Official Baby Time Capsule Discussion

HTB Content Challenges
23

Solved!! Thank you very much for this challenge.

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24

I have this expectation that ā€˜very easyā€™ challenges are all going to be solvable in 15 minutes. I have to get away from that mindset (especially for crypto which is apparently myā€¦ cryptonite).

This took me all day, and I ended up with exposure to way more RSA than I expected. Which is a good thing. Tough challenge for me, loads of Google before I was on the right track thanks to nudges from others.

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25

Should I be getting a syntax error on line 34? its not missing any quotes.?

26

In line 34 f-strings are used the frist time, see Formatted String Literals. The f-string are introduced in Python version 3.6, PEP498. May be you used an older Python version.

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27

thanks!

28

Can anyone give me a hint? I have unciphered data from one tool for ctf, but that data is kind of chinese in utf-16 :grin:

29

Hi, i think i need a hint, i been implementing a c****** r******** solution but Iā€™m not able to recover any usable flag :frowning:
Anyone can give me a hint or tell me what Iā€™m missing?

30

maybe you are implementing it incorrectly? Have you tried one thatā€™s been implemented for you?

you can PM me and give me the details of what youā€™ve tried and I can point you in the right direction

31

Iā€™m running in to the problem that my solution for the offline server.py file does not work for the actual server any tips maybe

32

i can get part of the flag but it cuts out the rest HTB{t3h the rest is missing. im using external libraries to calculate c****** and r*** to avoid big number problems. im using python.

Anyone had that problem? should i just use a different language?

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34

I have the same problem. I tried to convert a large float to bytes, but I receive only the beginning of the flag, just as you. Did you solve it creepto?

35

I have got it. Information gets lost when the int value is too large and you are doing log computations and devisions.
Hint: use libnum.nroot

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36

I have a quick question, is every time capsule solvable or is the expectation that we try to find a weak one? I can reliably solve for the redacted flag with a couple methods but the real capsules are just a little bit bigger and Iā€™m losing accuracy when trying to work with the larger numbers. For reference Iā€™ve worked with numpy, gmpy2 and libnum.

37

Ok, I figured it out. Read through this thread carefully, specifically @Hilbertā€™s comment. It should get you started on the right track

39

I am stuck in 2 days . I know little bit about RSA but i dont understand how to get flag . Some guy previous tell he get flag
Without looking python code . How to get flag can anyone give me a hint .

40

should i brute force the value of m which is the int representation of the flag? because we canā€™t factorize N, i donā€™t have any idea this is my first time with crypto & RSA and i suck at math ):

edit:
After some math it turned out that i need at least 1E22 years to brute force that m, int representation of bā€™HTB{ā€“REDACTEDā€“}ā€™ which is 125 bit long, so the actual flag on the server would be much harder to brute force cuz i donā€™t know itā€™s length. any hint? about that ch** r** thing ?

41

while bruteforcing it i noticed that the modulus N does not affect the encryption of the flag so the m value is just byte_to_long(flag) ** 5 , then i noticed that the server always generate the same ā€œtime_capsuleā€ even that the N is changing, so i reversed the flag by : flag = M ** (1/5), and it worked! Locally, but the actual server doesnā€™t send the same time_capsule! i wonder why, any clarification?

42

Bruteforcing the key is a bad idea. Try to learn what each of the values corresponding to RSA does, and see if you can do anything with that.

43

what is that tecnic ch***** r****** ? Is this useful

I know that it is useless find d and factoring n and it is only way decrypt it ciper text ( i mean it always m^e<n ) use another way but how i try convert ciper msg to int and nroot (c**1/5) it
But is nt working then how to do it please give me hint

44

Thought Iā€™d add as a supplementary that if you think you know what the method to crack this one is, donā€™t use any online tools! I worked out the correct answer to this one quickly and ended up spending way longer than I should, because most online tools ended up hitting the INTEGER_MAX and modulating my answer down to a reasonable size. Implement the decryption yourself using some science/math libraries that will keep track of large numbers. Happy hunting!