Tag: password

How To: Remove A PDF Password

This will be a straightforward task for anyone who would like to know how to remove a PDF password in the Linux terminal. If you deal with a lot of PDFs and want to remove the password, it’s a fairly easy task. Read this to learn more!

As mentioned before, PDF stands for Portable Document Format. This is a ratified ISO standard (ISO 32000) and is an open standard. You can see a bit about the PDF standard here on the ISO website. However, unless you have a subscription, they’ll want you to pay for this. I am not paying for this as I do not need to know the specifics.

Many people think that it’s proprietary because it comes from Adobe, but it’s an open standard and there’s a bunch of software available to manipulate and create PDF files. The standard has been open since 2008 which explains the myriad choices for editors.

Seeing as you’re here, you might as well read this interesting Wikipedia article:

History of PDF

PDFs can come with different levels of security. They can have passwords that lock the ability to edit the file and they can have passwords that you need just to open the PDF file.

This article assumes that you know the password! The exercise in this article only applies if you already know the password. I did write an article about cracking a PDF password, but that can take a long time.

How To: Crack A PDF Password

So then, which tools are we going to use?

poppler:

We’ll be installing a meta package known as poppler. This may come pre-installed on your system, or you may need to install poppler manually. We’ll go over installation instructions for a variety of distros, as it’s widely packaged and available in the various distro’s default repositories.

You’ll find that poppler is a meta package. That is, it contains other packages. In this case, poppler contains other applications that are used to manipulate PDF files. There’s no such thing as man poppler for example. It’s just the package name for a package that contains other packages. (That’s a meta-package.)

If you dig into it, you’ll find that poppler contains applications like pdffonts and pdfimages. At this point, we’ve previously covered pdftotext. This time around, we’ll be using pdftops. We’ve not yet used this tool in other articles, so now is as good a time as any to learn about it.

pdftops:

This pdftop application is mostly intended to turn PDF files into PS (PostScript) files but has other uses. Sort of like how a medication can be prescribed off-label, so too can you use this tool for other things. This time around, we’ll be using the pdftops to remove a PDF password.

If you had poppler installed already and checked the man page, you’d see something that should be close to this:

pdftops – Portable Document Format (PDF) to PostScript converter (version 3.03)

We’ll be skipping that whole bit about converting it to a file formatted for PostScript. That’s not necessary for our goal – removing a password from a PDF-formatted document.

But, this tool contains the necessary commands to remove a PDF password. If the file has multiple passwords it will remove the password specified. Your best bet is to remove the password that enables editing. This will also unlock the PDF for viewing purposes.

Remove A PDF Password:

If you want to remove a PDF password, you can use a GUI tool and then choose the ‘export’ option – or maybe the ‘save as’ option. In our case, and as mentioned above, we’ll be using the terminal to remove a PDF password. If you don’t know how to open a terminal, that’s usually accomplished by finding the application in your menu or by pressing CTRL + ALT + T on your keyboard.

With your terminal now open, we need to install the poppler meta package. I’ll include the commands as I understand them but you may need to doublecheck my work. Depending on your package manager, try the following:

Debian/Ubuntu/etc:

RHEL/CentOS/etc:

OpenSUSE/SUSE/etc:

Gentoo:

Arch/Manjaro/etc:

One of those should work with all the major distros out there. If you’re using an obscure distro with an obscure package manager, the poppler utilities should be available to you. You’ll just need to edit your installation command to match your package manager.

Also, if you do need to do that, please let me know. If you let me know, I can include the command in the article, thereby making the article more useful to more people. One of my primary goals is to be useful. It’s good to be useful to more people.

On to the meat of the article:

Removing A PDF Password:

As you’ve already got your terminal open, you might as well keep that terminal open. The application we’re using is pdftops and you can use the following command to ensure that pdftops is properly installed:

The output should look similar to this:

While you’re there, you can check the man page. There are many options available for the pdftops command and you can check them with this command:

Now that we’ve checked the man page, we’re looking for the -upw flag. That’s the flag that’s going to do the heavy lifting and the man page describes it like so:

Specify the user password for the PDF file.

So, you can see where this is going…

The syntax is quite simple. It will look like this:

If you want to specify the owner password, you use the -opw flag. You can pick which password it is that you’re using and the output file will not have that password. Specifying this flag will remove all restrictions, of course.

Let’s try to give you an example…

I wrote an article about how to crack a PDF password and I included a link. For the sake of clarity, you can now download that PDF file.

Example PDF File

The password for that file is ‘abab’ and not one of you took the time to crack it. I made it nice and simple for you, but not one of you took the time to crack the password.

Still, we can use that in our example:

Rather than converting to PostScript, we are just opening and unlocking the file. At that point, we’re redirecting that unlocked content to a new PDF file. In the process, we’re stripping the existing password, meaning you can easily access the file in the future – even if you’ve long since forgotten the password.

Closure:

I’m not sure how often you work with PDF files, but this might be something you can use. You don’t need to remember complex passwords unless you want to. Very few people are interested in maintaining a mental list of all the passwords they use.

It’s not like there’s a password manager for PDF files (as far as I know). You’re stuck referencing the original place the password was shared or keeping some sort of list. Well, you do have another choice. You can learn how to remove a PDF password in the Linux terminal and be done with it. It’s up to you.

Anyhow, I figured this would make a good article. I don’t mention PDFs often and don’t write many articles on the PDF subject. There have been a few of them but there’s always more to cover. Today we just covered how to remove a PDF password. Maybe we’ll cover something else in the next article – but I’m more likely to skip a few articles so that it’s not just PDF content for a week.

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How To: Crack A PDF Password

I don’t know how handy today’s article is going to be in reality but it’s sort of possible to crack a PDF password. Once you read the article, you’ll see why I said “sort of possible”. The odds of success will vary greatly.

Everybody knows what a PDF file is. It’s a Portable Document Format. This is actually a standard (ISO 32000). You don’t need Adobe products to create, edit, or read PDF-formatted documents. Odds are good that your distro comes with tools for manipulating PDF documents.

It’s possible to password-protect a PDF document. You can have an owner’s password (allowing editing) or you can have a user’s password (allowing you to read the document). This may be something you’ve encountered in the past.

Well, like all things password-protected, it’s possible to crack the password.

What do I mean by crack? I mean it will reveal the password to you in plain text. This will allow you to access the document in one form or another, depending on which password you crack.

This is gonna take some time…

Also, I’ll assume you’re using something based on Debian because I’ve not tested this with other distros. I’ve only tested this on my systems.

The tool we’ll be using is a ‘brute-force’ password cracker. That means it starts from the letter a and works its way up, adding new letters after the rest of the letters have been tried. So, you’ll see aa, ab, ac, ad, and progression along those lines. You can immediately see why this is going to take a while.

The tool we’ll be using is helpfully called ‘pdfcrack’.

pdfcrack:

This pdfcrack is a terminal-based PDF password-cracking tool. You can use brute force or lists of words such as common passwords. You can also specify the character list, though the default is to just use the regular alphabet in both uppercase and lowercase formats.

The pdfcrack application is helpfully described as such:

pdfcrack – Password recovery tool for PDF-files

I’ll assume that you’re only trying to recover passwords on documents you should legally have access to. I assume that you won’t use this to access content that does not belong to you. That seems like a safe assumption!

As you can see, this is the correct tool if you want to crack a PDF password.

Crack A PDF Password:

As mentioned above, you’ll crack passwords in the terminal. That requires an open terminal, so we might as well install pdfcrack in the terminal. Just press CTRL + ALT + T and that will usually open up a terminal for you.

With your terminal now open, install pdfcrack:

With that installed, check the man page:

Download:

Example PDF File

Now, crack it…

As it’s a download, it’s probably in your ~/Downloads directory, but mine is stored in my ~/Documents directory because it’s a document. So, my example:

That uses a very simple password that should be cracked in a few seconds. On my older and slower computer, I was able to do more than 20,000 words per second. This short password should crack almost instantly.

Leave a comment telling me what the password is!

By default, pdfcrack will crack the user password. You can specify which password you wish to crack. Though the syntax is a little wonky. In this case, the syntax is as follows:

Which translates into the following…

For the owner:

For the user:

If you want to pause this, you can! 

To pause a running pdfcrack instance just press CTRL + C. This will save the progress as savedstate.sav. The program will automatically resume when you run the command again. Pretty neat!

There’s a lot you can do with this command. Let’s say you recall the password was between 8 and 12 characters and want to just search in that area.

You can also specify the character set. If you want to use uppercase, lowercase, and numbers you can do that. You just add them to the command with the -c flag, making sure to put them in quotes. That’d look like this:

You can specify a wordlist like so:

The format for that file appears to require one word per line and there are collections of common passwords you can download to help you crack a PDF password.

As you can imagine, and as you were warned near the start, this process can take a while. Assuming you have the right characters loaded and enough time, it’s certain to work eventually.

Go ahead and crack my example file above. That one won’t take you very long, even on a slow computer. It won’t be instantaneous, but it’ll be pretty quick.

If you want, you can also run a benchmark to see how fast your computer is. The command to do that is quite simply this:

I ran this on the slowest computer I use. I didn’t run it on anything faster because I don’t care that much. I’m sure you’ll do better on your computers, though you can share the results as a way to compare your rig with others.

Anyhow, my output was this:

Be sure to check out the man page. It’s a simple application but there are many options available for pdfcrack and you might as well learn about them now. You never know when you’ll find an old PDF document with a forgotten password. It can (and does) happen!

Also, be sure to check the pdfcrack project page.

Closure:

So, you might wonder why I’d include an article like this. After all, isn’t cracking passwords a potential legal mess? Isn’t it immoral to crack passwords? Is it even legal to crack passwords?

The answer is simple enough. It’s a tool you can use to recover your lost passwords. You can use this tool to access things that you shouldn’t be accessing, just like you can use a screwdriver to poke things you shouldn’t be poking. I’m just giving information.

I am also not a lawyer. I permit you to crack the password of the included file. For other files, don’t do anything illegal in your jurisdiction. If it’s a crime, don’t do it. I’m decidedly not your lawyer. If you think this requires asking a lawyer, go ahead and do so.

That and it’s not a great secret. If you’re relying on a password to protect PDF files from anyone serious, you’re probably doing your security wrong. It’s well known that this is possible and that the tools are easily installed. PDF passwords aren’t very good for security, though you can make complicated passwords.

The distro you’re using may very well have pdfcrack available, even if it isn’t one of the Debian-based distros. Just search and you can find it. With some work, you can even mostly install it with PIP. Just click the link above to the project page for more information about that.

As always…

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Make Passwords In The Linux Terminal

Today’s article should be fairly simple and is about something we all use because it’s about how to make passwords in the Linux terminal. Assuming my writing chops are up for it, this article should be easy for everyone to follow. I’ll do my best. It might not even be a very long article.

I don’t think I need to explain passwords to any modern computer user. Even mobile users use passwords. The rare people who don’t use this technology will likely still use a PIN for things like their ATMs and credit cards. A PIN is just a numeric password.

I think it’s safe to say that we all know what a password is and why we use one. I’m not sure we all understand how to create good passwords, but we all use them. Perhaps this xkcd comic will amuse you:

xkcd's thoughts on passwords
Hopefully, this works as a hotlink, per xkcd’s request. I also can’t resize it. Ah well…

I have written about passwords in the past. One of the first articles on this site was about generating complex passwords. Here’s a link:

How To: Generate Sufficiently Complex Passwords In The Terminal

There isn’t much to add about passwords. It’s safe to assume we’re on the same page and that we’ve all used many passwords in our lives. I guess it’s then time to move along to the software we’ll be using to generate passwords in the Linux terminal.

Installing makepasswd:

In a previous article, we made complex passwords (with some degree of randomness) in the Linux terminal with a tool known as ‘pwgen’. You’ll find that pwgen is perfectly adequate and does a fine job at creating unique passwords in the terminal.

This time around, as we accomplish the very same task, we’ll be using a tool known as makepasswd. When you install makepasswd you’ll see that it has some small dependencies involving encryption and randomness. That makes some sense when you see how makepasswd is described on the man page.

makepasswd – generate and/or encrypt passwords

We’ll be doing that first bit – that is generating passwords.

You will need an open terminal to follow along in this next section. You can also use your graphical software installer, assuming you have one. To open your terminal, you can usually just press CTRL + ALT + T. 

With your terminal now open, choose the right command for your distro:

Debian/Ubuntu/etc:

OpenSUSE/SUSE/etc:

Arch/Manjaro/etc:

RHEL/CentOS/etc:

You’ll find that makepasswd is available for other distros, but I’m not sure of the installation commands and don’t want to steer you wrong. As it stands, I’m pulling these from my notes and haven’t tested them to ensure the commands are current. If they’re not current, please leave a comment so that I can update them accordingly.

Now that you have makepasswd installed…

Make Passwords In The Linux Terminal:

If you used a GUI tool to install makepasswd, or if you closed the terminal after installing makepasswd, you’ll need to open a terminal. Fortunately, I told you how to do that in the previous section. If you want to use makepasswd to make passwords in the Linux terminal, you will of course need an open Linux terminal.

With the terminal now open, you can check the man page for more information about the makepasswd application. That’s done like so:

The application is pretty simple, at least for our needs. If you just want to generate a password that’s 12 characters long, you’d run this command:

An example output might be something like this:

If you want to use certain characters, you can use the --string flag. So, if you wanted to generate a 12 character password with just numbers, you’d use a command that looks like this:

An example output might be something like this:

So, I suppose, you could even use this as a tool to generate a pseudorandom PIN for your debit card. 

If you want to generate a list of passwords so that you can pick the one you like from the list, you can do that as well. That command would look a little bit like the following command:

For some reason, it seems to only want to output a maximum number of characters in that command and the maximum number is 10. Do not ask me why, but the option is there and the output of that command might look a bit like this:

You can do quite a bit more with the makepasswd application. As mentioned above, check the man page. You can seed your passwords, you can encrypt them, get the hashed password value, and more. You could even take the above command and output it to a text file called passwords.txt. You’d do that like this:

As you can see in that command, I’ve included the --maxchars flag. You can set both the minimum number of characters and the maximum number of characters with the two flags used in the above two commands.

See? You’ll find makepasswd to be a handy way to make passwords in the Linux terminal. There are all sorts of ways to do this. This is just one more way.

Closure:

I wasn’t sure what I’d write when I sat down to write this article. I started it much earlier in the day than I usually would and flipped through all sorts of text files to find an interesting article to write. The first two articles that piqued my writer’s interest were topics I’d previously covered. I eventually settled on makepasswd. After all, you never know when you will want to make passwords in the Linux terminal. It could happen!

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How To: Change Your Password In The Terminal

It’s considered good form to change your password once in a while. This may not be something important for you, but others may appreciate it. It may be corporate policy or regulations that make you need to change your password, or you could just be more security minded than many others. No matter what, this article tells you how.

The tool we’re using in today’s exercise is called ‘passwd‘, which is a tool to help make and manage passwords. It’s a bit complicated, but it uses something called hashing and stores a hash instead of a plain-text password.

When you login, your password is checked against the hash that was created when the password was created. This prevents people from easily reading your stored password, stored of course because there must be something to check against.

If one remembers way back to the start of this project, my goal is to put my notes online. This article is in my notes, which is why this is such a simple article. Indeed, this article should be pretty straightforward and easy to understand. I’d definitely call it a beginner-friendly article.

Change Your Password:

Like most always, you need to open your terminal. You can do so with your keyboard – just press CTRL + ALT + T and your default terminal should open.

Once you have your terminal open, the command you’re looking for is:

If you already have a password, you’ll need to type your current password and then you’ll type the new password twice. When you logout or next need to use your password, your new password will be required. You don’t need ‘sudo’ for this, as the password you’re changing belongs to you.

Seeing as this is short, I’ll toss in another use of passwd. If you want to change the password for a different user, you just use this command:

Change the obvious to the obvious, specifically the username. This command does require ‘sudo’, because you’re changing a password that doesn’t belong to the current user.

There’s more that can be done with passwd, but those things are beyond the scope of this article. I’d expect to see some more passwd uses covered in the future, but you can get a head start by typing man passwd into your terminal and learning about the other options.

Closure:

That’s it, really. I told you that this one would be short and easy! Sure enough, it’s pretty easy. Many of my notes are regarding people who are new to Linux, but it’s still nice to get more of them online. I dare say we’re coming along nicely.

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