Encryption

some good tools for breaking rsa encryptions:

GitHub - RsaCtfTool/RsaCtfTool: RSA attack tool (mainly for ctf) - retrieve private key from weak public key and/or uncipher dataGitHub

GitHub - ius/rsatool: rsatool can be used to calculate RSA and RSA-CRT parametersGitHub

---

The attacking side

The maths behind RSA seems to come up relatively often in CTFs, normally requiring you to calculate variables or break some encryption based on them. The wikipedia page for RSA seems complicated at first, but will give you almost all of the information you need in order to complete challenges.

There are some excellent tools for defeating RSA challenges in CTFs, and my personal favorite is https://github.com/Ganapati/RsaCtfTool which has worked very well for me. I’ve also had some success with https://github.com/ius/rsatool.

The key variables that you need to know about for RSA in CTFs are p, q, m, n, e, d, and c.

“p” and “q” are large prime numbers, “n” is the product of p and q.

The public key is n and e, the private key is n and d.

“m” is used to represent the message (in plaintext) and “c” represents the ciphertext (encrypted text).

---