Please, Don't Share - crypto challenge

I've got to the point where I believe I know the mechanism that is used to encrypt the thing. However, after trying a number of implementations of it, and tweaking the additional bit that is needed but not as obvious I'm still not cracking it. I've also tried some statistical methods to analyze the results to find the "right one" but also no luck. I'm currently out of ideas on how to proceed.

m0noc

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  • solved it - doing the right things but the "not so obvious" thing I needed was the thing I was miscalculating. So close for all this time yet so far.

    m0noc

  • @m0noc said:
    solved it - doing the right things but the "not so obvious" thing I needed was the thing I was miscalculating. So close for all this time yet so far.

    tried xor and some classic ciphers..but can't figure out anything

    a nudge in the right direction would be appreciated !!

  • The name of the challenge may help.

    m0noc

  • edited May 2018

    Ive found what I needed for the final part of it, but I have no clue how to convert and give it what it needs to give me what I need.

    @m0noc any of that sweet sweet experience you want to share? I tried DMing you but HTB seems to have a bug when it comes to logging in on the forum to send messages.

  • Hi, i'm stuck with the syntax, can someone PM me pls ?
    many tks

  • Could I get a nudge from a solver? I've been banging my head with this one for days now, have exhausted myself now!

    @m0noc care to help out?

  • I'm also struggling with this one.

    What (I think) I know:

    • The secret is encrypted using a certain algorithm invented in 1979 that requires >=k pieces of data to decrypt
    • Each share has a 2-character prefix followed by some data encoded with a 58-character alphabet

    I'm not sure where to go from here though. If I try to decrypt using anything from 1 share to 10 shares, I seem to get meaningless data.

  • edited October 2018

    @chenxiaolong said:
    I'm also struggling with this one.

    What (I think) I know:

    • The secret is encrypted using a certain algorithm invented in 1979 that requires >=k pieces of data to decrypt
    • Each share has a 2-character prefix followed by some data encoded with a 58-character alphabet

    I'm not sure where to go from here though. If I try to decrypt using anything from 1 share to 10 shares, I seem to get meaningless data.

    I'm in pretty much this same spot. I'm almost positive that I'm decoding the values properly, as the prime value decodes into something that's well-known.

    However, regardless of the number of shares I use, I'm getting (seemingly) junk data.

    I'd appreciate a nudge, if anyone is willing.

    opt1kz

  • Solved. A friend of mine gave me a hint towards a detail I was overlooking. I'd wager it was the same thing @m0noc was stuck on. It's very easy to overthink this one. Feel free to PM me if you need a nudge.

    opt1kz

  • Solved thanks to a hint from @opt1kz. For those working on this, hopefully this isn't too big of a hint: be sure to use all available data in the three relevant columns.

  • I could use some help with that challenge. I'm probably at the same point... I used couple of implementations of SSS, but couldn't figure out how to make it "spit out" what I need.

  • The point is to understand the correct "ingredients". Follow what chainxiaolong said, use the full data of those columns remembering that the all of the "ingredients" must be of the required type. :)

    mrlbender

  • Hi, Ive been trying to solve this challenge for the past few days. I'm currently at the same point as @opt1kz was, could someone give me a hint?

    Many tks :)

  • Just managed to crack this with the help of @chenxiaolong's hint, and reading carefully about the implementation of the relevant cipher. Without that it I could have wasted a lot of time on a minor detail - thank you.

  • Solved it! Big thanks to @opt1kz and @chenxiaolong for their hints. The only hint I can give other than the ones already given is once you've determined what kind of crypto is in play, the most common search result in Google should provide you with all you need.

    Hack The Box
    Discord: AzAxIaL#8633

  • Solved. The hardest part of the challenge was actually finding out what algorithm was being used here.

  • should the strings be decoded first with something like base64 before decription?

  • @chenxiaolong said:
    Solved thanks to a hint from @opt1kz. For those working on this, hopefully this isn't too big of a hint: be sure to use all available data in the three relevant columns.

    now this is something that nudged me in the right direction when i was completely stuck, thanks man!

  • can somebody give me a hint, i think i correctly did the algo from opt1kz but i don't get what to do with the '3rd' , or public column. tried xor'ing, even a second otrder sss with result from 1 and public. but seem to get nowhere.

  • Pfew, tough challenge, overlooked the simple things, and started with complex stuff..
    A little hint on the '3rd' column, it is only divisible by itself and by 1 ;)

    pm me if you need a nudge

    e-nigmaNL

  • Oh boy, that was quite something!
    If you're (like me) just using the last part of the second field, try to look up what exactly an IP address is (what data structure) and how it is represented.

    Feel free to PM if you need a pointer ;)

    Hack The Box

    GitHub repository with writeups: https://github.com/S7uXN37/HackTheBox

  • Someone can give me a hint? Please PM

  • The final step for me was to take into consideration the second column.
    "It is unlogical but it is CTF".

    tabacci

  • Done!

    Learnt a few things today :)

    Happy to help is anyone needs a hint.

  • I do it together with few people here. I learned some new things about python cus i can do few elements via python cli.
    PM me if you wanna help/hint :)

    I prefer private messages on forum than HTB messanger.

  • Got it!

    PM if you need a nudge :smile:

  • Type your comment

    Fighter81

  • Done. Thanks to @itssamlol for help.

    PM if you need help.

  • edited September 7

    Nice challenge. Done it today, while attending a reversing conference, during the breaks. Absolutely NOT difficult, once you know which algorithm is involved (all you need to solve it is already on these posts) and understand, as someone else pointed out, the 'ingredients' of the cipher.

    As for the kind of "types", don't forget how IP addresses are represented in memory ... and what a point actually is.

    Enjoy!

    Sociaslkas

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