similar., Simply type something like this:

~$ sudo ufw deny 4722/tcp

The above would deny all tcp connections on port 4722.

You can also prevent a particular ip from gaining access to your server:

~$ sudo ufw deny from 123.123.123.123

The above would block all packets from the ip address 123.123.123.123. It works with IPv6 addresses too:

~$ sudo ufw deny from 2607:f8b0:4003:c05::65

The above would block all packets from the ip address 2607:f8b0:4003:c05::65, which just happens to belong to Google.

Port Ranges

You can open a range of ports with a colon:

~$ sudo ufw allow 60000:61000/udp

The above will allow udp connections on any port in the range 60,000 - 61,000 (the ports used for mosh).

Deleting Rules

Deleting rules can be done like this:

~$ sudo ufw delete allow 4724/tcp

The above would delete the rule(s) allowing tcp connections on port 4724.

Summary

In this post, I have shown you how to activate and configure a simple firewall that is bundled with Ubuntu. Next time, I will talk about securing you ssh daemon.

If you spotted a mistake in this post, have a suggestion, or are having trouble following along, please leave a comment below.

Other useful posts

These posts helped me to understand and use the uncomplicated firewall:

Generating Session Tokens with PHP

Recently I needed to generate random strings to hex to act as a session token for Blow Worm. Using session tokens mean that you send the login credentials once, and then the server hands out a session token for use instead of the password for the rest of that session. In theory this is more secure than sending the password to the server every time.

The problem with generating random session tokens is that you need a secure random number generator, so that hackers can't attempt to guess the random numbers and hence guess the session tokens (that would be bad).

The way I did it (please leave a comment below if this is insecure!) is as follows:

  1. Generate ~128 bits of randomness using the OpenSSL function openssl_random_pseudo_bytes(). This randomness generator is apparently better than rand() and mt_rand().
  2. Hash that resulting randomness with SHA256 to ensure a constant session key length.

The PHP code I am currently using is as follows:

$sessionkey = hash("sha256", openssl_random_pseudo_bytes($session_key_length));

I thought that I would share this here since it took me a little while to look up how to do this. If anyone has a better way of doing this, I will gladly take suggestions and give full credit.

Security update to atom.gen.php

Since this website gets a lot of spam (ongoing investigations are currently in force in order to analyse the spambots' patterns, a post will be made here when they have been stopped) and this website also has a comments feed powered by atom.gen.php, I have had a chance to test atom.gen.php out in the wild with real data.

I discovered, unfortunately, that the script didn't handle invalid utf-8 and non printable characters very well, and this lead to the feed getting broken because XML doesn't like certain specific characters. This has now been fixed.

If you handle user input and use atom.gen.php to turn it into a feed, you will want to grab an updated copy of the script (quick link here) and overwrite your previous copy in order to fix this.

As well as fixing that, I also added a new option, $usecdata. This controls whether the <content> tag's contents should be wrapped in <![CDATA[...]]>. This should add extra protection again html / javascript injection attacks breaking your feeds. It defaults to false, though, so you need to manually enable it by setting it to true.

The reference has been updated accordingly.

If you find another bug, please comment below. You will recieve full credit at the top of the file (especially if you provide a fix!).

Art by Mythdael