I started the “Weak RSA” challenge today. It contains two files the “key.pub” which , as the name implies, is the public key and the “flag.enc” which is the file I need to decrypt.

I have tried to analyze the public key through OpenSSL but the modulo doesn’t seem to be non-random i.e ( lots zeroes or any specific sequence).

Also what puzzled me was that the Exponent seemed way to big

Am I heading in the right track? Any help would be appreciated

The tool does work. Be sure to install all dependencies. There is a requirements.txt in the folder. Do pip install -r requirements.txt to install them. And the extra one aswell.

Hi, i did it with the tool from @sender (thank you very much sender) and everthing works finally. I would really like to know, how the tool did it. How did it proceed after i typed the command and pressed enter? What exactly happened with the key, and possibly what mathematical operations were involved?

If someone is still interested in the (mathematical) methods of factorizing n, I recommend this 29C3 talk: 29C3: FactHacks (EN) - YouTube .
For the slides just search for “FactHacks: RSA factorization in the real world”.

Since I did not solve the challenge yet, I can’t say wether it is helpfull for the problem in “weak rsa”. But it is a clear recommendation for anyone interested in this topic.

@sender said:
Actually it is working with an older version I had in my notes. Could not get it to work with the recent version either. I uploaded the working tool Spoiler Removed.

The tool on offer is not working at all, it looks like you can no longer install gmpy2 and it’s not supported for python3. I have tried to start solving this manually (not by hand), am I on the right lines trying to factor N or am I wasting my time?

@REdwards365 said:
The tool on offer is not working at all, it looks like you can no longer install gmpy2 and it’s not supported for python3. I have tried to start solving this manually (not by hand), am I on the right lines trying to factor N or am I wasting my time?

Use python 2.7 and don’t forgot to use pip for the requirements .txt for the next one.

@AgentTiro said:
Gmpy2 is available, but you need to manually compile it. However this challenge doesn’t need the gmpy2 module. So just comment ut the import Gmpy2.

This is good suggestion. Tool working now for me Thanks