Show HN: I Dedicated 4 Years to Mastering Offline Password Cracking

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Show HN: I Dedicated 4 Years to Mastering Offline Password Cracking

264

by bojta-lepenye

Hi everyone,

I am Bojta Lepenye, and first of all, I want to thank the core developers of Hashcat. In my experience, it is quite literally the most capable tool available for offline password cracking across a wide range of use cases.

I have spent the last 4 years (from age 14 to 18) extensively working with Hashcat and the tools surrounding it, and I have documented what I have learned throughout that time (since January 18, 2022) in my first book. During that period, I also had to continuously update and rewrite major sections as the field evolved. One example was the introduction of GPU support for Argon2 and other memory-hard password hashing algorithms, which significantly changed some cracking workflows.

My passion for this book, or its “quick starter,” if you will, came from an ethically conducted penetration test I performed with full authorization at my school. This is something I am both hesitant and quite proud to acknowledge.

At the beginning, I simply wrote down everything I had learned from YouTube videos and online blogs. However, not long after starting my project, I realized I practically knew nothing about password security, and that small 10 to 15 pages I had written would never be enough if someone was looking for a professional guide to cracking passwords.

The other main driving force behind the book was the fact that while researching online, browsing forums, reading academic papers and white papers, watching videos, exploring blogs, inspecting presentations, and examining infographics, I did not find a single source that comprehensively covers and explains everything one needs to understand about offline password cracking. Literally. Not one.

Therefore, I continued my research and learned about password hashing algorithms, the security properties of hash functions, advanced hash cracking techniques, password analysis, attack optimization, and much, much more.

From the very beginning, I wanted to share this knowledge with the community because having access to a resource like this would have helped me tremendously when I first started learning password cracking.

I sincerely hope this work will be useful to both beginners and experienced professionals alike, and I look forward to hearing your thoughts and feedback.

I have also put together a little video to give you a little sneak peek into it. It is on Google Drive. It is the official domain, and you do not need to download anything. Here it is: https://drive.google.com/file/d/13LeysSZO8Mx-LGKt8UQjUGBKOYH...

If you are interested, the book is now publicly available on Amazon, and can be read for free with a Kindle Unlimited subscription: https://www.amazon.com/dp/B0GX36XRCD

raphman
122d
Thanks for sharing. This looks interesting. Impressive achievement.
This book is currently not really relevant for me, so I just skimmed the samples on Amazon. I found the technical content to be reasonably accurate and interesting although sometimes a little bit verbose (e.g., the section about 'what is a password') or slightly imprecise. In general, I think this book might have benefited from a thorough copyediting pass. There are quite a few grammar errors and unpolished sentences in the book, e.g.:
> The reason why Linux is imperative is that well, for one, most of the tools we will use, while indeed have builds for other systems, like Windows, in this book we will work with Linux.
Wishing you success and keep on writing!
1. copypaper
  02d
  Yea after skimming the samples on Amazon I noticed that nearly every single sentence had at least one comma in it (adding zero value). It feels like I'm reading someones thoughts.
  Personally, I love abusing commas for comments and shitposting, but they should be avoided in informative resources like books, otherwise, it looks like a word salad. Say your thoughts and ideas with boldness and certainty.
  But hey you write better than I did at 18, so I ain't judging. Just trying to provide helpful feedback for you (the op) to improve on.
2. nojvek
  02d
  In this day, I actually appreciate imperfect human written content.
  Too much AI slop, perfect grammar but no substance out there.
  This seems like a substance filled book.
  Congrats on shipping a book.
3. dugidugout
  92d
  What did you find slightly imprecise?
  1. raphman
    42d
    A few small things. You might call this nitpicking. And, as I wrote, I found the technical details generally accurate.
    > "Then there is also the fact that having a fully-fledged graphical desktop environment running in the background at all times is not quite optimal to say the least. 99 percent of the time when cracking passwords, you will be staring at a black terminal filled with white text, so using Windows, which is especially GUI-heavy, is usually impractical unless you are specifically testing something or showcasing some process."
    I am reasonably sure that the Windows UI has rather little practical effect on hashcat's speed, and this thread implies the same: https://hashcat.net/forum/archive/index.php?thread-8958.html Also, 99 percent of the time when cracking passwords, I am not staring at a black terminal filled with white text.
    (I am generally taking it a little bit personally when the author directly addresses me and tells me what I am probably thinking or doing.)
    > "Behind a hash function are a series of complicated mathematical operations that make deriving the input from the output literally impossible."
    I'd argue that the mathematical operations themselves are usually not that complicated. More importantly, the whole book seems to be about ways to derive the (probable) input of a hash function from the output. It is not literally impossible.
    > "It is important to note, however, that hash functions are not truly random;"
    As the author writes elsewhere, hash functions are deterministic and not random at all. Calling them not truly random seems to imply that they are somewhat random.
    > "When encrypting a file or any kind of data with AES for example, the program leveraging AES will prompt you for a password. Yes, a password."
    Yes, this is a book about password cracking, but there are lots of cases where programs use AES with a computer-generated key and won't prompt you for a password. E.g., TLS.
    (Just to reiterate: I am not trying to diminish the author's work, I wanted to suggest ways for improvement. I might be wrong or overly pedantic.)
eigenrick
22d
This is an amazing achievement for someone of any age, but to publish a book with this much research at 18 is phenomenal. I heartily congratulate you.
I've hopped through the book and it seems carefully laid out and organized. I may come back at you with questions once I've read further. Cheers.
1. MattPalmer1086
  11d
  I'll add my congratulations too.
  I work in info sec - I've always been interested in password cracking and hashcat specifically, but have never had the time to devote to really dig into it. I'll check it out.
  Well done!
mmastrac
22d
I've got an old datacenter KVM with a root password I've been unable to crack, even though it's an ancient DES one.
Does anyone have a good cloud-hosted password cracker? I can't seem to brute force it, no matter how long I let John the ripper run.
1. arcfour
  02d
  An EC2 instance with lots of cores like a c6i.32xlarge should do the trick, no? You could even pay for spot instances and just checkpoint frequently and copy the progress file to S3 when you get the interruption warning.
K0balt
21d
It’s always exciting to me when someone who has been so obviously passionate and obsessed with a technical discipline decides to take the time to write down what they have learned to help others. This is literally the foundation of civilization and what makes me happy to be a post-agricultural human. So, thank you.
I have followed a similar path in other technical subjects, and have authored a couple of books on those journeys. I look forward to reading yours.
Some people have brought up style and structure issues with your book.. try to take this in stride. Writing for publication is its own whole thing, and involves a lot more than just putting ideas to print. Creating text that conveys the spirit, personality, and information that you want it to is nontrivial, and it takes time and practice to master. It’s easy, as a reader, to feel the rough spots in a literary work… but that does not mean that the reader would do any better when confronted with writing a book level tome, so hear the critique but don’t overthink the critic.
Even though writing well was a side quest to my otherwise very technical focus, I found a joy in developing my literary voice… and I would encourage you to keep uncovering yours.
Don’t be bullied into writing “correctly”. If you want to ponder the senselessness of life you can read one of millions of “correctly” written papers that will have you wanting to end it all just so you don’t have to go on. In these informative but wasted pages you won’t find a shred of the author, and only find yourself bored by the subject that so enthralled them to spend a thousand hours or more writing about it. What a wasted opportunity. They became so focused on writing correctly that they lost their voice entirely. Their writing may inform, but it will rarely inspire.
In these little bits of your writing I have skimmed so far, there’s plenty of warts but I feel you in the work. Your passion is contagious, and I am encouraged to learn. Sure, work out the warts, but don’t be bullied into writing “correctly” by sticking to formality and convention.
Writing is about informing, inspiring, and guiding the frame of mind of the reader. Your work does that because your voice shines through. Sure, it could be easier to read, sometimes clearer, and you should work on that if you want to, but don’t sacrifice your voice in the process. The best written work has a definite personal opinion on how to write a voice, and it’s usually not the “correct” way.
Humans writing like humans is what makes writing worthwhile in the third industrial age. Frolic in your humanity and keep up the good work. Don’t let the well intentioned bastards keep you down, especially if they have a point.
gabrielsroka
32d
Great job. The book is 427 pages.
Why not put the video on YouTube?
1. bradgranath
  22d
  Are you drunk? He’s lucky Google and Amazon haven’t noticed yet. If he wants to keep access to his accounts he should pull them down immediately and distribute via torrent.
gettingoverit
02d
Nice to see someone going the same path as me!
Haven't read the book or used Hashcat, I have a question. Is there anything yet to generate rainbow tables out of password regex?
ViAchKoN
02d
Nice job! It is a massive achievement to publish a book let alone to be start a career so early at age! Now need to find time read the book. It seems it be quite interesting.
andai
22d
Congratulations! The book looks great.
I would love to hear more about the process of writing and preparing it for publishing. It's self-published? How did you do the typesetting and the diagrams?
1. TeaVMFan
  02d
  I too would be interested in hearing about the writing and formatting process. I described my own process as a software engineer and first-time novelist here: https://frequal.com/forwriters/
sijmen
02d
Congratulate on finishing such a big project on a complicated topic, and putting in all this effort so that others can learn as well. I enjoyed reading the first few pages on Amazon
mujib77
018h
Great like accomplishing something like this at the age of 18 is truly remarkable
aqsa_sajjad
12d
This is a really impressive project, especially starting at 14. The point about there being no single comprehensive resource rings true, I've tried to learn about password security before and always ended up jumping between five different tabs just to understand one concept.
1. raphman
  02d
  There are actually a few recent books on the topic (no clue about their quality but reviews look positive):
  Netmux (2019): Hash Crack: Password Cracking Manual¹
  James Leyte-Vidal (2024): Ethical Password Cracking: decode passwords using John the Ripper, hashcat, and advanced methods for password breaking²
  Daniel W. Dieterle (2024): Password Cracking with Kali Linux³
  ¹) https://www.amazon.com/gp/product/1793458618
  ²) https://www.amazon.com/Ethical-Password-Cracking-passwords-a...
  ³) https://www.oreilly.com/library/view/password-cracking-with/...
chadbennett
01d
I just bought the book and look forward to reading it. I also started in cyber at 14.
These are the kinds of real-world constraints where you actually learn how tools like Hashcat work under pressure.
You are going to do big things in the industry!
paulpauper
22d
relevant https://en.wikipedia.org/wiki/2022_LastPass_data_breach
probably a lot of ppl lost crypto this way.
1. Tamklomo
  12d
  I don't think so. Every lastpass vault is encrypted by the users password.
  Wikipedia states that there were some field unencrypted, sure, but not the critical data.
  More people probably lost crypto by forgetting their passwords like a friend of mine. 10k gone
Footprint0521
02d
The video url is down? This sounds super interesting!
nilirl
12d
I love the book cover! Great job, Bojta.
1. bojta-lepenye • OP
  01d
  Thank you. This really means a lot. My sister designed the book cover herself. You can check out some of her drawings here: https://www.instagram.com/angyalka_art/
  She is really amazing!
latchkey
32d
when i was running 150k amd gpus... i really wanted to use the cluster to run hashcat to help people recover lost things. i couldn't convince management that that was a profitable business to run.
1. dantillberg
  22d
  > help people recover lost things
  You mean "lost things" in quotes. Management may have been more concerned about jail time.
amelius
72d
Ok, so what should we use instead of passwords?
1. analogpixel
  22d
  I use a blank password for everything, no one ever thinks of trying nothing.
kelsey98765431
02d
can you discuss your coverage of password mask attacks, specifically is there any advances since EBM
photonair
01d
[dead]
mdhemalakhand
01d
[dead]
Dinhhoanghm
01d
[dead]
immanuwell
01d
[dead]
saberience
42d
There’s a reason there are no books about this, because most people are not interested in cracking local/offline passwords.
In fact, the people most interested in password cracking are usually criminals.
But good luck with the book. It’s just not a hugely in demand topic.
1. Tamklomo
  02d
  The reason is, that using hashcat is not complicated for people who have linux experience and the amount of people wanting to crack a password is probably not that high.
  Otherwise you do find plenty of people on YT walking you through hashcat. The first YT Video alone has 7 Million views: "how to HACK a password // password cracking with Kali Linux and HashCat"
  I wish him luck, great drive to do this, i hope it works out well enough, books are just in general not easy to sell.